1. Socket-based Client-Server Application
Client-Server application architecture
Choosing services – Connectionless atau Connection-oriented

2. Evolution of Application Architecture

3. 3-tier Client-server application architecture

4. Internet Protocol and Network Application
Internet protocol supports:
General-purpose service for reliable data transmission
Mechanism for connecting hosts
Network application programs:
Use Internet Protocol to connect to other application
Provide user-level services

5. Client-Server Model Server Application acts as a “listener”
Waits for incoming messages
Executes services
Returns the results/outcomes
Client Application makes connection
Sends messages to the server
Waits for response

6. Features of a Client An application program
Becomes a client when a network service is needed
It can also executes other calculation
Is directly created by the users
Is executed locally by at the users’ computer
Initiates connection to a server
Able to access various services (at a given time)
Does not require a special device or operating system

7. Features of a Server
Special-purpose application for providing a network service
Is executed on a remote computer (usually is centralised and shared)
Waits and receives request for services from the clients
Requires high-performance device and operating system

8. Transport Protocol and Client-Server
Client and server exchange messages via transport protocol such as TCP or UDP
Both client and server must have the same protocol stack and both interact with the transport layer

9. Transport Protocol and Client-Server

10. Several Services on a Server

11. Identifying a Service
Every service has a unique identifier which is used by the client and server
Example - TCP uses port number protocol (port_num) as identifier
Server is registered under a specific port number for a service
Client asks for a session with the port number for the service
Every transport session contains 2 unique indentifier
(IP address, port number) at the server
(IP address, port number) at the client

12. Connection-oriented and Connectionless Transport Protocol
Which one should be chosen?
UDP - connectionless
Client builds a message
Client sends the message to a server
The server responds
Message must be loaded into a UDP datagram
TCP - connection-oriented
Client makes a connection to a server
Client and server exchange messages
Client terminates the connection

13. UDP
UDP is a connectionless transport protocol, i.e. it doesn't guarantee either packet delivery or that packets arrive in sequential order.
With UDP, bytes of data are grouped together in discrete packets which are sent over the network.

14. No two packets are guaranteed the same route.
Packets may travel along different paths depending on the state of the network.
No two packets are guaranteed the same route.
Each packet has a time-to-live (TTL) counter, which is updated when it is routed along to the next point in the network. When the timer expires, it will be discarded, and the recipient will not be notified.

15. If a packet does arrive, it will always arrive intact
If a packet does arrive, it will always arrive intact. Packets that are corrupt or only partially delivered are discarded.

16. Advantages of UDP
UDP communication can be more efficient than guaranteed-delivery data streams.
Unlike TCP streams, which establish a connection, UDP causes fewer overheads.
Real-time applications that demand up-to-the-second or better performance may be candidates for UDP, as there are fewer delays due to error checking and flow control of TCP.

17. UDP sockets can receive data from more than one host machine.
Some network protocols specify UDP as the transport mechanism.

18. Java Support for UDP Two classes are provided:
DatagramPacket class (java.net)
DatagramSocket class (java.net)

19. DatagramPacket Class
A DatagramPacket object represents a data packet intended for transmission using UDP.
It contains addressing information such as an IP address and a port.
When a DatagramPacket is read from a UDP socket, the IP address/port number of the packet represents the address/port number of the sender.

20. When a DatagramPacket is used to send a UDP packet, the IP address/port represents the address/port of the recipient.
DatagramPacket
IP address (java.net.InetAddr)
Port address (int)
Packet data (byte[])

21. Creating a DatagramPacket
Constructor to use for creating a DatagramPacket for receiving incoming UDP packets:
DatagramPacket(byte[] buffer, int length)
Example:
DatagramPacket packet;
packet = new DatagramPacket(new byte[256], 256);

22. Constructor to use for sending a DatagramPacket to a remote machine
DatagramPacket(byte[] buffer, int length, InetAddress dest_addr, int dest_port)
Example:
DatagramPacket packet;
InetAddress addr;
addr = InetAddress.getByName(" ");
packet = new DatagramPacket(new byte[128], ,addr, 2000);

23. DatagramPacket Methods
InetAddress getAddress()
byte[] getData()
int getLength()
int getPort()
void setAddress(InetAddress addr)
void setData(byte[] buffer)
void setLength(int length)
void setPort(int port)

24. DatagramSocket Class
The DatagramSocket class provides access to a UDP socket, which allows UDP packets to be sent and received.
The same DatagramSocket can be used to receive as well as to send packets.
Read operations are blocking - i.e. the application will continue to wait until a packet arrives.

25. Each DatagramSocket binds to a port on the local machine
Each DatagramSocket binds to a port on the local machine. The port number need not match the port number of the remote machine.
If the application is a UDP server, it will usually bind to a specific port number.

26. Creating a DatagramSocket
Constructor to use for creating a client DatagramSocket:
DatagramSocket() throws java.net.SocketException
Example:
DatagramSocket socket;
try {
socket = new DatagramSocket();
} catch (SocketException exception) { … }

27. Constructor to use for creating a server DatagramSocket:
DatagramSocket(int port) throws java.net.SocketException
Example:
DatagramSocket socket;
try {
socket = new DatagramSocket(2000);
} catch (SocketException exception) { … }

28. DatagramSocket Methods
void close()
void connect(InetAddress r_addr, int r_port)
void disconnect()
InetAddress getInetAddress()
int getPort()
InetAddress getLocalAddress()
int getLocalPort()
int getReceiveBufferSize() throws java.net.SocketException

29. int getSoTimeout() throws java.net.SocketException
int getSendBufferSize() throws java.net.SocketException
int getSoTimeout() throws java.net.SocketException
void receive(DatagramPacket packet) throws java.io.IOException
void send(DatagramPacket packet) throws java.io.IOException
int setReceiveBufferSize(int length) throws java.net.SocketException
int setSendBufferSize(int length) throws java.net.SocketException
void setSoTimeout(int duration) throws java.net.SocketException

30. Listening for UDP Packets
Before an application can read UDP packets, it must
bind a socket to a local UDP port using DatagramSocket
create a DatagramPacket that will contain the data.

31. Packet DatagramSocket DatagramPacket UDP application Reads packets
Translates packets
Into a DatagramPacket
UDP application

32. The following code illustrates the process for reading UDP packets.
DatagramPacket packet;
DatagramSocket socket;
packet = new DatagramPacket(new byte[256], 256);
socket = new DatagramSocket(2000);
boolean finished = false;
while (!finished) {
socket.receive(packet);
// process the packet }
socket.close();

33. ByteArrayInputStream
Java I/O streams are usually used to access the contents of the byte array in a DatagramPacket. See example later.
ByteArrayInputStream
DatagramPacket
DataInputStream
IP address (java.net.InetAddr)
Port address (int)
Packet data (byte[])
UDP
application

34. Sending UDP Packets
When sending a packet, the application must create a DatagramPacket that will contain the data. The address and port information must also be set.
When the packet is ready for transmission, the send method of DatagramSocket should be invoked.

35. DatagramSocket UDP application Packet DatagramPacket Binds to a
UDP port
UDP application
Send DatagramPacket
using DatagramSocket
Packet
Constructs
packet
DatagramPacket

36. The following code illustrates the process for sending UDP packets.
DatagramPacket packet;
DatagramSocket socket;
packet = new DatagramPacket(new byte[256], 256);
socket = new DatagramSocket(2000);
packet.setAddress(…);
packet.setPort(2000);
boolean finished = false;
while (!finished) {
// write data to packet buffer
socket.send(packet); … }
socket.close();

37. User Datagram Protocol Example
Run receiving application
java PacketReceiveDemo
Run sending application
java PacketSendDemo

42. ByteArrayOutputStream
PacketSendDemo
PrintStream
print(str)
ByteArrayOutputStream
DatagramPacket
toByteArray()
send(packet)
DatagramSocket

43. ByteArrayInputStream
DatagramSocket
receive(packet)
ByteArrayInputStream
DatagramPacket
getData()
read()
PacketReceiveDemo

44. Building a UDP Client/Server
Run echo server
java EchoServer
Run echo client
java EchoClient

45. Algorithm for Echo Server
Create socket
Create an empty packet
Repeat the following forever
Wait for a packet
Send the packet back to sender

46. Algorithm for Echo Client
Create socket
Set timeout value for socket
Repeat the following ten times
Create the message to be sent
Create packet containing the message as well as the destination IP and the port
Send the packet through socket
Wait for packet from receiver through socket or timeout
if packet received
Create an input stream to access data in the packet
Use the input stream to read the data and then display it on the screen.
Sleep for a second

47. Overcoming UDP Limitations
Lack of Guaranteed Delivery
Lack of Guaranteed Packet Sequencing
Lack of Flow Control

48. Lack of Guaranteed Delivery
Packets sent via UDP may become lost in transit.
UDP packets can also become damaged or lost.
For some applications, the loss of individual packets may not have a noticeable effect (e.g. video streams).
For other applications, loss of packets is not acceptable (e.g. file transfers).

49. If guaranteed delivery is required,
avoid packet-based communication, and use a more suitable transport mechanism (e.g. TCP).
send acknowledgement to sender after receiving packets.

50. Lack of Guaranteed Packet Sequencing
Applications that require sequential access to data should include a sequence number in the contents of a datagram packet.
This enables detection of duplicate packets and also missing packets.

51. Lack of Flow Control
The technique of flow control is important to avoid flooding a system with more data than it can handle due to limited bandwidth.
One technique of flow control is to limit the number of unacknowledged packets. E.g.: increase control when number of acknowledgement packets received is much less than the number of packets sent.

52. Transmission Control Protocol

53. Overview
Unlike UDP which is concerned with the transmission of packets of data, TCP establishes a "virtual connection" between two machines through which streams of data may be sent.
TCP guarantees delivery and order, providing a reliable byte communication stream between client and server that supports two-way communication.

54. Establish a virtual connection
Transmit data back and forth
Terminate the connection

55. TCP uses IP (Internet Protocol) to establish the connection between machines.
This connection provides an interface that allows streams of bytes to be sent and received, and transparently converts the data into IP datagram packets.
The virtual connection between two machines is represented by a socket.

56. TCP sockets are different from UDP sockets:
TCP sockets are connected to a single machine.
UDP sockets only send and receive packets of data. TCP allows tansmission of data through byte streams. They are converted into datagram packets for transmission over the network without programmer intervention.

57. Advantages of TCP over UDP
Automatic Error Control
Data transmission is more dependable. Delivery of data is guaranteed - lost data packets are retransmitted.
By means of a timer, TCP retransmits a packet if an acknowledgement is not received from the recipient within a specified amount of time.

58. Reliability
As packets are delivered by IP, they will frequently arrive out of order. However, each packet contains a sequence number. Using this sequence number and queuing out-of-order packets, TCP is able to pass arriving packets to the application in the correct sequence.

59. Ease of Use
Network programmers will find programming communication via TCP sockets far simpler than via datagram packets. This is because data sent and received can be treated as a continuous stream (like I/O streams). The data need not be packaged into discrete units like UDP.

60. Communication Using Ports
Both UDP and TCP uses the concept of a communications port, which distinguishes one application from another.
When a TCP socket establishes a connection to another machine, the following information will be required:
the IP address of the remote machine
the port number

61. Like ports in UDP, ports in TCP are also represented by a number in the range 1 - 65535.
Ports below 1024 are restricted to use by well-known services. For example,
Telnet (port 23)
SMTP (port 25)
HTTP (port 80)
POP3 (port 110)

62. Socket Operations TCP sockets can perform a variety of operations:
Establish a connection to a remote host
Send data to a remote host
Receive data from a remote host
Close a connection

63. There is a special type of socket that provides a service that will bind to a specific port number. Normally used only in servers, this socket can perform the following operations:
Bind to a local port
Accept incoming connections from remote hosts
Unbind from a local port

64. TCP and the Client/Server Paradigm
In network programming, applications that use sockets are divided into clients and servers.
A client is software that initiates a connection and sends requests.
A server is software that listens for connections and processes requests.

65. Note that in the context of UDP programming, no actual connection is established. UDP applications may both initiate and receive requests on the same socket.
In the client/server paradigm, when there is a connection between two applications, one must be a client and the other must be a server.

66. Network Clients
Network clients initiate connections and control network transactions.
The server fulfills the requests of the client but not the other way round.
The network client speaks to the server using a network protocol. E.g an HTTP client communicates with an HTTP server using HTTP.

67. Port numbers are used to enable clients to locate servers. E. g
Port numbers are used to enable clients to locate servers. E.g. a web server uses port 80.

68. Network Servers
The role of the network server is to bind to a specific port and to listen for new connections.
Unlike the client, the server must run continually in the hope that some client will want its services.
The server runs indefinitely. Normally, it is automatically started when the host computer of the server is started.

69. Some servers can handle only one connection at a time, while others can handle many connections concurrently, through the use of threads.
Some protocols (e.g. HTTP/1.0) normally allow only one request per connection. Others, like POP3, support a sequence of requests.
Servers answer the client request by sending either a response or an error message.

70. TCP Sockets and Java
Java provide the following classes for TCP sockets:
java.net.Socket
java.net.ServerSocket
The Socket class should be used when writing client software.
The ServerSocket class should be used when writing server software.

71. Socket Class
Socket objects represent client sockets, and is a communication channel between two TCP communications ports belonging to one or two machines.

72. There are several constructors for the Socket class.
The easiest way to create a socket is shown below:
Socket mySocket;
try {
mySocket = new Socket(" 80);
} catch (Exception e) { … }

73. Some of the other constructors:
Socket(InetAddress addr, int port)
Throws java.io.IOException, java.lang.SecurityException
Socket(InetAddress rAddr, int rPort, InetAddress lAddr, int lPort)
Socket(String rHost, int rPort, InetAddress lAddr, int lPort)
Throws java.net.UnknownHostException, java.io.IOException, java.lang.SecurityException

74. Using a Socket
Refer section (pg 150) for a description of some of the methods of the Socket class.

75. Reading from and Writing to TCP Sockets
In Java, once a socket is created, it is connected and ready to read/write by using the socket's input and output streams. Use the methods getInputStream() and getOutputStream() to access those streams.

76. Example: } catch (Exception e) { … } Socket socket;
InputStreamReader isr;
BufferedReader br;
PrintStream ps;
try {
socket = new Socket("
isr = new InputStreamReader(socket.getInputStream());
br = new BufferedReader(isr);
ps = new PrintStream(socket.getOutputStream());
} catch (Exception e) { … }

77. SO_TIMEOUT Socket Option
Socket options are settings that modify how sockets work. They can affect the performance of applications.
SO_TIMEOUT is the most useful socket option. It allows a timer to be started when a read request is made on a socket. When no data arrives in time and the timer expires, a java.io.InterruptedIOException is thrown which can be caught to check for a timeout.

78. Use the setSoTimeout() method to set the duration of the timer
Use the setSoTimeout() method to set the duration of the timer. Example:
socket.setSoTimeout(5000);
The getSoTimeout() method can be used to get the duration of the timer. A value of zero means that timeouts are disabled and read operations will block indefinitely.

79. Creating a TCP Server
The given example is a TCP server which returns the current day and time to the client.

80. SocketServer Class
The server socket is a special type of socket used to provide TCP services.
Client sockets bind to any free port on the local machine, and connect to a specific port and host.
The difference with server sockets is that they bind to a specific port on the local machine so that remote clients may locate a service.

81. Client socket connections will connect to only one machine, whereas server sockets are capable of fulfilling the requests of multiple clients.

82. Creating a ServerSocket
Once a server socket is created, it will be bound to a local port and ready to accept incoming connections.
When clients attempt to connect, they are placed into a queue.
When this queue is full, further clients are refused.

83. There are several constructors for the ServerSocket class.
The easiest way to create a socket is shown below:
ServerSocket mySocket;
try {
mySocket = new ServerSocket(80);
} catch (Exception e) { … }

84. Some of the other constructors:
ServerSocket(int port)
Throws java.io.IOException, java.lang.SecurityException
If port is 0, then any free port will be used.
By default, the queue size is set to 50.
ServerSocket(int port, int maxClients)
Allocates sufficient space to the queue to support the specified number of client sockets.

85. Using a ServerSocket
Refer section (pg 161-Reilly) for a description of some of the methods of the ServerSocket class.
The most important method is the accept() method, which accepts client connection requests.

86. Accepting and Processing Requests from TCP Clients
The most important function of a server socket is to accept client sockets. Once a client socket is obtained, the server can perform all the "real work" of server programming, which involves reading from and writing to the socket to implement a network protocol.
Example: a mail server that provides access to stored messages would listen to commands and send back message contents.

87. Example: ServerSocket server; BufferedReader reader;
PrintWriter writer;
server = new ServerSocket(13);
while (true) {
Socket client = server.accept();
reader = new BufferedReader(
new InputStreamReader(
client.getInputStream()));
writer = new PrintWriter(
new OutputStreamWriter(
client.getOutputStream())); … }

88. TCP Socket Client-Server : ALI BABA…

89. ALI BABA Client-Server

90. Client Application In this example, there are 2 java programs
The client program is implemented as a class NyietInSengClient

91. public class NyietInSengClient {
import java.io.*;
import java.net.*;
public class NyietInSengClient {
public static void main(String[] args)
throws IOException {
Socket nisSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
nisSocket = new Socket("localhost", 8888);
out = new PrintWriter(nisSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(nisSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: localhost.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: localhost."); }
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("tata titi tutu"))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser); }
out.close();
in.close();
stdIn.close();
nisSocket.close();

92. Server Application Server application is implemented using 2 classes:
NyietInSengServer
NyietInSengServer contains method main() for the server program. It listens at a port for incoming connection, accept the connection and reads messages from client/writes responses to the client through a socket

93. public class NyietInSengServer {
import java.net.*;
import java.io.*;
public class NyietInSengServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(8888);
} catch (IOException e) {
System.err.println("Could not listen on port: 8888.");
System.exit(1); }
Socket clientSocket = null;
clientSocket = serverSocket.accept();
System.err.println("Accept failed.");
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
String inputLine, outputLine;
NyietInSengProtocol nis = new NyietInSengProtocol();
outputLine = nis.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = nis.processInput(inputLine);
if (outputLine.equals("tata titi tutu"))
break; }
out.close();
in.close();
clientSocket.close();
serverSocket.close();

94. Protocol class (part of server app)
NyietInSengProtocol
NyietInSengProtocol provides the jokes. It tracks the current joke, the current status (SENTTOKTOK, SENTCLUE, etc) and returns joke text based on the current status.
It implements a communication protocol (a language) agreed by the client and server.

95. Server App.
Begins by creating a ServerSocket object to listen (wait) at a certain port. When selecting a port no., pick one that is not reserved for other services.
NyietInSengServer waits at port 8888 as the port 8888 is not used in my computer environment:
try {
serverSocket = new ServerSocket(8888); }
catch (IOException e) {
System.out.println("Could not listen on port: 8888");
System.exit(-1);

96. Server App.
The constructor for ServerSocket throws an exception if it fail to listen the specified port (say if it is being used)
In this case NyietInSengServer has no other choice than to exit.

97. If the server is able to connect to the specified port, then a ServerSocket object is created and the server app. Will perform the following steps – accept connection from client (in bold):
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.out.println("Accept failed: 8888");
System.exit(-1); }

98. Server App.
Method accept() waits until a client program is executed and requesting for connection at a specified host and port (example, host : localhost and port : 8888.
When connection between the client and server is succesfully created, method accept() will return a new Socket object (in example :clientSocket) which is bound to a new port.
NyietInSengServer can communicate with NyietInSengClient through this new socket.
It can keep listening and waiting for new incoming connection using the original ServerSocket (in example : serverSocket)
However, in the example, the server application is not able to cater for more than 1 client.

99. Read/Write Process
Gets the socket's input and output stream and opens readers and writers on them
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader( new InputStreamReader( clientSocket.getInputStream()));
String inputLine, outputLine;

100. Server App.
After the server successfully establishes a connection with a client, it communicates with the client using this code:
// initiate conversation with client
NyietInSengProtocol nis = new NyietInSengProtocol();
outputLine = nis.processInput(null);
out.println(outputLine);
Initiates communication with the client by writing to the socket (shown in bold).

101. Server App. while ((inputLine = in.readLine()) != null) {
outputLine = nis.processInput(inputLine);
out.println(outputLine);
if outputLine.equals(“tata titi tutu"))
break; }
Communicates with the client by reading from and writing to the socket (the while loop).

102. 1 is already familiar. Step 2 is shown in bold and is worth a few comments.
After the NyietInSengProtocol is created, the code calls NyietInSengProtocol 's processInput method to get the first message that the server sends to the client.
For this example, the first thing that the server says is “NyietInSeng MatekAji Semar Ngiseng!" Next, the server writes the information to the PrintWriter connected to the client socket, thereby sending the message to the client.

103. Communication Protocol of AliBaba Client-Server
Following is the implementation of the protocol:

104. public class NyietInSengProtocol {
import java.net.*;
import java.io.*;
public class NyietInSengProtocol {
private static final int WAITING = 0;
private static final int SENTTOKTOK = 1;
private static final int SENTCLUE = 2;
private static final int ANOTHER = 3;
private static final int NUMJOKES = 3;
private int state = WAITING;
private int currentJoke = 0;
private String[] clues =
{ "Ali", "Di Sini", "Hari"};
private String[] answers =
{ "Ali Baba, Bujang Lapok la.. ",
"Di Sini lah, Oi Di Sana! ",
"Harimau Kuat! Grrrrrr "};
public String processInput(String theInput) {
String theOutput = null;
if (state == WAITING) {
theOutput = "NyietInSeng MatekAji Semar Ngiseng!";
state = SENTTOKTOK;
} else if (state == SENTTOKTOK) {
if (theInput.equalsIgnoreCase("Siapa tu?")) {
theOutput = clues[currentJoke];
state = SENTCLUE;
} else {
theOutput = "Sepatutnya awak cakap \"Siapa tu?\"! " +
"Cuba lagi. NyietInSeng MatekAji Semar Ngiseng!"; }
} else if (state == SENTCLUE) {
if (theInput.equalsIgnoreCase(clues[currentJoke] + " mana?")) {
theOutput = answers[currentJoke] + " Main lagi? (y/n)";
state = ANOTHER;
theOutput = "Sepatutnya awak cakap \"" +
clues[currentJoke] +
" mana?\"" +
"! Cuba lagi. NyietInSeng MatekAji Semar Ngiseng!";
} else if (state == ANOTHER) {
if (theInput.equalsIgnoreCase("y")) {
if (currentJoke == (NUMJOKES - 1))
currentJoke = 0;
else
currentJoke++;
theOutput = "tata titi tutu";
state = WAITING;
return theOutput;

105. Socket-based Client-Server Application
Client-Server application architecture
Choosing services – Connectionless atau Connection-oriented

106. Evolution of Application Architecture

107. 3-tier Client-server application architecture

108. Internet Protocol and Network Application
Internet protocol supports:
General-purpose service for reliable data transmission
Mechanism for connecting hosts
Network application programs:
Use Internet Protocol to connect to other application
Provide user-level services

109. Client-Server Model Server Application acts as a “listener”
Waits for incoming messages
Executes services
Returns the results/outcomes
Client Application makes connection
Sends messages to the server
Waits for response

110. Features of a Client An application program
Becomes a client when a network service is needed
It can also executes other calculation
Is directly created by the users
Is executed locally by at the users’ computer
Initiates connection to a server
Able to access various services (at a given time)
Does not require a special device or operating system

111. Features of a Server
Special-purpose application for providing a network service
Is executed on a remote computer (usually is centralised and shared)
Waits and receives request for services from the clients
Requires high-performance device and operating system

112. Transport Protocol and Client-Server
Client and server exchange messages via transport protocol such as TCP or UDP
Both client and server must have the same protocol stack and both interact with the transport layer

113. Transport Protocol and Client-Server

114. Several Services on a Server

115. Identifying a Service
Every service has a unique identifier which is used by the client and server
Example - TCP uses port number protocol (port_num) as identifier
Server is registered under a specific port number for a service
Client asks for a session with the port number for the service
Every transport session contains 2 unique indentifier
(IP address, port number) at the server
(IP address, port number) at the client

116. Connection-oriented and Connectionless Transport Protocol
Which one should be chosen?
UDP - connectionless
Client builds a message
Client sends the message to a server
The server responds
Message must be loaded into a UDP datagram
TCP - connection-oriented
Client makes a connection to a server
Client and server exchange messages
Client terminates the connection

117. UDP
UDP is a connectionless transport protocol, i.e. it doesn't guarantee either packet delivery or that packets arrive in sequential order.
With UDP, bytes of data are grouped together in discrete packets which are sent over the network.

118. No two packets are guaranteed the same route.
Packets may travel along different paths depending on the state of the network.
No two packets are guaranteed the same route.
Each packet has a time-to-live (TTL) counter, which is updated when it is routed along to the next point in the network. When the timer expires, it will be discarded, and the recipient will not be notified.

119. If a packet does arrive, it will always arrive intact
If a packet does arrive, it will always arrive intact. Packets that are corrupt or only partially delivered are discarded.

120. Advantages of UDP
UDP communication can be more efficient than guaranteed-delivery data streams.
Unlike TCP streams, which establish a connection, UDP causes fewer overheads.
Real-time applications that demand up-to-the-second or better performance may be candidates for UDP, as there are fewer delays due to error checking and flow control of TCP.

121. UDP sockets can receive data from more than one host machine.
Some network protocols specify UDP as the transport mechanism.

122. Java Support for UDP Two classes are provided:
DatagramPacket class (java.net)
DatagramSocket class (java.net)

123. DatagramPacket Class
A DatagramPacket object represents a data packet intended for transmission using UDP.
It contains addressing information such as an IP address and a port.
When a DatagramPacket is read from a UDP socket, the IP address/port number of the packet represents the address/port number of the sender.

124. When a DatagramPacket is used to send a UDP packet, the IP address/port represents the address/port of the recipient.
DatagramPacket
IP address (java.net.InetAddr)
Port address (int)
Packet data (byte[])

125. Creating a DatagramPacket
Constructor to use for creating a DatagramPacket for receiving incoming UDP packets:
DatagramPacket(byte[] buffer, int length)
Example:
DatagramPacket packet;
packet = new DatagramPacket(new byte[256], 256);

126. Constructor to use for sending a DatagramPacket to a remote machine
DatagramPacket(byte[] buffer, int length, InetAddress dest_addr, int dest_port)
Example:
DatagramPacket packet;
InetAddress addr;
addr = InetAddress.getByName(" ");
packet = new DatagramPacket(new byte[128], ,addr, 2000);

127. DatagramPacket Methods
InetAddress getAddress()
byte[] getData()
int getLength()
int getPort()
void setAddress(InetAddress addr)
void setData(byte[] buffer)
void setLength(int length)
void setPort(int port)

128. DatagramSocket Class
The DatagramSocket class provides access to a UDP socket, which allows UDP packets to be sent and received.
The same DatagramSocket can be used to receive as well as to send packets.
Read operations are blocking - i.e. the application will continue to wait until a packet arrives.

129. Each DatagramSocket binds to a port on the local machine
Each DatagramSocket binds to a port on the local machine. The port number need not match the port number of the remote machine.
If the application is a UDP server, it will usually bind to a specific port number.

130. Creating a DatagramSocket
Constructor to use for creating a client DatagramSocket:
DatagramSocket() throws java.net.SocketException
Example:
DatagramSocket socket;
try {
socket = new DatagramSocket();
} catch (SocketException exception) { … }

131. Constructor to use for creating a server DatagramSocket:
DatagramSocket(int port) throws java.net.SocketException
Example:
DatagramSocket socket;
try {
socket = new DatagramSocket(2000);
} catch (SocketException exception) { … }

132. DatagramSocket Methods
void close()
void connect(InetAddress r_addr, int r_port)
void disconnect()
InetAddress getInetAddress()
int getPort()
InetAddress getLocalAddress()
int getLocalPort()
int getReceiveBufferSize() throws java.net.SocketException

133. int getSoTimeout() throws java.net.SocketException
int getSendBufferSize() throws java.net.SocketException
int getSoTimeout() throws java.net.SocketException
void receive(DatagramPacket packet) throws java.io.IOException
void send(DatagramPacket packet) throws java.io.IOException
int setReceiveBufferSize(int length) throws java.net.SocketException
int setSendBufferSize(int length) throws java.net.SocketException
void setSoTimeout(int duration) throws java.net.SocketException

134. Listening for UDP Packets
Before an application can read UDP packets, it must
bind a socket to a local UDP port using DatagramSocket
create a DatagramPacket that will contain the data.

135. Packet DatagramSocket DatagramPacket UDP application Reads packets
Translates packets
Into a DatagramPacket
UDP application

136. The following code illustrates the process for reading UDP packets.
DatagramPacket packet;
DatagramSocket socket;
packet = new DatagramPacket(new byte[256], 256);
socket = new DatagramSocket(2000);
boolean finished = false;
while (!finished) {
socket.receive(packet);
// process the packet }
socket.close();

137. ByteArrayInputStream
Java I/O streams are usually used to access the contents of the byte array in a DatagramPacket. See example later.
ByteArrayInputStream
DatagramPacket
DataInputStream
IP address (java.net.InetAddr)
Port address (int)
Packet data (byte[])
UDP
application

138. Sending UDP Packets
When sending a packet, the application must create a DatagramPacket that will contain the data. The address and port information must also be set.
When the packet is ready for transmission, the send method of DatagramSocket should be invoked.

139. DatagramSocket UDP application Packet DatagramPacket Binds to a
UDP port
UDP application
Send DatagramPacket
using DatagramSocket
Packet
Constructs
packet
DatagramPacket

140. The following code illustrates the process for sending UDP packets.
DatagramPacket packet;
DatagramSocket socket;
packet = new DatagramPacket(new byte[256], 256);
socket = new DatagramSocket(2000);
packet.setAddress(…);
packet.setPort(2000);
boolean finished = false;
while (!finished) {
// write data to packet buffer
socket.send(packet); … }
socket.close();

141. User Datagram Protocol Example
Run receiving application
java PacketReceiveDemo
Run sending application
java PacketSendDemo

146. ByteArrayOutputStream
PacketSendDemo
PrintStream
print(str)
ByteArrayOutputStream
DatagramPacket
toByteArray()
send(packet)
DatagramSocket

147. ByteArrayInputStream
DatagramSocket
receive(packet)
ByteArrayInputStream
DatagramPacket
getData()
read()
PacketReceiveDemo

148. Building a UDP Client/Server
Run echo server
java EchoServer
Run echo client
java EchoClient

149. Algorithm for Echo Server
Create socket
Create an empty packet
Repeat the following forever
Wait for a packet
Send the packet back to sender

150. Algorithm for Echo Client
Create socket
Set timeout value for socket
Repeat the following ten times
Create the message to be sent
Create packet containing the message as well as the destination IP and the port
Send the packet through socket
Wait for packet from receiver through socket or timeout
if packet received
Create an input stream to access data in the packet
Use the input stream to read the data and then display it on the screen.
Sleep for a second

151. Overcoming UDP Limitations
Lack of Guaranteed Delivery
Lack of Guaranteed Packet Sequencing
Lack of Flow Control

152. Lack of Guaranteed Delivery
Packets sent via UDP may become lost in transit.
UDP packets can also become damaged or lost.
For some applications, the loss of individual packets may not have a noticeable effect (e.g. video streams).
For other applications, loss of packets is not acceptable (e.g. file transfers).

153. If guaranteed delivery is required,
avoid packet-based communication, and use a more suitable transport mechanism (e.g. TCP).
send acknowledgement to sender after receiving packets.

154. Lack of Guaranteed Packet Sequencing
Applications that require sequential access to data should include a sequence number in the contents of a datagram packet.
This enables detection of duplicate packets and also missing packets.

155. Lack of Flow Control
The technique of flow control is important to avoid flooding a system with more data than it can handle due to limited bandwidth.
One technique of flow control is to limit the number of unacknowledged packets. E.g.: increase control when number of acknowledgement packets received is much less than the number of packets sent.

156. Transmission Control Protocol

157. Overview
Unlike UDP which is concerned with the transmission of packets of data, TCP establishes a "virtual connection" between two machines through which streams of data may be sent.
TCP guarantees delivery and order, providing a reliable byte communication stream between client and server that supports two-way communication.

158. Establish a virtual connection
Transmit data back and forth
Terminate the connection

159. TCP uses IP (Internet Protocol) to establish the connection between machines.
This connection provides an interface that allows streams of bytes to be sent and received, and transparently converts the data into IP datagram packets.
The virtual connection between two machines is represented by a socket.

160. TCP sockets are different from UDP sockets:
TCP sockets are connected to a single machine.
UDP sockets only send and receive packets of data. TCP allows tansmission of data through byte streams. They are converted into datagram packets for transmission over the network without programmer intervention.

161. Advantages of TCP over UDP
Automatic Error Control
Data transmission is more dependable. Delivery of data is guaranteed - lost data packets are retransmitted.
By means of a timer, TCP retransmits a packet if an acknowledgement is not received from the recipient within a specified amount of time.

162. Reliability
As packets are delivered by IP, they will frequently arrive out of order. However, each packet contains a sequence number. Using this sequence number and queuing out-of-order packets, TCP is able to pass arriving packets to the application in the correct sequence.

163. Ease of Use
Network programmers will find programming communication via TCP sockets far simpler than via datagram packets. This is because data sent and received can be treated as a continuous stream (like I/O streams). The data need not be packaged into discrete units like UDP.

164. Communication Using Ports
Both UDP and TCP uses the concept of a communications port, which distinguishes one application from another.
When a TCP socket establishes a connection to another machine, the following information will be required:
the IP address of the remote machine
the port number

165. Like ports in UDP, ports in TCP are also represented by a number in the range 1 - 65535.
Ports below 1024 are restricted to use by well-known services. For example,
Telnet (port 23)
SMTP (port 25)
HTTP (port 80)
POP3 (port 110)

166. Socket Operations TCP sockets can perform a variety of operations:
Establish a connection to a remote host
Send data to a remote host
Receive data from a remote host
Close a connection

167. There is a special type of socket that provides a service that will bind to a specific port number. Normally used only in servers, this socket can perform the following operations:
Bind to a local port
Accept incoming connections from remote hosts
Unbind from a local port

168. TCP and the Client/Server Paradigm
In network programming, applications that use sockets are divided into clients and servers.
A client is software that initiates a connection and sends requests.
A server is software that listens for connections and processes requests.

169. Note that in the context of UDP programming, no actual connection is established. UDP applications may both initiate and receive requests on the same socket.
In the client/server paradigm, when there is a connection between two applications, one must be a client and the other must be a server.

170. Network Clients
Network clients initiate connections and control network transactions.
The server fulfills the requests of the client but not the other way round.
The network client speaks to the server using a network protocol. E.g an HTTP client communicates with an HTTP server using HTTP.

171. Port numbers are used to enable clients to locate servers. E. g
Port numbers are used to enable clients to locate servers. E.g. a web server uses port 80.

172. Network Servers
The role of the network server is to bind to a specific port and to listen for new connections.
Unlike the client, the server must run continually in the hope that some client will want its services.
The server runs indefinitely. Normally, it is automatically started when the host computer of the server is started.

173. Some servers can handle only one connection at a time, while others can handle many connections concurrently, through the use of threads.
Some protocols (e.g. HTTP/1.0) normally allow only one request per connection. Others, like POP3, support a sequence of requests.
Servers answer the client request by sending either a response or an error message.

174. TCP Sockets and Java
Java provide the following classes for TCP sockets:
java.net.Socket
java.net.ServerSocket
The Socket class should be used when writing client software.
The ServerSocket class should be used when writing server software.

175. Socket Class
Socket objects represent client sockets, and is a communication channel between two TCP communications ports belonging to one or two machines.

176. There are several constructors for the Socket class.
The easiest way to create a socket is shown below:
Socket mySocket;
try {
mySocket = new Socket(" 80);
} catch (Exception e) { … }

177. Some of the other constructors:
Socket(InetAddress addr, int port)
Throws java.io.IOException, java.lang.SecurityException
Socket(InetAddress rAddr, int rPort, InetAddress lAddr, int lPort)
Socket(String rHost, int rPort, InetAddress lAddr, int lPort)
Throws java.net.UnknownHostException, java.io.IOException, java.lang.SecurityException

178. Using a Socket
Refer section (pg 150) for a description of some of the methods of the Socket class.

179. Reading from and Writing to TCP Sockets
In Java, once a socket is created, it is connected and ready to read/write by using the socket's input and output streams. Use the methods getInputStream() and getOutputStream() to access those streams.

180. Example: } catch (Exception e) { … } Socket socket;
InputStreamReader isr;
BufferedReader br;
PrintStream ps;
try {
socket = new Socket("
isr = new InputStreamReader(socket.getInputStream());
br = new BufferedReader(isr);
ps = new PrintStream(socket.getOutputStream());
} catch (Exception e) { … }

181. SO_TIMEOUT Socket Option
Socket options are settings that modify how sockets work. They can affect the performance of applications.
SO_TIMEOUT is the most useful socket option. It allows a timer to be started when a read request is made on a socket. When no data arrives in time and the timer expires, a java.io.InterruptedIOException is thrown which can be caught to check for a timeout.

182. Use the setSoTimeout() method to set the duration of the timer
Use the setSoTimeout() method to set the duration of the timer. Example:
socket.setSoTimeout(5000);
The getSoTimeout() method can be used to get the duration of the timer. A value of zero means that timeouts are disabled and read operations will block indefinitely.

183. Creating a TCP Server
The given example is a TCP server which returns the current day and time to the client.

184. SocketServer Class
The server socket is a special type of socket used to provide TCP services.
Client sockets bind to any free port on the local machine, and connect to a specific port and host.
The difference with server sockets is that they bind to a specific port on the local machine so that remote clients may locate a service.

185. Client socket connections will connect to only one machine, whereas server sockets are capable of fulfilling the requests of multiple clients.

186. Creating a ServerSocket
Once a server socket is created, it will be bound to a local port and ready to accept incoming connections.
When clients attempt to connect, they are placed into a queue.
When this queue is full, further clients are refused.

187. There are several constructors for the ServerSocket class.
The easiest way to create a socket is shown below:
ServerSocket mySocket;
try {
mySocket = new ServerSocket(80);
} catch (Exception e) { … }

188. Some of the other constructors:
ServerSocket(int port)
Throws java.io.IOException, java.lang.SecurityException
If port is 0, then any free port will be used.
By default, the queue size is set to 50.
ServerSocket(int port, int maxClients)
Allocates sufficient space to the queue to support the specified number of client sockets.

189. Using a ServerSocket
Refer section (pg 161-Reilly) for a description of some of the methods of the ServerSocket class.
The most important method is the accept() method, which accepts client connection requests.

190. Accepting and Processing Requests from TCP Clients
The most important function of a server socket is to accept client sockets. Once a client socket is obtained, the server can perform all the "real work" of server programming, which involves reading from and writing to the socket to implement a network protocol.
Example: a mail server that provides access to stored messages would listen to commands and send back message contents.

191. Example: ServerSocket server; BufferedReader reader;
PrintWriter writer;
server = new ServerSocket(13);
while (true) {
Socket client = server.accept();
reader = new BufferedReader(
new InputStreamReader(
client.getInputStream()));
writer = new PrintWriter(
new OutputStreamWriter(
client.getOutputStream())); … }

192. TCP Socket Client-Server : ALI BABA…

193. ALI BABA Client-Server

194. Client Application In this example, there are 2 java programs
The client program is implemented as a class NyietInSengClient

195. public class NyietInSengClient {
import java.io.*;
import java.net.*;
public class NyietInSengClient {
public static void main(String[] args)
throws IOException {
Socket nisSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
nisSocket = new Socket("localhost", 8888);
out = new PrintWriter(nisSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(nisSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: localhost.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: localhost."); }
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("tata titi tutu"))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser); }
out.close();
in.close();
stdIn.close();
nisSocket.close();

196. Server Application Server application is implemented using 2 classes:
NyietInSengServer
NyietInSengServer contains method main() for the server program. It listens at a port for incoming connection, accept the connection and reads messages from client/writes responses to the client through a socket

197. public class NyietInSengServer {
import java.net.*;
import java.io.*;
public class NyietInSengServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(8888);
} catch (IOException e) {
System.err.println("Could not listen on port: 8888.");
System.exit(1); }
Socket clientSocket = null;
clientSocket = serverSocket.accept();
System.err.println("Accept failed.");
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
String inputLine, outputLine;
NyietInSengProtocol nis = new NyietInSengProtocol();
outputLine = nis.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = nis.processInput(inputLine);
if (outputLine.equals("tata titi tutu"))
break; }
out.close();
in.close();
clientSocket.close();
serverSocket.close();

198. Protocol class (part of server app)
NyietInSengProtocol
NyietInSengProtocol provides the jokes. It tracks the current joke, the current status (SENTTOKTOK, SENTCLUE, etc) and returns joke text based on the current status.
It implements a communication protocol (a language) agreed by the client and server.

199. Server App.
Begins by creating a ServerSocket object to listen (wait) at a certain port. When selecting a port no., pick one that is not reserved for other services.
NyietInSengServer waits at port 8888 as the port 8888 is not used in my computer environment:
try {
serverSocket = new ServerSocket(8888); }
catch (IOException e) {
System.out.println("Could not listen on port: 8888");
System.exit(-1);

200. Server App.
The constructor for ServerSocket throws an exception if it fail to listen the specified port (say if it is being used)
In this case NyietInSengServer has no other choice than to exit.

201. If the server is able to connect to the specified port, then a ServerSocket object is created and the server app. Will perform the following steps – accept connection from client (in bold):
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.out.println("Accept failed: 8888");
System.exit(-1); }

202. Server App.
Method accept() waits until a client program is executed and requesting for connection at a specified host and port (example, host : localhost and port : 8888.
When connection between the client and server is succesfully created, method accept() will return a new Socket object (in example :clientSocket) which is bound to a new port.
NyietInSengServer can communicate with NyietInSengClient through this new socket.
It can keep listening and waiting for new incoming connection using the original ServerSocket (in example : serverSocket)
However, in the example, the server application is not able to cater for more than 1 client.

203. Read/Write Process
Gets the socket's input and output stream and opens readers and writers on them
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader( new InputStreamReader( clientSocket.getInputStream()));
String inputLine, outputLine;

204. Server App.
After the server successfully establishes a connection with a client, it communicates with the client using this code:
// initiate conversation with client
NyietInSengProtocol nis = new NyietInSengProtocol();
outputLine = nis.processInput(null);
out.println(outputLine);
Initiates communication with the client by writing to the socket (shown in bold).

205. Server App. while ((inputLine = in.readLine()) != null) {
outputLine = nis.processInput(inputLine);
out.println(outputLine);
if outputLine.equals(“tata titi tutu"))
break; }
Communicates with the client by reading from and writing to the socket (the while loop).

206. 1 is already familiar. Step 2 is shown in bold and is worth a few comments.
After the NyietInSengProtocol is created, the code calls NyietInSengProtocol 's processInput method to get the first message that the server sends to the client.
For this example, the first thing that the server says is “NyietInSeng MatekAji Semar Ngiseng!" Next, the server writes the information to the PrintWriter connected to the client socket, thereby sending the message to the client.

207. Communication Protocol of AliBaba Client-Server
Following is the implementation of the protocol:

208. public class NyietInSengProtocol {
import java.net.*;
import java.io.*;
public class NyietInSengProtocol {
private static final int WAITING = 0;
private static final int SENTTOKTOK = 1;
private static final int SENTCLUE = 2;
private static final int ANOTHER = 3;
private static final int NUMJOKES = 3;
private int state = WAITING;
private int currentJoke = 0;
private String[] clues =
{ "Ali", "Di Sini", "Hari"};
private String[] answers =
{ "Ali Baba, Bujang Lapok la.. ",
"Di Sini lah, Oi Di Sana! ",
"Harimau Kuat! Grrrrrr "};
public String processInput(String theInput) {
String theOutput = null;
if (state == WAITING) {
theOutput = "NyietInSeng MatekAji Semar Ngiseng!";
state = SENTTOKTOK;
} else if (state == SENTTOKTOK) {
if (theInput.equalsIgnoreCase("Siapa tu?")) {
theOutput = clues[currentJoke];
state = SENTCLUE;
} else {
theOutput = "Sepatutnya awak cakap \"Siapa tu?\"! " +
"Cuba lagi. NyietInSeng MatekAji Semar Ngiseng!"; }
} else if (state == SENTCLUE) {
if (theInput.equalsIgnoreCase(clues[currentJoke] + " mana?")) {
theOutput = answers[currentJoke] + " Main lagi? (y/n)";
state = ANOTHER;
theOutput = "Sepatutnya awak cakap \"" +
clues[currentJoke] +
" mana?\"" +
"! Cuba lagi. NyietInSeng MatekAji Semar Ngiseng!";
} else if (state == ANOTHER) {
if (theInput.equalsIgnoreCase("y")) {
if (currentJoke == (NUMJOKES - 1))
currentJoke = 0;
else
currentJoke++;
theOutput = "tata titi tutu";
state = WAITING;
return theOutput;

209. Web-based Client-Server Application
Server-side programming
Servlet
209

210. SERVLET

211. Where are we? JAVA Object-oriented design Introduction Advanced topics
Server-side coding
10. JDBC
4. Object
Classes
1. Intro to
Java, Course
7. Inheritance
11.Streams
2. Java lang.
basics
6. Exception
Handling
13. Servlets
5. Encapsulation
14. JSP
3. Arrays
8. Polymorphism
12. Networking
9. Abstract classes
and Interfaces
Newbie
Programmers
Designers
Developers
Professionals

212. Outline Concepts Features javax.servlet.Servlet
Example: get and send a page to client
Example: post
Image generating
Session tracking
Cookie, HttpSession, URL-rewriting
Practical examples

213. Today’s buzzwords Applets Servlets Session tracking
Java programs capable of running within a web browser
Servlets
Java code running on server side
Session tracking
Keeping context information during a session of browsing related web pages

214. What is java servlet ? A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol. Servlet is an opposite of applet as a server-side applet. Applet is an application running on client while servlet is running on server.

215. What is Java Servlets? = Servlet
module run inside request/response-oriented server
Browser
Java-enabled
Web Server
Servlet
Database
HTML form
Servlets are to Servers what Applets are to Browsers
Servlet =
Applet
1. 서블릿의 개념
- 서버측에서 클라이언트측의 요구를 받아 그에 대한 처리를 한 후 결과를 되돌리는 모듈이다.
2. 애플릿/서블릿
애플릿은 서버측에서 작성되었지만, 코드가 클라이언트로 다운로드되어 실행되는 반면, 서블릿은 서버 측에서 직접 실행되어 그 결과만 반환된다는 점에서 오히려 CGI와 비슷하다. 하지만,CGI보다는 요구와 결과를 처리하는 방법이 더 쉽다.
3. JDK의 기본 패키지가 아니다. 서블릿을 작성하려면, JDK외에 JSDK(98년 중반 현재 2.0까지 발표)를 다운로드받아야 한다.
4. 서블릿을 동작시키려면, 서블릿 실행을 처리할 수 있는 웹 서버 또한 존재해야 한다.
Server
Browser
Substitute for CGI scripts
easier to write and fast to run
Not part of the core Java Framework

216. Example use of servlet
Processing data POST over HTTPs using HTML form as purchase order or credit card data
Allowing collaborative between people such as on-line conferencing
Many servlet can chain together among Web servers to reduce load on one Web server.

217. Why Use Servlets ?
One of the reasons that Java became popular is Applets.
but there are problems with Applets
Browser compatibility
Download bandwidth
Server-side Java
the code is executed on the server side not the client side
a dynamically loaded module that services requests from a Web server

218. Servlets (contd.) vs. Common Gateway Interface (CGI)
create new process for each request
most platform independent CGI language - Perl
start a new instance of interpreter for every request
CGI runs in a completely separate process from the Web server
vs. Server-Side JavaScript
only available on certain web servers
vs. Active Server Pages (ASP)

219. CGI Communication (traditional approach)
1. Web browser requset a response from CGI program.
2. Web server create CGI profile file that was contain information about CGI variable, server and CGI output file.
3. Web server starts CGI application and wait for its termination.
4. CGI program runs and writes the result to CGI output file and then terminates.
5. Web server reads from CGI output file and send back to Web browser.

220. Servlet Communication
Web browser request servlet by specified URL as
Web server call service() method in ServletLoader class which will dynamically load a specified servlet name from a special directory call servlet.

221. Servlet vs CGI Servlet run as light weight thread in process.
CGI run as heavy weight process.

222. Advantage of servlet over CGI
PlatForm Independence
Servlets can run on any platform. PERL also can be moved from platform to platform while CGI such as C are not portable.
Performance
Servlets only needs be loaded once, while CGI programs needs to be load for every request so that servlet should performs faster than CGI
Security
While CGI can do many insecure things, java provided security in language level.

223. Three Tier Applications.

224. Java Servlet Development Kit installation

225. Requirement for running java servlet
Java Servlet API
A set of java classes. This is a Java Servlet Development Kit(JSDK) that can be download from
JSDK allows most standard Web server such as Netscape servers, IIS, Apache and others to load servlets
Java-enabled Web server
There are many web server that support java virtual machine such as Java Web server by SUN, WebSite Pro V2.0 by O’Reilly and the latest version of World Wide Web Consortium’s free jigsaw Web Server.

226. Java Web Server (JWS) response request Servlet Java Web Server

227. Servlet Lifecycle Server loads Servlets - run init method
No Concurrency Issue
Server runs init only once, not per request
Server loads Servlets
- run init method
Servlets Accept Request from
Clients and return Data back
- run service method
service must be thread-safe
- multiple service method at a time
if that is impossible, servlet must
implement SingleThreadModel interface
Server removes Servlets
- run destroy method
destroy must be thread-safe
- when server runs destroy, other threads
might be accessing shared resources
Server reloads Servlets
- run init method

228. A Typical Servlet Lifecycle
from Servlet Essential by Stefan Zeiger

229. Servlet class Example Interface Servlet
Define the standard way in which a network server will access a servlet. All servlet classes must (fundamentally) implement this interface.
GenericServlet
Defines a generic, protocol-independent servlet. For servlet that is not intended to use with Web server. To write an HTTP servlet for use on the Web, extend HttpServlet instead
HttpServlet
For Servlet that is intended to use with Web server. This class adds HTTP-specific to work with a Web server context

230. Servlet Structure
All servlet classes and interfaces that form the API are found in the javax.servlet package.
All servlets, no matter what type of server they are destined to be used with, implement the javax.servlet.Servlet interface. This interface defines the basic functionality that a servlet must possess

231. ServletConfig
When the servlet first starts up, the system can pass specific initialization information to the servlet for possible processing via the init(...) method.
Parameters are passed in using a key/value pairing, and two methods are provided to access this data: getInitParameter(...) and getInitParameterName().

232. ServletContext
allows the servlet to interrogate the server about various pieces of environmental data
Example :
Many servers, particularly web servers, refer to files and resources as virtual files.
However, this makes opening up files difficult, as the virtual file or alias needs to be mapped onto a real file.
The ServletContext interface, for example, provides a method to convert an alias and real path file names.

233. ServletContext

234. GenericServlet
The base class on which the majority of servlets are based is the GenericServlet class.

235. Interface Servlet class
void init(ServletConfig)
Initialized the servlet when it is loaded into server (system).
abstract void service(ServletRequest, ServletResponse)
This is an abstract class so that it must be implemented by a subclass of GenericServlet class. A method that the servlet processes each client request
destroy()
This method is called when the server remove a servlet from memory.

236. ServletRequest

237. ServletRequest
If, on the other hand, data is coming from a non-HTTP client, then the data may be coming in as a stream.
The ServletInputStream can be used to read this stream.
Additional information about the client that may be useful is the home network address from which it is sending.
This information can be made available through the getRemoteAddr() and getRemoteHost() methods.

238. ServletResponse
The most important method of this interface is the getOutputStream() method.
This returns the ServletOutputStream, which can be used to provide any other preferred output stream class from the java.io package.

239. GenericServlet : Example

240. GenericServlet

241. Web-Based Servlet
The developers at Java recognized the fact that the majority of servlets would be employed in the field of the Internet, with particular emphasis on the world wide web.
The servlet API offers you a direct alternative to using CGI and Microsoft's Active Server Pages (ASP) to implement server-side solutions.
To make coding servlets for the web relatively easy, a special HttpServlet class was developed.
This provided methods to access the more common header fields found in the HTTP protocol.

242. HttpServlet class void doGet(HttpServletRequest, HttpServletResponse)
This method handle HTTP GET requests.
void doPost(HttpServletRequest, HttpServletResponse)
This method handle HTTP POST requests. The Form parameter are read via HttpServletRequest parameter.
void service(HttpServletRequest, HttpServletResponse)
This method can handle both GET and POST method. Normally, service() method used to overide one or both of the previous method
void service(servletRequest,ServeletResponse)
This method overides service() method of GenericServlet class

243. HttpServlet The HttpServlet, based on the GenericServlet class.
It provides an improved interface for dealing with HTTP-specific client requests.
In addition to the service(...) method that is used to deal with all requests, seven additional methods exist for processing requests; doGet(...), doPost(...), doHead(...), doPut(...), doTrace(...), doOptions(...) , and doDelete(...).

244. Servlet Architecture Overview - HTTP servlets
IS-A
Servlet
interface
Client
GET
POST
doGet(ServletRequest req, ServletResponse res);
ServletRequest
ServletResponse
ServletResponnse
doPost(ServletRequest req, ServletResponse res);
parameters, protocol, remote host,
ServerInputStream(binary data etc..)
mime type to reply,reply data,
ServletOutputStream

245. HttpServlet Interface

246. ServletRequest Interface
This interface return information about parameter sent with
the request.
int getContentLength()
String getContentType()
String getProtocol()
String getScheme()
String getServerName()
int getServerPort()
String getRemoteAddr()

247. HttpServletRequest :

248. ServletRequest Interface(continued)
String getRemoteHost()
String getRealPath(String path)
ServletInputStream getInputStream()
String getParameter(String name)
String[] getParameterValues(String name)
Enumeration getParameterNames()
Object getAttribute(String name)

249. ServletResponse Interface
This interface defined method for sending information back to Web browser.
void setContentLength(int len)
void setContentType(String type)
ServletOutputStream getOutputStream()

250. HttpServletRequest Interface
The method of HttpServletRequest interface inherits the method in ServletRequest interface. GET, POST, and HEAD in HTTP are also supported.

251. Servlets (contd.) HttpServletRequest HttpServletResponse
information sent from the client
getParameter()
getParameterValues()
getParameterNames()
will discuss in detail later in FormPost
HttpServletResponse
information sent to the client
getWriter()
return an instance of PrintWriter
you can use print and println with a PrintWriter
see SimpleServlet

252. HttpServletResponse Interface(continued)
boolean containHeader(String name)
void setStatus(int statusCode, String statusMessage)
void sendError(int statusCode, String Message)
void sendError(int statusCode)
void setDateHeader(String name, long date)
void sendRedirect(String location)

253. HttpServletResponse Interface
String getMethod()
String getServletPath()
String getPathInfo()
String getPathTranslated()
String getQueryString()
String getRemoteUser()
String getAuthType
String getHeader(String name)
String getIntHeader(String name)
long getDateHeader()
Enumeration getHeaderNames()

254. Writing the Servlet Implement the javax.servlet.Servlet interface
HTTP: extends javax.servlet.http.HttpServlet class
public class SurveyServlet extends HttpServlet {
/* typical servlet code, with no threading concerns
* in the service method. */
... }

255. Interacting with Clients(1) - HTTP servlets
methods
doGet
Get
Client
Post
doPost
Put
doPut
Delete
doDelete
HttpServletRequest - argument & HTTP header data
String[] getParameterValues(String name) - get user parameter
For GET method
- String getQueryString()
For POST, PUT, DELETE method
- BufferedReader getReader() - text data
- ServletInputStream getInputStream() - binary data

256. Interacting with Clients(2) - HTTP servlets
HttpServletResponse - return the response data to the user
PrintWriter getWriter() - text data
ServletOutputStream getOutputStream() - binary data
Before accessing the Writer or OutputStream, HTTP header data should be set

257. Example of an HTTP Servlet - GET/HEAD methods
public class SimpleServlet extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
// set header field first
res.setContentType("text/html");
// then get the writer and write the response data
PrintWriter out = res.getWriter();
out.println("<HEAD><TITLE> SimpleServlet</TITLE></HEAD> <BODY>");
out.println("<h1> SimpleServlet Output </h1>");
out.println("</BODY>");
out.close(); }
public String getServletInfo() {
return "A simple servlet";
} }

258. Example (2) use of HttpServlet

259. Accessing web-based servlets
Assume the servlets' class file has been placed in the server's servlets directory.
The servlet can be called by including /servlet/ before the servlet name in the URL.
For example, if you set the class name of the sample servlet to TestServlet, then it could be accessed using

260. Apache-Tomcat Directory Structure

262. Starting Tomcat

264. Email database example : emaildb.html
<head>
<title> DB Example</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso ">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<form name="form1" method="get" action="
<p>Nama
<input type="text" name="name" width = "20">
</p>
<p>
<input type="text" name=" " width="30">
<p> WebSite Address
<input type="text" name="website" width="30">
<p>
<input type="submit" name="submit" value="Submit">
<input type="reset" name="reset" value="Reset">
</form>
</body>
</html>

265. HTML Form Example

266. Saving data to emaildb – inserttodb servlet/*
Servlet to JDBC - save into database */
import java.io.*;
import java.util.Enumeration;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import java.net.*;
public class inserttodb extends HttpServlet{
static final String dbURI = "jdbc:mysql:/// db";
String str = "INSERT INTO list VALUES(?, ?, ?)";
Connection theConnection = null;
private ServletConfig config;
public void init(ServletConfig config)
throws ServletException{
this.config=config; }

267. throws ServletException, IOException {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String nameS = request.getParameter("name");
String S = request.getParameter(" ");
String websiteS = request.getParameter("website");
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<HTML><HEAD><TITLE> List.</TITLE>");
out.println("</HEAD>");
out.println("<BODY bgColor=blanchedalmond text=# topMargin=0>");
out.println("<P align=center><FONT face=Helvetica><FONT color=fuchsia style=\"BACKGROUND-COLOR: white\"><BIG><BIG>Save these data to database.</BIG></BIG></FONT></P>");
out.println("<P align=center>");
out.println("<form name=form1 action=\"
out.println("<p>");
out.println("<input type=submit name=\"submit\" value=\"Retrieve Data\">");
out.println("</p>");
out.println("</form>");

268. // Load database driver Class.forName("org.gjt.mm.mysql.Driver");
try {
// Load database driver
Class.forName("org.gjt.mm.mysql.Driver");
} catch (ClassNotFoundException cnfe){
System.out.println("ClassNot found error"); };
// Create a Connection to db Data source
theConnection = DriverManager.getConnection(dbURI); //Connect to db Data source
} catch (SQLException sqle) {
System.out.println(sqle);
// prepare statement for inserting data into table
PreparedStatement theStatement=theConnection.prepareStatement(str);
//Set parameters for INSERT statement and execute it
theStatement.setString(1, nameS);
theStatement.setString(2, S);
theStatement.setString(3, websiteS);
theStatement.executeUpdate();
theConnection.close(); //Close database Connection
} catch(Exception e){
out.println(e.getMessage());//Print trapped error. }

269. Saving to database and use a button to retrieve data back

270. Retrieve List from emaildb

271. Retrieve data from emaildb database/*
Servlet to retrieve data from database using JDBC */
import java.io.*;
import java.util.Enumeration;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import java.net.*;
public class dbServlet extends HttpServlet{
static final String dbURI = "jdbc:mysql:/// db";
Connection theConnection;
private ServletConfig config;
public void init(ServletConfig config)
throws ServletException{
this.config=config; }

272. Continued
public void service (HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
HttpSession session = req.getSession(true);
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<HTML><HEAD><TITLE> List.</TITLE>");
out.println("</HEAD>");
out.println("<BODY bgColor=blanchedalmond text=# topMargin=0>");
out.println("<P align=center><FONT face=Helvetica><FONT color=fuchsia style=\"BACKGROUND-COLOR: white\"><BIG><BIG>List of addresses.</BIG></BIG></FONT></P>");
out.println("<P align=center>");
out.println("<TABLE align=center border=1 cellPadding=1 cellSpacing=1 width=\"75%\">");
out.println("<TR>");
out.println("<TD>Name</TD>");
out.println("<TD> </TD>");
out.println("<TD>Website</TD></TR>");

273. Class.forName("org.gjt.mm.mysql.Driver");//Loading mysql Driver
try{
Class.forName("org.gjt.mm.mysql.Driver");//Loading mysql Driver
theConnection = DriverManager.getConnection(dbURI); //Connect to db
Statement theStatement=theConnection.createStatement();
ResultSet theResult=theStatement.executeQuery("select * from list"); while(theResult.next()) { //Fetch all the records and print in table
out.println();
out.println("<TR>");
out.println("<TD>" + theResult.getString(1) + "</TD>");
out.println("<TD>" + theResult.getString(2) + "</TD>");
String s=theResult.getString(3);
out.println("<TD><a href=" + s + ">" + s + "</a></TD>");
out.println("</TR>"); }
theResult.close();//Close the result set
theStatement.close();//Close statement
theConnection.close(); //Close database Connection
}catch(Exception e){
out.println(e.getMessage());//Print trapped error.
out.println("</TABLE></P>");
out.println("<P> </P></FONT></BODY></HTML>");
public void destroy(){

274. Teknologi Rangkaian Komputer Lapisan Pengangkutan TCP/IP :
TK3133
Teknologi Rangkaian Komputer
Lapisan Pengangkutan TCP/IP :
TCP dan UDP

275. Unit Data Protokol Pengangkutan

276. Elemen Protokol Pengangkutan
Pengalamatan
Pembinaan Sambungan
Penamatan Sambungan
Kawalan Aliran dan Penimbalan
Pemultipleksan
Pemulihan kerosakan

277. Protokol Pengangkutan
(a) Persekitaran Lapisan Pautan Data
(b) Persekitaran Lapisan Pengangkutan

278. Pengalamatan

279. Pembinaan Sambungan
Bagaimana sesuatu proses pada Hos 1 membina satu sambungan kepada server di Hos 2

280. Lapisan Pengangkutan TCP/IP
Internet Protocol (IP) menyediakan perkhidmatan datagram kurang/tidak- dipercayai di antara hos-hos
Protokol Pengangkutan bertujuan untuk menyediakan pengangkutan data antara hujung ke hujung yang boleh dipercayai (juga kurang-dipercayai) dan kos efektif tanpa mengira jenis rangkaian
Hujung ke hujung bermaksud proses ke proses atau aturcara

281. Lapisan Pengangkutan TCP/IP
Isu yang diambil-kira
memeriksa integriti paket
penghantaran semula paket yang rosak atau hilang
penyediaan dan pengurusan sambungan
Pengalamatan
perlu mentakrifkan hos dan proses
proses ditentukan oleh nombor pengkalan yang digunakan
biasanya dalam pasangan <hos, pengkalan>

282. Perkhidmatan dan Protokol Pengangkutan dalam Internet
2 jenis perkhidmatan Internet dalam Lapisan Pengangkutan
Berorientasikan sambungan / Connection oriented
Tanpa sambungan / Connectionless
2 protokol pengangkutan yang utama :
TCP (Transmission Control Protocol)
UDP (User Datagram Protocol)

283. Transmission Control Protocol (TCP)
TCP ialah protokol pengangkutan yang paling kerap/popular digunakan
Membekalkan penghantaran data yang dipercayai dengan menggunakan penghantaran datagram IP yang kurang dipercayai

284. Transmission Control Protocol (TCP)
TCP menjalankan fungsi lapisan pengangkutan yang biasa iaitu:
Segmentation - pecahkan sesuatu utusan kepada paket-paket
Membetulkan kesalahan - diperlukan kerana IP merupakan perkhidmatan yang tidak boleh dipercayai
Kawalan point-to-point - untuk mengelakkan limpahan penimbal
pemultipleks dan penyahmultipleks sesi

285. Protokol Kawalan Penghantaran (Transmission Control Protocol (TCP))
Perkhidmatan yang diberikan oleh TCP
boleh dipercayai
litar maya - berdasarkan orientasi-sambungan
dupleks penuh - pindahan selari pada kedua-dua arah
berpenimbal - TCP menerima data dan menghantarnya mengikut kesesuaian masa yang diperlukan

286. Pengalamatan dan Pemultipleksan TCP
Perkhidmatan TCP diperolehi dengan kedua-dua penghantar dan penerima mencipta soket
Komputer yang berkomunikasi mesti setuju pada satu nombor pengkalan
Pelayan buka pengkalan tertentu dan tungu mesej yang masuk
Pelanggan/Klien pilih pengkalan tempatan dan hantar mesej kepada pengkalan yang dipilih

287. Pengalamatan dan Pemultipleksan TCP
TCP mengenali hubungan sebagai pasangan soket
Alamat soket mengandungi alamat Internet dan nombor pengkalan
Alamat Internet hos diberikan oleh IP
Nombor pengkalan menentukan id pemprosesan pada hos

288. Pengalamatan dan Pemultipleksan TCP (samb)
Nombor Pengkalan boleh jadi dikhaskan (well-known port) atau diumpukkan secara dinamik.
No. Pengkalan dibawah 256 adalah pengkalan well-known : untuk perkhidmatan piawai
23 untuk telnet, 25 untuk smtp, 80 untuk http, 21 untuk ftp
Secara konsep, TCP boleh membuat hubungan secara multipleks ke beberapa soket pada sesuatu hos melalui satu sambungan lapisan rangkaian

289. Contoh Umpukan Pengkalan
Port
Protocol
Use 21
FTP
File transfer 23
Telnet
Remote login 25
SMTP 69
TFTP
Trivial File Transfer Protocol 79
Finger
Lookup info about a user 80
HTTP
World Wide Web
110
POP-3
Remote access
119
NNTP
USENET news

290. Penghantaran TCP Segmen TCP dihantar dalam datagram IP
Internet router hanya lihat pada kepala IP untuk majukan datagram
TCP pada destinasi menterjemahkan segmen TCP

291. TCP dan penghantaran boleh-dipercayai
TCP guna banyak teknik yang (dibincangkan selepas ini) dalam kawalan ralat, aliran dan kesesakan untuk menyediakan penghantaran yang boleh dipercayai
Guna ACK untuk penghantaran semula
Masa-tamat
Nombor jujukan untuk segmen
Sliding window

292. Format Segmen TCP
Kepala TCP segmen bermula dengan kepala format tetap 20 byte

293. ‘Jabat-tangan tiga arah’ TCP
TCP menggunakan ‘jabat-tangan tiga arah’ ketika memulakan dan menamatkan hubungan untuk menyediakan kebolehpercayaan
Tentukan kedua-dua nod bersedia dan selaraskan nombor jujukan rawak untuk sinkronikan hubungan

294. Memulakan Sambungan TCP
Guna segmen SYN untuk cipta satu sambungan
Hos 1 hantar segmen SYN dan nombor jujukan rawak
Hos 2 membalas segmen SYN, acknowledgment kepada Hos 1 dan nombor jujukan rawak
Host 1 balas dengan acknowledgment

295. Menamatkan Sambungan TCP
TCP guna segmen FIN untuk menamatkan sambungan

296. Protokol Datagram Pengguna (User Datagram Protocol (UDP))
UDP merupakan protokol pengangkutan dalam set TCP/IP
UDP menyediakan perkhidmatan datagram yang tidak dapat diharap/dipercayai sepenuhnya
Paket mungkin hilang atau tidak menurut urutan
Pengguna bertukar-tukar datagram, bukannya aliran data
Berdasarkan tanpa-sambungan
Tidak berpenimbal pada penghantar - UDP menerima data dari aplikasi dan terus menghantarnya
Dupleks penuh - pindahan datagram boleh pada dua arah
Digunakan apabila tiada kawalan ralat diperlukan

297. User Datagram Protocol
UDP hantar mesej tak-bersandaran dipanggil datagram di antara aplikasi atau proses pada hos komputer
Penghantaran “Best effort'' – datagram boleh jadi hilang, dihantar tanpa turutan dsb.
Checksum memastikan data integriti
Titik hujung UDP dipanggil pengkalan/port

298. Well-known Port UDP Port Name Description 11 systat System statistics53
domain
DNS 69
tftp
Trivial File Transfer Protocol (TFTP
161
snmp
Simple Network Management Protocol (SNMP)

299. User Datagram Protocol (UDP)
UDP mempunyai ‘overhead’ yang rendah berbanding TCP
Kepala UDP mudah :
Nombor pangkalan
Panjang mesej
checksum

300. User Datagram Protocol (UDP)
UDP source port
UDP destination port
UDP message length
UDP checksum
Data

301. Kepala UDP

302. Ringkasan 2 protokol utama dalam lapisan pengangkutan TCP/IP :
TCP menyediakan aplikasi dengan perkhidmatan boleh-percaya, kawalan aliran, dupleks penuh dan berorientasikan sambungan
UDP menyediakan aplikasi dengan perkhidmatan kurang dipercayai dan tanpa sambungan

303. Teknologi Rangkaian Komputer Senibina Internet dan Protokol TCP/IP
TK3133
Teknologi Rangkaian Komputer
Antara Rangkaian :
Senibina Internet dan Protokol TCP/IP

304. Pengenalan Antara Rangkaian : Konsep Senibina Protokol

305. Pengenalan
Dalam dunia sebenar, komputer dihubungkan dengan pelbagai jenis teknologi LAN dan WAN
Realitinya, rangkaian adalah heterogeneous iaitu rangkaian pelbagai jenis (dan bukan homogeneous)
Mengandungi berjuta-juta rangkaian yang dihubungkan kepada tulang-belakang berkelajuan tinggi
Mana-mana sistem perlu menyesuaikan dengan pelbagai teknologi
Memperkenalkan konsep internetworking

306. Internetworking / Antara Rangkaian
Internetworking ialah skima untuk menyambungkan pelbagai rangkaian yang berlainan teknologi
Menggunakan kedua-dua perkakasan dan perisian
Perkakasan tambahan diletakkan di antara rangkaian
Perisian berada pada komputer yang terhubung dengannya
Sistem rangkaian yang bersambungan ini juga dipanggil internetwork / internet
Juga dikenali sebagai rangkaian maya

307. AntaraRangkaian / Internetworking
Kenapa rangkaian berbeza?
Rangkaian berbeza dengan protokol yang berbeza
Install rangkaian sendiri
Rangkaian berbeza guna teknologi berbeza
Senario internetworking

308. Antara Rangkaian / Internetworking

309. Internet ialah koleksi sambungan pelbagai rangkaian
Koleksi Sub Rangkaian
Internet ialah koleksi sambungan pelbagai rangkaian

310. Perbezaan Rangkaian

311. Sambungan Rangkaian Fizikal menggunakan Peranti Router
Router merupakan komponen atau peranti perkakasan yang digunakan untuk menyambungkan rangkaian
Router mempunyai lebih antaramuka pada pelbagai rangkaian
Router hantar dan serahkan paket di antara rangkaian-rangkaian
Tukar paket jika perlu untuk memenuhi piawaian untuk setiap rangkaian yang berbeza teknologi (juga dipanggil sebagai gateway)

312. Router
Contoh dua rangkaian fizikal disambungkan dengan satu router yang mengandungi 2 antaramuka berasingan untuk setiap sambungan rangkaian

313. Senibina Internet
internetwork terdiri daripada pelbagai rangkaian yang dihubungkan oleh router (rangkaian boleh jadi LAN atau WAN)

314. Senibina Internet Router boleh mempunyai lebih daripada dua antaramuka

315. Internet
The internet concept. (a) The illusion of a single network that TCP/IP software provides to users and applications, and (b) the underlying physical structure in which a computer attaches to one physical network, and routers interconnect the networks

316. Internet dilihat oleh TCP/IP

317. Protokol untuk Internet
TCP/IP merupakan protokol internetworking yang paling popular digunakan
Protokol internetworking yang pertama
Dibiayai oleh ARPA dan diambil alih oleh NSF
Pelantar dan pengeluar tidak-bersandar

318. Lapisan TCP/IP Model OSI 7-lapisan tidak termasuk internetworking
Model Lapisan TCP/IP mengandungi lima lapisan

319. Lapisan TCP/IP dan Model OSI

320. Lapisan TCP/IP Lapisan 5: Aplikasi Lapisan 4: Pengangkutan
Menyamai lapisan 5,6 dan 7 dalam Model OSI
Lapisan 4: Pengangkutan
Menyamai lapisan 4 dalam Model OSI ; menyediakan penghantaran data boleh-percaya
Lapisan 3: Internet
Menakrifkan format seragam paket dihantar melalui rangkaian pada teknologi yang berbeza dan memberikan mekanisma untuk penghantaran paket oleh router

321. Lapisan TCP/IP Lapisan 2: Antaramuka Rangkaian
Menyamai lapisan 2 dalam Model OSI; takrifkan format kerangka
Lapisan 1: Fizikal
Menyamai lapisan 1 dalam Model OSI; takrifkan asas perkakasan rangkaian

322. Hos, Router dan Lapisan Protokol
Hos komputer ialah mana-mana sistem komputer yang terhubung pada internet yang melaksanakan aplikasi
TCP/IP membenarkan pasangan hos pada internet berkomunikasi secara terus
Kedua-dua hos dan router mempunyai/memerlukan timbunan TCP/IP
Hos biasanya mempunyai satu antaramuka dan tidak majukan/forward paket
Router majukan/hantar paket tetapi tidak memerlukan lapisan 4 dan 5

323. Lapisan Rangkaian Protokol Internet (IP)
Bagaimana mengendalikan rangkaian di dalam rangkaian ?
Guna protokol lapisan rangkaian yang dipanggil sebagai Internet Protocol (IP)
Membolehkan satu aturcara yang dilarikan pada satu komputer menghantar data kepada aturcara aplikasi yang dilarikan pada komputer lain pada rangkaian berjauhan

324. Protokol Internet (IP)
IP bertanggungjawab menyediakan penghantaran best-effort untuk paket (atau dikenali sebagai datagram dalam lapisan IP)
Bagaimana komunikasi dalam Internet ?
Lapisan pengangkutan ambil aliran data dan pecahkan kepada datagram
Lapisan rangkaian hantar setiap datagram melalui Internet. Pemecahan kepada unit yang lebih kecil boleh berlaku sewaktu proses ini

325. Protokol Internet (IP) samb.
Pada destinasi , datagram akan dikumpulkan kembali oleh lapisan rangkaian kepada datagram asal dan dihantar kepada lapisan pengangkutan
Best-effort tidak menjamin akan mengendalikan masalah tindanan datagram, lambatan atau penghantaran tidak-berjujukan, data rosak dan hilang
Perkhidmatan yang ditawarkan oleh IP ialah tanpa-sambungan
IP takrifkan format paket bebas-perkakasan yang boleh dihantar dipanggil Datagram IP

326. IP Datagram IPv4 takrifkan datagram maksimum 64Kb
Format kepala IP datagram

327. Kepala Protokol IPv4

328. Format IP Datagram Medan Penerangan VERSION Nombor versi IP datagram
IHLEN
Berapa panjang kepala IP datagram
TOS
Jenis perkhidmatan yang ditawarkan
Total Length
Berapa panjang datagram

329. Protokol IP Medan Penerangan Identification
Pengenalan unik kepada datagram
Fragment Offset
Ofset bagi pecahan
Time To Live
Pembilang kepada bil maksima jangkahayat datagram
Protocol
Memberikan protokol pada lapisan atas mana
Checksum
Menakrifkan kesahihan kepala
Source/destination address
Alamat penuh nod sumber/destinasi
Option
Mungkin mengandungi option keselamatan

330. Pemecahan/Fragmentation
Setiap teknologi rangkaian takrifkan jumlah maksimum data yang boleh dihantar dalam satu paket. Batasan ini dikenali sebagai MTU (Maximum Transmission Unit)
Apabila satu router terima satu datagram yang lebih besar dari MTU rangkaian dimana ia perlu dihantar, router akan pecahkan datagram kepada datagram lebih kecil dipanggil fragment (pecahan)
Setiap fragment dihantar kepada destinasi yang kemudiannya bertanggungjawab memadan/menyambung kembali kepada datagram asal

331. Fragmentation Transparent fragmentation Nontransparent fragmentation

332. Fragmentation (2)
Fragmentation when the elementary data size is 1 byte.
(a) Original packet, containing 10 data bytes.
(b) Fragments after passing through a network with maximum packet size of 8 payload bytes plus header.
(c) Fragments after passing through a size 5 gateway.

333. Isu alamat
Aspek utama dalam rangkaian maya ialah satu format alamat yang seragam
Tidak boleh guna alamat perkakasan kerana teknologi berlainan menggunakan format alamat yang berbeza
Format alamat mestilah tidak-bersandaran dengan mana-mana format alamat perkakasan yang tertentu
Hos penghantar letakkan alamat internet destinasi dalam paket/datagram
Router periksa alamat destinasi dan hantarkan paket pada destinasi

334. Alamat TCP/IP
Pengalamatan dalam TCP/IP ditakrifkan oleh Internet Protocol (IP)
Setiap hos diumpukkan dengan satu nombor 32-bit
Dipanggil alamat IP atau alamat Internet
Unik pada keseluruhan Internet
Setiap datagram mengandungi alamat IP sumber dan destinasi

335. Alamat IP
Setiap alamat IP dibahagikan kepada dua bahagian : no. rangkaian (prefix) dan no. hos (suffix)
No. rangkaian menunjukkan rangkaian fizikal di mana komputer dihubungkan
No. hos pula menunjukkan nombor unik komputer pada rangkaian
Format alamat ini menjadikan routing lebih efisyen

336. Merekabentuk Alamat IP
Daripada 32-bit, beberapa bit diumpukkan pada prefix dan beberapa lagi bit pada suffix
Prefix besar, suffix kecil - banyak rangkaian, sedikit hos pada rangkaian
Prefix kecil, suffix besar - sedikit rangkaian, banyak hos pada rangkaian
Oleh kerana adanya pelbagai jenis teknologi, perlu benarkan kedua-dua rangkaian besar dan kecil

337. Pengkelasan Alamat
Pelbagai format alamat untuk benarkan kedua-dua prefix besar dan kecil
Setiap format dipanggil satu kelas alamat
Sesuatu kelas alamat dikenalpasti melalui empat bit yang pertama

338. Format Kelas Alamat IP

339. Alamat IP Khas

340. Menggunakan kelas alamat IP
Kelas A, B dan C adalah kelas primari
Digunakan untuk pengalamatan hos yang biasa
Kelas D untuk tujuan multicast, satu bentuk terhad broadcast/terpancar
Kelas E dikhaskan untuk tujuan masa depan

341. Dotted Decimal Notation
Nombor IP adalah dalam nombor binari 32-bit.
Untuk memudahkan manusia, notasi dotted decimal digunakan
Nombor 32-bit diungkapkan sebagai 4 seksyen 8-bit dalam nombor decimal dan guna titik/noktah untuk memisahkan seksyen
Untuk mengenalpasti kelas dari nombor decimal, boleh guna julat alamat

342. Dotted Decimal Notation

343. Dotted Decimal Notation

344. Julat Kelas daripada Alamat IP

345. Bilangan Rangkaian dan Hos

346. Contoh Pengalamatan kelas
Contoh pegumpukan alamat IP pada hos

347. Subnet Membolehkan rangkaian dipecahkan kepada beberapa sub rangkaian
Contoh : satu tapak mengandungi satu alamat IP kelas B diumpukkan pada rangkaian tetapi mempunyai dua atau lebih rangkaian fizikal. Hanya router setempat tahu tentang pelbagai subrangkaian dan bagaimana nak hantar data padanya, router lain hanya tahu ada satu rangkaian sahaja

348. Satu rangkaian kampus mengandungi LAN untuk pelbagai jabatan
Subnet
Satu rangkaian kampus mengandungi LAN untuk pelbagai jabatan

349. Satu rangkaian Kelas B disubnetkan
Memerlukan maklumat tambahan yang mengkhususkan batas di antara prefiks dan suffiks dipanggil subnet mask
Satu rangkaian Kelas B disubnetkan
kepada 64 subnet

350. IPv6 128 bit bit alamat Kepala lebih mudah Lebih sokongan perkhidmatan
keselamatan

351. Kepala IPv6

352. Protokol Kawalan Internet
Sebagai tambahan kepada IP, lapisan Rangkaian Internet mempunyai beberapa protokol kawalan pada lapisan rangkaian/internet
Protokol Resolusi Alamat (Address Resolution Protocol (ARP))
Protokol Songsangan Resolusi Alamat (Reverse Address Resolution Protocol (RARP))
Protokol Utusan Kawalan Internet (Internet Control Message Protocol (ICMP))
Protokol Pengurusan Kumpulan Internet (Internet Group Management Protocol (IGMP))

353. Protokol Resolusi Alamat (Address Resolution Protocol (ARP))
Hubungan antara hos menggunakan alamat IP, tetapi hubungan lapisan pautan data menggunakan alamat MAC
protokol ini digunakan untuk mencari alamat MAC bagi NIC yang digunakan oleh hos yang menggunakan IP tertentu
Hantar permintaan secara broadcast
hos yang mempunyai IP akan menjawab

354. Protokol Resolusi Alamat (Address Resolution Protocol (ARP))

355. Protokol Sonsangan Resolusi Alamat (Reverse ARP)
Biasanya digunakan oleh komputer tanpacakera. Pada masa di boot, diketahui alamat MAC, ingin diketahui alamat IP nya.
Hanya boleh dibuat dalam segmen yang sama.

356. Protokol Utusan Kawalan Internet (Internet Control Message Protocol (ICMP))
Digunakan untuk konfigurasi dan menjalankan rangkaian IP (oleh kerana IP tidak boleh dipercayai)
Dapat memberi maklum balas tentang masalah rangkaian
Jenis utusan
destinasi tidak dapat dicapai
masa hidup dilampaui (kiraan TTL mencapai 0)
masalah parameter (header tidak dikenali)

357. Protokol Utusan Kawalan Internet (Internet Control Message Protocol (ICMP))
mengarahkan ke tempat lain
membalas permintaan/sambutan (paket ping)
membalas permintaan/sambutan dengan maklumat masa (ping yang perlukan maklumat masa (timestamped)
menggunakan IP, jadi ia sendiri tidak boleh diyakini sampai
Contoh arahan yang menggunakan ICMP
Ping dan Traceroute

358. Protokol Utusan Kawalan Internet (Internet Control Message Protocol (ICMP))

359. Internet Group Management Protocol (IGMP)
Untuk terlibat dalam IP multicast pada rangkaian tempatan dan pelbagai rangkaian lain, hos dan multicast router mestilah mempunyai perisian yang membenarkannya hantar dan terima multicast datagram.
Mesti guna Internet Group Management Protocol untuk komunikasi maklumat ahli kumpulan
Hampir sama dengan ICMP – guna IP datagram dan bertukar mesej

360. IGMP Secara konsepnya ada dua fasa :
Fasa 1 : apabila satu hos sertai satu kumpulan multicast, ia akan hantar satu IGMP mesej kepada alamat kumpulan multicast mengistiharkan keahliannya. Multicast router tempatan terima mesej dan maklumkan maklumat ahli kumpulan ke multicast router lain dalam internet

361. IGMP
Fasa 2 : oleh kerana keahlian adalah dinamik, multicast router secara berkala mestilah membuat undi untuk hos pada rangkaian setempat untuk memastikan samada mana-mana hos masih menjadi ahli (aktif atau tidak). Jika aktif, maklumkan pada multicast router yang lain.

362. Ringkasan
Internet ialah koleksi rangkaian fizikal yang disambungkan menjadi satu rangkaian maya
Router menyediakan sambungan fizikal dan majukan paket diantara rangkaian
Hos berkomunikasi melalui pelbagai rangkaian melalui paket yang dimajukan oleh router
TCP/IP ialah protokol internetworking yang paling popular digunakan

363. Ringkasan
Rangkaian maya perlu skima pengalamatan yang seragam, tidak bersandar pada perkakasan
IP takrifkan pengalamatan internet
Protokol tambahan dalam lapisan Internet lain ialah ARP, RARP, ICMP dan IGMP

364. Teknologi Rangkaian Komputer Teknologi Rangkaian Kawasan Luas (WAN)
TK3133
Teknologi Rangkaian Komputer
Teknologi Rangkaian Kawasan Luas (WAN)

365. Pengenalan Keperluan untuk meliputi jarak lebih jauh
Pekerja syarikat perlu capai rangkaian mereka ketika di luar pejabat
Menghubungkan cawangan-cawangan organisasi
Berkongsi maklumat dengan organisasi lain yang terpisah jauh oleh jarak
Badan kerajaan, swasta, pendididikan dan individu perlu capaian kepada maklumat yang ada pada Internet
Teknologi ini dipanggil WAN - Wide Area Network (Rangkaian Kawasan Luas)

366. WAN
Memerlukan satu set teknologi dan peraturan implementasi yang berbeza dari LAN.
membincangkan konsep rangkaian pada jarak jauh dan teknologi yang biasa digunakan untuk menyambungkan komputer yang berada di lokasi berbeza (negeri, negara & benua)

367. Jenis pensuisan rangkaian
Data boleh dihantar ke destinasi yang jauh melalui pelbagai jenis talian, menggunakan salah satu daripada dua jenis ini
Pensuisan litar (circuit switching)
Pensuisan paket (packet switching)

368. Pensuisan litar
Teknologi lama sesuai untuk penghantaran data masa-nyata (seperti percakapan telefon)
Pensuisan litar ialah kaedah yang digunakan sama bagi membuat sambungan telefon (litar fizikal dikhaskan)
Sambungan fizikal perlu dibina antara dua stesen sebelum penghantaran data dapat dilakukan
Berjenis orientasi-sambungan (connection oriented) kerana ada satu sambungan dibina sebelum penghantaran dimulakan

369. Pensuisan paket
Data dipecahkan kepada beberapa unit yang lebih kecil dipanggil paket dan dihantar dari satu hos ke hos yang lain dengan boleh mengikut laluan yang berbeza (walaupun tiada laluan terus) untuk sampai kepada destinasi dan kemudiannya digabungkan kembali pada penghujungnya

370. Pensuisan
(a) Pensuisan Litar (b) Pensuisan Paket

371. Pensuisan Pensuisan Litar (b) Pensuisan Mesej (c) Pensuisan Paket

372. Perbandingan Rangkaian Pensuisan

373. Pensuisan paket
Dua pendekatan dalam menghantar data melalui pensuisan paket :-
Datagram (tanpa sambungan)
Pastikan setiap paket mengandungi maklumat mencukupi untuk membolehkan mana-mana suis menghantar kepada destinasi
Litar Maya (berorientasikan sambungan)
Memerlukan pembinaan sambungan maya daripada hos sumber ke destinasi
Samada Litar Maya Bersuis atau Litar Maya kekal

374. Perbandingan Litar Maya & Datagram

375. Contoh Sistem Komunikasi WAN
Cth WAN :
Sistem Telefon PSTN
ISDN
xDSL
Arpanet
X.25
Frame Relay
ATM

376. PSTN PSTN – Public Switched Telephone Network
Asalnya untuk menghantar suara
rangkaian telefon dial-up awam biasa guna
Sedia ada di seluruh dunia
murah
Sambungan pelbagai pusat pensuisan dan sambungan kepada pelanggan
Jenis rangkaian pensuisan litar

377. Dail-up dan leased line
2 cara : guna dial-up dan leased line (talian pajak)
Modem digunakan pada infrastruktur telefon yang telah sedia ada untuk sambungan dail-up (sambungan sementara sepanjang sessi)
Untuk leased line, sambungan tetap berkelajuan tinggi tanpa melibatkan mendail khas dari satu titik kepada titik yang lain (contoh dari pejabat ke ISP)

378. ISDN ISDN – Integrated Services Digital Network Pembaikan daripada IDN
Menyokong suara, data dan video menggunakan penghantaran medium digital melalui satu talian lebarjalur tinggi
Kombinasi teknik pensuisan litar dan paket

379. ISDN Perkhidmatan asas (basic) ialah 2B + D (BRI)
di mana B = satu saluran data 64kbps
D = satu saluran sekunder (pengisyaratan) 16kbps
ISDN Primary Access - 23B+D (64kbps) (PRI)
B-ISDN – Broadband ISDN
Lebih lebarjalur dari ISDN
Guna fiber optik dan lebarjalur 600Mbps

380. Teknologi Pensuisan Litar yang lain
xDSL – Digital Subscriber Line
Koleksi teknologi untuk hantar data pada kelajuan tinggi melalui talian biasa
Cth : ASDL (Asymmetric DSL)
untuk mengoptimakan pengguna yang terima banyak maklumat berbanding dengan yang dihantar (high-bit downstream dan low-bit upstream)
Kelajuan antara 16 – 640 kbps (upstream) dan Mbps hingga 6 Mbps downstream

381. Teknologi Pensuisan Litar yang lain
DSL
SDSL (Symmetric DSL)
Simetrik kadar bit pada kedua-dua hala
HDSL (High Data Rate DSL)
Kadar bit Mbps kedua-dua arah
VDSL (Very HDSL)
Kadar bit dari Mbps hingga 55.2 Mbps tetapi untuk jarak dekat dan perlu Optical Network Unit (ONU)

382. Teknologi Pensuisan Paket
ARPANET dibangunkan oleh ARPA untuk Jabatan Pertahanan USA
merupakan WAN pertama menggunakan pensuisan paket
membentuk Internet seperti kini

383. Pensuisan paket X.25
Rangkaian pensuisan paket komersial yang pertama dengan rujukan CCITT
X.25 – sebenarnya satu protokol piawai bagaimana WAN berkomunikasi menggunakan X.25 suis paket yang dihubungkan oleh talian pajak
Menyediakan antaramuka antara satu DTE (hos) dan DCE (suis rangkaian)
Berkongsi talian melalui multipleksan
Satu sambungan di antara penghantar dan penerima dipanggil litar maya (atau sambungan logikal)
Lambat dan pengurusan tinggi serta kelambatan panjang

384. Senibina Lazim bagi X.25

385. Perbezaan di antara Protokol X.25 dan TCP/IP
Messages have boundaries
Messages have no boundaries
Urgent data may overtake ordinary data in the data streams
With TCP, urgent data cannot preceed ordinary data that has been sent
The X.25 packet layer depends upon the datalink level for reliable delivery of data
TCP/IP requires very little reliance on the lower layers
X.25 protects data against errors on the data link by CRC code
TCP protects data against errors with checksum
X.25's CRCs are computed separately for each transmission link, hence protection is end-to-end
TCP's checksums are computed once by the sender and checked once by the receiver, hence protection is not end-to-end
The packet layer depends on the data link layer to tell it when delivery is not possible
TCP/IP retransmit data if acknowledge-ment is not received. If this happens after a certain number of times, it decides that the network's reliability is too poor to continue data transmission
The maximum number of virtual circuits that can be "open" at any time is limited by the amount of free buffer memory on the X.25 interface
In contrast, TCP's buffering is taken from a pool on the host, hence there is no limit on the number of open connections

386. Frame Relay
Teknologi pensuisan paket baru (fast-packet) berkelajuan tinggi digunakan pada talian digital untuk blok data yang besar yang berubah-ubah saiznya
Pembaikan daripada X.25 – perlaksanaan tinggi, kebolehpercayaan tinggi, kos-effektif
Guna PVC (berorientasikan sambungan)

387. ATM Asynchronous Transfer Mode (ATM)
Sama seperti pensuisan paket rangkaian tetapi paling popular
Menyokong aplikasi berkelajuan tinggi (data, streaming audio dan video)
Kadar data 25Mbps, 155Mbps, 622Mbps, 1Gbps
Pecahkan data kepada pecahan lebih kecil (sel) yang tetap saiznya iaitu 53 byte (48 byte data dan 5 byte overhead)

388. ATM Berjenis berorientasikan sambungan
Sambungan di antara dua titik dipanggil litar maya (VC) – (samada PVC atau SVC)
Guna pre-defined circuit

389. Rangkaian Wayarles
Contoh rangkaian selular menggunakan GSM (Global System for Mobiles) untuk hantar mobil suara dan perkhidmatan data digital
Teknologi GSM : 2G
GPRS 3G

390. Ringkasan Pelbagai teknologi WAN dari dua jenis : Pensuisan litar
PSTN, ISDN, DSL
Pensuisan Paket
Arpanet, X.25, Frame Relay dan ATM

391. Teknologi Rangkaian Komputer
TK3133
Teknologi Rangkaian Komputer
Laluan dalam WAN

392. Pengenalan
Untuk menghubungkan komputer jarak jauh, rangkaian perlu guna suis paket menghubungkan medium
Suis Paket (Packet Switches) juga dikenali sebagai router
Setiap suis bawa keseluruhan paket dari satu sambungan kepada satu sambungan yang lain
Satu komputer khas dengan antaramuka rangkaian, ingatan dan aturcara digunakan sebagai memproses paket

393. Sambungan pada router
Router dihubungkan dengan komputer dan router yang lain

394. Sambungan pada router
Router boleh dihubungkan bersama-sama membentuk WAN
Setiap router boleh dihubungkan dengan satu atau lebih suis dan satu atau lebih komputer

395. Sambungan pada router
Cth : Sambungan 4 router dan 8 komputer membentuk WAN

396. Simpan dan Hantar (Store and Forward)
WAN membenarkan banyak komputer menghantar paket serentak
Asas prinsip dalam sistem pensuisan paket kawasan luas ialah simpan dan hantar
Perlukan penimbal untuk simpan paket yang tiba, proses paket untuk tentukan output antaramuka untuk dihantar dan hantar paket

397. Pengalamatan dalam WAN
Hampir sama seperti LAN
Data dihantar dalam paket (sama spt. kerangka)
Setiap paket mempunyai format beserta kepala
Kepala paket termasuk alamat destinasi dan sumber

398. Maklumat Pada Router
Router mesti memilih sambungan keluar untuk penghantaran serahan (samada local/tempatan atau router lain (next-hop)
Pilihan adalah berdasarkan alamat destinasi pada paket
Maklumat pada router (jadual) hanya mengandungi maklumat next-hop
Jadi, pada setiap paket, router lihat destinasi pada jadual dan hantar melalui sambungan hop seterusnya
Proses penghantar seterusnya dipanggil ‘routing/laluan’
Maklumat disimpan dalam jadual laluan (routing table)

399. Teknik Penentuan Laluan
Untuk menentukan laluan suatu hos atau router memerlukan routing table
Satu teknik utk mengurangkan kandungan routing table ialah next-hop routing

400. Figure 19.28 Next-hop routing

401. Figure 19.29 Network-specific routing

402. Penentuan Laluan Strategi
Tepat : paket sampai dengan selamat ke tempat tuju
Mudah : mudah dilaksanakan dan dikemaskini
Lasak : kegagalan dalam rangkaian masih membenarkan komunikasi
Stabil : perubahan yang kecil dalam penambahan hubungan tidak menjejaskan keseluruhan laluan
Adil : setiap hos mempunyai peluang yang sama
Optimum : menggunakan kesemua jejak dan lebarjalur yang dipunyai

403. Penentuan laluan 2 jenis Statik Dinamik
Laluan dikira lebih awal dan tidak berubah
Shortest Path Routing
Lambakan (Flooding)
Dinamik
Pemilihan laluan berubah bergantung kepada situasi rangkaian
Distance vector routing
Link state routing

404. Shortest Path Routing Algoritma statik
cari “jarak terpendek” dalam laluan dari hos sumber kepada hos destinasi
Algoritma popular untuk mengira ialah Dijkstra Algorithm guna perwakilan graf

405. Figure 21.12 Example of an internet
Contoh suatu antara rangkaian (internetwork) kecil yg terdiri drp 7 rangkaian (N1, N2, .. N5) + 2 rangkaian titik-ke-titik
A, B, .., F merupakan router

406. Figure 21.13 Graphical representation of an internet

407. Dijkstra Algorithm
1. Start with the local node (router): the root of the tree.
2. Assign a cost of 0 to this node and make it the first permanent node.
3. Examine each neighbor node of the node that was the last permanent node.
4. Assign a cumulative cost to each node and make it tentative.
5. Among the list of tentative nodes Find the node with the smallest cumulative cost and make it permanent.
2. If a node can be reached from more than one direction
1. Select the direction with the shortest cumulative cost. 6. Repeat steps 3 to 5 until every node becomes permanent.

408. Setiap router menggunakan algoritma Dijkstra untuk mengira laluan terpendek di antara 2 titik dlm rangkaian

409. Figure 21.20 Shortest-path calculation for Router A

410. Table 21.2 Link state routing table for router A
Network
Cost
Next Router
Other Information N1 5 C N2
  7 D N3 10 B N4 11 N5 15

411. Shortest Path Routing Kira laluan terpendek di antara dua nod
Setiap nod dilabelkan dengan jaraknya dari nod sumber di sepanjang laluan terbaiknya yang diketahui

412. Lambakan
Setiap paket akan dihantar kepada semua nod yang berhampiran kecuali nod penghantar
Masalah bila berlaku tindanan
Cara atasi
Kira nod
Jejak paket
Selective flooding – pilih hanya laluan yang sedang menuju kepada arah yang betul

413. Distance Vector Routing
Algorithma penentuan laluan dinamik
Juga dikenali sebagai Bellman-Ford routing atau Ford-Fulkerson algorithm
Digunakan di Internet
Setiap router menyelenggara jadual laluan dari semasa ke semasa
Setiap router akan memberi jadual laluannya kepada jiran pada masa tertentu
2 bahagian – laluan keluar yang dipilih dan jarak destinasi

414. Distance Vector Routing
(a) A subnet. (b) Input from A, I, H, K, and the new
routing table for J.

415. Link State Routing
Juga dikenali sebagai Shortest Path First (SPF) routing
Router hantar mesej melalui rangkaian dengan membawa status talian antara dua router, dan mesej tersebut dipancar kepada semua router
Setiap router terima mesej status dan gunakannya untuk bina graf rangkaian
Router kemudiannya guna Dijkstra algorithm untuk menghasilkan jadual laluan dengan dirinya sendiri sebagai sumber

416. Link State Routing Satu subnet
Keadaan/status sambungan paket untuk subnet

417. Ringkasan WAN guna router dan sambungan titik-ke-titik
Router hantar paket ke destinasi guna jadual laluan dan strategi penentuan laluan

418. Teknologi Rangkaian Komputer
TK3133
Teknologi Rangkaian Komputer
Teknologi LAN (1)

419. Pengenalan Konsep rangkaian kawasan setempat (LAN) dan teknologinya
Kepentingan perkongsian dalam LAN
Asas topologi rangkaian
Pengalamatan perkakasan dan pengecaman jenis kerangka

420. Kategori Rangkaian Jenis sambungan rangkaian:
Titik-ke-titik atau Rangkaian Mesh
Perkongsian Saluran Komunikasi

421. Komunikasi Titik-ke-Titik
Konfigurasi talian asal sistem komunikasi
Komputer dihubungkan oleh saluran komunikasi yang setiap satunya menghubungkan dua komputer
membentuk rangkaian mesh atau titik-ke-titik
membenarkan fleksibiliti dalam komunikasi perkakasan, format paket dan sebagainya
membekalkan keselamatan oleh kerana saluran komunikasi tidak dikongsi

422. Sambungan dalam titik-ke-titik
Bilangan wayar bertambah apabila bilangan komputer turut bertambah
Cth : sambungan 2,3,4 komputer

423. Sambungan dalam titik-ke-titik
menambah satu komputer (komputer ke-N) memerlukan N-1 sambungan baru
Bil. sambungan = (N2 – N)/2
Kelemahannya mahal dan talian terlalu banyak

424. Perkongsian Saluran Komunikasi
Berbeza dengan rangkaian jarak jauh
Mengatasi kelemahan titik-ke-titik yang mahal, berdedikasi dan tindanan
Memperkenalkan LAN – Rangkaian Kawasan Setempat yang berkongsi satu saluran komunikasi (kabel) oleh beberapa komputer

425. Rangkaian Kawasan Setempat
Mengurangkan bilangan saluran komunikasi dengan memperkenalkan Rangkaian Kawasan Setempat (LAN)
LAN dibangunkan pada awal 1970an
Idea utama - mengurangkan bilangan saluran dengan berkongsi sambungan di antara komputer
Tetapi tidak sesuai untuk jarak jauh kerana masalah koordinasi

426. Rangkaian Kawasan Setempat
Teknologi LAN mengurangkan kos dengan mengurangkan bilangan sambungan
Tetapi komputer yang terhubung terpaksa bersaing untuk menggunakan sambungan yang dikongsi
menggunakan prinsip locality of reference untuk dapatkan corak komputer berkomunikasi

427. Rangkaian Terpancar LAN adalah rangkaian terpancar
paket data yang dihantar oleh satu stesen akan dihantar kepada kesemua stesen
Pengenalan topologi dalam LAN
rangkaian boleh dikategorikan mengikut bentuk
3 topologi yang popular
bintang, cincin dan bas

428. Topologi Bintang
Semua komputer dihubungkan kepada satu titik tengah dipanggil hub
Hub sebagai peranti yang terima paket data dan hantar kepada destinasi

429. Topologi Bintang
Secara praktiknya, pemasangan kabel boleh selari (atau tidak) dengan komputer

430. Topologi Bintang
Akibatnya :-

431. Topologi Cincin Komputer dihubungkan dalam satu gelung tertutup
Hos pertama akan hantar data kepada kedua, kedua hantar data kepada ketiga dan seterusnya.
Kabel penyambung yang pendek dari komputer kepada cincin

432. Topologi Cincin Satu komputer menghubungkan dua komputer

433. Topologi Bas Satu kabel menghubungkan semua komputer
Setiap komputer mempunyai penyambung kepada kabel yang dikongsi
Komputer mesti sinkroni dan benarkan hanya satu komputer menghantar data pada satu masa

434. Topologi Bas Satu kabel menghubungkan banyak komputer

435. Pelbagai Topologi
Topologi masing-masing mempunyai kebaikan dan kelemahannya
Pilihan bergantung kepada skema pendawaian

436. Contoh Rangkaian Kawasan Setempat Bas - Ethernet
Ethernet ialah kawalan capaian rangkaian LAN yang paling biasa digunakan
Dibangunkan oleh Xerox pada pertengahan 70an - diurus oleh IEEE
Menggunakan topologi bas
satu kabel sepaksi (ether)
sambung pelbagai komputer

437. Rangkaian Kawasan Setempat - Ethernet
Satu kabel Ethernet dipanggil segmen
had sehingga 500m panjangnya
Kadar penghantaran data ialah 10Mbps, 100Mbps (Fast Ethernet) dan 1Gbps (Gigabit Ethernet)
Menggunakan pemodulatan isyarat Pengenkodan Manchester

438. Pengenkodan Manchester
(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.

439. Rangkaian Kawasan Setempat - Operasi Ethernet
Satu komputer hantar pada satu masa
isyarat ialah pembawa yang dimodulasikan yang dibawa daripada penghantar pada dua arah sepanjang segmen

440. Carrier Sense Multiple Access with Collision Detection CSMA/CD
Tidak ada kawalan pusat yang uruskan apabila komputer hantar pada ether
guna CSMA untuk koordinasi penghantaran di antara komputer yang terhubung
Carrier sense: stesen mendengar saluran sebelum hantar
Collision Detection: stesen boleh tentukan samada kerangka mengalami pertembungan dengan mendengar saluran ketika menghantar

441. CSMA/CD - IEEE 802.3 Piawaian 802.3
Asas ialah 10-Mbps “Ethernet”

442. LAN Tanpa Wayar 802.11 dan CSMA/CA
Beroperasi pada 11Mbps menggunakan frekuensi dalam julat 2.4 GHz
Mengelakkan pertembungan guna CSMA dengan Collision Avoidance

443. LocalTalk Teknologi LAN yang guna topologi bas
antaramuka termasuk komputer Macintosh
kos-rendah, senang untuk pemasangan dan penyambungan
guna CSMA/CD

444. Bas Token - IEEE 802.4
Kelemahan bas sebab ada pertembungan – Pilih teknik elak pertembungan
Konsep Token – bas dan ring
Hanya penghantar yang terima token dibenarkan menghantar kerangka
Lepas giliran hantar, passkan token

445. Bas Token
Tetapkan giliran siapa selepas ini untuk terima token untuk keadilan capaian

446. Cincin Token - IEEE 802.5 (IBM Token Ring)
Beroperasi pada 4 dan 16 Mbps
Tiada bas hanya nod dan talian
guna penghantaran token untuk sinkronikan capaian pada cincin
Setiap nod hantar kerangka mengikut pusingan jam dengan mendapatkan token terlebih dahulu

447. FDDI
Fiber Distributed Data Interconnect (FDDI) adalah teknologi cincin
guna fiber optik di antara stesen
hantar pada kadar 100Mbps
guna sepasang fiber untuk membentuk 2 gelung sepusat
untuk tujuan back-up jika berlaku kerosakan

448. FDDI
Penggunaan dua arah aliran

449. ATM - Rangkaian Bintang
Teknologi Asynchronous Transfer Mode mengandungi suis paket di mana komputer boleh dihubungkan
Suis ATM membentuk hub di mana komputer dihubungkan dalam topologi bintang
data daripada penghantar dilalukan terus melalui suis kepada destinasi

450. ATM - Rangkaian Bintang
Kadar penghantaran melebihi 100Mbps
menggunakan fiber optik untuk sambungkan komputer kepada suis
setiap sambungan mengandungi 2 fiber

451. Komunikasi Pasangan Komputer dalam LAN
Teknik bagaimana menghantar mesej melalui medium LAN kepada satu destinasi komputer yang khusus
Penghantar komputer menggunakan alamat perkakasan untuk mengenalpasti destinasi yang dituju dalam kerangka
Penghantar turut kenalpasti jenis data yang dibawa di dalam kerangka

452. Mengenal destinasi
Data dihantar pada rangkaian yang dikongsi sampai pada semua komputer yang dihubungkan kepadanya
perantaramuka perkakasan kesan penghantaran kerangka dan ekstrak kerangka daripada medium
Tapi kebanyakan aplikasi hanya mahu data dihantar kepada destinasi sahaja dan bukannya semua komputer

453. Pengalamatan Perkakasan
Kebanyakan teknologi rangkaian mempunyai satu skima pengalamatan perkakasan yang mengenalpasti sesuatu stesyen atau komputer
Setiap stesen diumpukkan satu alamat perkakasan numerik atau alamat fizikal yang unik
Penghantar akan masukkan alamat perkakasan pada setiap kerangka yang dihantar (sumber dan destinasi)
Hanya stesyen yang dikenal dari kerangka terima salinan kerangka tersebut

454. Perkakasan LAN dan penapisan paket
Organisasi perkakasan LAN dan komputer

455. Format Alamat Perkakasan
Nilai numerik
saiz dipilih dari teknologi rangkaian tertentu
Panjangnya dari satu sehingga enam bytes
unik dalam satu LAN
statik, dinamik dan boleh-konfigur

456. Format Kerangka dan Kepala Kerangka
Piawaian Teknologi LAN takrifkan format kerangka untuk setiap teknologi
format am:
Kepala mempunyai alamat dan maklumat tambahan (dalam medan saiz tetap)
kawasan data boleh pelbagai saiz

457. Contoh Format Kerangka
Format Kerangka Ethernet

458. Ringkasan
Teknologi LAN menggunakan medium komunikasi yang dikongsi untuk menyambungkan pelbagai komputer pada jarak yang dekat
perlu sinkronikan penggunaan medium untuk perkongsian muatan
Topologi LAN - bintang, cincin, bas
Teknologi LAN - Ethernet, LocalTalk, FDDI, ATM, tanpa wayar

459. Ringkasan
Teknologi LAN menggunakan alamat perkakasan untuk kenalpasti destinasi untuk kerangka yang dihantar pada saluran komunikasi yang dikongsi
Setiap teknologi LAN takrifkan format perkakasan
Alamat boleh jadi umpukan statik, dinamik dan boleh-konfigur
Kerangka termasuk kepala yang terkandung alamat destinasi, sumber dan maklumat lain serta kawasan data

460. Teknologi Rangkaian Komputer
TK3133
Teknologi Rangkaian Komputer
Teknologi LAN (2)

461. Pengenalan Kad Antaramuka Skima Pendawaian LAN
kenapa perlu kad yang berasingan
apakah dia ‘transceiver’?
Skima Pendawaian LAN
Topologi logikal dan fizikal
Bagaimana boleh meluaskan LAN?

462. Kelajuan LAN dan komputer
Kelajuan penghantaran data LAN adalah sangat pantas berbanding kelajuan CPU
Kelajuan LAN tidak bergantung kepada mana-mana kelajuan pemproses
membenarkan campuran sistem padanya
komputer baru boleh disambung tanpa mempengaruhi kelajuan LAN

463. Perkakasan Antaramuka Rangkaian
Komputer guna perkakasan khas untuk sambungan rangkaian
kad antaramuka rangkaian (NIC) yang memahami isyarat elektrik digunakan pada rangkaian, kadar di mana data diterima dan dihantar serta perincian kerangka
penyambung pada belakang komputer terima kabel kepada rangkaian fizikal

464. NIC dan perkakasan Rangkaian
NIC dibina hanya untuk satu jenis rangkaian fizikal
antaramuka Ethernet tak boleh guna dengan Token Ring
Walaubagaimanapun, sesetengah NIC boleh digunakan dengan perkakasan lain yang bersamaan
thick, thin dan 10BaseT Ethernet
10Mbps dan 100Mbps Ethernet

465. Sambungan antara NIC dan rangkaian fizikal
2 cara :-
NIC terus sambung kepada medium
Kabel dari NIC sambung kepada tambahan litar yang bersambung dengan medium
Cara Pendawaian Ethernet
Piawaian 10Base5
Piawaian 10Base2
Piawaian 10BaseT

466. Sambungan antara NIC dan rangkaian fizikal

467. 10Base5 - Thick Ethernet Guna kabel sepaksi
kabel AUI (drop cable) dari NIC kepada transceiver
Kabel AUI bawa isyarat digital dari NIC kepada transceiver
Transceiver janakan signal analog pada kabel sepaksi

468. 10Base5 - Thick Ethernet
Satu kabel AUI menyambung komputer kepada transceiver

469. 10Base5

470. 10Base5 Transceiver

471. Segmen Ethernet

472. 10Base2 - Thin Ethernet
Guna kabel sepaksi yang lebih nipis/kurus - lebih murah dan senang dipasang daripada Thick-net coax
Transceiver dibina pada NIC - terus sambung kepada medium
kabel sepaksi guna BNC connector

473. 10Base2

474. 10Base2 - Thin-Net

475. 10Base-T 10Base-T (Twisted pair/ TP Ethernet)
gantikan kabel AUI dengan kabel pasangan terpiuh
gantikan thick coax dengan hub

476. 10BaseT

477. Kategori Kabel UTP

478. Ethernet
Semua teknologi pendawaian guna spesifikasi Ethernet yang sama
format kerangka sama
algorithma CSMA/CD yang sama
NIC boleh terima semua ketiga-tiga teknologi sambungan

479. Perbandingan skima pendawaian

480. Topologi dan Teknologi Rangkaian
10Base-T
logikalnya topologi bas;
tetapi pendawaian fizikal ialah bintang
Juga dikenali sebagai star-bus Ethernet

481. Ethernet Berkelajuan Tinggi

482. Fast Ethernet
Pengkabelan Fast Ethernet

483. Gigabit Ethernet Kadar data 1000 Mbps atau 1 Gbps
Dikenali sebagai 1000BaseSX/LX atau 1000BaseT
Guna suis
Menggunakan fiber optik
Bertindak sebagai tulang belakang rangkaian untuk hubungkan LAN dan LAN kelajuan tinggi

484. Perluasan LAN
Teknologi LAN direkabentuk dengan kekangan kelajuan, jarak dan kos
Teknologi LAN biasanya boleh merangkumi, paling jauh beberapa ratus meter
Bagaimana boleh meluaskan LAN?

485. Merekabentuk LAN untuk jarak
Kebanyakan LAN menggunakan medium yang dikongsi - Ethernet, token ring
Panjang medium mempengaruhi keadilan, berkongsi capaian kepada medium
CSMA/CD – kelambatan di antara kerangka, minimum panjang kerangka
Penghantaran Token – masa mengelilingi untuk token
Panjang medium mempengaruhi kekuatan isyarat elektrik dan imunisasi hingar

486. Perluasan LAN Beberapa teknik meluaskan lingkungan diameter medium LAN
Kebanyakkannya menggunakan tambahan perkakasan
Isyarat LAN dibawa di antara segmen LAN
Hasilnya teknologi yang bercampur-campur tetapi tetap dengan kekangan kejuruteraan asal sementara memperluaskan jarak

487. Repeater (Pengulang) Untuk memanjangkan medium LAN
Kekuatan isyarat mempengaruhi had panjang
Untuk atasinya guna Repeater – dua-arah, amplifier (penguat) analog yang menghantar semula isyarat analog

488. Repeater
Satu repeater secara efektifnya mengandakan panjang satu segmen LAN

489. Ethernet repeater Hanya salin isyarat di antara segmen
Tidak memahami format kerangka
Tidak mengandungi alamat perkakasan
Mana-mana segmen Ethernet terhad kepada 500 meter
Repeater boleh gandakan kepada 1,000 meter

490. Had Ethernet Repeater
Piawaian Ethernet termasuk menghadkan 4 repeater di antara mana-mana dua stesen Ethernet

491. Kelebihan dan Kelemahan Repeater
Mudah untuk digunakan – terus plug-in
Repeater hanya hantar-semula isyarat analog
Pertembungan mempengaruhi keseluruhan rangkaian
Hingar juga turut di bawa sepanjang rangkaian

492. Bridge (Jambatan) Juga hubungkan dua segmen LAN
Menghantar-semula kerangka daripada satu segmen ke segmen yang lain
Menguruskan keseluruhan kerangka
Menggunakan NIC seperti stesen yang lain
Laksanakan pemprosesan pada kerangka

493. Bridge Penggunaan bridge dalam menyambungkan dua segmen LAN

494. Kelebihan Bridge Sangat mudah untuk digunakan – hanya plug-in
Asingkan pertembungan, hingar
Lakukan penapisan kerangka
Hanya hantar kerangka bila perlu sahaja pada segmen LAN kepada destinasi
Hantar paket multicast dan broadcast
Guna jadual

495. Bagaimana bridge bina jadual
Bridge periksa alamat sumber pada setiap kerangka
Tambah kemasukkan kepada senarai untuk segmen LAN daripada mana kerangka tersebut diterima
Mesti hantar mana-mana kerangka yang destinasinya tidak ada dalam senarai ke setiap antaramuka bridge

496. Jadual Bridge

497. Bridge Boleh guna banyak bridge untuk sambungkan LAN segmen
Kelemahan mengakibatkan gelung – atasinya dengan algorithma Distributed Spanning Tree

498. Bridge di antara bangunan
Bridge berada pada satu bangunan dengan penyambung yang panjang kepada segmen LAN di bangunan yang lain

499. Bridge jarak jauh
Boleh guna talian pajak, gelombang mikro, laser atau satelit untuk sambungkan dua bridge dan segmen LAN

500. Pensuisan Bagi setiap port/pengkalan untuk pisahkan satu LAN segmen
Seperti hub – hub kongsi satu segmen dengan semua port

501. Switch/Suis
Dengan pensuisan, banyak stesen boleh hantar dengan serentak
Menyediakan lebarjalur yang lebih tinggi
Lebih mahal per port
Secara ekonominya, ada yang sesuai guna hub, yang lain sesuai guna suis

502. Ringkasan
Repeater bertindak sebagai amplifier dan hantar-semula isyarat analog
Bridge terima kerangka keseluruhan kerangka dan hantar-semula
Mengelakkan pertembungan pada segmen destinasi
Tapis kerangka
Pensuis membekalkan kelajuan LAN sepenuhnya kepada setiap port

503. Ringkasan NIC sambungkan komputer dengan rangkaian
terdapat banyak skima pendawaian fizikal untuk topologi rangkaian logikal

504. Rangkaian Komputer Setempat Wayarles (WLAN)
Ethernet Wayarles
Bluetooth

505. Pengenalan
Permintaan utk meyambungkan peranti tanpa wayar semakin tinggi
WLan lazim diguna dlm kampus, bgnan pejabat, bahkan di tempat awam seperti kafe, stesen minyak, dll.
WLan juga boleh dipasang di rumah utk mengunjurkan sambungan Internet kpd peranti-peranti mudah alih yg lain

506. IEEE
Piawaian mentakrifkan spesifikasi yg merangkumi lapisan fizikal dan pautan data bg WLAN
Senibina
Lapisan Fizikal
Lapisan Kawalan Capaian Media (MAC)
Mekanisma Pengalamatan

507. Senibina WLAN : Set Perkhidmatan Asas(BSS)
BSS ditakrifkan sebgi blok asas WLAN
Terdiri drp set stesen mudah alih/tetap & satu stesen pangkalan (access point -AP)
BSS tanpa AP tidak blh hantar data ke BSS lain (dikenali : senibina ad-hoc)
Stesen2 bersetuju utk menjadi sebhgn drp BSS

508. Senibina WLAN : Set Perkhidmatan Lanjutan (ESS)

509. Senibina WLAN:Set Perkhidmatan Lanjutan (ESS)
ESS terdiri drp >= 2 BSS dgn AP
Lazimnya BSS dihubungkan melalui suatu sistem teragih iaitu LAN (wired)
Sistem teragih bertindak sebagai penghubung kpd AP utk setiap BSS
IEEE tidak mengenakan kekangan terhdp jenis sistem teragih – blh terdiri drp sebrg LAN (cth: Ethernet)
Stesen dlm ESS: mudah alih & tetap
Mudah alih: stesen biasa dlm BSS
Tetap: AP yg merupakan sebhgn drp LAN
Apabila BSS2 bersambung, senibina ini dipanggil rangkaian infrastruktur, dan stesen dlm BSS tidak perlukan AP utk berkomunikasi antara 1 sama lain
Namun komunikasi antara 2 stesen dr 2 BSS berbeza lazimnya berlaku menerusi 2 AP

510. Jenis-jenis Stesen
IEEE mentakrifkan 3 jenis stesen berasaskan pergerakannya:
Pergerakan Tanpa-Peralihan
Stesen tetap atau bergerak di dlm suatu BSS
Pergerakan Peralihan-BSS
Stesen blh bergerak dr 1 BSS ke BSS lain, teapi terhad dlm 1 ESS shj
Pergerakan Peralihan-ESS
Stesen blh bergerak dr 1 ESS ke ESS lain, tetapi IEEE tidak menjamin komunikasi akan kekal sepanjang pergerakan

511. Spesifikasi Lapisan Fizikal
IEEE mentakrifkan spesifikasi utk menukar bit ke isyarat (lapisan fizikal)
Terdpt 5 spesifikasi dlm julat frekuensi radio

512. Frequency Hopping Spread Spectrum
Penjanaan isyarat dlm jalur 2.4 GHz ISM
Penghantaran data guna 1 frekuensi pembawa utk jangkamasa tertentu dan meloncat ke frekuensi yg lain pula, dan seterusnya …
Selepas N loncatan, kitaran berulang.
Jika lebarjalur isyarat asal adalah B, lebarjalur sebaran spektrumnya : N x B
Menyukarkan intipan, kadar data: 2 Mbps, guna modulasi FSK pd 1M baud/s

513. Direct Sequence Spread Spectrum
Juga dlm jalur 2.4-GHz ISM (industrial, scientific, medical)
Setiap bit yg dihantar diganti dgn jujukan bit (kod cip)
Utk elak penggunaan penimbal, masa utk hantar 1 kod cip perlu = masa utk hantar bit asal
Jika bil. Bit dlm setiap kod cip = N, kadar data utk hantar cip kod = N x kadar data strim bit asal
Tidak serupa spt CDMA krn ini implementasian pd lapisan fizikal
Jujukan bit menggunakan keseluruhan jalur
Kadar data 2 Mbps, guna modulasi PSK pd 1Mbaud/s

514. Lapisan MAC dlm piawaian IEEE 802.11
2 sub-lapisan MAC
Fungsi Koordinasi Teragih (DCF)
Fungsi Koordinasi Titik (PCF) – lebih kompleks hanya utk rangkaian infrastruktur

515. Kaedah Capaian : CSMA/CA

516. CSMA/CA dan Network Allocation Vector
NAV ialah cara CA diimplementasikan
Bila RTS dihantar oleh 1 stesen (termasuk jangkamasa yg diperlukan utk guna saluran)
Stesen lain akan mulakan NAV masing2 – masa harus tunggu sebelum boleh semak status talian
Distributed IFS dan Short IFS adalah masa menunggu antara kerangka

517. Format Kerangka lapisan MAC
Persekitaran wayarles memp. tahap hingar tinggi, byk kerangka perlu hantaran semula
Pecahkan kerangka supaya hanya perlu ganti kerangka bersaiz kecil (fragmentation)

518. Submedan dlm medan FC Field Explanation Version
The current version is 0.
Type
Type of information: management (00), control (01), or data (10).
Subtype
Defines the subtype of each type (see ).
To DS
Defined later.
From DS
More flag
When set to 1, means more fragments.
Retry
When set to 1, means retransmitted frame.
Pwr mgt
When set to 1, means station is in power management mode.
More data
When set to 1, means station has more data to send.
WEP
Wired equivalent privacy. When set to 1, means encryption implemented.
Rsvd
Reserved.

519. Kerangka Kawalan

520. Nilai Submedan dlm Kerangka Kawalan
Subtype
Meaning
1011
Request to send (RTS)
1100
Clear to send (CTS)
1101
Acknowledgment (ACK)

521. Submedan dlm medan FC To DS From DS Address 1 Address 2 Address 3
Destination station
Source station
BSS ID
N/A 1
Sending AP
Receiving AP

522. Mekanisma Pengalamatan : kes 1
Pengalamatan dlm sgt kompleks krn melibatkan byk AP
Addr 1 : peranti berikutnya
Addr 2 : peranti sebelumnya
Addr 3 : peranti destinasi jika tak dinyatakan oleh Addr 1
Addr 4 : peranti asal jika != dgn Addr 2

523. Figure 15.12 Addressing mechanism: case 2

524. Figure 15.13 Addressing mechanism: case 3

525. Figure 15.14 Addressing mechanism: case 4

526. Bluetooth
Teknologi WLAN direkabtk utk menyambungkan peranti pelbagai fungsi: telefon, PDA, kamera, pencetak, tetikus, earpiece, dll
Ia merupakan suatu rangkaian ad hoc – blh dibtk secara spontan
Peranti2 bluetooth saling mengesan utk membtk suatu rangkaian dipanggil piconet
Bluetooth LAN juga blh dihubungkan ke Internet jika salah satu perantinya memp. keupayaan tersebut
Piawaian : IEEE yg mentakrifkan rangkaian kawasan personal (PAN) wayarles yg merangkumi suatu bilik atau dewan

527. Senibina Rangkaian: Piconet
Piconet blh terdiri drp 8 stesen dgn salah satunya berfungsi sbgi master
Peranti slave sinkronikan jam dan jujukan loncatan frekuensinya (hop) supaya sama dgn master
Komunikasi antara master-slave blh jadi 1-1 atau 1-byk
Slave blh bertukar keadaan dr aktif ke parkir dan sebaliknya

528. Senibina Rangkai : Scatternet
Piconet 1
Piconet 2

529. Scatternet Piconet boleh digabungkan membtk Scatternet
Stesen slave dlm 1 piconet akan menjadi master bagi piconet yg lain
Stesen ini blh menerima mesej drp master (piconet 1) dan bertindak sbgi master (piconet 2) utk sampaikan kpd slave dlm piconet 2

530. Peranti Bluetooth
Peranti bluetooth memp. transmitter radio jarak dekat
Kadar data: 1Mbps dgn lebarjalur 2.4-GHz, oleh itu mungkin berlaku gangguan di antara WLAN IEEE b dan LAN Bluetooth

531. Lapisan Bluetooth Lapisan bluetooth tidak sepadan dgn model TCP/IP
Lapisan radio ~ lapisan fizikal
Perantinya berkuasa rendah meliputi kwsan seluas 10 m
Band: guna jalur 2.4-GHz ISM dibhgi kpd 79 saluran (1 MHz setiap satu)

532. Lapisan Bluetooth
Bluetooth guna kaedah FHSS pd lapisan fizikal utk elakkan gangguan drp peranti atau rangkaian lain
Bluetooth melakukan loncatan 1600 kali/s, bermakna ia menukar modulasi frekuensinya 1600 kali/s – beroperasi selama 625 μs utk setiap frekuensi
Utk tukar bit ke isyarat, modulasi GFSK (Gaussian)
Lapisan Baseband: hampir sama lapisan MAC dlm LAN dgn kaedah capaian Time Divison Duplexing-TDMA (sejenis komunikasi dupleks separa)
Komunikasi hanya antara master-slave
Tiada komunikasi langsung antara slave-slave

533. Komunikasi Single-slave

534. Komunikasi Multiple-slave

535. Format Kerangka

536. Format Paket Data L2CAP

537. Kaedah Capaian Dalam Rangkaian
Talian Khas (Capaian Titik-ke-titik)
Perkongsian Talian (Capaian berbilang)
Protokol Capaian

538. Dedicated Link or Shared Link
2 peranti di dlm satu rangkaian boleh dihubungkan oleh:
Talian yg dikhaskan (dedicated)
Talian yg dikongsi (shared)

539. Talian Khas (Titik-ke-titik)
Kaedah capaian untuk sambungan menggunakan dedicated link dikenali sbgi Capaian Titik-ke-titik
Protokol yg lazim diguna utk capaian ini pula : Point-to-Point Protocol (PPP)
Cth kegunaan: pengguna Internet membuat sambungan dr rumah ke ISP

540. Pengguna lazimnya menggunakan modem biasa (DSL atau kabel)
Talian telefon atau kabel TV menyediakan sambungan fizikal, tetapi utk mengawal dan mengurus pemindahan data protokol titik-ke-titik diperlukan

541. What PPP provides:
Ia menakrifkan format kerangka yg diguna oleh kedua peranti dlm pertukaran
Ia menakrifkan proses tawar-menawar di antara kedua peranti dlm mewujudkan sambungan dan melakukan pertukaran data
Ia menakrifkan bgimana data lapisan rangkaian dikapsulkan di dlm kerangka pautan data
Ia menakrifkan bgimana dua peranti boleh mengesahkan identiti masing2

542. Timbunan PPP (PPP Stack)
Wlupun PPP merupakan protokol lapisan pautan data, namun ia menggunakan beberapa protokol lain:
Link Control Protocol
Utk membuat, menyenggara, mengkonfigurasi dan menamatkan talian
Authentication Protocol
Utk mengesahkan identiti pengguna (cth: dail up session)
PAP (password) dan CHAP (challenge handshake)
Network Control Protocol
Utk mengkapsulkan data (network layer protocol
-> PPP frame)

543. Kerangka PPP –versi HDLC

544. Keadaan Peralihan dlm PPP

545. Timbunan Protokol

546. Pengkapsulan paket LCP dlm suatu kerangka

547. Password Authentication Protocol

548. Paket PAP

549. Challenge Handshake Authentication Protocol

550. Contoh CHAP

551. Kaedah Perkongsian Talian
Apabila berbilang stesen disambung menggunakan satu talian, protokol capaian berbilang diperlukan utk mengkoordinasikan capaian kpd talian

552. Terdpt beberapa prosedur utk memastikan :
Perkongsian Talian
Terdpt beberapa prosedur utk memastikan :
Setiap stesen boleh mencapai media (talian)
Tiada 2 stesen yg mencapai media pd masa yg sama
Tiada stesen yg menyampuk stesen lain
Tiada stesen yg memonopoli capaian

553. Protokol Capaian Berbilang
Protokol Capaian Rawak
Protokol Capaian Terkawal
Protokol Saluran

554. Protokol Capaian Rawak
Setiap stesen berhak mencapai talian tanpa dikawal oleh stesen lain
Jika > 1 stesen cuba mencapai talian, akan berlaku konflik dlm capaian (perlanggaran) dan kerangka akan dimusnahkan atau diubahsuai

555. Protokol Capaian Rawak
Utk mengelakkan atau menangani konflik ini, kita perlukan suatu protokol yang berupaya utk menjawab soalan:
Bila suatu stesen blh mencapai talian?
Apa tindakan stesen jika talian sedang sibuk?
Bgimana stesen menentukan sama ada transmisinya berjaya atau gagal?
Apa tindakan stesen jika berlaku konflik capaian?

556. Evolusi Kaedah Capaian Rawak

557. Multiple Access: ALOHA – Protokol Capaian Berbilang Pertama
Univ. of Hawaii (1970-an) utk rangkaian LAN radio(wayarles) dgn kadar data 9600bps
Stesen pangkalan – pengawal terpusat
Utk hantar data perlu melalui stesen pangkalan

558. Multiple Access : ALOHA
Protokol ALOHA mengikut peraturan:
Capaian Berbilang : Mana2 stesen menghantar kerangka bila ia ada data utk dihantar
Perakuan : Slps menghantar kerangka, stesen menunggu perakuan.
Jika tiada yg diterima dlm jangkamasa tertentu, stesen menunggu (guna strategi backoff ) dan hantar semula
Stesen berhenti jika telah mencuba beberapa kali

559. Prosedur Protokol ALOHA

560. Carrier Sense Multiple Access (CSMA)
Dibina utk meminimakan kebrgkalian berlakunya perlanggaran dgn mengesan media/talian sblm menggunakannya
Setiap stesen perlu mendengar sebelum menghantar data
Bgimanapun perlanggaran masih boleh berlaku krn propagation delay – masa yg diambil oleh bit pertama utk sampai ke destinasi

561. Perlanggaran dlm CSMA

562. Strategi Gigih
Dgn strategi gigih-p, bergtg kpd kebrgkalian tersebut. Jika p=0.2, stesen mempunyai 20 kemungkinan (drp 100) utk menggunakan talian.
Jika stesen mengesan talian sedang idle, ia akan janakan suatu no. rawak (1-100), jika no. tersebut < 20, stesen akan menghantar data

563. Carrier Sense Multiple Access/Carrier Detect (CSMA/CD)
CSMA tidak menakrifkan prosedur sekiranya berlaku perlanggaran
Dlm CSMA/CD, mana2 stesen boleh menghantar data
Stesen kemudian memantau talian utk mengetahui status penghantaran (berjaya/gagal)
Jika berlaku perlanggaran, kerangka akan dihantar semula
Bgimanapun utk elakkan perlanggaran drp berulang, ia menunggu (strategi backoff ) utk suatu jangkamasa
Jangkamasa bertambah jika perlanggaran lebih kerap berlaku
Diguna dlm rangkaian Ethernet tradisional

564. Prosedur CSMA/CD

565. Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA)
Kaedah ini berbeza kerana ia mengelak berlakunya perlanggaran
Stesen menggunakan strategi gigih.
Jika talian didapati dlm keadaan melahu (idle), stesen menunggu selama IFG (interframe gap)
Stesen menunggu lagi utk suatu jangkamasa rawak
Kemudian ia menghantar data dan menunggu perakuan utk suatu jangkamasa tertentu
Jika tidak diterima, nilai backoff ditingkatkan dan talian didengar sebelum penghantaran semula
Diguna dlm rangkaian WLAN

566. Prosedur CSMA/CA

567. Capaian Terkawal
Stesen berunding dgn 1 sama lain utk menentukan stesen yg berhak menghantar data
Stesen tidak boleh menghantar tanpa kebenaran stesen lain
3 kaedah yang popular:
Berasaskan tempahan
Berasaskan tinjauan
Berasaskan token

568. Stesen perlu membuat tempahan sebelum menghantar data
Capaian Terkawal Berasaskan Tempahan
Stesen perlu membuat tempahan sebelum menghantar data
Masa dibahagikan kpd sela-sela
Dlm setiap sela, kerangka tempahan akan mendahului kerangka data yg dihantar pd sela tersebut
Dlm sistem yg terdiri dr n stesen, akan ada n slot mini yg mewakili setiap stesen
Utk hantar data, setiap stesen perlu membuat tempahan dlm slot yg diperuntukkan utknya

569. Capaian Terkawal Berasaskan Tinjauan
Sesuai utk topologi dgn 1 stesen primer dan yg lainnya sekunder
Pertukaran data mesti melalui stesen primer
Stesen primer yg mengawal talian
Jika primer bersedia menerima data, ia akan meninjau (tanya) stesen sekunder jika ada data utk dihantar : proses polling
Jika ia ingin menghantar data, primer akan memberitahu sekunder sasaran supaya bersedia utk menerima data : proses selecting

570. Proses Memilih (Selecting)

571. Proses Meninjau (Polling)

572. Dlm kaedah ini stesen2 disusun dlm lingkaran seumpama cincin
Capaian Terkawal Berasaskan Token
Stesen diberi kebenaran utk menghantar data bila ia menerima suatu kerangka khas yg dipanggil token
Dlm kaedah ini stesen2 disusun dlm lingkaran seumpama cincin
Setiap stesen ada predecessor dan successor
Kerangka diterima dr predecessor dan dihantar kpd successor

573. Apabila data sedang dihantar, token akan mengelilingi lingkaran
Capaian Terkawal Berasaskan Token
Apabila data sedang dihantar, token akan mengelilingi lingkaran
Jika suatu stesen ingin menghantar data, ia perlu menunggu token, menyimpannya dan menghantar sebyk mana kerangka selagi masa utknya belum luput
Token kemudian dilepaskan semula

574. Prosedur Penghantaran Token

575. Protokol Saluran
Kaedah capaian berbilang yg mana lebarjalur talian dikongsi di antara stesen-stesen melalui pembahagian masa, frekuensi atau kod
3 protokol saluran yg popular:
FDMA – lebarjalur dibhgi kpd jalur2 utk setiap stesen
TDMA – seluruh lebarjalur merupakan 1 saluran, stesen diberi slot masa
CDMA – berbeza dr FDMA krn hanya 1 saluran menggunakan seluruh lebarjalur, berbeza dr TDMA krn semua stesen boleh hantar data serentak – tiada perkongsian masa

576. CDMA Implementasiannya masih baru
Satu saluran membawa kesemua transmisi data secara serentak
Berasaskan teori pengkodan yg mana setiap stesen diberi suatu kod – jujukan nombor dipanggil cip

577. Peraturan Pengenkodan

578. Pemultipleksan CDMA

579. Pendemultipleksan CDMA

580. Penjanaan Jujukan Cip Guna Jadual Walsh : W1 danW2N

581. Penjanaan Jujukan Cip

582. Example 1
Check to see if the second property about orthogonal codes holds for our CDMA example.
Solution
The inner product of each code by itself is N. This is shown for code C; you can prove for yourself that it holds true for the other codes.
C . C = [+1, +1, -1, -1] . [+1, +1, -1, -1] = = 4
If two sequences are different, the inner product is 0.
B . C = [+1, -1, +1, -1] . [+1, +1, -1, -1] = = 0

583. Example 2
Check to see if the third property about orthogonal codes holds for our CDMA example.
Solution
The inner product of each code by its complement is -N. This is shown for code C; you can prove for yourself that it holds true for the other codes.
C . (-C ) = [+1, +1, -1, -1] . [-1, -1, +1, +1] = = -4
The inner product of a code with the complement of another code is 0.
B . (-C ) = [+1, -1, +1, -1] . [-1, -1, +1, +1] = = 0

584. DETAILS OF PROTOCOLS
The Zoo Protocol
TCP IP

585. A programmer can create Internet application software without understanding the underlying network technology or communication protocols - we will take a different approach Understanding the Zoo Protocol

586. Transmission Control Protocol (TCP)

587. Protokol pada paras pengangkutan
Menghantar mesej dari proses klien kepada proses pelayan
Bagaimana proses klien dapat mencapai perkidmatan daripada proses pelayan?
Komunikasi antara-proses (interprocess) ini dilakukan melalui port protokol

588. Port Protokol
Nombor port diumpukkan kepada proses oleh sistem pengoperasian
Terdapat 216 port (0 hingga 65535)
Terdapat 2 set port
untuk protokol UDP
untuk protokol TCP

589. Hos sun1.ftsm.ukm.my /etc/services

590. Untuk perkhidmatan piawai
Port well-known (1 – 1023)
Untuk perkhidmatan piawai
HTTP [80], SMTP[25], FTP[21, 22], POP3[110], Telnet [23]
Ephemeral port (1024 – 65535)
Diumpukkan secara dinamik
Diumpukkan kepada proses klien
Apabila proses klien tamat, port akan dibebaskan
Senarai lengkap umpukkan port dapat dilihat dengan arahan /etc/services (pada *nix)

591. Transmission Control Protocol (TCP)
Menyediakan perkhidmatan penghantaran yang dipercayai
Menggunakan port protokol untuk proses pengalamatan
Untuk aplikasi yang memerlukan kebolehpercayaan spt: telnet, http, ftp dll

592. Format Pengepala TCP

593. Sambungan TCP
Sambungan TCP dikenalpasti dengan titik hujung (nombor port) sambungan tersebut
Untuk membuka sambungan TCP memerlukan kerjasama dua hala
Klien akan membuat permintaan kepada satu port pada pelayan
Pelayan akan membuka port dan memulakan sambungan

594. Jabat-tangan tiga arah
TCP menggunakan ‘jabat-tangan tiga arah’ ketika memulakan dan menamatkan hubungan untuk menyediakan kebolehpercayaan
Tentukan kedua-dua nod bersedia dan selaraskan nombor jujukan rawak untuk sinkronikan hubungan

595. Memulakan Sambungan TCP
Guna segmen SYN untuk cipta satu sambungan
Hos 1 hantar segmen SYN dan nombor jujukan rawak
Hos 2 membalas segmen SYN, dengan menghantar ACK kepada Hos 1 dan nombor jujukan rawak
Host 1 balas dengan ACK

597. Menamatkan Sambungan TCP
TCP guna segmen FIN untuk menamatkan sambungan
Jabat tangan empat arah

598. User Datagram Protocol (UDP)
Merupakan protokol pengangkutan
Menyediakan komunikasi tanpa hubungan yang tidak dapat diharap (unreliable)
Paket mungkin hilang atau tidak mengikut urutan
Tiada berpenimbal – menerima data dari aplikasi dan terus menghantarnya
Digunakan apabila tiada kawalan ralat diperlukan
Untuk proses seperti
DNS [53], echo [7], tftp [69], SNMP[161]

599. Format UDP Datagram Pengepala Data Port sumber UDP Port destinasi UDP
Port sumber UDP (16 bit)
Port destinasi UDP (16 bit)
Panjang mesej UDP (16 bit)
Checksum UDP (16 bit)
Data
Port sumber UDP
Port destinasi UDP
Panjang mesej UDP
Checksum UDP
Data

600. Internet Protocol (IP)

601. IP Protokol pada paras rangkaian
Menyediakan penghantaran paket secara komunikasi tanpa sambungan
Menggunakan alamat IP untuk pengalamatan
Menentukan laluan paket melalui satu atau lebih lompatan (hop) sepanjang laluan
Menyediakan mekanisma yang terdiri dari
Unit data yang dinamakan IP datagram
Perisian untuk menghantar datagram
Petua bagaimana komputer hos memproses datagram

602. Figure 19.2 Links in an internetwork

603. Bagaimana komunikasi dalam Internet ?
IP bertanggungjawab menyediakan penghantaran cara terbaik (best-effort) untuk paket/datagram
Bagaimana komunikasi dalam Internet ?
Lapisan pengangkutan ambil aliran data dan pecahkan kepada datagram
Lapisan rangkaian hantar setiap datagram melalui Internet. Pemecahan kepada unit yang lebih kecil boleh berlaku sewaktu proses ini
Pada destinasi, datagram akan dikumpulkan kembali oleh lapisan rangkaian kepada datagram asal dan dihantar kepada lapisan pengangkutan

604. Figure 19.4 Network layer at the source

605. Figure 19.5 Network layer at a router

606. Figure 19.6 Network layer at the destination

607. Pengalamatan Perlu satu format alamat yang seragam
Format alamat mestilah tidak bersandaran dengan format alamat perkakasan
Alamat mestilah unik pada keseluruhan rangkaian (Internet)
Badan yang mengawal pendaftaran alamat – Internet Information Center (InterNIC)

608. Alamat IP (IPv4) Diwakilkan oleh integer 32-bit
Menggunakan notasi dotted decimal quad
Terdiri daripada 4 bahagian 8 bit
Dipisahkan dengan noktah

609. Kelas Rangkaian Alamat IP diorganisasi mengikut kelas rangkaian
Kelas A: 0nnnnnnn.iiiiiiii.iiiiiiii.iiiiiiii
Kelas B: 10nnnnnn.nnnnnnnn.iiiiiiii.iiiiiiii
Kelas C: 110nnnnn.nnnnnnnn.nnnnnnnn.iiiiiiii
Kelas D: 1110bbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
Kelas E: untuk kegunaan masa depan
Perwakilan:
n – nombor rangkaian
i – nombor hos
b – id kumpulan

610. Julat Alamat untuk kenalpasti Kelas Alamat

611. Setiap alamat IP dibahagikan kepada dua bahagian
No. rangkaian (prefix) - menunjukkan rangkaian fizikal di mana komputer dihubungkan
No. hos (suffix) - menunjukkan nombor unik komputer pada rangkaian
Internet Corporation for Assigned Names and Numbers (ICANN) bertanggungjawab mengumpukkan kelas A, B dan C kepada organisasi

612. Kelas A, B dan C adalah kelas primari Kelas D untuk tujuan multicast,
Digunakan untuk pengalamatan hos yang biasa
Kelas D untuk tujuan multicast,
Untuk broadcast mesej
Kelas E dikhaskan untuk tujuan masa depan
Setiap hos mempunyai antaramuka alamat maya yang dikenali sebagai loopback interface iaitu
juga dikenali sebagai localhost

613. Figure 19.19 A network with two levels of hierarchy

614. Kelemahan Sistem Alamat IP
Sebahagian hos mempunyai lebih dari satu alamat
Kelas rangkaian adalah terlalu rigid
Tidak cukup alamat IP untuk kembangan masa hadapan

615. Subnet (subrangkaian)
Alamat IP diorganisasi sebagai subnet bagi memudahkan pengurusan rangkaian
Setiap subnet adalah set alamat yang ditentukan oleh
Alamat subnet (cth: )
Subnet mask (cth: )

616. Satu rangkaian kampus mengandungi LAN untuk pelbagai jabatan
Subnet
Satu rangkaian kampus mengandungi LAN untuk pelbagai jabatan

617. Figure 19.20 A network with three levels of hierarchy (subnetted)

618. Figure 19.21 Addresses in a network with and without subnetting

619. Contoh Subnet Bagi rangkaian Kelas B:
3 bit digunakan sebagai subnet menjadikan 15 subnet
subnet mask:
13 bit lagi mewakili hos

620. Routing
Jika hos destinasi tidak berada pada rangkaian yang sama, datagram akan dihantar ke gateway
Bagaimana IP memilih laluan untuk menghantar datagram ke rangkaian jauh?
Menggunakan jadual routing yang mempunyai maklumat next hop – iaitu nod lain dihubung secara terus kepada gateway

621. Contoh routing table netstat -nr
Routing Table: IPv4
Destination Gateway Flags Ref Use Interface
U hme0
U hme0
default UG
UH lo0

622. Figure 19.31 Default routing

623. Protokol Internet Version 6 (IPv6)
AKA Protokol Internet generasi akan datang (IPng)
Panjang alamat ditambah kepada128 bit
Membenarkan tambahan hos Web pada Internet
Membenarkan perkembangan Internet

624. Diagnostic tools ping traceroute (pada microsoft: tracert) netstat -nr
Untuk menguji hubungan dengan hos
Mengukur round trip time
traceroute (pada microsoft: tracert)
Menunjukkan laluan data dari hos ke destinasi
netstat -nr
Menunjukkan jadual routing

625. ipconfig (pada microsoft) ifconfig -a (pd *nix)
Menunjukkan no IP, subnet dan gateway komputer

626. Tools hostname domainname nslookup Nama komputer Nama domain
Network and Server Information Tools from Myloca (Telekom Malaysia)

627. Latihan
Dapatkan satu komputer yang dihubungkan pada LAN di UKM. Tentukan
alamat IP
kelas rangkaian
subnet mask
pelayan DNS
Tukarkan alamat IP di bawah kepada notasi dotted-decimal
Tentukan kelas rangkaian bagi alamat berikut: