1. Java Socket Support Presentation by: Lijun Yuan Course Number: cs Course Name: Software Engineering

2. What Is Socket A socket is one endpoint of a two-way communication
link between two programs running on the network.
A socket is bound to a port number so that the TCP layer
can identify the application that data is destined to be sent.
A socket in use usually has an address bound to it. The
nature of the address depends on the communication
domain of the socket.
A single socket can communicate in only one domain.

3. Where Is Socket From?
Originally developed in 4.2BSD (Berkeley Software
Distribution), cka Berkeley UNIX.
In UNIX, a process has a set of I/O descriptors that one
reads from and writes to. These descriptors may refer to
communication channels (sockets).
The lifetime of a descriptor is made up of three phases:
creation (open socket), reading and writing (receive and
send to socket), and destruction (close socket).

4. Three Major Protocols Used For Socket
Internet Protocol (IP): a low-level routing protocol that
breaks data into small packets and sends them to an
address across a network, which is not reliable.
Transmission Control Protocol (TCP): a higher-level
protocol that strings together the packets, routing and
retransmitting them as necessary to reliably transmit your
data.
User Datagram Protocol (UDP): sits next to TCP and can
be used directly to support fast, connectionless, unreliable
transport of packets.

5. Five Socket Types Datagram socket Stream socket
Reliably delivered message socket
Raw socket
Sequenced packet socket

6. Java Socket Support Three types of sockets in Java
The Java environment implements portable socket objects by stacking several object layers on top of low-level, platform-specific procedures.
Three types of sockets in Java
TCP/IP Socket (supported by Socket and SeverSocket classes)
UDP Socket (supported by DatagramSocket class)
Multicast Socket (supported by MulticastSocket class)

7. TCP/IP Socket in Java TCP/IP sockets are used to implement reliable,
bi-directional, persistent, point-to-point, stream-
based connections between hosts on the Internet
Useful for implementing network services –
such as remote login (telnet, rlogin) and file
transfer (FTP) – which require data of
indefinite length to be transferred.

8. blocks until connection from client
TCP/IP Server
Figure 1 Socket function for TCP client-server
ServerSocket
well-known port
bind
listen
TCP/IP Client
accept
Socket
blocks until connection from client
connection establishment
connect
(TCP three-way handshake)
write
Read
data (request)
process request
data (reply)
read
Write
end-of-file notification
read
Close Conn.
Close Conn.

9. Seven Basic Operations
Connect to a remote machine
Send data
Receive data
Close a connection
Listen for incoming data
Bind to port
Needed only by the server
Accept connections from remote machines
on the bound port

10. Socket Class -Characteristics
Socket class is Java’s fundamental class for performing
client-side TCP operation.
This class is used for creating TCP connections over an
IP network
This class itself uses native code to communicate with the
local TCP stack of the host operating system
The interface that the Socket class provides to the
programmer is streams

11. Socket Class -Constructors Four public constructors:
Public Socket(String host, int port) throws UnknownHostException, IOException
Public Socket(InetAddress host, int port) throws IOException
Public Socket(String host, int port, InetAddress interface, int localPort) throws IOException
Public Socket(InetAddress host, int port, InetAddress interface, int localPort) throws IOException
Two protected constructors
Protected Socket()
Protected Socket(SocketImpl impl)

12. Socket Class -How does it work? Step one Step two
The creation of a Socket object implicitly establishes a connection between the client and server.
Server p o r t
Connection request
Client
Step two
Server p o r t
Client p o r t
connection
port

13. ServerSocket Class
The SeverSocket is designed to be a “listener”, which
waits for clients to connect before doing anything
Server sockets wait for connections while client sockets
initiate connections
Listen for either local or remote client programs to connect
to them on published ports.

14. How many request I can hold?
ServerSocket Class
-Constructors
Three Public Constructors
ServerSocket(int port),
ServerSocket(int port, int maxQueue)
ServerSocket(int port, int maxQueue, InetAddress localAddress)
How many request I can hold?

15. UDP Socket in Java Less complex Incurs fewer overheads
Used in bandwidth-limited applications, where
the overhead associated with resending packets
is not tolerable. A good example: real-time
network audio applications.
Implemented by DatagramPacket class &
DatagramSocket class

16. blocks until datagram received from a client
UDP Sever
Socket()
bind
recvfrom
UDP Client
Socket()
blocks until datagram received from a client
data (request)
sendto
process request
data (reply)
sendto
recvfrom
close
Socket functions for UDP client-server

17. The Two Major Classes DatagramPacket class DatagramSocket Class
Each DatagramPacket contains a data buffer, the address of the remote host to send the data to, and the port number the remote agent is listening to
DatagramSocket Class
In order for two agents to talk to each other over a UDP connection, a DatagramSocket object is created to ensure they both connected to a port on their local machines.

18. How does it work?
The DatagramPacket class stuffs bytes of data into UDP
packets called datagrams and lets you unstuffy datagrams
that you receive
A DatagramSocket sends and receives data using UDP
packets, represented as DatagramPacket objects
The remote process can receive the data in the form of a
DatagramPacket by calling the receive() method on its
DatagramSocket

19. Multicast Sockets
Multicasting sends data from one host to many different
hosts, but not to everyone; the data goes only to clients
that have expressed and interest in the data by joining a
particular multicast group
On the Internet, such event like video conference, is best
implemented using Multicasting that built on top of UDP
Multicast Sockets in Java uses the DatagramPacket class
along with a new MulticastSocket class.

20. With Multicast Sockets Without Multicast Sockets
Client
Router
The Internet
Router
Server
the simplest possible multicast configurations

21. Why need Multicasting? The growing requirement
All the unicast sockets provide point-to-point communication and create a connection with two well-defined endpoints. However, many tasks require a different model. For example, the television station need to broadcast to every user and Video conferencing, by contrast, sends an audio-video feed to a select group of people using multicast. Multicasting is broader than unicast, but narrower and more targeted than broadcast communication.
The resources saving and the traffic relief
The goal of multicast sockets is that no matter how complex the network, the same data should never be sent more than once over any given network segment

22. How to do it? Step one Step two Step three
Create a MulticastSocket object and have the socket join a multicast group
Step two
Stuff the address of the multicast group in the DatagramPacket you want to send.
Step three
The routers and the MulticastSocket class take care of the rest .

23. Four Key Operations
The behavior of MulticastSocket is very similar to DatagramSocket’s
Join a multicast group
Send data to the member of the group
3. Receive data from the group
4. Leave the group

24. Problems Performance Security Complexity
Restriction on multicast socket

25. Thank You