1 All rights reserved to Chun-Chuan Yang Upon completion you will be able to: The OSI Model and the TCP/IP Protocol Suite Understand the architecture of the OSI model Understand the layers of the OSI model and their functions Understand the architecture of the TCP/IP Protocol Suite Differentiate between the OSI model and the TCP/IP Suite Differentiate between the three types of Internet addresses Objectives

2 2.1 The OSI Model Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. The topics discussed in this section include: Layered Architecture Peer-to-Peer Processes Encapsulation

3 ISO is the organization. OSI is the model Note:

4 Figure 2.1 The OSI model

5 Figure 2.2 OSI layers

6 Figure 2.3 An exchange using the OSI model

7 2.2 Layers in the OSI Model The functions of each layer in the OSI model is briefly described. The topics discussed in this section include: Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Summary of Layers

8 Figure 2.4 Physical layer

9 The physical layer is responsible for the movement of individual bits from one hop (node) to the next. Note:

10 Figure 2.5 Data link layer

11 The data link layer is responsible for moving frames from one hop (node) to the next. Note:

12 Figure 2.6 Hop-to-hop delivery

13 Figure 2.7 Network layer

14 The network layer is responsible for the delivery of individual packets from the source host to the destination host. Note:

15 Figure 2.8 Source-to-destination delivery

16 Figure 2.9 Transport layer

17 The transport layer is responsible for the delivery of a message from one process to another. Note:

18 Figure 2.10 Reliable process-to-process delivery of a message

19 Figure 2.11 Session layer

20 Figure 2.12 Presentation layer

21 Figure 2.13 Application layer

22 Figure 2.14 Summary of layers

TCP/IP Protocol Suite The TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model. The three topmost layers in the OSI model, however, are represented in TCP/IP by a single layer called the application layer. The topics discussed in this section include: Physical and Data Link Layers Network Layer Transport Layer Application Layer

24 Figure 2.15 TCP/IP and OSI model

Addressing Three different levels of addresses are used in an internet using the TCP/IP protocols: physical (link) address, logical (IP) address, and port address. The topics discussed in this section include: Physical Address Logical Address Port Address

26 Figure 2.16 Addresses in TCP/IP

27 Figure 2.17 Relationship of layers and addresses in TCP/IP

28 In Figure 2.18 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical (link) addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection. Example 1 See Next Slide

29 Figure 2.18 Physical addresses

30 As we will see in Chapter 3, most local area networks use a 48-bit (6 bytes) physical address written as 12 hexadecimal digits, with every 2 bytes separated by a colon as shown below: Example 2 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.

31 In Figure 2.19 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use link addresses only; the link addresses have only local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic. Example 3 See Next Slide

32 The packet at the network layer contains the logical addresses, which remain the same from the original source to the final destination (A and P, respectively, in the figure). They will not change when we go from network to network. However, the physical addresses will change as the packet moves from one network to another. The boxes labeled routers are internetworking devices, which we will discuss in Chapter 3. Example 3 (Continued) See Next Slide

33 Figure 2.19 IP addresses

34 Example 4 As we will see in Chapter 4, an Internet address (in IPv4) is 32 bits in length, normally written as four decimal numbers, with each number representing 1 byte. The numbers are separated by a dot. Below is an example of such an address An internet address in IPv4 in decimal numbers

35 Figure 2.20 shows an example of transport layer communication. Data coming from the upperlayers have port addresses j and k ( j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the service-point addresses ( j and k). Then in the network layer, network addresses (A and P) are added to each packet. Example 5 See Next Slide

36 The packets can travel on different paths and arrive at the destination either in order or out of order. The two packets are delivered to the destination transport layer, which is responsible for removing the network layer headers and combining the two pieces of data for delivery to the upper layers. Example 5 (Continued) See Next Slide

37 Figure 2.20 Port addresses

38 As we will see in Chapters 11, 12, and 13, a port address is a 16-bit address represented by one decimal number as shown below. Example A 16-bit port address represented as one single number.

IP Versions IP became the official protocol for the Internet in As the Internet has evolved, so has IP. There have been six versions since its inception. We look at the latter three versions here. The topics discussed in this section include: Version 4 Version 5 Version 6

40 Socket programming (Judy Franklin) Socket API introduced in BSD4.1 UNIX, 1981 explicitly created, used, released by apps client/server paradigm two types of transport service via socket API: unreliable datagram reliable, byte stream- oriented a host-local, application- created/owned, OS-controlled interface (a “door”) into which application process can both send and receive messages to/from another (remote or local) application process socket Goal: learn how to build client/server applications that communicate using sockets

41 Socket-programming using TCP Socket: a door between application process and end-end-transport protocol (UDP or TCP) TCP service: reliable transfer of bytes from one process to another process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server internet

42 Socket programming with TCP Client must contact server server process must first be running server must have created socket (door) that welcomes client’s contact Client contacts server by: creating client-local TCP socket specifying IP address, port number of server process When client creates socket: client TCP establishes connection to server TCP When contacted by client, server TCP creates new socket for server process to communicate with client allows server to talk with multiple clients

43 Socket programming with TCP Example client-server app: client reads line from standard input ( inFromUser stream), sends to server via socket ( outToServer stream) server reads line from socket server converts line to uppercase, sends back to client client reads, prints modified line from socket Input stream: sequence of bytes into process Output stream: sequence of bytes out of process client socket inFromUser outToServer iinFromServer

44 Client/server socket interaction: TCP wait for incoming connection request connectionSocket = welcomeSocket.accept() create socket, port= x, for incoming request: welcomeSocket = ServerSocket() create socket, connect to hostid, port= x clientSocket = Socket() close connectionSocket read reply from connectionSocket close clientSocket Server (running on hostid ) Client send request using clientSocket read request from connectionSocket write reply to connectionSocket TCP connection setup

45 Example: Java client (TCP) import java.io.*; import java.net.*; class TCPClient { public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence; BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket = new Socket("hostname", 6789); DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream()); Create input stream Create client socket, connect to server Create output stream attached to socket

46 Example: Java client (TCP), cont. BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); sentence = inFromUser.readLine(); outToServer.writeBytes(sentence + '\n'); modifiedSentence = inFromServer.readLine(); System.out.println ("FROM SERVER: " + modifiedSentence ); clientSocket.close(); } Create input stream attached to socket Send line to server Read line from server

47 Example: Java server (TCP) import java.io.*; import java.net.*; class TCPServer { public static void main(String argv[]) throws Exception { String clientSentence; String capitalizedSentence; ServerSocket welcomeSocket = new ServerSocket(6789); while(true) { Socket connectionSocket = welcomeSocket.accept(); BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())); Create welcoming socket at port 6789 Wait, on welcoming socket for contact by client Create input stream, attached to socket

48 Example: Java server (TCP), cont DataOutputStream outToClient = new DataOutputStream (connectionSocket.getOutputStream()); clientSentence = inFromClient.readLine(); capitalizedSentence = clientSentence.toUpperCase() + '\n'; outToClient.writeBytes(capitalizedSentence); } Read in line from socket Create output stream, attached to socket Write out line to socket End of while loop, loop back and wait for another client connection

49 Socket programming with UDP UDP: no “connection” between client and server no handshaking sender explicitly attaches IP address and port of destination server must extract IP address, port of sender from received datagram UDP: transmitted data may be received out of order, or lost application viewpoint UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server

50 Client/server socket interaction: UDP close clientSocket Server (running on hostid ) read reply from clientSocket create socket, clientSocket = DatagramSocket() Client Create, address ( hostid, port=x), send datagram request using clientSocket create socket, port= x, for incoming request: serverSocket = DatagramSocket() read request from serverSocket write reply to serverSocket specifying client host address, port number

51 Example: Java client (UDP) import java.io.*; import java.net.*; class UDPClient { public static void main(String args[]) throws Exception { BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); DatagramSocket clientSocket = new DatagramSocket(); InetAddress IPAddress = InetAddress.getByName("hostname"); byte[] sendData = new byte[1024]; byte[] receiveData = new byte[1024]; String sentence = inFromUser.readLine(); sendData = sentence.getBytes(); Create input stream Create client socket Translate hostname to IP address using DNS

52 Example: Java client (UDP), cont. DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876); clientSocket.send(sendPacket); DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); clientSocket.receive(receivePacket); String modifiedSentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedSentence); clientSocket.close(); } Create datagram with data-to-send, length, IP addr, port Send datagram to server Read datagram from server

53 Example: Java server (UDP) import java.io.*; import java.net.*; class UDPServer { public static void main(String args[]) throws Exception { DatagramSocket serverSocket = new DatagramSocket(9876); byte[] receiveData = new byte[1024]; byte[] sendData = new byte[1024]; while(true) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); serverSocket.receive(receivePacket); Create datagram socket at port 9876 Create space for received datagram Receive datagram

54 Example: Java server (UDP), cont String sentence = new String(receivePacket.getData()); InetAddress IPAddress = receivePacket.getAddress(); int port = receivePacket.getPort(); String capitalizedSentence = sentence.toUpperCase(); sendData = capitalizedSentence.getBytes(); DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port); serverSocket.send(sendPacket); } Get IP addr port #, of sender Write out datagram to socket End of while loop, loop back and wait for another client connection Create datagram to send to client

55 Summary on Application Layer application service requirements: reliability, bandwidth, delay client-server paradigm Internet transport service model connection-oriented, reliable: TCP unreliable, datagrams: UDP Our study of network apps now complete! specific protocols: http ftp smtp, pop3 dns socket programming client/server implementation using tcp, udp sockets

56 Summary on Application Layer typical request/reply message exchange: client requests info or service server responds with data, status code message formats: headers: fields giving info about data data: info being communicated Most importantly: learned about protocols control vs. data msgs in-based, out-of-band centralized vs. decentralized stateless vs. stateful reliable vs. unreliable msg transfer “complexity at network edge” security: authentication