Computer Communication & Networks

1. Computer Communication & Networks Lecture # 02 Nadeem Majeed Choudhary nadeem.majeed@uettaxila.edu.pk

2. Layering & Protocol Stacks

3. Reference Models • OSI reference model • TCP/IP

4. OSI Reference model • Open System Interconnection • 7 layers • Crate a layer when different abstraction is needed • Each layer performs a well define function • Functions of the layers chosen taking internationally standardized protocols • Number of layers – large enough to avoid complexity

5. Seven layers of the OSI model

6. Exchange using OSI Model

7. Peer-to-peer Processes • Layer x on one machine communicates with layer x on another machine - called Peer-to-Peer Processes. • Interfaces between Layers • Each interface defines what information and services a layer must provide for the layer above it. • Well defined interfaces and layer functions provide modularity to a network • Organizations of the layers • Network support layers : Layers 1, 2, 3 • User support layer : Layer 5, 6, 7 • It allows interoperability among unrelated software systems • Transport layer (Layer 4) : links the two subgroups

8. The interaction between layers in the OSI model

9. OSI Layers

10. Physical layer physical connection Transporting bits from one end node to the next • type of the transmission media (twisted-pair, coax, optical fiber, air) • bit representation (voltage levels of logical values) • data rate (speed) • synchronization of bits (time synchronization) • deals with the optical, mechanical and electrical features • transmission modes ( half duplex, full duplex)

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

12. Protocols: - Modems - Optical Cables, Connectors • Network Devices: - Hubs, Repeaters, and Amplifier.

13. Data Link layer logical connection Transporting frames from one end node to the next one • - framing - physical addressing • - flow control - error control • access control

14. Data Link layer- hop-to-hop delivery-

15. Data Link layer- example-

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

17. Data Link layer • Network Devices: -Bridge, Switch, ISDN Router, Intelligent Hub, NIC, Advanced Cable Tester

18. Data Link layer • Protocols: Logical Link Control • error correction and flow control• manages link control and defines SAPsMedia Access Control • controls the type of media being used:802.3 CSMA/CD (Ethernet)802.4 Token Bus (ARCnet)802.5 Token Ring802.12 Demand Priority

19. Network Layer • The network layer is responsible for the delivery of individual packets from the source host to the destination host.

20. Network layer Not a message • End-to-End packet delivery • From the original source to a destination • Needed when 2 devices are attached to different networks • What is the network definition here? • Main duties: • Logical addressing • Routing • Switching • Congestion control and QoS 20

21. Source to destination delivery Data Link Network layer 21

22. Network layer- example - Network layer addresses Data Link layer addresses 22

23. Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. 23

24. Network Layer • Router works as the post office and network layer stamps the letters (data) for the specific destinations. • Protocols: These protocols work on the network layer IP, ICMP, ARP, RIP, OSI, IPX and OSPF. • Network Devices: Network devices including Router, Frame Relay device and ATM switch devices work on the network layer.

25. Transport layer Process-to-Process delivery of the entire message From the original source to a destination Needed when several processes (running programs) active at the same time Main tasks: Port addressing Segmentation and reassembly Congestion control Flow control Error control 25

26. Transport Layer • The transport layer is responsible for the delivery of a message from one process to another.

27. Transport Layer 27

28. Transport layer-an example of a reliable delivery - 28

29. Note The transport layer is responsible for the delivery of a message from one process to another. 29

30. Transport Layer • Protocols: These protocols work on the transport layer TCP, UDP, SPX, NETBIOS, ATP and NWLINK. • Network Devices: The Brouter, Gateway and Cable tester work on the transport layer.

31. Note The session layer is responsible for dialog control and synchronization. 31

32. Session Layer • The session layer is responsible for dialog control and synchronization.

33. Presentation Layer

34. Presentation Layer • Presentation layer is a best layer for cryptography.

35. Note The presentation layer is responsible for translation, compression, and encryption. 35

36. Application Layer • The application layer is responsible for providing services to the user.

37. Application Layer • Services provided by Application layer: - File transfer, Access - Mail services

38. Application layer Enables user to access the network Provides services to a user E-mail Remote file access and transfer (Telnet, FTP) Access to WWW (HTTP) 38

39. Note The application layer is responsible for providing services to the user. 39

40. Application Layer • Protocols: FTP, DNS, SNMP, SMTP, FINGER, TELNET, TFTP, BOOTP and SMB protocol are operated on the application layer. • Network Devices: Gateway network device is operated on the application layer.

41. OSI Reference Model A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing 41

42. Summary of layers and protocols Low-level protocolsdefine the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream High-level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages 42

43. TCP/IP Protocol 43

44. TCP/IP Vs OSI Model 44

45. Four Level of Addresses 45

46. Relationship of Layers & Addresses in TCP/IP 46

47. Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same. 47

48. Example 2.1 In Figure 2.19 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.

49. Figure 2.19 Physical addresses

50. Example 2.2 most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.