Understanding OSI Model in Data Communication

1. ECOM 4314Data CommunicationsFall September, 2010

2. Lecture #2 Outline • OVERVIEW • LAYERED TASKS • THE OSI MODEL • LAYERS IN THE OSI MODEL. • TCP/IP PROTOCOL SUITE • ADDRESSING Data Communication

3. LAYERED TASKS Data Communication

4. Open Systems Interconnection (OSI) Model • the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. • OSI –Open System Interconnection model • The OSI model developed in 1978s & 1974s • The purpose of the OSI model is to show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software. Data Communication

5. Open Systems Interconnection (OSI) Model • The OSI model is not a protocol; it is a model for understanding and designing a network architecture that is flexible, robust, and interoperable. • It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network. • An understanding of the fundamentals of the OSI model provides a solid basis for exploring data communications. Data Communication

6. Open Systems Interconnection (OSI) Model Data Communication

7. Peer-to-Peer Processes Data Communication

8. Interfaces Between Layers • The passing of the data and network information from sender to receiver made possible by an interface between each pair of adjacent layers. • Each interface defines the information and services a layer must provide for the layer above it. • As a result the specific implementation of layer functions can be modified or replaced without requiring changes to the surrounding layers. Data Communication

9. Interfaces Between Layers Data Communication

10. Interfaces Between Layers Data Communication

11. LAYERS IN THE OSI MODEL Data Communication

12. Physical Layer • The physical layer is responsible for ensuring that a stream of bits transmitted between two nodes sharing a single link. • The physical layer coordinates all the functions required to transmit a bit stream over the physical medium. Data Communication

13. Physical Layer The physical layer is responsible for movements of individual bits from one hop (node) to the next. Data Communication

14. Physical Layer • The physical layer concerned with: • Physical characteristics of interfaces and medium. • Representation of bits. • Data rate: The transmission rate-the number of bits sent each second. • Synchronization of bits. The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level. • Line configuration (point-to-point) (multipoint). • Physical topology. • Transmission mode. Data Communication

15. Data Link Layer • The data link layer is responsible for ensuring that a packet of data is successfully transmitted between two adjacent nodes in the network. • The data link layer attempts to make the physical layer appear error free to the layers above in the model as well as controlling node-to-node delivery. Data Communication

16. Data Link Layer Data Communication

17. Data Link Layer • Responsibilities of the data link layer • Framing: divides the stream of bits received into frames. • Physical addressing: The address of the next node along the route to intended final destination. • Flow control :Prevent overwhelming the receiver. • Error control: Detect and retransmit damaged or lost frames and Prevent duplication of frames. • Access control: determine which device has control over the link at any given time. Data Communication

18. Data Link Layer Data Communication

19. Hop-to-hop (node-to-node) delivery Data Communication

20. Network Layer • The network layer is responsible for the delivery of packets from the original source to the final destination. • If two systems are connected to the same link, there is usually no need for a network layer. Data Communication

21. Network Layer • Network Layer responsibilities: • Logical addressing: The physical addressing implemented by the data link layer handles the addressing problem locally. If a packet passes the network boundary, we need another addressing system. • Routing: When independent networks or links are connected to create an internetwork (network of networks) or a large network, the connecting devices (called routers or switches) route or switch the packets to their final destination Data Communication

22. Network Layer Data Communication

23. Transport Layer • The transport layer is responsible for delivery of a message from one process to another. • A process is an application program running on a host • The transport layer, ensures that the whole message arrives intact and in order Data Communication

24. Transport Layer Data Communication

25. Transport Layer • Responsibilities of the transport layer • Port addressing: indicating a process. • Segmentation and reassembly: A message divide into segments having sequence number. • Connection control • Connectionless: each segment as an independent packet and delivers it to the transport layer at the destination machine. • A connection oriented: transport layer makes a connection with the transport layer at the destination machine first before delivering the packets • Flow control • Error control Data Communication

26. Transport Layer Data Communication

27. Session Layer • The session layer allows two communicating processes to co-ordinate the exchange of data • The session layer is the network dialog controller. • It establishes, maintains, and synchronizes the interaction among communicatingsystems. Data Communication

28. Session Layer Data Communication

29. Session Layer • Session Layer responsibilities include • Dialog control: allows two systems to enter into a dialog defining whether communication is half-duplex or full-duplex. • Synchronization: allows a process to define synchronization checkpoint in the message. This makes error/disaster recovery more efficient Data Communication

30. Presentation Layer • The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. • Responsibilities • Translation: from machine specific character sets and data formats to generic character sets (unicode, ascii) • Encryption:for security purpose. • Compression: to minimize the amount of bits needing to be transmitted and so reduce delivery time Data Communication

31. Presentation Layer Data Communication

32. The Application Layer • The application layer is the interface between the user and the network. • Enables the user, whether human or software, to access the network. • Network virtual terminal • Logon to a remote host. • File transfer, access, and management • Access files in a remote host. • Mail services • Basis for email forwarding and storage. • Directory services • Distributed database sources and access for global information about various objects and services. Data Communication

33. The Application Layer Data Communication

34. TCP/IP Protocol Suite Data Communication

35. TCP/IP Protocol Suite Data Communication

36. TCP/IP and OSI model Data Communication

37. ADDRESSING • Four levels of addresses are used in an • internet employing the TCP/IP protocols: • Physical (48-bit) • Logical (32-bit) • Port • Specific Data Communication

38. Data Communication

39. Physical Address • Link address • Size and format depends on network • Ethernet (6 bytes) (NIC) • 07:01:02:01:2C:4B Data Communication

40. References • Ayman, Maliha, “Data Communication Lectures”, IUG. • BehrouzA. Forouzan , “Data Communications and Networking”, 4rdEdition, Chapter2, 2007 Data Communication

41. Thanks Data Communication