1. 1 Protocols and Standards Protocol zset of rules that govern data communication القواعد التي تحدد كيف يمكن لأجهزة الكمبيوتر أن تتفاهم مع بعضها البعض عبر الشبكة التي تتواجد عليها. In Summary, the key elements of the protocol define WHAT is communicated, HOW it is communicated, and WHEN it is communicated zKey elements  Syntax: defines the structure of information communicated, including the data format, the coding, and signal representations  Semantics: defines the meaning of the signals, exchanged including control information for coordination and error handling  Timing: defines the time at which data should be exchanged

2. Standards zRequired to allow for interoperability between equipment zAdvantages  Ensures a large market for equipment and software  Allows products from different vendors to communicate zDisadvantages  Freeze technology  May be multiple standards for the same thing 2

3. 3 Standards Defined by public organizations. Open standards  Avaliable to everyone (but not necessarily for free)  Everyone has the possibility to propose, criticize, and influence zStandards organizations  ISO: International Organization for Standardization  IETF: Internet Engineering Task Force  IEEE: Institute of Electrical and Electronics Engineers  ANSI: American National Standards Institute  ETSI: European Telecommunications Standard Institute  ITU: International Telecommunication Union  ITU-T: International Telecommunication Union—Telecommunication Standards  EIA: Electronic Industries Association

4. Services :What a network operator offers to customers (subscribers) zApplication: What the customer uses the service for Examples zTelephone connection  Service: voice transmission  Application: conversation between two parties zComputer communication via modem  Service: same as above plus Internet connectivity  Application: Web browsing, e-mail, file transfer, chat, etc Services and Applications 4

5. The task of designing a communication network is too complex to be handled as a monolithic unit. An alternative, a structured approach. Divide the communication task into manageable parts. Need to describe the communication functions in terms of an architecture. The architecture defines the relationship and interactions between network services and functions through common interfaces and protocols. Network Architectures 5

6. 2-1 LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office.

7. Figure 2.1 Tasks involved in sending a letter A network model is a layered architecture Task broken into subtasks Implemented separately in layers in stack Functions need in both systems Peer layers communicate Protocol: A set of rules that governs data communication It represents an agreement between the communicating devices 2.7

8. The architecture is divided into multiple layers.  Each layer performs a related subset of functions required for communication, and adds value to the services provided by lower layers.  Layer N relies on services of layer N-1 to provide a service tolayer N+1  Service required from lower layer is independent of how that  service is implemented Information and complexity hiding Changes in layer N do not affect other layers Layered Architecture 8

9. A Layered Model 1.Layers are independent 2.Modify one without affecting the other 9

10. 2.10 ISO is the organization. OSI is the model. Note

11. 2.11 2-2 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. Layered Architecture Topics discussed in this section:

12.  Define the rules and conventions for various functions within each layer.  Specify the general relations among these functions.  Determine the constraints on the types of functions and their relation The basic goals of the model 12

13. 2.13 Figure 2.2 Seven layers of the OSI model

14. 2.14 PEER – TO – PEER PROCESS Communication must move down through the layers on the sending device, over to receiving device Are the receiving device, communication must move up through the layers Each layer in the sending device adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it At the receiving device, the message is unwrapped layer by layer, with each process receiving and removing the data meant for it

15. 2.15 PEER-TO-PEER PROCESS The passing of the data and network information down through the layers of the sending device and backup through the layers of the receiving device is made possible by interface between each pair of adjacent layers Interface defines what information and services a layer must provide for the layer above it.

16. 2.16 2-3 LAYERS IN THE OSI MODEL In this section we briefly describe the functions of each layer in the OSI model. Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Topics discussed in this section:

17. 2.17 Figure 2.4 An exchange using the OSI model

18. 2.18 The physical layer is responsible for movements of individual bits from one hop (node) to the next Transmission of raw bits (0/1) over physical wires) Physical characteristics of interfaces and media Multiplexing Guided and Unguided transmission media Data rates Transmission impairments Transmission mode Parallel vs. serial Synchronous vs. asynchronous Direction of transmission Representation of bits Analog and Digital signals Modulation and demodulation

19. 2.19 Figure 2.5 Physical layer

20. 2.20 The data link layer is responsible for moving frames from one hop (node) to the next. Function Framing Physical addressing Flow control Error control Access control

21. 2.21 Figure 2.6 Data link layer

22. 2.22 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. Example 2.1  Most LANs use a (6-byte) physical address written as 12 Hex digit  Every byte (2 Hex digits) is separated by a colon  07:01:02:01:2C:4B

23. 2.23 NETWORK LAYER Responsible from the delivery of packets from the original source to the final destination across multiple networks If 2 systems are connected to the same link, there is no need for network layer Functions of the layer  Logical addressing  Controls access to the network  Provides routing of packets within the network  Manages contention and bottlenecks within the network

24. 2.24 Figure 2.9 Source-to-destination delivery

25. 2.25 TRANSPORT LAYER Responsible for delivery of a message from one process to another (End-to-end data delivery) Functions Port addressing Segmentation and reassembly Connection control Connection oriented Transport layer makes a connection with its peer layer at the destination before sending packets After all data are transferred, the connection is terminated Connectionless oriented A connectionless Transport layer treats each segment as an independent packet and delivers it to the transport layer at the destination machine Flow control Error control

26. 2.26 Figure 2.11 Reliable process-to-process delivery of a message

27. 2.27  Two PC communicating via the Internet.  The sending PC is running 3 processes at this time with port addresses a, b, and c.  The receiving PC is running 2 processes at this time with port addresses j and k.  Process a in the sending PC needs to communicate with process j in the receiving PC Example Port address is a 16-bit address represented by one decimal number

28. 2.28 Session layer It is the network dialog controller Bind two communicating entities into a “relationship”,  Session setup (authentication), failure recovery (broken session), It establishes, maintains and synchronize the interaction between communicating system Function Dialog control It allows the communication between two processes to take place in either half-duplex or full-duplex. Synchronization It allows a process to add checkpoints into a stream of data

29. 2.29 Presentation layer Concerned with the syntax and semantics of the information exchanged between two systems Conversion of data to conform to a common format Functions Translation Translation The running programs in two systems are usually exchanging information in the form of char strings, numbers,… Information must be changed to bit stream before being transmitted But different computers use different encoding methods The presentation layer is responsible for interoperability between these different encoding systems It changes the information at the sender from its sender-dependent format into its receiver-dependent format Encryption Encryption Compression Compression

30. 2.30 Application layer Responsible for providing services to the user Functions  Mail services  File transfer and access  Remote log-in  Accessing the World Wide Web www  distributed databases

31. 2.31 Figure 2.14

32. 2.32 Figure 2.16 TCP/IP and OSI model

33. TCP/IP Protocol Architecture(1) zApplication Layer yCommunication between processes or applications zEnd to end or transport layer (TCP/UDP/…) yEnd to end transfer of data yMay include reliability mechanism (TCP) yHides detail of underlying network zInternet Layer (IP) yRouting of data 33

34. TCP/IP Protocol Architecture(2) zNetwork Layer yLogical interface between end system and network zPhysical Layer yTransmission medium ySignal rate and encoding 34

35. PDUs in TCP/IP 35

36. Some Protocols in TCP/IP Suite 36

37. Required Reading zStallings chapter 2 zComer,D. Internetworking with TCP/IP volume I zComer,D. and Stevens,D. Internetworking with TCP/IP volume II and volume III, Prentice Hall zHalsall, F> Data Communications, Computer Networks and Open Systems, Addison Wesley zRFCs 37

38. Key Elements of a Protocol zSyntax yData formats ySignal levels zSemantics yControl information yError handling zTiming ySpeed matching ySequencing 38

39. 2.39 Addresses in TCP/IP Addresses in TCP/IP

40. 2.40 Relationship of layers and addresses in TCP/IP Relationship of layers and addresses in TCP/IP

41. 2.41 Figure 2.16 TCP/IP and OSI model