Why Networking Standards Are Needed

1. Why Networking StandardsAre Needed • To help ensure that manufacturers build equipment that can intercommunicate • To protect customer from wasted time and expense dealing with incompatibility • To advance networking technologies in a cooperative environment • To bring consistency and reliability to the industry

2. Bus design CPU design Serial port design Parallel port design Keyboard architecture Display architecture Modem communications Printer communications Network communications Types of Standards

3. Standards for Networking • Provide common ground for transmitting data, manufacturing compatible network equipment, and designing operating systems for use on a network • Define the maximum time a packet has to travel from one node to another • Define how packets are handled

4. Key Networking Standards Organizations • American National Standards Institute (ANSI) • Institute of Electrical and Electronics Engineers (IEEE) • Consultative Committee on International Telegraph and Telephone (CCITT) • International Standards Organization (ISO)

5. ANSI • An organization that works to set standards for all types of products, including computer network equipment

6. To Visit the ANSI Web Site • Accessing ANSI’s Web site

7. IEEE • An organization of scientists, engineers, technicians, and educators that has influenced in particular standards for network cabling and data transmissions

8. To Find Information about the IEEE 802.3 Standards • Accessing IEEE’s Web site

9. CCITT • An international standards body that develops telecommunications standards for modems, digital telephone systems, and e-mail

10. ISO • An international body that establishes communications and networking standards • Best known for its contributions to network protocol standards

11. OSI Layered Communications • The Open Systems Interconnect (OSI) model provides a framework for network communications based on seven functional layers. • Developed by the ISO and ANSI

12. The OSI Model The OSI model affects: • How signals are transmitted • How packets are constructed • Reliability of network communications • Error detection • Sharing of network resources continued

13. The OSI Model • How network equipment is designed and implemented • How network equipment affects network software services

14. The Seven Layersof the OSI Model

15. Physical Layer (Layer 1) • Provides the transfer medium (such as cable) • Translates data into a transmission signal appropriate to the transfer medium • Sends the signal along the transfer medium continued

16. Physical Layer (Layer 1) • Includes the physical layout of the network • Monitors for transmission errors • Determines the voltage levels used for data signal transmissions and to synchronize transmissions • Determines the signal type, such as digital or analog

17. Physical Layer Definitions • An analog transmission is one that can vary continuously, such as in a wave pattern with positive and negative voltage levels. • A digital transmission has distinct levels to represent binary 1s and 0s, such as On and Off or +5 volts and 0 volts. continued

18. Physical Layer Definitions • Electromagnetic interference (EMI) and radio frequency interference (RFI) are two sources of interference at the physical layer. • EMI: caused by magnetic force fields that are generated by electrical devices • RFI: caused by electrical devices that emit radio waves at the same frequency used by network signal transmission

19. Data Link Layer (Layer 2) • Constructs data packets using the appropriate format for the network • Creates cycle redundancy check (CRC) information • Checks for errors using CRC information • Responsible for data retransmission if there is an error continued

20. Data Link Layer (Layer 2) • Initiates the communications link and makes sure it is not interrupted for node-to-node physical reliability • Examines packet addresses • Acknowledges receipt of a packet

21. Data Link Layer Definitions • A cycle redundancy check (CRC) is an error detection method that calculates a value for the total size of the information fields contained in the frame. • Logical link control (LLC) is a data link sublayer of the OSI model that initiates the communication link between nodes and ensures that the link is not broken unintentionally. continued

22. Data Link Layer Definitions • Media access control (MAC) is a data link layer sublayer that examines addressing information contained in network frames and controls how devices share communications on the same network. continued

23. Data Link Layer Definitions • Services used for communications between LLC sublayer and network layer • Type 1 operation (connectionless service): does not establish logical connection between sending and receiving nodes • Type 2 operation (connection-oriented service): logical connection must be established between sending and receiving nodes before full communications begin

24. Network Layer (Layer 3) • Determines the network path on which to route frames • Helps reduce network congestion • Establishes virtual circuits • Routes frames to other networks, resequencing packet transmissions when needed

25. Network Layer Definitions • A router is a physical device that contains software to enable frames formatted on one network to reach a different network in a format that the second network understands. • A virtualcircuit is a logical communi-cation path established by the OSI network layer for sending and receiving data.

26. Transport Layer (Layer 4) • Ensures reliability of packet transmissions from node to node • Ensures data packets are sent and received in the same order • Provides acknowledgment when a packet is received • Monitors for packet transmission errors and resends bad packets

27. Transport Layer Definitions • Flow control is used to make sure one device does not send information faster than can be received by another device.

28. Session Layer (Layer 5) • Initiates the communication link • Makes sure the communication link is maintained • Determines which node transmits at any point in time • Disconnects when a communication session is over • Translates node addresses

29. Presentation Layer (Layer 6) • Translates data to a format the receiving node understands, such as from EBCDIC to ASCII • Performs data encryption • Performs data compression

30. Presentation Layer Definitions • Extended Binary Coded Decimal Interchange (EBCDIC) • Used mainly on IBM mainframe computers • Specially coded 256-character set • American Standard Code for Information Interchange (ASCII) • Commonly used character set • 96 uppercase & lowercase characters and numbers, plus 32 nonprinting characters

31. Application Layer (Layer 7) • Enables sharing remote drives • Enables sharing remote printers • Handles e-mail messages • Provides file transfer services • Provides file management services • Provides terminal emulation services

32. Application Layer Definitions • The Microsoft redirector is a service used via the application layer that makes one computer visible to another for access through the network.

33. Communication Between Stacks Building and receiving a frame from layer to layer

34. Communication Between Stacks Peer protocol communication between the same layers

35. Communication Between Stacks • A primitive is a command used to transfer information from one layer in an OSI stack to another layer.

36. Communication Between Stacks Communications using service data units (SDUs) and protocol data units (PDUs)

37. Communication Between Stacks Definitions • Peer protocols enable an OSI layer on a sending node to communicate with the same layer on a receiving node. • A protocol data unit (PDU) is the information transferred between layers in the same OSI stack. • A service data unit is the PDU minus control and transfer information used to transfer the data from the previous layer in the OSI stack.

38. Applying the OSI Model