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Chapter11 Homework

Chapter11 Homework. 15, 16, 20. Data Link Layer. High-Level Data Link Control (HDLC). HDLC is based on IBM's Synchronous Data Link Control (SDLC) protocol, which is widely used by IBM's large customer base in mainframe computer environments. High-Level Data Link Control (HDLC).

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Chapter11 Homework

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  1. Chapter11 Homework • 15, 16, 20

  2. Data Link Layer

  3. High-Level Data Link Control (HDLC) • HDLC is based on IBM's Synchronous Data Link Control (SDLC) protocol, which is widely used by IBM's large customer base in mainframe computer environments.

  4. High-Level Data Link Control (HDLC) · A group of protocols for transmitting data between network nodes. • Data is organized into a frame and sent across a network to its destination • The successful arrival of data is verified. • The HDLC protocol also manages the flow at which data is sent.

  5. Types of Stations Defined By (HDLC) • · Primary stations • · Secondary stations • · Combined stations

  6. Primary Stations • Control the operation of other stations or links. • Primary polls the secondaries in a predetermined order, and secondaries can then transmit if they have outgoing data. • Primary sets up and tears down links and manages the link while it is operational. • Frames issued by primary stations are called commands. • Primary generates commands and interprets responses • Responsible for initiating error recovery procedures, and handling the flow of transmitting data to and from the primary

  7. Secondary Stations ·Controlled by a primary ·Frames issued by secondary stations are called responses. ·It responds to requests from a primary station. ·Needs permission from primary to send information. ·May initiate its own transmission • when it runs out of buffer space, at which point it sends RNR (receiver not ready) to the primary station. • When the buffer space is cleared, it sends RR (receiver ready).

  8. Combined Stations • ·Has the features of primary and secondary stations. • · It can issue both command and response frames.

  9. HDLCLink Configuration • Refers to relations between primary and secondary stations

  10. HDLCLink Configuration • Unbalanced configuration (master/slave) • Consists of one primary and one or more secondary • Supports full-duplex and half-duplex transmission. • Balanced configuration • Consists of two or more combined stations • Supports full-duplex and half-duplex transmission. • Symmetrical configuration • Each physical station Consists of two logical stations (one primary and one secondary) • Separate line links the primary aspect of the physical station to secondary aspect of the physical station and vice versa.

  11. One primary and one or more secondary • Supports full-duplex and half-duplex transmission.

  12. Two or more combined stations • Supports full-duplex and half-duplex transmission.

  13. Each physical station Consists of two logical stations (one primary and one secondary) • Separate line links the primary aspect of the physical station to secondary aspect of the physical station and vice versa.

  14. HDLC Data Transfer Modes • Normal response mode (NRM) • Used with unbalanced configuration • Primary may initiate data transfer to secondary • Secondary may only transmit data in response to a primary command. • The link may be point-to-point or multipoint. In the latter case only one primary station is allowed.

  15. HDLC Data Transfer Modes • Asynchronous response mode (ARM) • Used with unbalanced configuration • Primary has the line responsibility, initialization, error control, and logical disconnection. • It allows a secondary station to initiate a transmission without receiving permission from the primary station when the line is idle. • This mode is normally used with point-to-point configurations and full duplex links.

  16. HDLC Data Transfer Modes • Asynchronous balanced mode (ABM) • Used with balanced configuration • Either combined station may initiate transmission without permission from the other combined station. • ABM, is used mainly on full duplex point-to-point links for computer to computer communications and for connections between a computer and a packed switched data network. • Each station has an equal status and performs the role of both primary and secondary functions. • This mode is used in the protocol set known as X.25.

  17. HDLC • HDLC uses synchronous transmission • HDLC frame format is discussed next.

  18. Flag Fields • Flag: • Unique pattern of 01111110 used to indicate the beginning and end of a fame.

  19. Address Fields • Address: • Identifies the address of the secondary station that transmitted or is to receive data. • Not necessary for PPP links but, is included anyway.

  20. Control Field • HDLC defines three types of frames, each with different control field format. • Information frames (I-frames) • Supervisory frames (S-frames) • Unnumbered frames (U-frames)

  21. Control Field • Information frames (I-frames) • Carry the data to be transmitted for the user • Error and flow control data, using ARQ (automatic repeat request) are piggybacked on an I-frame.

  22. Control Field • Supervisory frames (S-frames) • Carry the control information (flow and error control info of data link layer) • Provide ARQ mechanism when piggybacking is not used.

  23. Control Field • Unnumbered frames (U-frames) • Used for link management control information. • A U frame can be used to initialize secondaries.

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