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CHAPTER 6 Logical Link Control

Chapter 6. Networking for Manufacturing. 6-2. 6.1 LLC SERVICES. three forms of service-unacknowledged connectionless service-connection-mode service-acknowledged connectionless serviceLLC service primitives-request-indication-response-confirm. Chapter 6. Networking for Manufacturing.

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CHAPTER 6 Logical Link Control

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    1. CHAPTER 6 Logical Link Control LLC Services Flow Control and Error Control LLC Protocols

    2. Chapter 6 Networking for Manufacturing 6-2 6.1 LLC SERVICES three forms of service - unacknowledged connectionless service - connection-mode service - acknowledged connectionless service LLC service primitives - request - indication - response - confirm

    3. Chapter 6 Networking for Manufacturing 6-3

    4. Chapter 6 Networking for Manufacturing 6-4 Unacknowledged Connectionless Service simplest service - datagram service - simple transmission and reception of LLC PDUs - no acknowledgment, no flow control, no error control - individual, multicast, and broadcast addressing DL-UNITDATA.request - to pass down data to LLC for transmission - source and destination addresses for MAC address and LLC SAP - priority for desired priority level if provided by MAC DL-UNITDATA.indication - to pass data up to the destination LLC user

    5. Chapter 6 Networking for Manufacturing 6-5

    6. Chapter 6 Networking for Manufacturing 6-6 Connection-Mode Service virtual circuit style between users - connection establishment and termination - flow control, sequencing, and error recovery - individual addressing only DL-CONNECT - to establish a logical connection between two LLC users - DL-DISCONNECT.request to refuse the request by the remote LLC user - connection request refused by either local or remote LLCs

    7. Chapter 6 Networking for Manufacturing 6-7

    8. Chapter 6 Networking for Manufacturing 6-8 DL-DATA to transfer data with no ACK due to an established connection DL-DISCONNECT to terminate the connection DL-RESET to reset a connection to its initial state with the reset sequence number DL-CONNECTION-FLOWCONTROL to specify the amount of data that may be passed across the SAP

    9. Chapter 6 Networking for Manufacturing 6-9 Acknowledged Connectionless Service acknowledgment without establishing a connection - DL-DATA-ACK - DL-DATA-ACK-STATUS.indication - DL-REPLY - DL-REPLY-UPDATE

    10. Chapter 6 Networking for Manufacturing 6-10 Appendix 6B FLOW CONTROL preventing overflow by a transmitter - limited buffer size at the receiver - time required for receiver processing flow control with - no errors - the same order - arbitrary delay

    11. Chapter 6 Networking for Manufacturing 6-11

    12. Chapter 6 Networking for Manufacturing 6-12 Stop-and-Wait Flow Control simplest - acknowledged connectionless service - source transmitting a PDU - wait until an ACK is received - destination sending an ACK * PDU received without an error * ready to receive another - flow control by withholding an ACK - adequate for transmitting a few large blocks need to break a message into smaller blocks

    13. Chapter 6 Networking for Manufacturing 6-13 problem for transmitting multiple packets in series - only one PDU in transit at a time - inefficient when link length is greater than PDU length

    14. Chapter 6 Networking for Manufacturing 6-14 Sliding-Window Flow Control allowing multiple PDUs in transit - n buffers at the destination - n PDUs sent in series without waiting for ACKs - sequence number required to keep track of PDUs acknowledged - ACK including a sequence number, k, for a PDU that it is expecting * acknowledging up to k-1 * implying the next n PDUs starting from k - source maintaining a list of sequence numbers that it is allowed to send - destination maintaining a list of sequence numbers that it is prepared to receive - windows

    15. Chapter 6 Networking for Manufacturing 6-15 limited field for sequence number

    16. Chapter 6 Networking for Manufacturing 6-16 smaller window size allowed

    17. Chapter 6 Networking for Manufacturing 6-17 flow control by allowing 7 PDUs to be sent beyond the one acknowledged last - RR k: ACK up to k-1 and ready to receive PDU k - RNR k: ACK up to k-1 and not ready to receive PDU k two-way data exchange - two windows at each side - piggybacking

    18. Chapter 6 Networking for Manufacturing 6-18 Appendix 6C ERROR CONTROL error types - lost PDU - damaged PDU error control techniques - error detection - positive ACK - retransmission after timeout - negative ACK and retransmission ARQ - automatic repeat request

    19. Chapter 6 Networking for Manufacturing 6-19 Stop-and-Wait ARQ based on stop-and-wait flow control technique damaged or lost packet - damaged packet ignored by the destination - timer started after the packet is sent by the source - the same packet retransmitted when no ACK is received by the time of timer expiration damaged or lost ACK - duplicate PDUs - PDU sequence number with 0 and 1 - ACK also with 0 or 1 to indicate that it’s ready for 1 and 0, respectively

    20. Chapter 6 Networking for Manufacturing 6-20

    21. Chapter 6 Networking for Manufacturing 6-21 Go-Back-N ARQ based on the sliding-window flow control technique damaged or lost PDU i - more PDUs following PDU i - no PDUs after PDU i damaged or lost RR (i+1) - no problem when other RR k (k >i+1) is received before timer expiration - RR PDU transmitted with P bit = 1 when timer expires - P-bit timer damaged REJ

    22. Chapter 6 Networking for Manufacturing 6-22

    23. Chapter 6 Networking for Manufacturing 6-23 6.2 LLC PROTOCOLS LLC Types and Classes three types of operation - type 1 operation: unacknowledged connectionless service - type 2 operation: connection-mode service - type 3 operation: acknowledged connectionless service four classes of protocols

    24. Chapter 6 Networking for Manufacturing 6-24 LLC Protocol Data Units common PDU format for all classes - DSAP - SSAP - control - information

    25. Chapter 6 Networking for Manufacturing 6-25 control field - 8 or 16 bits - poll/final (P/F) bit to link commands and responses - different format for information, supervisory, and unnumbered PDUs

    26. Chapter 6 Networking for Manufacturing 6-26

    27. Chapter 6 Networking for Manufacturing 6-27 Type 1 Operation UI PDU - unnumbered information - no ACK, no flow control, no error control - error detection and discard by MAC XID and TEST PDUs - for all types of operation to support management functions - an LLC issuing a command (C/R bit = 0) - receiving LLC sending a corresponding PDU in response

    28. Chapter 6 Networking for Manufacturing 6-28 Type 2 Operation Connection Establishment: initiated by DL-CONNECT.request - SABME PDU to request a connection - UA PDU to accept a connection - DM PDU to reject the request Data Transfer: I-PDU for data transfer S-PDU for RR, RNR, and REJ for error and flow control

    29. Chapter 6 Networking for Manufacturing 6-29 Disconnect: initiated by DL-DISCONNECT. request - by issuing DISC PDU - responding with UA PDU

    30. Chapter 6 Networking for Manufacturing 6-30 Examples of Operation:

    31. Chapter 6 Networking for Manufacturing 6-31

    32. Chapter 6 Networking for Manufacturing 6-32 Type 3 Operation AC PDU - acknowledged connectionless information PDU - AC command to send data - AC response to acknowledge - only one PDU in transit - 1-bit sequence number, 0 and 1

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