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LAN Protocol Architecture

LAN Protocol Architecture. LAN Protocol Architecture. Lower layers of OSI model IEEE 802 reference model, is a standardized protocol architecture for LANs, which describes: Physical layer. Logical link control (LLC) sub-layer, Media access control (MAC) sub-layer. IEEE 802 v OSI.

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LAN Protocol Architecture

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  1. LAN Protocol Architecture

  2. LAN Protocol Architecture • Lower layers of OSI model • IEEE 802 reference model, is a standardized protocol architecture for LANs, which describes: • Physical layer. • Logical link control (LLC) sub-layer, • Media access control (MAC) sub-layer.

  3. IEEE 802 v OSI

  4. IEEE 802 Protocol Layers • Physical layer, includes such functions as: • Encoding and decoding of signals • Preamble generation and removal (for synchronization) • Bit transmission and reception • Logical Link Control, functions: • Assemble data into a frame with address and error-detection fields • Disassemble frame and perform address recognition and error detection • Govern access to the LAN transmission medium • Interface to higher levels and performs flow and error control

  5. Logical Link Control • LLC is concerned with transmission of link-level PDUs between two stations • LLC has two special characteristics: • Must support multiaccess, shared medium (no primary node as in multidrop line) • Relieved of some link access details by MAC layer • Addressing involves specifying source and destination LLC users • Referred to as service access points (SAP) • Service users are typically higher level protocols

  6. LLC Services • The operation and format of this standard is based on HDLC. • Provide three different services for attached devices: • Unacknowledged connectionless service: • Datagram-style service. • No flow-control and no error-control mechanisms. • Reliability depend to some higher layer of software. • Connection mode service: • Similar to that of HDLC. • Provides flow- and error-control. • Acknowledged connectionless service • Datagrams are to be acknowledged. • No prior logical connection is set up.

  7. LLC Protocol • Is modeled after HDLC, and has similar functions and formats. • LLC protocol operation: • LLC use asynchronous balanced mode of operation of HDLC to support connection mode LLC service (type 2 operation) • LLC supports an unacknowledged connectionless service using unnumbered information PDUs (type 1 operation) • LLC supports acknowledged connectionless service using unnumbered information PDUs (type 3 operation) • LLC permits multiplexing using LLC service access points (LSAPs)

  8. Media Access Control • Key parameters of MAC technique is where and how: • Where • Central • Adv.: Greater control and simple access logic at station (no coordination complexities) • Disadv.: Single point of failure and potential bottleneck • Distributed: opposite of central. • How • Synchronous: specific capacity dedicated to connection • Asynchronous: in response to demand; can be subdivided into three categories (round robin, reservation, contention)

  9. Asynchronous MAC Techniques • Round robin: • Each station is given the opportunity to transmit. The right to transmit passes in a logical sequence. • Reservation: a node will reserves future slots from the medium time to transmit, this is good for stream traffic. • Contention • Good for bursty traffic • All stations contend for time • Distributed control • Simple to implement • Efficient under moderate load • Tend to collapse under heavy load

  10. MAC Frame Format • MAC layer receives data from LLC layer • The fields of MAC frame: • MAC control: protocol control like priority. • Destination MAC address • Source MAC address • LLC: data from next higher layer. • CRC: FCS for error detection. • MAC layer detects errors and discards frames • LLC optionally retransmits unsuccessful frames

  11. Generic MAC Frame Format

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