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LAN layers

Jamal Munshi, Sonoma State Univesity, 1992
IEEE 802 committee

Rationale
    as in OSI layers
    organize LAN specifications into insular layers
    facilitate enterprise-wide LAN integration
    MIS manager may use multiple technologies from various vendors
    compatilbility established at given layers using bridges and routers
Layer definitions
    Layer 1: physical layer: same as OSI: IEEE 802.3 and 802.5
      specify wire and connector hardware and pinouts
      specify wiring distances and repeaters
      specify voltages and bit definitions and bit timing
      upper layers may assume that bits exist and these bits may be transmitted across physical distances

    Layer 2: MAC layer: media access control: IEEE 802.3 and 802.5
      specify topology
      specify wire sharing rules
      specify packet design (data framing)
      specify within-packet error detection only (but not recovery)
      upper layers may assume that reliable (=error-free) data frames exist

    Layer 2.5: "bridge layer": IEEE 802.1
      specify bridge specifications for LANs with bridges
      bridges are used to manage backbone traffic and isolate local traffic
      bridges and wiring hubs are also used to overcome wiring distance limitations

    Layer 3: LLC layer: logical link control: IEEE 802.2
      specify LLC layer framing design
      specify detection of missing packet
      specify error recovery procedure for missing packet
      upper layers may assume "reliable packet delivery"
      upper layers see the same LLC regardless of MACs and wires: this makes it easy for MIS managers to integrate different LAN technologies

    Upper layers: application interface
      specifications in OSI layers 5 to 7 may now send and receive packets from the LAN

    Summary of IEEE 802 committees
      1 bridge specs and network mgt
      2 LLC
      3 CSMA/CD bus topology
      4 token passing bus topology
      5 token passing ring topology
      6 FDDI and metropolitan area networks (MAN)
      7 broadband LAN backbone
      8 optical fiber LAN backbone
      9 voice data integration
      10 LAN security and privacy issues
      14 cable modems: cable TV as a MAN backbone