Local Area Networks

1. A LAN is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographic area.

2. IEEE Project 802
   • Split the data link layer into logical link control (LLC) and media access protocol (MAC)

   • 802.1 -- Internetworking

   • 802.2 -- (LLC), takes structure of an HDLC frame and divides it into two sets of functions; LLC and MAC

   • MAC Modules -- resolves the contention of the shared media, and the protocols are specific to the LAN using them
     • 802.3 -- CSMA/CD

     • 802.4 -- Token Bus

     • 802.5 -- Token Ring

3. IEEE 802.3 -- Ethernet, collision domain limited to 2,500 meters.
   • Baseband -- digital signal with Manchester encoding
     • 10Base5 -- thick Ethernet or Thicknet
       • Bus topology with maximum segment length of 500 meters

       • RG-8 cable

       • MAU (Medium attachment unit) or transceiver attached by a AUI (attachment unit interface) cable

     • 10Base2 -- thin ethernet (Thinnet, cheapnet, cheapernet)
       • Bus topology with maximum segment length of 185 meters

       • Transceiver circuitry in NIC (Network Interface Card)

       • No need for AUI cables

       • RG-58 cable and BNC-T connector

     • 10Base-T -- Twisted-pair ethernet, shared media network
       • Physical star topology, logically a bus with maximum segment length of 100 meters

       • Only one station can send a frame at any time

       • Uses unshielded twisted pair (UTP), or four-pair RJ-45 cable

       • Places all of its networking operations in an intelligent hub with a port for each station.

     • Switched ethernet -- twisted pair ethernet
       • Physical star topology, logically a bus

       • Can route the frame to the port to which the destination station is connected, can theoretically increase the capacity of a network with N devices to N x 10 Mbps.

     • Fast ethernet - operates at 100 Mbps, collision domain now 250 meters
       • Star topology similar to 10Base-T

       • 100Base-TX -- uses two Cat 5 UTP or STP. Encoding is 4B/5B with NRZ-I signaling, max distance to hub is 100 meters

       • 100Base-FX -- uses two optical fibers, 4B/5B encoding, NRZ-I signally, max distance to hub or switch is 2000 meters

       • 100Base-T4 -- four pairs of cat 3 UTP, 8B/6T encoding

       • Gigabit ethernet -- data rate of 1000 Mbps, designed to primarily use optical fiber, 1000Base-LX, 1000Base-SX, 1000Base-CX, 1000Base-T.

     • Broadband -- analog signal (PSK encoding)

   • IEEE 802.4 -- Token Bus
     • Used in factory automation and process control

     • A physical bus that operates as a logical ring using tokens

   • IEEE 802.5 -- Token Ring
     • Stations take turn sending a frame via token passing

     • Differential manchester encoding

     • Supports data rates up to 16 Mbps

     • Each station is connected to an automatic switch, which can bypass an inactive station, these switches are usually combined in an MAU (multistation access unit).

   • FDDI -- standardized by ANSI and the ITU-T (ITU-T X.3)
     • Supports data rates of 100 Mbps

     • Stations may send as many frames as they can within an allotted access period.

     • Synchronous and asynchronous (S-frames, A-frames) frames that is real time and and not respectively

     • Uses four bits/five bits (4B/5B) encoding via NRZ-I signaling.

     • Implemented as a dual ring, where data transmission occurs on the primary ring, and the secondary is a backup.