Thick Ethernet (10Base-5)   

  This document contains cabling tips for thick ethernet (10Base5) 
  networks.  For more information on cabling a thick ethernet network,
  contact your local network supplier or call the IEEE (800-678-IEEE).

  THICK ETHERNET:
  ---------------
  
  Thick ethernet is a linear bus topology that uses a COAX cable.  
  If their is a break in the cable it will disrupt the entire segment.

  The thick ethernet COAX cable is usually brightly colored - yellow 
  or blue.  It will have "tap" markings every 2.5 meters.  (These 
  marks show where to connect transceivers.)
  
  Workstations are connected to a thick ethernet cable through the AUI
  port on the NIC, a "drop" cable (sometimes calles a transceiver cable)
  and a transceiver (or MAU).

                         -----      thick ehternet cable
     |------------------|     |------------------------------------|
                         --+-- transceiver
                           |
                           | drop cable
                           |
                       ----+-------  
                      |    | nic   | workstation
                      |            |
                       ------------

  A thick ethernet cable must be terminated at each end (50ohm terminators),
  and one end must be earth grounded.  The internal coax shield must not 
  make electrical contact with the earth ground.
  
  CABLE LENGTHS 
  ---------------------------------------------------------------------
  Max trunk length                  500 meters (1640 feet)
  Max number of nodes per trunk     100
  Max number of trunks                5 (only 3 can have wkst attached)  
  Max length of entire network     2500 meters (8200 feet)
   (all trunks added together)
  Min cable length between taps     2.5 meters (8 feet)
  Max length of drop cable           50 meters (164 feet)
  ---------------------------------------------------------------------
  
  Up to 5 trunk segments may be connected (through repeaters), but
  only 3 of these segments can have workstations attached.  Repeaters 
  count as a workstation so if you have two repeaters on a segment then 
  the maximum number of user workstations is 98.

  Example:    
                no workstations               no workstations
                       |                             |
                       v                             v
  |--+----------+  +--------+  +------+-------+  +--------+  +----+----|   
     |          |  |        |  |      |       |  |        |  |    |
     |        repeater     repeater   |     repeater    repeater  |
     |                                |                           |
  workstation                    workstation                workstation
     1-99                           1-98                        1-99


  PINOUT FOR AUI PORT:
  --------------------
                          shell = protective ground
                                               |
          ---------------------------------------------
          |       o   o   o   o   o   o   o   o       |
           \      1   2   3   4   5   6   7   8      /
            \                                       /
             \      o   o   o   o   o   o   o      /
              \     9  10  11  12  13  14  15     /
                ---------------------------------

  PIN  NAME AND FUNCTION
   1   Control-in Shield.  The shield for the CI twisted pair on the 
       AUI cable.

   2   Control-in Circuit A.  The positive signal for the CI circuit.
       This circuit is used to send the mau_available and
       signal_quality_error messages to the equipment.

   3   Data-out circuit A.  The positive signal for the DO circuit.

   4   Data-in Shield.  The shield for the DI twisted pair in the AUI
       cable.

   5   Data-in Circuit A.  The positive signal for the DI circuit.

   6   Voltage Common.  The ground return for the VP circuit.

   7   not connected

   8   not connected

   9   Control-in Circuit B.  The negative signal for the CI circuit.
       This circuit sends the same signals as listed under pin 2.

   10  Data-out Circuit B.  The negative signal for the DO circuit.

   11  Data-out Shield.  The shield for the DO twisted pair in the AUI
       cable.

   12  Data-in Circuit B.  The negative signal for the DI circuit.

   13  Voltage Plus.  The power supply to the transceiver.  The supply
       must remain in the range of 12V - 6% to 15V + 5%.

   14  Voltage Shield.  The shield for the VC and VP (pins 6 and 13)
       twisted pair.

   15  not connected