Ref: 09330027
Title: Ethernet Specifications and Intermittent Network Problems
Date:  8/4/87

Copyright 3Com Corporation, 1991.  All rights reserved.

ETHERNET, 802.3, AND 3COM SPECIFICATIONS:

The following information about Ethernet specs is not readily
available.  Different sources have different specs, and we have
most sources are hard to read.  Here is a summary of the specs of
most concern to network planners and users.

The chart is organized first by Thick and Thin Coaxial cable, and
then into 802.3 specs, Ethernet specs, and 3Com specs.  To use
3Com specs, all transceivers on the network must be 3Com's.  You
might find it interesting that `Cheapernet' is actually an
attachment to the 802.3 standard.  It is referred to as type
10base2 specs.

THICK COAXIAL:
                        _________________________________________

                          802.3           Ethernet         3Com
                       _________________________________________

1. Max trunk length:      500M             500M            1000M
  (excludes txvr drop cables)

2. Max network addresses
   (typically equivalent to
   the # of Stations & Servers)
   on the network:        1024             1024             1024

3. Max transceivers
   (Typically equiv. to #
   Stations and Servers)
   on a segment:           100              100               100
 (includes repeaters)

4. Max repeaters
   between 2 stations:     4                4                 4

   Note: 4 repeaters would make up 5 segments, only 3 of the 5
   segments could have stations on them, the other 2 for distance

5. Max distance
   between stations:      3000M            3000M            3000M
   (includes txvr drop cables, 500M)

6. Min distance
   between stations:      2.5M              2.5M            2.5M

   Note: With the piercing tap connector on 3Com's transceiver,
   the minimum distance is 2.5M

7. Max txvr drop
   cable length:          50M               50M            50M

*****************************************************************
THIN COAXIAL:
                       __________________________________________

                               802.3                3Com
                       ------------------------------------------
1. Max trunk length:            185M                 333M

2. Max network addresses
   on network:                  1024                 1024

3. Max transceivers
   on segment:                  30                   100

4. Max repeaters
   between 2 stations:           4                    4

   Note: 2 of the 5 segments could not have any stations on them

5. Max distance
   between 2 stations:          1500M                2165M

   (includes txvr drop cables, 500M)

6. Min distance
   between 2 stations:          .5M                  .5M


NOTES:  (1) In the context that you use a repeater to EXTEND a
segment in 3Com's LAN, the practical number of repeaters you can
put along the 3000M of coax path is 2. Theoretically you should
be able to put in 4 repeaters, but then it'll be a waste of
money. As the price of repeaters go down, people may want to use
them to CREATE NEW SEGMENTs (as in the case of making star
configuration) rather than merely to extend a segment. In that
case the 4-repeater limitation that is outlined in the 802.3 spec
should be observed.

Also the mininum distance between transceivers (rather than
stations) is 2.5M across the board.

(2) A network number defines a network.  A network, with very few
exceptions, is defined as everything encompassed within one
unique Name Service.

(3)  You may interconnect multiple 3Com Name services to create
larger "networks".  For further information, you may want to
investigate 3+Route, 3+NetConnect, and 3+Open Internetwork
Communication Service, as well as internet bridge products such
as the 3Com/Bridge IB2 and IB3 products.

(4)  You may also interconnect 3Com Name services with Name
services from other vendors.  For further information, you may
want to investigate 3+Name Service Enhanced, as well as the
products mentioned above.

COMMON SYMPTOMS OF EXCEEDING CABLING SPECS:

As your network grows, it is sometimes difficult to assure that
your cabling remains within specifications.  Common symptoms of
exceeding cabling specs are any and all of the following:

(1) Every activity on the network slows down

(2) Increasing frequency of the message "Network retry, press
ctrl break...", sometimes requiring station reboot to recover

(3) Intermittent DOS data fault errors when reading/writing a
network drive