Ref: 99980126
Title: CS/200-TE
Date: 8/4/88

Copyright 3Com Corporation, 1991.  All rights reserved.

Enclosed is a CS/200-TE featuring a thin Ethernet interface.
This release memo is an addendum to the Series/200 Installation
Guide.  It describes thin Ethernet cabling requirements and the
procedure for installing thin Ethernet cable.

Overview

Thin Ethernet refers to the IEEE 802.3 10Base2 standard.  Its
transfer rate is 10 Mbps, and its baseband encoding scheme
conforms to the IEEE 802.3 10Base5 standard.  It has the
following advantages over the regular Ethernet network:

1.  It uses a low-cost thin coaxial cable.

2.  The transceiver is integrated in the DTE, so no bulky
transceiver cable is required to attach the transceiver to
the DTE.

Other advantages of thin Ethernet cable are its light weight and
flexibility.  It can, however, extend only about one-third the
distance of regular Ethernet cable, and is normally used in
networks that are smaller than the regular Ethernet network.

The CS/200-TE is similar to the CS/200.  The difference is that
the CS/200-TE is directly attached to the thin Ethernet network
via a BNC T-type connector on its backpanel, and no external
Ethernet transceiver is needed.

.h1;Thin Ethernet Cable Preinstallation Guidelines

The following issues must be considered before installing thin
Ethernet cable:

.br;Safety
Wear protective goggles or a face mask, especially when
clipping cable or removing shield.

.br;Cable length
The maximum length of a single cable segment containing no
repeaters is 185 meters (600 feet).  Section lengths of 23.4
meters (76.8 feet), 70.2 meters (230.3 feet), and 117 meters
(383.8 feet) produce the minimum signal reflection.  The
best signals are produced when all sections of the cable are
obtained from the same manufacturer.

There should be no more than four repeaters on the maximum
transmission path between two Bridge servers.  On this path,
no more than three cable segments should be tapped (IEEE
802.3 specification).

.br;Node placement
The maximum number of nodes per 185-meter (600-foot) cable
segment is 30.  To maintain reflection at an acceptable
level, the minimum length of a cable section is 0.5 meter.

.br;Cable specifications
The thin Ethernet cable must be either an RG-58 A/U
(standard specification) or RG-58 C/U (military
specification) cable.  Do not use an RG-58 /U cable.

.h1;Thin Ethernet Cable Installation

Follow these guidelines to install the thin Ethernet cable:

1.  Keep the cable ends tightly sealed during transportation,
storage, and installation to prevent damage caused by
moisture or foreign matter.  After removing a portion of
cable from a spool, reseal the cut end of the cable
remaining on the spool.

2.  Do not twist the cable or exceed the maximum recommended
pulling force of the cable.  When removing cable from a
spool, unroll the cable; do not pull cable from the roll.

3.  Route cables to allow easy access when stations are added,
moved, or serviced.

4.  Ensure that nothing strikes or dents the cable during
installation and that the routing of the cable is such that
it will not be physically degraded during service.

5.  Install the cable as a daisy chain, with no branches.  If
the network must be sectioned, connect the sections with
barrel connectors for flexibility and ease of fault
isolation.

6.  Terminate each cable segment with a 50-ohm terminator.
There should be at least 0.05 meter of cable between the
T-connector and the terminator.

7.  Grounding the cable ensures reliable communications and
prevents safety hazards during installation and
maintenance.  Cables that are not grounded or that are
grounded at more than one point may appear to function, but
problems occur as network size and traffic increase.

Ground the thin Ethernet cable at one, and only one, point.
To ground the cable, connect the electrostatic shield to a
reliable earth ground, e.g., at one of the terminators.
The shield of the thin Ethernet cable is isolated from the
chassis.  Therefore, grounding the shield is still
necessary when the chassis has been grounded.
All elements connected to the shield (e.g., T-connectors, section
connection barrels, terminators) must be electrically isolated to
ensure that the cable is grounded at one point only.

If the cable is divided by repeaters, each segment of the cable
must be grounded individually. Grounding is not passed through
the transceivers that attach each cable segment to the repeater.

Perform the following electrical continuity tests to detect
problems caused by faulty connectors or damaged cable:

1.  Thoroughly inspect all cables for manufacturing faults or
shipping damage.

2.  Test each cable length for electrical continuity by
removing the terminator from one end of the cable and
checking for a 50-ohm resistance between the electrostatic
shield and center conductor.  The opposite end of the cable
must have a terminator installed during testing.  Check the
other end of the cable in the same manner.

3.  Use a Time Domain Reflectometer (TDR) to verify successful
installation of each section.

A Time Domain Reflectometer is a valuable tool for testing,
installing, and troubleshooting cables.  TDRs can be used to
determine the position of problems such as cable shorts, damage,
kinks, and bad connectors.  The TDR sends out a sample pulse and,
depending on the resultant return pulse, indicates abnormalities.

The cable can be tested with a TDR before it is unrolled from the
spool and after it is first installed.  A hard copy of the TDR
graphs can be kept as a reference point.

The TDR may be used to determine the distance between a test
point and the location of the problem.  Remove a terminator and
attach the TDR to the end of the cable.  With an accurate cable-
plant diagram, the affected section of cable is easy to find.

.h1;Connector and Terminator Installation

A BNC connector must be installed at each end of any length of
thin Ethernet cable. The cable must then be either electrically
terminated by attaching a terminator or extended using a barrel
extender.  Barrel extenders join sections of a thin Ethernet
cable that contains connectors.  The combined distance for
multiple sections connected with barrel extenders and T-
connectors cannot exceed 185 meters (600 feet) without a
repeater.

To install the BNC connectors, follow these steps:

1.  Cut the cable end square and strip  in. of the jacket.

2.  Install the collar on the cable, followed by the rubber
gasket and boot.  The boot should be the closest to the
square end.

3.  Fold all layers of the shield back against the boot.

4.  Strip the dielectric back to the shield (approximately
in.) to expose the center conductor.

5.  Solder a contact pin to the center conductor, ensuring that
the pin is pressed against the dielectric.

6.  Thread the connector into the collar and tighten it.

7.  To terminate the cable segment, attach a 50-ohm BNC-series
terminator to the connector.  To extend the cable, attach a
BNC-series barrel extender to the connector.  Then attach
another section of cable to the extender.

.h1;Compatibility

The CS/200-TE can communicate with all other Bridge servers that
are on the thin Ethernet network.  These servers are attached to
the thin Ethernet cable via a thin Ethernet transceiver (part
number: 66-0033-00).  Some servers, such as the CS/50-TE and the
PCS/1-TE, have a built-in thin Ethernet transceiver.

.h1;Documentation

The current manuals for the CS/200 are listed below:

 + Connection Service User's Guide (8/86)
 (Part number: 09-0063-01)

 + Connection Service User's Quick Reference Guide (12/85)
 (Part number: 09-0062-00)

 + Network Management Guide (1/87)
 (Part number: 09-0067-01)

 + Configuration Guide (1/87)
 (Part number: 09-0093-00)

 + Series/200 Installation Guide (6/87)
 (Part number: 09-0060-01)

If you have any questions, contact an authorized Bridge service
representative for assistance.
