Browse Prior Art Database

Cable Performance Evaluator

IP.com Disclosure Number: IPCOM000111382D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 114K

Publishing Venue

IBM

Related People

Haas, LC: AUTHOR [+2]

Abstract

Described is an apparatus for indirect cable evaluation and determination of performance margin for a telecommunication link by controlled degradation of the telecommunication signals.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Cable Performance Evaluator

      Described is an apparatus for indirect cable evaluation and
determination of performance margin for a telecommunication link by
controlled degradation of the telecommunication signals.

      The telecommunications equipment shown in the diagram could be
two portable computers, each equipped with telecommunication features
(e.g., FDDI adapter cards).  Appropriate software is installed and
running in the computers so that signals are transmitted and errors
are detected by the receiving equipment.  This is typical for many
popular telecommunication products.

      The test apparatus introduces a calibrated, variable amount of
degradation to the signal being received.  The degradation could be
of different forms.  One form of degradation useful for FDDI systems
is the addition of a variable-level interfering signal such as could
be produced by the combination of a sine-wave oscillator, a variable
RF attenuator, and a circuit for connecting to the receiver end of
the wire pair without otherwise disturbing the original transmitted
signal.

      To perform the evaluation, the amount of degradation is
gradually increased until the performance of the link is affected
sufficiently to cause the telecommunications equipment to report
errors or inoperation of the link.  The measure of the cable margin
available is determined from the amount of degradation that was
necessary to cause the error conditions.  One method of determining
the margin is by comparing the amount of degradation to cause the
error conditions to a table constructed from readings made on test
cables.

      IBM's Shielded Twisted Pair (STP) cable used in the original
IBM Cabling System (ICS) was designed for 16 megabits per second
(Mbps) token ring data rates.  When IBM announced a copper FDDI
adapter in 1991 to transmit 100 Mbps signals over STP cable, also
released was a new cable specification which would guarantee
error-free transmission at distances up to 100 meters.  There was
concern about the large installed base of STP and how to answer
customers' concerns about whether their old ICS installations would
work with the new high-speed LAN adapters.  We wanted a portable
tester that we could take to customers' premises and determine not
only whether their cable would work, but also how close the cable was
to marginal performance (a simple go/nogo test was not sufficient).
The tester also had to be simple for unskilled operators to use --
this eliminates Network Analyzers, TDRs, etc.

      The cable to be tested consists of two pairs of twisted wires,
with one pair transmitting signals in one direction, and the other
pair transmitting in the other direction.  The tester includes two
portable computers, each containing an FDDI adapter card, attached to
opposite ends of the cable to be tested. ...