Contents of this document:

Benefits of Testing
The Difference Between a Channel and a Link
General Notes on Testing
Required Tests for Category 5 Cabling
General Test Rules
Tools

This section is intended to familiarize the reader on fíeld testing requirements for Category 5 cabling systems, which have been defined by the TIA in their Technical Service Bulletin TSB-67, "Link Performance Transmission Specification For Field Testing of Unshielded Twisted Pair Cabling Systems". The document defines pass/fail criteria to ensure that the installed cabling is capable of supporting high speed LAN equipment.

The following section is based on TSB-67 and provides basic testing guidance. For more information, please read TSB-67 and consult test-unit instructions for the Category 5 field tester you use.

OVERVIEW
HOW TESTING BENEFITS BOTH END-USERS AND INSTALLERS

Category 5 cabling system certification verifies that no faults occurred during installation, and ensures that the system will perform to the end-user's requirements. This gives everyone peace of mind, and for the installer can help prevent later callbacks, or blame for problems which can be proven not due to installer workmanship.

However, remember that while TSB-67 allows you to test all or part of a cable run to verify that it meets the TIA-568A Category 5 limits, the connection of equipment will change how the network behaves; TSB-67 cannot guarantee how high-speed network equipment will work on or affect a tested cable run.

THE DIFFERENCE BETWEEN A CHANNEL AND A LINK

It is important to differentiate between the terms channel and link, because they describe two Category 5 certification tests. These tests cover the two instances in which cable would be tested, and they differ in how much of a horizontal cabling run they include for testing. The basic difference is that a channel includes patching or equipment cords, while a link does not.

"Basic Link" Test Configuration	"Channel" Test Configuration
1. Covers just the permanent portion of the cable run. 2. Intended primarily for cable installers who must test cable before patch cords and network equipment are installed.	1. Measures end-to-end cable run performance. 2. More comprehensive test coverage.

Separating the tests this way allows the contractor to verify that link and channel installations are performed correctly. This is very important information, as workmanship has a direct impact on system performance. Initial test results also provide performance guidelines that are a valuable baseline reference for future testing.

The first test covers the link (also called Basic Link, Contractor Link or Contractor Model). The link is the permanent part of the cable run. A link is defined as up to 90 meters of horizontal cable; a telecommunications outlet; an optional transition connection close to the work area; and two connections at the cross-connect in the telecommunications closet. The total maximum length of equipment cords, patch cords and jumpers for the cable run is 10 meters.

A second round of testing can be done after the end-user has connected their patch cords and equipment cords. At this time the horizontal run is called the channel, or User Modem. The channel test provides more comprehensive, end-to-end test coverage (although the Link test is actually more stringent because it must allow for the later installation of patch cords).

GENERAL NOTES ON TESTING

The Effects of Workmanship And Patch/ Equipment Cordage Upon Cabling Performance:   Another reason why channel and link tests evolved has to do with quality of workmanship and materials. Channel performance is greatly affected by cable characteristics, connecting hardware, patch cords and cross-connect wiring, total number of connections, and the care with which they are installed and maintained. You can go a long way toward preserving performance by simply choosing good quality components, and installing them with care and proper techniques.

Effects of Workmanship Upon Cabling System Performance

Condition	Next Performance Reduction
Full Channel, Properly Installed	Benchmark
Cable flexed 1000 times	No Change
Replace 2 ft Cat 5 patch cord with 2 ft Cat 3	8.0 db
Replace 2 ft Cat 5 patch cord with 20 ft Cat 3	13.0 db
Coiled Cable in a 6' circle, 2" dia. cross sect.	No change
Bundled and secured cable with ties (20 lbs)	No Change
Removed 1" of cable sheath at station end	1.2 db
Removed 12" of cable sheath at station end	2.0 db
Untwisted Pairs 1/2" at station end	1.5 db
Untwisted Pairs 2" at station end	3.8 db
Untwisted Pairs 6" at station end	11.6 db
Bend Cable around a 3" diameter	1.9 db
Bend Cable around a 1" diameter	2.1 db
Kinked Cable	2.4 db
Cable run in aluminum conduit	No Change

Link and Channel Pass/Fail Limits:  Pass/Fail limits for attenuation and crosstalk (NEXT) differ for links and channels. Channel limits are the same as in the original TIA-568A, but since there are fewer connectors in a link, link P/F limits have been defined and introduced in TSB-67.

Specifications To Follow When Testing:  Use TSB-67 as your reference for Category 5 Test Specification Data. Prior to TSB-67, many installers used the laboratory test specifications in Annex E of TIA-568 to determine if a system performed to Category 5. Because these were not field test specs, Annex E is NOT to be used to test or verify installed systems.

Importance of Marking Cat 5 Cable Prior to Installation:  It is very important to mark Category 5 cable ends prior to pulling them to outlets, as conventional locating equipment (toner and probe) does not work for identifying the run along the length of the cable. This is because Category 5 cable works so well at canceling out external signals, that the tone cannot be detected through the cable jacket. A Cat 5 cable tester will perform the task, but ideally this step will be saved by properly marking the cable before installation.

Test Cable Immediately After Cable Pull-In:Installation of cabling systems typically occurs in four basic stages:

1) Identifying/marking the cable ends.

2) Pulling the cables.

3) Punching down the cables on the crossconnects and the outlets.

4) Installing and crossconnecting the equipment.

The cabling system should be verified immediately after or during the third stage. This simplifies subsequent troubleshooting if problems arise after the equipment is installed, by ruling out the cabling system as a probable cause.

Use testing and troubleshooting equipment specifically designed for Category 5 network installation and repair -- and read the instructions which come with the unit. Experience has shown that when substitute test equipment is used, the procedures will take longer, be less reliable in finding the fault, and often will find only part of the problem.

REQUIRED TESTS FOR CATEGORY 5 CABLE

The primary field test parameters are Wire Map, Length, Attenuation, NEXT, and Propagation delay.

Test 1. The Wire Map test is intended to identify installation wiring errors. (Correct connectivity is defined in TIA-568A section 10.4.5.) Any incorrect pairing must be re-terminated in the correct fashion.

Test 2. The Length test verifies that lengths fall within TIA-568A specified maximums. Physical length is defined as the sum of the physical length of the cables between the two end points in the link. Physical length may be derived from either physically measuring the length of the cables, as determined from the length markings on the cable or estimated from the electrical length measurement. The length of the longest pair shall be reported.

The maximum length of the basic link shall be 94 meters (including test equipment cords). The maximum length of the channel shall be 100 meters, including equipment cords/patch cords.

Test 3. The Attenuation test is a measure of signal loss from one end of the link to the other. You must test all wire pairs within a cable, and compare the worst performance reading to the allowable attenuation. The worst-case pair must not perform worse than the TSB-67 specified attenuation value.

Test 4. NEXT  (Near-End Crosstalk) is a measure of signal coupling from one pair to another within a UTP cable link. A balanced input signal is applied to a disturbing pair at the near end of the connector, while the induced signal on the disturbed pair is measured at the near-end. The resulting NEXT loss must be better than the worst case values given in TSB-67. All pair combinations must be measured, from both ends.

Field tests of NEXT shall be done at both ends of the cable to ensure that far-end connections are checked for compliance.

Test 5. Propagation Delay.  This test measures the time it takes for a signal to travel from one point to another. The worst case (longest delay) shall be reported.

Note that having a non-TIA-568A system pass these tests does not make it TIA-568A compliant.

GENERAL TEST RULES

No cabling or components shall be moved during the tests.

In addition to pass/fail indications, the actual measured values (at whatever frequency taken) should be recorded in the administration system for use in future configuration or analyses of the premises network.

NEXT must be measured from both ends of a cable run.

Reconfiguration may require re-testing.

Qualified adapter cords shall be used to attach the test instruments to the link under inspection.

In a channel (see definition), end-user patch cords shall be tested in place. End-user patch cords may be verified by inserting the user cords in the link under test at the cross-connect.

Allowance is made for 10 meters of equipment and patch cordage, and jumpers for the channel. (5 meters on each end is assumed.)

UTP test leads and associated connecting hardware to connect between the test equipment and the link under test, shall be 0.5 mm (24 AWG) and shall be taken from cable that meets or exceeds the requirements for Category 5 cable specified in TIA-568A.

Coaxial cable assemblies between network analyzer and baluns should be as short as possible, preferably not exceeding 0.6 m (24 in) each.

100 ohm four-pair Category 3 or 5 UTP cable may be tested while still on the reel, if the length is under 100 meters.

The field tester must meet the TSB-67 accuracy requirements for Level 1 or 2 (see below).

If a run barely passes (the result is within the tester's accuracy limit), the data must carry a warning (such as an asterisk) to indicate that the result was marginal.

TOOLS

About Category 5 Test Sets:   For Category 3 and 4 UTP, 20 MHz 150 ohm STP and optical fiber, portable test sets are available to verify link performance. But for Category 5 UTP and Extended l50 ohm STP, test sets to verify performance to the upper limit of the cabling system characterization are defined by TS13-67.

Tester Accuracy Levels I and II:  Testers have been categorized by TSB-67 into two levels of accuracy. Level I testers are those available before TSB-67 as published, and are not as accurate as post-standard field testers are. Level II testers are closer to laboratory grade and thus more accurate, so they pass fewer 'bad' runs and fail fewer 'good' runs.

Parameters That Category 5 Testers Must Be Able To Test For:  The TSB-67 testing specification requires the following tests: length for all pairs of an installed link; attenuation; NEXT; and the delay on all pairs of an installed link.

Tester Must-Have Features:  A Category 5 Tester must be capable of measuring all required data (see above), and have a 310 meter range to allow for approximate measurements of available cable on spools. The unit should also come with manufacturer's information on how to interpret data with the device.

Tester Nice-to-Have Features:  Some features which are nice to have in a test instrument are: LED or LCD readout; data storage; auto test; and ease of use. Also, the faster the better. For example, on a 1000 workstation job, having a 90-second tester takes half the time of a 3-minute tester -- or 25 hours instead of 50 hours of labor.