1 Guide to Network Cabling Fundamentals Chapter 8.

transcript

Guide to Network Cabling Fundamentals

Chapter 8

Chapter 8 - Testing and Troubleshooting

Understand the necessity for testing your cable system

Define and perform tests on copper and fiber Understand troubleshooting methods and general

techniques Identify and use testing and troubleshooting tools Design a disaster avoidance plan Manage your documentation

After the cabling is in place, a final critical step remains in the installation: testing the system

Three types of cable testing exist: Operational testing ensures that a system is working

properly and includes these procedures: checking all cables for continuity; performing polarity tests of cable pairs; running a connectivity test; testing for cable shorts and opens

Performance testing is designed to ensure that a system complies with all applicable codes and standards

Testing Your Cabling System

Three types of cable testing (cont.): Acceptance testing is designed to demonstrate

functionality, prove conformity to specifications, and ensure performance based on customer’s measurement criteria, called parameters

Acceptance testing serves to satisfy the contract with the customer and these requirements: the types of cable to use for each portion of the installation; the acceptable means for running the cable; various types of termination equipment; the performance expected from each type of cable; complete documentation of the installation and test results

Testing Your Cabling System

Test copper UTP cable in accordance with the TIA TSB-67 standard, which specifies methods, parameters, and minimum requirements for testing installed Category 3, 4, and 5 cabling

There are several benefits of testing and certifying according to TSB-67: Verifying that no faults occurred during the installation,

and ensure that the system will perform according to the user’s requirements

Protecting the installer from blame if a problem occurs

Testing Copper and Fiber Media

TSB-67 defines two types of tests for UTP: The basic link is the permanent part of a cable run that

includes 90 meters of horizontal cable, the telecommunications outlet, and the first punch-down in the telecommunications room

The channel encompasses the basic link plus all patch cords and equipment cords

These tests should both be performed; they are important in verifying proper workmanship, and they provide a future reference for the system’s proper state of operation or performance (or baseline)

TSB-67 tests for copper UTP cable: The wire map test identifies wiring errors (opens and

shorts, crossed-pair, reversed-pair, split-pair), and checks connectivity

The length test verifies that cable length is within the specifications for maximum allowable length

The attenuation test measure a cable’s signal loss from end to end; all cable pairs must be tested

The near-end crosstalk (NEXT) test measures the signal coupling from one pair of wires to another pair within the same cable

Proposed new tests for copper UTP cable are known as TSB-95: Propagation delay measures the time, in nano-seconds

(nS), it takes a signal to travel a cable Attenuation-to-crosstalk ratio (ACR) is the difference

between the NEXT and attenuation measurements The power sum measurement compares the crosstalk

effects on all pairs in a cable Return loss is a measurement of the signal that echoes or

reflects back into the transmitter

General testing rules for copper UTP cable: Do not move any cable or equipment during testing Record pass/fail indications and always record the actual

measured values and the date If any part of the system is reconfigured, retest it Always perform the NEXT test and record the

measurements from both ends of the cable When performing channel tests, always test with the end-

user cords and patch cords in place If a cable barely passes a test, record this marginal result

in the report of actual test measurements

Test fiber-optic cable to demonstrate that any exhibited loss does not exceed the acceptable limits defined by ANSI/EIA/TIA-568-B.3

Testing ensures that the cabling system: Meets the customer’s attenuation specifications Provides documentation of baseline readings, which are

an essential gauge for future troubleshooting

When testing, test the power levels on the transmitter and receiver to ensure proper operation

Attenuation testing of fiber is crucial after installation because interruptions in the cable (splices and connections) provide more opportunities for signal loss During attenuation testing, measure cables in both

directions and at both available wavelengths A wavelength is the measure of the color of light,

expressed in nanometers (nm) Spare fibers or unterminated fibers do not require

attenuation testing, but the do need to be tested for continuity

Attenuation testing must be done on every link segment of cable Link segments consist of cable, connectors, other

connections, and splices between two fiber-optic termination units in the system

The three basic link segment types are horizontal, backbone, and composite

To compute the acceptable attenuation value for any link segment, use this equation:acceptable link attenuation = cable attenuation + connector attenuation + splice attenuation

Optical connectors, adapters, and cable assemblies must comply with the requirements of ANSI/EIA/TIA-604-3-1997, FOCIS 3; also test the system in accordance with TIA FOTP Follow these procedures before testing begins: read the

equipment manufacturer’s testing instructions; ensure that all connectors, jumpers and adapters are properly cleaned; ensure that the light source or optical domain reflectometer (OTDR) operates within the range of 850±30 nm for multimode cable and1300 ±20 nm for single-mode cable

The steps for testing end-to-end attenuation:1. Take a reference reading by connecting a test jumper from

the power meter to the optical source

2. Take a check reading by connecting a second jumper to the first with an interconnection sleeve

3. Subtract the reference from the check reading

4. If attenuation is acceptable, proceed, otherwise, clean connectors and return to step 2

5. Take an official attenuation test reading by performing an end-to-end attenuation test

6. Determine end-to-end attenuation by subtracting the reference from the official attenuation test reading

Successful troubleshooters must be logical, methodical, and good at problem solving

Perform the following troubleshooting steps: Identify the symptoms Verify user competency Identify the scope of the problem Recreate the problem Verify the physical integrity of all connections Determine if due to recent system changes Determine, implement, and test the solution

Troubleshooting Methods and General Techniques

In many cases, it is more efficient to use a tool that can analyze and isolate system problems Tools for testing copper cable include: multimeters test

shorts, opens, continuity verifications, attenuation measurements, and electrical outlets; continuity testers test for proper wiring mapping, opens, shorts, bad terminations and reversed-pairs; certified field testers test all parameters required by TSB-67 and TSB-95; time domain reflectometer (TDR) tests for line impedance, attenuation, opens, shorts, NEXT, cable distances, and connector or terminator problems

Tools for Testing and Troubleshooting

Tools (cont.): Tools for testing fiber-optic cable include: power meters

and optical light sources, which measure a cable’s signal strength and attenuation, and the light source can also determine leakage at connectors and bends; optical time domain reflectometers (OTDRs) measure a cable’s length and signal strength; jumpers connect the power meter and the light source; interconnection adapters are circuit administration points that provide access to a circuit and mates connectors

Tools for Testing and Troubleshooting

A disaster is an event that prevents a business from performing its critical functions Disaster avoidance, or disaster prevention, is a series of

measures designed to prevent, detect, or contain potentially calamitous incidents

The first priority is to prevent disasters, but since this is impossible, the next priority is to develop procedures that minimize a disaster’s impact

Proper planning can greatly reduce the trauma of rebuilding and repairing systems after a disaster, and it can help ensure the rebuilding is successful

Disaster Avoidance

Disaster planning: To ensure disaster avoidance plan soundness, increase

the amount of installed cables in the system, select the proper equipment, and think through as many “what if” scenarios as possible

One of the best and easiest disaster avoidance methods is redundancy, which is built into a system by adding duplicate parts at any or all points

Another method involves adding diversity to the system, using both fiber and copper to ensure that service continues through the copper if fiber is disabled

Disaster Avoidance

Disaster planning (cont.): Redundancy and diversity can be planned in backbone

cables by running more than one and installing them along different paths

Other aspects of network planning and installation are also critical to disaster avoidance, including: grounding, firestopping, and physical connectivity

Create redundancy for important network data and applications by mirroring part of the network to another building, city, or state

Disaster Avoidance

Managing test results Test results are a critical part of the documentation Use the following guidelines to manage test results from

cable testers: document the standards used for testing; ensure the latest software version for the cable tester and record that too; select a labeling scheme (cable ID) that matches the label on the patch panel or outlet; select the format and media to use for test results

Most newer cable testers come with the ability to download test results - do this every day

Managing Your Documentation

Data Management Equipment An important part of effective management is selecting

the right tools for the job Consider the following equipment: label printers range

from simple models that require manual keypad input to models that connect to test tools and print labels after each test is performed; software solutions such as spreadsheets and databases help manage test results, and mapping software to provide a logical view of the network

Managing Your Documentation

Chapter Summary

Test your cable installation before activating the service to guarantee that the system is working properly. Testing also ensures that all installed components meet the customer’s performance specifications, as well as codes and standards

Operational testing includes continuity testing, verification of polarity, and connectivity testing to ensure that there are no shorts or opens. Performance testing ensures that the system complies with all applicable codes and standards. Acceptance testing is designed to prove conformity to specifications and ensure performance based on the customer’s measurement criteria

Chapter Summary

Always test UTP cable systems in accordance with the TIA TSB-67 standard, which specifies methods and parameters for testing installed Category 3, 4, and 5 cabling with a hand-help instrument. This standard also defines basic link and channel test configurations for UTP cable. TSB-67 tests that are currently required for Category 5 certification include wire map tests, length tests, attenuation tests, NEXT (near-end crosstalk) tests, and propagation delay tests

Chapter Summary

You must test fiber-optic cable for attenuation to comply with current standards. You should also test for attenuation on all link segments, connectors, adapters, and cable assemblies

Even if you only perform new installations, you still need to know how to troubleshoot your system. A successful troubleshooter is logical, methodical, and good at problem solving. Troubleshooting steps include identifying symptoms, identifying the scope of a problem, and recreating the problem

Chapter Summary

Many of the tools you use for everyday installation and maintenance are the same ones you use to test cables or troubleshoot problems

Disaster avoidance is designed to ensure the continuous availability of critical business services in case of disaster. Although you cannot prevent all disasters, you can minimize their effects by planning redundancy and diversity into telecommunications systems

Chapter Summary

The documentation manual provides important information about your network. This information can assist you in troubleshooting network problems, and it provides an accurate hardware and software inventory

1 Guide to Network Cabling Fundamentals Chapter 8.

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