T3 Group 12 Evening News Presentation

CABLE TESTING EQUIPMENT AND PROCEDURES

Good evening, everyone. Welcome to the T3 Group 12 Evening News highlighting Cable Testing Equipment and Procedures. Tonight's headlines include a Mystery Breakdown in Alohalani Elementary School's local area network and at the OJ Simpson trial, Judge Lance Ito's networked computer breaks down during the trail with the database of all the blood samples.

Along with the news, we will be discussing the importance of being knowledgeable in troubleshooting breakdowns in any networking situation. We will be demonstrating the use of the continuity tester and the TDR (Time Domain Reflectometer) cable analyzer also known as the cable tester.

Our Group 12 News Team includes:
Lester Tanji, Central District Fine Arts Resource Teacher
Sandra Lee, Technology Coordinator at Waimalu Elementary School
Edita Kusumoto, Newswriting Teacher at Wheeler Intermediate School
Elaine Akashi, Technology IRA at Pearl Harbor Kai Elementary School

And now to the news...

One report from Naumaka Elementary School tells about a library work station that shut down just as a student began working on it. What happened? Did the student touch something to corrupt the system? After scolding the student, the tech coordinator went about finding the real cause of the problem.
After finding out that the internal hardware (ethernet card & hard drive) and system software were okay, the focus turned to the link between the work station and the server (the cable). When the cable analyzer was brought in that afternoon, it was found that the cable had an open connection.

The next story involves Mahalo Intermediate School's LAN installation in the administration building which includes the office, health room, teacher's workroom, library and computer lab. Because of limited funding, parents and teachers, along with the cable company employees, volunteered to help with the pulling and terminating of the cables. After being instructed on the procedures for pulling the cables, the volunteers were assigned specific tasks and completed the job in 2 days. The cable analyzer showed that 3 of the 30 installed cables in the library did not test for Category 5. The volunteers that worked on that specific punchdown block were asked to redo the punchdown and then to the delight of the team, everything checked out okay.

But testing at Category 5 does not guarantee that it will always remain Cat 5. Many things can happen as you will hear in our headline story next.

The time finally came when the LAN was installed at Alohalani Elementary School and all cables tested and passed for Category 5. After 6 months of planning and anticipation, everyone was looking forward to sharing all the resources in the computer lab. During Period 1 the computers were turned on and all but one successfully logged on to the server. Fortunately, there were enough computers for the students to use. During Period 2 another computer logged off the network. Throughout the day four additional computers also logged off. The stumped technology coordinator wondered...how could the computers not work now when they all tested okay previously? The server and workstation software checked out okay. So the next step was to retest the cabling and connectors with a cable analyzer or TDR. Two cables were found to have open wires and one of them was the cable to the server. That is why it was acting so strange...logging off at different times. Apparently, after the floor was waxed, someone unknowingly jostled the cables.


Cabling is important because it provides the link between computers in internetworking. Installed cables do not guarantee that a necessary connection is going to be made, so cable testing training and equipment is a necessary part of LAN installation and maintenance.
Cable testing procedures and equipment are part of the Physical Layer of the ISO/OSI model. The Physical layer describes the physical, electrical and procedural specifications required to transmit data across the physical medium or cables.

Some of the testing equipment that was used in these school situations include a continuity tester and a cable analyzer.

Before you begin testing, your bag of tricks should include:

This is a diagram of a continuity tester. On the left is a signal generator that sends a signal through the wires to the loop back plug at the other end of the wire. When the signal returns from the loop back plug, it completes the circuit and lights the light emitting diode (LED).

This is a testing device created to demonstrate one method for testing two-pair twisted cable. It consists of a power source, LEDs which are paired corresponding to the twisted pair and RJ11 jacks (on a network it would be RJ45 jacks). This meter will test for cable continuity, crossed wiring within a pair, crossed wiring between pairs and open circuits.
By placing both ends of a two pair twisted cable with these RJ11 plugs into the RJ11 test jack, the following conditions will be indicated by the LEDs:

  • First, 4 LEDs on means that the cable is okay.
  • One pair LEDs on and one pair off means that one or both of the off pair is open or the pair is cross wired.
  • When none of the side-by-side LEDs are on that means that it is cross-wired between other pairs.
  • When all of the LEDs are off there is open or cross wired within the pair.

    The continuity tester tests for open wire which could be due to poor crimp, bad wall plate or bad patch panel connection. It also tests for a short circuit which can be caused by poor attachment to wall plates or damaged insulation inside the wall jacket.

    Since the continuity tester is limited in the detection of cabling errors, the tool that is more commonly used for Category 5 would be the cable analyzer. In addition to testing for open cable and short circuit, the cable analyzer will test for reverse pair, impedance, near-end crosstalk (NEXT), cable length, wire map, attenuation and ambient noise.
    (PowerPoint slides showing Initial testing with the cable analyzer)


    After pulling the main cables and hardwiring between the punchdown block and the modular outlet, the cables are tested in this manner. The red line on the screen indicates the length of the tested wire. If cables test at Category 5, the connections are made by patch cable to the hub and the workstation. In the event of failure, both the patch cable and the hardwire need to be retested. The patch cable is disconnected from the punchdown block and tested on the analyzer. This is also done to the patch cable that is connected to the workstation. Even if there are commercially made patch cables they need to be tested to assure integrity.

    As we discovered in one of our featured reports, a cable tested at Category 5 may not remain at Cat 5 forever. As problems occur, cables need to be retested.

    Visualize cable as a smooth highway. Imagine a crimp or slice in the cable as 2 highways coming together. The merge of the 2 highways must be smooth so there are no traffic hazards. Similarly in a crimped or spliced cable the crimp or splice must be smooth.
    Some of the problems you can encounter are:
    Open or broken line - a break in the wire or failure to terminate connection. This prevents the signal from reaching its destination.
    Shorted lines - are exposed wires anywhere along the cabling or at a termination which are touching (this can happen when wires are pulled or bent; by constant rubbing such as footsteps; or when terminated, too much bare wire is exposed).
    Reversed pairs - are wires that are not terminated in the same order (if a wire is at pin 4, its termination must be at pin 4 on the other end instead of pin 6 as in the diagram).
    Near end crosstalk (NEXT) - Signals on the wire should be transmitted on one pair and received on one pair, but when the signal is strong at the transmit side it may jump over prematurely to the receiving pair, causing noise.
    Attenuation - When a signal is transmitted, there is a loss of received signal strength due to the characteristic of the material and distance that it must travel. It is usually expressed in db/km (decibels per kilometer).
    Ambient noise - is the coupling of signals not related to the station's own transmitter onto the receive pair. This noise could be caused by a variety of sources and is often high frequency and intermittent.


    Tonight our topic focuses on testing UTP(unshieled twisted pair) copper wire. You need to be aware that there is equipment to test fiber, however, we exhausted all of our resources, but could not bring equipment to test fiber optic (the testing equipment costs about $30,000). The fiber testing equipment (OTDR) Optical Time Domain Reflectometer works similarly to the TDR. Instead of sending an electrical pulse, a light pulse is sent via a laser diode transmitter. The light pulse is scattered by the fiber cable continuously along its length; its reflection along the link will be picked up by the ODTR. The reflected pulses tells the ODTR the condition of the fiber at certain points on the cabale. ODTR detects primarily for splits, bad splices, bad connections and broken connections. We have two cable analyzers to demonstrate. Sandra Lee will be demonstrating the LanTECH 100 and Lester Tanji will be demonstrating the WireScope 100.

    The LanTech100 is a LAN analyzer and its function is to detect shorts, opens, cross polarity, crosstalk and is able to determine the length of the cable being tested. Within all of these, the LanTech100 can resolve 99% of all the wiring problems. The LanTech100 also tests 10base2 thinnet coaxial (RG58) cables.

    The WireScope 100 has a software upgradable database of standards. So, as the EIA/TIA & ISO/IEC standards change, the specifications in the WireScope 100 can be updated to assure adherance to current standards. The passive loopback plug offers one very helpful feature. Rotary switches on one side of the unit can be configured with a unique 3-digit ID. This feature is helpful in trying to identify unlabeled cables. When the WireScope 100 sends impulses to the far end of a cable, the loopback plug returns the impulse with the ID that it is set to.

    This checklist can assist you when troubleshooting cable system failures:

  • Consult your network wiring layout or use cable tracing tools and then record the cable location.
  • Define the most likely location of the cable failure and isolate the problem to one segment of cable.
  • Consider the less than obvious problems, such as open or shorted BNC connectors, miswired modular plugs or open terminators.
  • Look for cable damage, such as cuts, frays or breaks in the insulation. No piece of cable test equipment can make up for a well-planned design and a careful installation. Take a little extra time on the front end of a LAN installation project and you will save countless hours later.

    With this information about Cable Testing Equipment and Procedures, we know that you're now ready to get your LAN connected and running smoothly.

    A late breaking story. Tomorrow at Kalani High School, the T3 Group 12 news team will be reporting about T3ers assisting in pulling and terminating cables. Will they be making the right connections? Well, we shall see. The T3ers are to bring a ruler, a scissors, a sharpie pen, a wire cutter and Phillips & standard screw drivers. Also, dress is formal...girls wear your gowns and men your tux. Nah, dress comfortably and bring your cable analyzer.

    Now about our headline news...At the OJ Simpson trial, our reporters were not allowed to enter Judge Lance Ito's courtroom so we were not able to find out what happened to the downed computer. Sorry!

    Well, that is our report for this evening. If you have any questions about any news item discussed this evening, you may post your question on Telnet to peterson@hawaii.edu..

    Good night and thank you for joining us from your T3 Project 12 News team. Good night all!!!