Chapter 9 Review Structured Cabling Project

Chapter 9 Focus The focus of this chapter is standards for networking media. You read that when RJ-45 jacks are used at the telecommunications outlet in a horizontal cabling scheme, the wiring sequence is critical for optimal network performance. A LANs performance is closely linked to the quality of its connections. When you use RJ-45 jacks at the telecommunications outlet in a horizontal cabling scheme, the wiring sequence is critical to ensure the best possible network performance. Sequencing refers to the process of matching the wires of a cable to the proper terminals on the jack.

TIA/EIA A TIA/EIA-568-A specifies that, in a horizontal cabling scheme, you must use an RJ-45 jack for making the connection to a CAT 5 UTP cable, at the telecommunications outlet. One side of the RJ-45 jack contains eight color-coded slots, or pins. The individual Cat5 wires are punched down into the slots according to color. A punch tool is used to do the punch down.

Surface Mount Boxes There are two types of boxes that you can use to surface mount RJ-45 jacks to a wall. The first is a screw-mounted box. The second type of box that you can use is an adhesive-backed box. You must take several factors into consideration before you decide to flush mount an RJ-45 jack into a wall. If there are wide wood baseboards on the wall, you may want to install jacks there, because this wood is a more solid material than the wall itself. If you do choose to place the jack on a wood baseboard, avoid cutting the opening into the bottom 5 cm of the baseboard. If you attempt to place the box in that location, the wall's bottom plate will block you from pushing it in.

Safety Rules Whenever you work in walls, ceilings, or attics, the first thing you should do is turn off power to all circuits that might pass through those work areas! If you are not sure whether, or which, wires pass through the section of the building in which you are working, a good rule to follow is to shut off all power. Never, ever, touch power cables! Even if you think you have cut all power to the area where you will be working, There is no way to know if they are "live".

Cut Sheets Whenever you install cable, it is important that you document your actions. You can do this by using a cut sheet as you install the cable. A cut sheet is a rough diagram that shows the locations of the cable runs.

Labeling TIA/EIA-606 specifies that each hardware termination unit have some kind of unique identifier. This identifier must be marked on each termination hardware unit, or on its label and you must label the cables at each end.

No Staples! Never use staples to attach cable to walls. The use of staples to secure cable does not conform to TIA/EIA- 568A specification. Tie Wraps are a much better idea!

Raceway Raceway and gutter are two preferred ways of routing cable. Raceway is a wall-mounted channel that has a removable cover. There are two types.  decorative raceway - presents a more finished appearance. Decorative raceway is used to enclose cable on a wall inside a room where it might otherwise be visible.  gutter raceway - a less attractive alternative to decorative raceway. Its primary advantage is that it is big enough to hold several cables. Generally, the use of gutter is restricted to spaces such as attics and spaces created by dropped ceilings.

Routing Cable in Raceway There are generally two concerns with routing cable in existing raceway. First, is there room? The new bundle of cable you want to route in the raceway may exceed the capacity of the raceway. Second, it is preferable not to route cable in a raceway with power wiring. This can potentially cause noise problems. If you find that you must route cable through spaces where air is circulated, you will need to use a fire- rated cable.

Support wall-mounted gutter offers one option for supporting the cable. Another option is to attach tie-wraps to the wires that suspend the dropped ceiling. If you use this option, string the cable from tie to tie. A third option for supporting the cable is to use a ladder rack. Ladder racks are hung from the ceiling and provide the best type of support for networking cable.

Wiring Closet A wiring closet serves as a central junction point for the wiring (cable) and wiring equipment used to connect devices in a local area network (LAN). A wiring closest can either be a specially designed room or cabinet.

Secondary Wiring Closets It is not unusual for large networks to have more than one wiring closet. Usually, when this occurs, one wiring closet is designated as the main distribution facility (MDF). All others, referred to as intermediate distribution facilities (IDFs), are dependent on it.

Patch Panels In an Ethernet LAN star topology, the horizontal cabling runs, which come from the work areas, usually terminate at a patch panel. A patch panel is an interconnecting device through which horizontal cabling runs can be connected to other networking devices, such as hubs and repeaters. More specifically, a patch panel is a gathering of pin locations and ports. A patch panel acts as a switchboard, where horizontal cables coming from workstations, can connect to other workstations to form a LAN.

Crosstalk In any LAN system, connectors are the weakest links. If not properly installed, connectors can create electrical noise, and can cause intermittent electrical contact between wires and pins. When this occurs, transmission of data on the network can be disrupted, or will occur at a reduced throughput; therefore, it pays to do it right. To ensure that cable is installed correctly. You must not untwist the wire pairs any more than necessary. Untwisted wires reduce data throughput, and can lead to crosstalk.

Crosstalk Continued Several factors can contribute to near-end crosstalk. The most common cause is crossed pairs. As mentioned earlier, you can detect these with the wire map feature of a cable tester. If you measure near- end crosstalk, you should do a visual check of the horizontal cabling. If you find nothing, then split pairs have most likely caused the problem.

Distribution Racks You can mount patch panels on walls, you can stand them in racks, or you can place them in cabinets. One of the most commonly used pieces of equipment is the distribution rack. The advantage of a distribution rack is that it allows easy access to both the front and the back of the equipment.

Baseline Measurement The baseline is the set of data about your network that you check periodically to ensure the network is still functioning properly. Repeated testing of your network, and comparisons against its baseline, will help you spot specific network problems that may be caused by aging, poor maintenance practices, weather, or other factors.

TDR Distance measurements using TDR -- time domain reflectometry -- are described in Chapter 9. Using the formula: distance = rate x time, the meter sends out a pulse and waits for the return "echo" reflection. You might think of this as cable radar. A TDR measures distance on a cable by sending an electrical signal through the cable. The signal is reflected when it encounters the most distant open connection.

Interference Many outside factors can contribute to interference on the networking media. Some examples of sources are:  fluorescent lights  heaters  radios  air cleaners  televisions  computers  motion sensors  radar  motors  switches  welders  auto ignitions  electronic devices of all kinds

Summary In Chapter 9, you learned about installing, and running cable and the basics of wiring closets and patch panels along with testing cable. In the next chapter, you will start to see how routing and addressing operate at the network layer.