Network Cabling

This section may be skipped by those more interested on the software aspects of networking or those learning networking, but all readers should at some time be aware of the terminology used in this section since they are used with regard to cabling. If this section is skipped by those learning networking, it should be read later. This section should be read by those who plan to physically install their own network.

Types of Transmission

1. Baseband – Data bits are defined by discrete signal changes.

2. Broadband – Uses analog signals to divide the cable into several channels with each channel at its own frequency. Each channel can only transmit one direction.

Physical media

1. Twisted pair – Wire is twisted to minimize crosstalk interference. It may be shielded or unshielded.

• UTP-Unshielded Twisted Pair. Normally UTP contains 8 wires or 4 pair. 100 meter maximum length. 4-100 Mbps speed.
• STP-Shielded twisted pair. 100 meter maximum length. 16-155 Mbps speed. Lower electrical interference than UTP.

2. Coaxial – Two conductors separated by insulation such as TV 75 ohm cable. Maximum length of 185 to 500 meters.

1. Thinnet – Thinnet uses a British Naval Connector (BNC) on each end. Thinnet is part of the RG-58 family of cable*. Maximum cable length is 185 meters. Transmission speed is 10Mbps. Thinnet cable should have 50 ohms impedance and its terminator has 50 ohms impedance. A T or barrel connector has no impedance.

2. Thicknet – Half inch rigid cable. Maximum cable length is 500 meters. Transmission speed is 10Mbps. Expensive and is not commonly used. (RG-11 or RG-8). A vampire tap or piercing tap is used with a transceiver attached to connect computers to the cable. 100 connections may be made. The computer has an attachment unit interface (AUI) on its network card which is a 15 pin DB-15 connector. The computer is connected to the transceiver at the cable from its AUI on its network card using a drop cable.

Coax cable types:

• RG-58 /U – 50 ohm, with a solid copper wire core.
• RG-58 A/U* – 50 ohm, with a stranded wire core.
• RG-58 C/U* – Military version of RG-58 A/U.
• RG-59 – 75 ohm, for broadband transmission such as cable TV.
• RG-62 – 93 ohm, primarily used for ArcNet.
• RG-6 – Used for satellite cable (if you want to run a cable to a satellite!).

*Only these are part of the IEEE specification for ethernet networks.

3. Fiber-optic – Data is transmitted using light rather than electrons. Usually there are two fibers, one for each direction. Cable length of 2 Kilometers. Speed from 100Mbps to 2Gbps. This is the most expensive and most difficult to install, but is not subject to interference. Two types of cables are:

1. Single mode cables for use with lasers.

2. Multimode cables for use with Light Emitting Diode (LED) drivers.

Cable Standards

The Electronic Industries Association and Telecommunications Industries Association (EIA/TIA) defined a standard called EIA/TIA 568 which is a commercial building wiring standard for UTP cable. It defines transmission speed and twists per foot.

Category         Speed Notes

1                      None               Used for old telephone systems

2                      4Mps

3                      10Mps             The minimum category for data networks

4                      16Mps

5                      100Mps           Cat 5 network cable, used by most networks today

6                                              Data patch, Two pair with foil and braided shield

7                                              Undefined

8                                              Flat cable for under carpets with two twisted pair

9                                              Plenum cable with two twisted pair. It is safe if you’re having a fire.

The maximum transmission length is 100 meters. This cable is susceptible to interference.

STP

Shielded twisted pair has a maximum cable length of 100 meters (328 feet). Data rate from 16 to 155 Mbps. Cables require special connectors for grounding but this cabling method resists electrical interference and is less susceptible to eavesdropping. Costs more than UTP or Thinnet, but not as much as Thicknet or Fiber-optic.

Terms

• Attenuation – Signal loss due to impedance.
• Bandwidth – Indicates the amount of data that can be sent in a time period. Measured in Mbps which is one million bits per second.
• Impedance – The amount of resistance to the transmission device.
• Interference – Electromagnetic Interference (EMI). Crosstalk – When wires pick up electromagnetic signals from nearby wires also carrying signals.
• Plenum – Space above a false ceiling in an office area where heat ducts and cables may be run. Plenum cabling is special fire resistant cabling required for use in these areas due to fire hazards.
• Shielding – Used to minimize interference.