Cabling LAN - Part I

In a network, a machine has to be connected to at least other machine, through metal cabling, fiber-optic cabling or radio waves. Even new technologies such as radio based networks and infrared light based networks produce new ways of connecting two devices to each other, but least expensive and most popular medium for networking is still copper wires.

Cables use copper wires to transmit electrical signals or fiber optic to transfer optical light signals. Cabling is also called as wiring because copper wire is used in greater part in the network cables. Electrical signal, which is transmitted through cable, generate magnetic field and radio frequency interfaces. When cables are used, the electrical signal emits radiation, which may interfere with other signals. When this happens it is called as cross talk. In order to overcome this, metallic wires are manufactured in such a way that it reduces the effects of radiation and interference. The wires, which are close to one another, can interfere with the transmission, changing the electrical signal and can cause bit error. Because of interference, cables produce emission and are susceptible to nearby cables. The popular way to reduce these effects of emission is to send the information, through a pair of wires and to twist the pair of wires together, Using an opposite current on each wire generates magnetic field but in opposite

direction. So by twisting the wires, the two magnetic fields cancel each other. Another popular way to reduce emissions of copper cables is to shield the wires by some material which blocks electromagnetic radiation. Shielding the wires makes the cables less flexible and increases material and manufacturing costs. In this lesson, you will learn some of the cable type, its uses and features.

Cabling types

A wide range of cabling types has been used to connect Ethernet systems. Network uses three types of cables: coaxial, twisted and fiber optic cables. Twisted pair is similar to telephone cable. It consists of pairs of cables twisted around each other to reduce electrical interference. For high speed and high secure systems, Fiber optic cables are used. However, it is less commonly used, as the cable is expensive and more difficult to install.

1. Unshielded Twisted Pair (UTP) Cable
2. Shielded Twisted Pair (STP) Cable
3. Coaxial Cable
4. Fiber Optic Cable

Twisted Pair Cables:

Twisted pair cable is a type of cable, which consists of two independently insulated wires around one another. The use of twisted pairs helps to reduce crosstalk and electromagnetic induction. High quality twisted pair cables have 1to 3 twists per inch. Twisted pair cables is the ordinary copper wire which is used to connect most of the home and business computers to Telephone company. Each wire in twisted pair cables has color plastic insulation attached to it. Twisted-pair cables are lighter, thinner, more flexible and easier to install than coaxial and fiber-optic cabled. There are two types of twisted pairs: Unshielded twisted pair and shielded twisted pair.

Shielded Twisted pair (STP):
The twisted pair in STP are individually wrapped in a foil shield and enclosed in an outer braided wire shield. The shielding is designed to minimize electromagnetic radiation and susceptibility to crosstalk. Each pair is surrounded by insulating material, with another insulator covering all pairs together. The extra material makes the cable white bulky and cause lack of flexibility. Shielded twisted pair cables are commonly used on networks using Token Ring topology.

Unshielded Twisted Pair (UTP):
Unshielded Twisted pair cable is the most popular of all the cable types. UTP cables are used not only for networking but also for traditional telephone (UTP) cable consists of four pairs of wires inside the jacket. Each wire has some colored plastic insulation attached to it. As copper wire is smaller in diameter, it may break easily. So, a thin plastic insulation provides more strength to each individual wire. Each pair has different twists per inch, which helps to eliminate interference from adjacent pairs or from other electrical devices.

Unshielded Twisted pairs standards

A great many different cabling standards exist. EIA/TIA (Electronic Industries Association / Telecommunications Information Association) standard  568A is one of several standard that specify “Categories” of unshielded twisted pair cabling systems in terms of data rates that they can carry. Under UTP type of cables for Ethernet wiring, the categories number. For computer networks the most common are category5, category5e and category6

CATI (category1) is typically used for telephone wire. This type of wire is not capable of supporting network traffic and it is twisted. CATI is not suitable to use with Ethernet. Only telephone companies who provide ISDN use it. There fore, the wiring between the customer’s site and Phone Company’s network use CATI cable.

CAT2 is used most commonly used for token ring networks, supporting speeds up to 4 Mbps. For higher speeds (100 Mbps) CAT5 cables are suitable. CAT3, CAT4 andCAT5 cables are generally 4 pairs of twisted copper wires. CAT5 has more twists per inch than CAT3, therefore it can run at higher speeds and greater lengths. CAT3 and CAT4 are also used for token ring networks. Category5e is a new standard that will specify transmission performance, which exceeds CAT5. Like CAT5, it consists of unshielded twisted pair with 100-ohm impudence and electrical characteristics supporting at frequencies up to 100MHz. CAT6 wire was originally designed to support multi gigabyte Ethernet. It is similar to CAT5 but contains a physical separator between the four pairs to further reduce electromagnetic interference. CAT7 is a proposed standard that aims to support transmission at frequencies up to 600MHz over 100 ohm twisted pair.

Most common cable categories

Category	Bandwidth	Applications	Notes
Cat1	0.4 MHz	Telephone and modem lines	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat2	? MHz	Older terminal systems, e.g. IBM 3270	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat3	16MHz	10BASE-T and 100BASE-T4 Ethernet	Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s.
Cat4	20MHz	16 Mbit/s Token Ring
Cat5	100MHz	100BASE-TX & 1000BASE-T Ethernet
Cat5e	100MHz	100BASE-TX & 1000BASE-T Ethernet	Enhanced Cat5. Practically the same as Cat5, but with better testing standards so Gigabit Ethernet works reliably.
Cat6	250MHz	1000BASE-T Ethernet	Most commonly installed cable in Finland according to the 2002 standard. SFS-EN 50173-1
Cat6e	250MHz (500MHz according to some)	10GBASE-T (under development) Ethernet	Not a standard; a cable maker's own label.
Cat6a	500MHz	10GBASE-T (under development) Ethernet	Standard under development (ISO/IEC 11801:2002 Amendment 2).
Cat7	600MHz	No applications yet.	Four pairs, U/FTP (shielded pairs). Standard under development.
Cat7a	1200MHz	Telephone, CATV, 1000BASE-T in the same cable.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.
Cat8	1200MHz	Under development, no applications yet.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.

Coaxial cable

Coaxial cable is a type of communication transmission cable in which solid center conductor is surrounded by an insulating medium, which is surrounded by tubular outer conductor (foil). The entire assembly is then surrounded with an insulating and protective outer layer. Coaxial cables are capable of carrying many data, voice and video conversations simultaneously. The two type of coaxial cabling used with Ethernet are.

• Thicket
• Thinnet

Thicket

Thicket coaxial is used with Ethernet 10BASE5 network, which supports a 100Mbps transmission rata and consists of 500 meter segment length. Thick Ethernet consists of mark at every 2.5 meters, which  indicates proper placement of 10Base5 transceivers used to connect  stations to the network Transceiver placed at any multiple of 2.5 meters intervals minimizes signal reflection, which may spoil the transmission quality in the cable. Vampire tap is used to connect  to the segment. Vampire tap is piece of metal, which is cylindrical in shape when tap is closed. When tap is closed around the cable, it is pushed through the shielding to provide the metal in the vampire tap to touch the copper wire inside the cable.

Thinnet

Thinnet coaxial cable is used with Ethernet 10 Base2 networks. Compared to thicknet cables, thicknet are cheaper, Lighter, flexible and easier to install. It consists of 185 meter maximum segment Length. 10Base2 transceiver is connected to the thinnet cable segment through “BNC (British Naval Connector) T” connector. To connect to computer, one end of T connector plugs directly into Ethernet card in the computer station, another end is plugged into cable from upstream cable, and another cable attached to next device downstream.

10Base5 and 10Base2 Connectors

Transceiver is a term formed by combining the terms transmitter and receiver. Instead of Ethernet card, it consists of electronics that send and receive signal on the Ethernet cable.
Disadvantages of coaxial cable includes that are more expensive, heavier and relatively inflexible. Also, when it is used for Ethernet, a single break in cable causes the failure of entire segment.

Fiber-Optic Cable

An optical fiber breakout cable

A multi-fiber cable

Fiber-optic cabling is a technology in which the electrical signal is converted into optical signal that is transmitted through a thin glass fiber and it is converted back into electrical signal. The figure below shows the components of a fiber-optic cable.


Fiber-optic cable is made from fiberglass and it does not break easily. The plastic and Kevlar coating provides more strength to the fiber glass. Kevlar is the material that most of bullet proof vests is made of.

Fiber-optic cable consists of two concentric layers of high-purity silica glass- the core and the cladding. The “core” is the inner part of an optical fiber through which light is transmitted. The “cladding” is the material in the middle layer. The light stays confined to the core because the cladding has lower refractive index than the core, which means that when light hits the outer wall, it is reflected back to core. The outer protective layer serves to protect core and cladding from damage.

The devices such as Ethernet switches, which are at the end of the cable, generate optical light signal. These signals travel through the optical fiber in the canter of cable. Electricity is not used across the cable; only light is transmitted.

Optical fiber connector

FC connector	MIC (FDDI) connector
LC connector	MT-RJ connector
LuxCis connector	SC connector
ST connector