Several physical data-transmission media are available to connect together the various devices on a network. One possibility is to use cables. There are many types of cables, but the most common are:
Coaxial cable has long been the preferred form of cabling, for the simple reason that it is inexpensive and easily handled (weight, flexibility, ...).
A coaxial cable is made of up a central copper wire (called a core) surrounded by an insulator, and then a braided metal shield.
Thanks to its shield, coaxial cable can be used over long distances at high speed (unlike twisted pair cable), however it is usually used for basic installations.
Note that there are also coaxial cables that have a double shield (one insulating layer, one shield layer) and coaxial cables with four shields (two insulating layers, two shield layers).
Normally, two types of coaxial cable are used:
|RG-58 / U||Central core consisting of a single copper strand|
|RG-58 C/U||Military version of RG-58 A/U|
|RG-59||Wide band transmission (cable television)|
|RG-6||Thicker diameter, recommended for higher frequencies than RG-59|
Thinnet and Thicknet are connected using a transceiver. It is equipped with a so-called "vampire" plug that makes the real physical connection to the central part of the Thinnet by piercing the insulating envelope. The transceiver cable (drop cable) connects to an AUI (Attachment Unit Interface) connector, also called a DIX (Digital Intel Xerox) connector or a DB 15 (SUB-D 15) connector.
Thinnet and Thicknet both use BNC (Bayonet-Neill-Concelman or British Naval Connector) connectors to hook up the cables to computers.
The following connectors are in the BNC family:
In its simplest form, twisted-pair cable consists of two copper strands woven into a braid and covered with insulation.
Two types of twisted pair cable are generally recognized:
A cable is often made of several twisted pairs grouped together inside a protective jacket. The twisting eliminates noise (electrical interference) due to adjacent pairs or other sources (motors, relays, transformers).
Twisted pair is therefore suitable for a local network with few nodes, a limited budget and simple connectivity. However, over long distances at high data rates it does not guarantee data integrity (i.e. loss-less data transmission).
UTP cable complies with the 10BaseT specification. This is the most commonly used twisted pair type and the most widely used on local networks. Here are some of its characteristics:
Most telephone installations use UTP cable. Many buildings are pre-wired for this type of installation (often in sufficient number to satisfy future requirements). If the pre-installed twisted pair is of good quality, it can be used to transfer data in a computer network. Attention must be paid, however, to the number of twists and other electrical characteristics required for quality data transmission.
STP (Shielded Twisted Pair) cable uses a copper jacket that is of better quality and more protective that the jacket used for UTP cable. It contains a protective envelope between the pairs and around the pairs. In an STP cable, the copper wires of one pair are themselves twisted, which provides STP cable with excellent shielding, (in other words, better protection against interference). It also allows faster transmission over a longer distance.
Twisted pair cable is connected using an RJ-45 connector. This connector is similar to the RJ-11 used in telephony, but differs on a few points: RJ-45 is slightly larger and cannot be inserted into an RJ-11 jack. In addition, the RJ-45 has eight pins while the RJ-11 has no more than six, usually only four.
Optical fibre is a cable with numerous advantages:
Fibre optic cabling is particularly suited to links between distributors (central link between several buildings, known as backbone) as it allows connections over long distances (from several kilometres to 60 km in the case of single-mode fibre) without requiring earthing. Furthermore, this type of cable is very secure as it is extremely difficult to tap in to such a cable.
However, despite its mechanical flexibility, this cable type is not suitable for local network connections as it is difficult to install and is very expensive. For this reason, twisted pair or coaxial cable are preferred for short links.