Computer Network Physical Media

Physical Media :

A lot of us rely on wireless networking methods that work using technologies like radio frequency and infrared, but even wireless depends on a physical media backbone in place somewhere. And the majority of installed LANs today communicate via some kind of cabling, so let’s take a look at the three types of popular cables used in modern networking designs.

  • Coaxial
  • Twisted-pair
  • Fiber optic

Coaxial Cable :

Coaxial cable, referred to as coax, contains a center conductor made of copper that’s surrounded by a plastic jacket with a braided shield over it. A plastic such as polyvinyl chloride (PVC) .

Thin Ethernet, also referred to as thinnet or lOBase2, is a thin coaxial cable. It is basically the same as thick coaxial cable except it’s only about 5 mm, or 2/10” diameter coaxial cable. Following image shows an example of thinnet. This connector resembles the coaxial connector used for cable TV, which is called an F connector.

coaxial cable

If you use thinnet cable, you’ve got to use BNC connector to attach stations to the network, as shown in below image and you have to use 50 ohm terminating resistors at each end of the cable in order to achieve the proper performance.

BNC Connector

Twisted Pair Cable :

Twisted-pair cable consists of multiple individually insulated wires that are twisted together in pairs. Sometimes a metallic shield is placed around them, hence the name shielded twisted-pair (STP). Cable without outer shielding is called unshielded twisted-pair (UTP), and it’s used in twisted-pair Ethernet networks.

UTP cable is rated in these categories:

  • Category 1: Two twisted wire pairs (four wires). It’s the oldest type and is only voice grade it isn’t rated for data communication. People refer to it as plain old telephone service (POTS). Before 1983, this was the standard cable used throughout the North American telephone system POTS cable still exists in parts of the Public Switched Telephone Network (PSTN) and supports signals limited to the 1MHz frequency range.
  • Category 2: Four twisted wire pairs (eight wires). It handles up to 4Mbps, with a frequency limitation of 10MHz, and is now obsolete.
  • Category 3: Four twisted wire pairs (eight wires) with, three twists per foot. This type can handle transmissions up to 16MHz. It handles up to 10Mbps.
  • Category 4: Four twisted wire pairs (eight wires), rated for 20MHz. It handles up to 16Mbps
  • Category 5: Four twisted wire pairs (eight wires), rated for 100MHz. It handles up to 100Mbps
  • Category 6 : Four twisted wire pairs , rated for 250Mhz. It handles up to 1Gbps.

Connecting UTP :

BNC connectors won’t fit very well on UTP cable, so you need to use a registered jack (RJ) Connector which you’re familiar with because most telephones connect with them. The connector used with UTP cable is called Rj-11 for phone that us four wires, RJ- 45 has four pairs (eight wires)

RJ45 Connector

Advantages :

  • It’s cheaper than other types of cabling.
  • It’s easy to work with.
  • It allows transmission rates that were impossible 10 years ago.
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