Transmission Media

The physical pathways that connect computers and devices on a network.

Compatibility

A transmission medium allows two or more computers to communicate on a network.

It requires specialized hardware to transfer information.

The hardware such as NIC's must be compatible with the transmission medium.

Combined Media

Many different types of transmission media.

Smaller networks usually constructed using one medium.

Larger networks may use different types in different parts of the network.

That makes the network more complex and difficult to build and maintain.

Cable

Oldest and most commonly used type of medium.

Copper wires covered with protective plastic coating.

Inexpensive compared to other types of media.

Three types of electrical cable.Coaxial

Unshielded Twisted Pair

Shielded Twisted Pair

Light

Fiber-optic cable uses light signals sent through a core of plastic or glass.

Very fast, but expensive and difficult to install.

Wireless

Used when parts of a network cannot be physically close.For example, a facility with two buildings on opposite sides of a lake.Examples of wireless media

InfraredRadioMicrowaveSatellite

Considerations

Many factors to consider when deciding which transmission media to use.

Cost

Cost of transmission media is a major factor in determining the cost of implementing a network.

Prices range from a few cents per foot of cable up to multi-million dollar satellite networks.

Expansion

Networks grow as needed by growing companies.

New users, new demands, new equipment.

Some types of TM are difficult to alter once installed.

Future expansion must be considered carefully when installing a network.

Cable-based networks easy to manipulate.

Fiber-optics are not.

Bandwidth

Amount of information that can be transferred at once via a particular medium.

More information at once means higher bandwidth.

Bandwidth usually measured in megabits per second (Mbps).

Signal Degradation

Further a signal has to go, the weaker it becomes.

This weakening is called attenuation.

Each type of TM can transmit signals a certain distance.

These maximum capacities may determine which medium you will need to use.

Interference

Many devices in modern offices may interfere with the signals in transmission media.

PhotocopiersElevatorsFluorescent lights

These may emit signals that could interfere with the signals in cables.Some types of TM are designed to better withstand interference than others.

Coaxial Cable

Has a core of solid copper surrounded by a layer of plastic.

An outer layer of metal mesh or foil surrounds that plastic coating.

Then there is another coating of protective plastic.

Coaxial Cable

One of the most common types of TM.

Linked using devices called British Naval Connectors (BNC).

Rated using an RG number.

Most common types of cable rate RG-11, RG-58, or RG-62.

Interference

Coaxial cable transmits electrical signals throughout the network.The wire mesh protects somewhat against interference.Sometimes, though, nearby devices can affect the signal being transferred.Coaxial cables can sometimes interfere with other devices nearby.

Electrical Resistance

Rated according to the resistance the cable has to electrical transmission.

Electrical resistance measured in ohms.

Most common rating is 50 ohms.

Terminators

Coaxial cable on a bus network has to have a terminator at each end.

Terminator must have same rating as the cable on which it is installed.

50 ohm cable must have 50 ohm terminators.

Bandwidth

Most coaxial cables transmit at speeds of up to 10 Mbps.

Thicker cables can transmit much faster.

Cost

Coaxial cable is very inexpensive.

Widely used because of the lower cost per foot than other transmission media.

Unshielded Twisted Pair (UTP)

Most popular type of cable to be used for new networks.Commonly have 2, 4, 6, or 8 wires in an unshielded pair cable.Each wire in a UTP cable is coated with a different color coating.Entire cable is coated with another coating.Pairs of copper wire are twisted around each other.This reduces interference from other devices.

Connectors

The connectors on the UTP's are connected with connectors that resemble telephone jacks.

These connectors are referred to as RJ-45 connectors.

Cost

Least expensive of all cable types.

Installation

Very lightweight and flexible compared to other types of cable.

Makes UTP cables very easy to install.

Except for very simple installations, cable contractors should install all networking cable.

Cable Lengths

Not suitable for devices that are far apart.

The farther a signal travels, as you know, the weaker it gets.

UTP cables reliable for distances up to a few hundred feet, but not more.

Bandwidth

Five main categories of UTP cables:Category 1 and 2 - speeds up to 4 Mbps

Category 3 - speeds up to 16 Mbps

Category 4 - speeds up to 20 Mbps

Category 5 - speeds up to 100 Mbps

Category 5 = Cat5 like we use here.

Shielded Twisted Pair (STP)

Similar to UTP but has an additional metal or foil protective covering.

Can contain a single pair of wires or several pairs of wires.

Interference

The shield (the metal or foil) protects more thoroughly against electrical interference.

Construction is just like a UTP except for that additional metal coating.

The shield also prevents the cable from interfering with other devices.

Bandwidth

STP's are capable of speeds up to 150 Mbps.

Most networks using STP's rarely use speeds over 16 Mbps.

Installation

Difficult sometimes because STP's are bulky and not very flexible.

Can be up to a half inch in diameter

That makes installation awkward when a lot of cables need to be grouped together.

Connectors

Two types of connectors depending on the network type.Apple LocalTalk networks use small pin and socket connectors.IBM token-ring networks use bulky two-way connectors.Both of these connectors are difficult to install.Cable can often be purchased with the connectors already attached.

Cost

STP's are more expensive, as you might know, than UTP's.

But still considered very inexpensive compared to other transmission media.