Computer Project Work

Guided And Unguided Media

Guided Media

Guided Transmission Media uses a cabling system that guides the data signals along a specific path . The data signals are bound by the cabling system . Guided Media is also known as Bound Media or Wired media . There three basic types of Guided Media :

1. Twisted Pair2. Coaxial Cable3. Optical Fiber

1. Twisted Pair Cable• Pair of twisted conductors•Twisting reduces interference (two parallel wires constitute a simple antenna; a twisted pair does not.)•Cheap medium •Commonly used for communications within buildings and in telephone networks•Produced in unshielded (UTP) and shielded (STP) forms, and in different performance categories.•Cables may hold hundreds of pairs. Neighbor pairs typically have different twist lengths to reduce crosstalk.

2. Coaxial CableCoaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor.

3. Optical Fiber • Three components: light source, transmission system, and a detector .• The detector generates an electric pulse when hit by light• 1-a pulse of light; 0-missing pulse of light.• optical rays travel in glass or plastic core• Light at shallow angles propagate along the fibre, and those that are less

than critical angle are absorbed in the jacket• The cladding is a glass or plastic with properties that differ from those of the

core• Used in long distance communication, in locations having small amount of

space, and with reduction in price is starting to get also to LANs.• Not affected by external electromagnetic fields, and do not radiate energy.

Hence, providing high degree of security from eavesdropping.• Provide for multimode of propagation at different angles of reflections. Cause

signal elements to spread out in time, which limits the rate in which data can be accurately received.

• Reduction of the radius of the core implies less reflected angles. Single mode is achieved with sufficient small radius.

• A multimode graded index transmission is obtained by varying the index of reflection of the core to improve on the multi mode option without resolving to the cost of single mode. (index of reflection=speed in vacuum / speed in medium.)

• 1 Gbps is the current limitation, with the bottle neck in the conversion from electrical to optical signals. Large improvements are expected.

Unguided Media

• Here information is transmitted by sending electromagnetic signals through free space and hence the name unguided media, as the signals are not guided in any specific direction or inside any specific medium.

• All unguided media transmission are classified as wireless transmission.

• Wireless transmission can be used as the medium in both LAN and WAN environments.

Some of the types of wireless media are:

• RADIO WAVES• MICRO WAVES• INFRARED WAVES

1. Radio Wave• Although there is no clear limit distinction

between radio waves and microwaves, • electromagnetic waves ranging in frequencies

between 3 kHz and 1 GHz are normally • called radio waves; waves ranging in

frequencies between 1 and 300 GHz are called • microwaves. However, the behavior of the

waves, rather than the frequencies, is a better • criterion for classification.• Radio waves, particularly those of low and

medium frequencies, can penetrate • walls.

2. MicrowaveMicrowave signals are used to transmit data without the use of cables, similar to that of radio and television signals but at different frequency range . It is line-of-sight transmission , which means the signal travels in straight line free of material obstacles .

3. Infrared

This type of transmission uses infrared light to send data. You can see the use of this type of transmission in everyday life - TV remotes, automotive garage doors, wireless speakers etc., all make use of infrared as transmission media.

The infrared light transmits data through the air and can propagate throughout a room(bouncing off surfaces), but will not penetrate walls. The infrared transmission has become common in PDAs(Personal digital assistants)e.g., hand held devices like palm pilots etc.

Made By Sanaa Sial

Student of class IXD.AV. ACC Public School , Katni