ICT Course LowerSixth Science part 2
Chapter 3: TRANSMISSION MEDIA
courseA transmission medium is the pass way that links computers and other devices in the network. There are two categories of transmission media: guide and unguided media.
- GUIDE MEDIA
Guide media are the physical cables used to connect computers in the network. They are made up of an internal conductor bounded by jacket material. Three common type of guided media are coaxial cable, optic fibre, twisted pair cables.
1.Coaxial cables
It consists of an inner core and an outer flexible braided shield, both of conductive materials separated by on insulator. The braided shield prevents the cable from picking up or remitting electrical noise.
To connect coaxial cable to devices, we need coaxial connector. The most common type of connectors used today is bayone-neill-concelman (BNC) connector
.
2.Twisted pair cable
Twisted pair cable is the most common type of cabling use in LAN network today. It consists of a pair of insulated wires twisted together. Cable twisting help to reduce noise pitch up from outside sources and cross talk of multi-paired cables. There are two types of twisted pair cables:
- shielded twisted pair (SIP) and unshielded twisted pair cables (UTP)
- Unshielded twisted pairs: UTP consists of two or four pairs of twisted cables. Cables with to pairs used RJ-11 connector and four pair used RS-45 connects. RJ stands for registered jack. UTP can be connected as straight through or cross over. A straight through cables have identical ends and cross over cable has different ends.
3Fibres optic cables
They use optical fibres that carry digital data signal in the form of modulated light pulses. An optic fibre consists of an extremely thin cylinder of glass called the core, surrounded by a concentric layer of glass known as the cladding. Each cable has 2 fibres, 1 for transmitting and the other for receiving
- Single mode fibres (SMF): it use a single ray of light to carry transmissions over long distance
- Multi-mode fibres (MMF):it uses multiple rays of light simultaneously with each ray of light running at a different reflection angle to carry transmission over short distance
- The light source can be LED (light emitting diode) or LD (laser diode).
- UNGUIDED MEDIA
Unguided media do not use physical means to connect to the computer. They provide a means for transmitting electromagnetic wave but do not guide them. They are also called unbounded media. Example of unguided media is infrared wave, radio waves, micro waves.
1.Infrared waves
It uses transmitters/receivers (transiever) that modulate non-coherent light. It is the propagation that can transmit and receive data only where the transmitter and receiver station are in view of each other without any sort of an obstacle between them.
2.Radio waves
Radio waves transmit signal by modulation of electromagnetic wave with frequencies below that of visible light. Radio waves are Omni-directional, this means that the signal speed out in all direction and can be receive by many antenna.
3.Micro waves
They are electromagnetic radiations beyond the frequency ranged of radio and television. There are two types of micro wave system: terrestrial micro waves system and satellite micro waves system.
- Terrestrial micro waves system
They are land-based, micro waves being line-of sight and travelling in a straight line, the earth curvature poses a problem to long distance micro wave transmission as such; long distance transmission requires directional antenna (repeaters) to be used at intervals of 25 to 30km between the transmitting and receiving end
- Satellite micro wave system
Satellite system use communication satellite to solve the problem pose by the earth curvature to terrestrial micro wave system. A communication satellite is a micro wave relay station placed in outer spaced the micro wave system is transmitted from earth to the satellite which amplifies the signal and sends it back to earth. The earth station transmit the signal to the satellite o an up-link, on one frequency and the satellite repeats those signal on a dorn-link which is on another frequency.
- ADVANTAGES OF MICRO WAVE SYSTEM
- No cables needed
- Multiple channels available
- Wide band width
- DISADVANTAGES
- Line-of sight will be distribute if any obstacle such as new buildings are in the way
- Signal absorption by atmosphere
- Micro wave suffer from attention due to atmospheric condition
- Towers are expensive to build.
QUESTIONS
1.Define: transmission media
2.Give the advantages of micro waves and disadvantages
3.Name the different categories of transmission media
4.What is the difference between coaxial cables and twisted pair cable?
5.Name the different types of unguided media