Communication Channels / Lines / Links / Carriers / Media
All the telecommunication channels use a variety of different medium to exchange the data on a network. Rate of transfer of data is known as band rate, and it is measured in bits per second.
Categories of Channels
1. Wire / Guided media
2. Wireless / Unguided media
WIRE / GUIDED MEDIA
Wire media (also known as GUIDED MEDIA) is commonly used type around the world.
Coaxial cables
These cables contain aluminum or copper wires which are wrapped. These wires are used in the past for transmission of a data at high speed.
Twisted pair cables
All around the world, the whole telecommunication network (Landline Telephone), depends upon this type of wire cables. It is most commonly used in telephones. It is composed of pair of wires that’s why it is called twisted pair cables.
Fiber Optic cables
This type is of high priority for transmission of video, data and voice. Comparatively with coaxial cable, it is 15 – 18 times faster. Its max transfer rate is up to 2 GBPS. On the basis of reliability, it is also on the top among the others. This is not enough in comparison, its name also comes first with respect to size and weight because a fiber optic cable can carry 10 times more channels as compare to coaxial cables. It is capable of being used on WAN and MAN.
Fiber Optic cables can also be used for WAN and MAN.
Integrated Services Digital Network (ISDN)
This system is available for many years and in which both the voice and the data are transmitted at the same time. The bandwidth of the ISDN is 64 kb/s. How much the signal will be handled 16kb/s or 64kb/s, is decided according to the type of the service.
Digital Subscriber Line / Asymmetrical Digital Subscriber Line
This service is provided on a regular telephone line and most commonly used for home users and for small businesses. By using the DSL modem, DSL line provides both the telephone and internet facility on the same line.
ASDL with respect to receiving of data is much faster than DSL because its receiving rates are fast. This facility is mostly used for those users who never wants to upload anything rather their main concern is only with downloading.
Different variants of DSL include:
ADSL – Most widely used, inexpensive as compared to other, downstream 400kbps to 6mbps, but there is upstream significantly slower
SDSL – Less widely used, expensive, downstream and upstream same speed
IDSL – Less expensive compared to ADSL, downstream and upstream 144kbps
HDSL – not available widely, faster than IDSL, downstream and upstream 768kbps
VDSL – most expensive, not widely available, downstream and upstream 13mbps to 52 mbps
WIRELESS / UNGUIDED MEDIA
Infrared transmission
The range for transmission of data of Infrared is very short among others. It is most commonly used in domestic appliances. The function of Infrared is performed using infrared LEDs (light emitting diodes), which are used to emit infrared radiation that are received by using a silicon photodiode which then converts the infrared radiation in to an electric current. This technology is for short range communications.
Bluetooth transmission
It is a wireless technology in which two wireless devices communicate and exchange data with each other. But this technology is for short range communications. It is mostly used in mobile phones, laptops, telephones and personal computers, and gives a more secure way than infrared technology. In this technology, data is exchanged via low power radio frequencies.
Wifi
Wifi (Wireless Fidelity) in other wireless technology that is used to transmit data to places which are square miles apart. Its range is more than the Infrared and Bluetooth.
WiMax
It is another wireless technology which is used to provide full mobile internet access. This technology supports more than 50 Mbps.
Microwave
It is used where we want to exchange data at high distances. The rate of error in microwave is very low as it is wireless and also it is more reliable. It is more expensive than discussed above. The reason of expensiveness is that it works by using relay stations normally placed at a distance of 25-35 miles which boost up the signal and also it only transmits data in line of sight path. Its speed capacity is in Gbps.
Communication Satellite
In today’s world, this is the most important medium used in microwave communications. Currently, there are thousands of satellites in the space which are performing their function in transmitting data. They act as a relay station which link the earth stations and they get the solar power to work. When these satellites receive signals from the earth stations, they amplify them and then, retransmit them to the other earth stations which are thousands of miles away. Initially, these satellites were only used for video and voice transmission, but today, many companies use them to transmit large volume of data at very high speed (in Gbps).
