A transmission medium is required to transport information from a source to a destination. Information is usually a signal that has to travel a long distance. For this, the transmission media can be wired or wireless. In cable transmission, the signal travels along the cable from one device to another. But in wireless transmission, electromagnetic waves are transmitted without using a physical conductor. There are three types of cables like.
1- Twisted pair cable
2- Coaxial cable
3- Fiber optic cable
Twisted pair cable
A twisted pair cable consists of two copper conductors, each with its own plastic insulation and twisted together. One wire carries the signal and the other is used as a ground reference. The advantage of twisting is that both cables are equally affected by external influences. So the unwanted signals are canceled when the receiver calculates the difference between the signals on two wires.
This cable is of two types like.
1- UTP (Unshielded Twisted Pair)
2- STP (shielded twisted pair)
The STP cable has an additional metal shield that covers the insulated twisted pair conductors. But this is absent in UTP cables. The most common UTP connector is the RJ45.
Unshielded twisted pair cable is classified into seven categories based on cable quality. Category 1 cables is used in telephone lines with a data rate of around 0.1 Mbps. Whereas Category 5 is used in LAN with a data rate of 100 Mbps.
Twisted pair cable performance is measured by comparing attenuation with frequency. Attenuation increases with frequency above 100 kHz.
These cables are used in telephone lines to provide voice and data channels. DSL lines and local area networks also use twisted pair cables.
Coaxial cable
Coaxial (coaxial) cable carries higher frequency signals than twisted pair cables. Coaxial cable has a solid wire center core conductor encased in an insulator, which is covered by an outer foil conductor. This outer conductor completes the circuit. The outer conductor is also encased in an insulator and the entire cable is protected by a plastic sheath.
These cables are classified by RG (Radio Government) ratings. RG-59 is used for cable TV, RG-58 for thin Ethernet, and RG-11 for thick Ethernet. The connector used in these cables is called the BNC connector; used to connect the end of the cable to a device.
Although coaxial cable has a higher bandwidth, its attenuation is much higher compared to twisted pair cables. It is widely used in digital telephone networks where a single cable can carry data of up to 600 Mbps. Cable television networks use RG-59 coaxial cable. Traditional Ethernet LANs also use this cable.
Fiber optic cable
A fiber optic cable transmits signals in the form of light. Fiber optics uses reflection to guide light through a channel. It consists of two main parts: core and cladding. The core is denser compared to the cladding and is made of plastic or glass. The cladding acts as a protective covering down to the core. The difference in the density of the core and cladding is such that a beam of light moving through the core is reflected off the cladding, rather than refracted from it.
In optical fiber, two modes of light propagation are possible, such as: multimode and singlemode. Multimode fiber allows multiple beams from a light source to move through the core. In multimode step index fiber, the core density remains constant from the center to the edges. But in graded-index multimode fiber, the core density gradually decreases from the center of the core to its edge. Gradual rate fiber creates less signal distortion compared to step rate.
There are two types of connectors for fiber optic cables. The SC connector is used for cable TV and the ST connector is used to connect the cable to network devices. The attenuation in fiber optic cable is very low compared to two other types of cable. Provides very high bandwidth and immunity to electromagnetic interference. The light weight and the higher shock immunity make the cable more preferable.
Fiber optic cable is often used in backbone networks due to its high bandwidth and cost effectiveness. Local area networks such as the 100Base-FX and 100Base-X network use this cable. It is also used by cable television companies.
