Guided Transmission Media
Guided Transmission Media – The role of the physical layer is to transfer bits from one computer to another through the channel. Different physical media can be used for the actual transfer. Each of them has its place in terms of throughput, time, cost and ease of installation and maintenance. Operators are grouped roughly in managed environments, such as copper and fiber optic cables, and in unmanaged environments, such as global wireless networks, satellites, and live lasers.
One of the most common ways of transferring data from one computer to another is by writing it on a magnetic tape or removable media (for example, recordable DVDs), physically transferring the tape or discs to the target computer and reread them. Although this method is not as complicated as using a geosynchronous communication satellite, it is often more cost-effective, especially for applications where high bandwidth or cost per bit transport is a key factor.
The twisted pair consists of two insulated copper wires of a thickness of about one (1) mm. The wires are twisted in a spiral, like a DNA molecule. Twisting is performed because two parallel cables constitute a thin antenna. When the cables are twisted, the waves of different turns are canceled and the cable radiates less efficiently. As a rule, the signal is transmitted as a voltage difference between two wires of a pair. The most common application of twisted pairs is the telephone system.
Twisted pairs can be used to transmit analog or digital information. The bandwidth depends on the thickness of the cable and the distance traveled, but in many cases, it can reach several megabits per second for several kilometers. Because of their adequate performance and low cost, twisted pairs are widely used and will likely remain so for many years.
Coax is another common means of transmission (known to many friends as “coax” and pronounced “coax”). It offers better protection and higher bandwidth than unshielded twisted pairs, allowing it to travel longer distances at higher speeds.
Two types of coaxial cables are widely used. One type, a 50-ohm cable, is typically used when it is designed for digital transmission from the start. The other type, a 75-ohm cable, is commonly used for analog transmission and cable television.
The coaxial cable consists of a hard copper wire surrounded by an insulating material. The insulation is covered with a cylindrical conductor, often similar to a dense woven mesh.
The optical fiber is used for long-distance transmission over main networks, high-speed local networks (although copper has always been removed), and high-speed Internet access such as the home network (FttH) (Fiber to the Home). The optical transmission system has three key components: the light source, the transmission medium, and the detector. As a general rule, a light pulse indicates bit 1 and the absence of light indicates bit 0. Ultra-thin fiberglass is the transmission medium. The detector generates an electrical pulse when the light hits it. By connecting the light source to one end of the optical fiber and the detector to the other, we get a unidirectional data transmission system that receives an electrical signal, converts it and transmits it using light pulses, and then converts the signal output into an electrical signal at the receiver. Optical fiber cables are similar to coaxial cables, except for cables without braids.