1. Twisted Pair
Although the bandwidth characteristics of magnetic tape is very nice, the delay bad characteristics. The transmission time is measured in minutes or hours, not milliseconds. For many applications, the connection is required. One of the transmission medium of the oldest and still the most common is a twisted pair. Twisted pair consists of two insulated copper wires, typically about 1 mm thick. The cord was twisted together in a helical shape, the same as the DNA molecule. Rotating completed because two parallel wires to form a smooth antenna. When the cable is twisted, the waves from different twists cancel, so the wire radiates less effective.
Twisted pairs can be used to transmit analog or digital information. Bandwidth depends on the thickness of the wire and the distance traveled, but several megabits / second can be achieved for several kilometers in many cases. Caused by their adequate performance and low cost, twisted pairs are widely used and are likely to remain so for many years to come Links which can be used in both directions at the same time, such as two-lane road, called full-duplex link. In contrast, a link that can be used in both directions, but only one direction at a time, such as rail single-track. called half-duplex link. The third category comprises a link that allows traffic only in one direction, such as one-way streets. They are called simplex link.
Twisted-pair cable has several variations. Many office buildings wear Category 5 cabling, or ” Cat 5. ” Category 5 twisted pair consists of two insulated wires gently twisted together. Four such couples are usually grouped in a plastic sheath to protect the cable and keep it together. Standard different LAN can use Twisted Pair differently. For example, a 100-Mbps Ethernet uses two (of four) pairs, one pair for each direction to achieve higher speed, 1-Gbps Ethernet uses all four pairs in both directions simultaneously; This requires the receiver to determine the locally transmitted signal. Cat 5 cable replaces the previous 3 categories with similar cable which uses the same connector, but it has more twists per meter. More twists produce less crosstalk and better quality signal over longer distances, making cable more suitable for high-speed computer communication, particularly the 100-Mbps and 1-Gbps Ethernet LANs. The new cables are more likely to be Category 6 or even Category 7. This category has more stringent specifications to handle signals with a larger bandwidth. Some cable Category 6 and over rated for the signal of 500 MHz and can support 10-Gbps links to be immediately used. Through Category 6, the cable type is referred to as UTP (Unshielded Twisted Pair) because they only consist of wires and insulators. In contrast to this, Category 7 cable has a shield on the twisted individual, as well as around the entire cable (but inside a plastic protective sheath). Shielding reduce vulnerability to external interference and crosstalk with other nearby cables meet demanding performance specifications. These cables are reminiscent of a shielded twisted pair cable is of high quality, but expensive and costly introduced by IBM in the early 1980s, but not proven popular outside of IBM installations.
2. Coaxial Cable
Another common transmission medium is a coaxial cable (known as’ co-ax ”). It has a better shield and a larger bandwidth than twisted pair, so it can reach longer distances and higher speeds. Two types of coaxial cable is widely used. One kind, 50-ohm cable, usually used when intended for digital transmission. The other type, 75-ohm cable, is commonly used for analog transmission and cable television. This distinction is based on historical, rather than technical, factors (eg, early dipole antennas have an impedance of 300 ohms, and it’s easy to use the impedance-matching transformer 4: 1 there). Starting in the mid-1990s, cable TV operators started providing Internet access via cable, which has made the 75-ohm cable is more important for data communication. The coaxial cable consists of a stiff copper wire as the core, surrounded by an insulating material. Isolator encased by a cylindrical conductor, often as a tightly woven fabric webbing. Outer conductor covered with protective plastic.
3. The power lines
Telephone and cable television networks are not the only source wiring which can be reused for data communication. There are the more common types of cables: power lines. Power lines deliver electricity to homes, and the electrical wiring in the house distributes electricity to an electrical outlet. The use of power lines for data communications is an old idea. Power lines have been used by power companies for communications such as remote measurement of low-level for many years, as well as at home to control the device. In recent years there has been renewed interest in high-level communication over these lines, both in the home as a LAN and outside the home for internet access. The convenience of using the electricity network to the network should be clear. Put simply plug the receiver to the TV and the wall, which must be done well because they need power, and they can send and receive movies via the electrical wiring. Many products use a variety of proprietary standards for electrical line network, so that international standards are actively under development.
4. Fiber Optic Cable
Many people in the computer industry are very proud that so fast computer technology increases due to follow Moore’s Law, which predicts penggandaanjumlah transistors per chip approximately every two years (Schaller, 1997). The original IBM PC (1981) ran at a clock speed of 4.77 MHz. Twenty delapantahun later, the PC can run a four-core CPU at 3 GHz. This increase is the gain factor of about 2500, or 16 per decade. Impressive. In the same period, wide area communication link changed from 45 Mbps (T3 line phone system) up to 100 Gbps (modern long lines). This gain is equally impressive, more than a factor of 2000 and almost 16 perdekade, while at the same time changing the error rate of 10-5 per bit becomes almost zero. Furthermore, a single CPU is approaching the physical limits, yangmengapa now increased the number of CPUs per chip. Instead, the bandwidth can be achieved with fiber technology over 50,000 Gbps (50 Tbps) and we were not to reach this limit. The practical limit is around 100 Gbps is due to our inability to convert between electrical and optical signals faster.
Optical fiber is used for long distance transmission in network backbones, high-speed LAN (though so far, copper has always managed to catch the end) and high-speed Internet access such as FTTH (Fiber to the Home). A transmission optiksistem has three main components: a light source, transmisisedang, and detectors. Conventionally, a pulse of light indicates a 1 bit and the absence of light indicates a 0 bit. The transmission medium is an ultra-thin glass fibers. The detector generates an electrical pulse when light falls on it. By attaching a light source to one end of the optical fiber and the detector to the other end, we have a unidirectional data transmission system that receives an electrical signal, convert and send it with a pulse of light, and then converts the output into electrical signals at the receiving end. The transmission system will leak and become useless in practice not to the principle of the interesting physics. When a ray of light passing from a sat medium to another – for example, from fused silica to air – beam is refracted (bent) at the limit of silica / air
Comparison of Fiber Optics and Copper Wire is instructive to compare fiber to copper. Fiber has many advantages. To begin with, he can handle a much higher bandwidth than copper. It only requires their use in high-end network. Because of low attenuation, repeaters are needed only about every 50 km on long lines, than every 5 km for copper produce substantial cost savings. Fiber also has the advantage of not terpengaruholeh power surge, electromagnetic interference, or electrical interference. These properties provide a good fiber security against potential eavesdroppers. On the downside, fiber is a less familiar technology requiring skills not all engineers have, and fibers can be damaged easily because of too much bent. Since optical transmission is inherently unidirectional, bidirectional communication requires either two fibers or two frequency bands on a single fiber. Finally, fiber interfaces cost more than electrical interfaces. However, the future of all fixed data communication over short distances clearly with fiber.