Network Technologies: A Comprehensive Guide to Wired and Wireless Communication
1. Twisted Pair
A twisted pair consists of two wires (usually copper), each covered by a plaited insulation. One cable carries the signal, and the other is the ground reference. Braiding cancels electromagnetic interference, and twisting effects are canceled.
Different Types of Copper Twisted Pair
There are two types of twisted pair: UTP (unshielded) and STP (shielded). There are seven categories that depend on the quality of the cable, the thickness, and the speed of data transmission, from CAT 1 to CAT 7.
- CAT 1 is used for basic telephony with a speed of 1.1.
- CAT 3 and 4 are used for LANs with transmission speeds of 10 and 20, respectively.
2. Transmission of Information by Optical Fiber
In optical fiber, light is transmitted through a cable with a core and a liner. The beam is sent and transmitted in the core by bouncing off the cross to the other surface. If the angle is greater than the critical angle, part of the beam moves back and loses power.
The numerical aperture is the range of valid angles of the beam.
Fiber Types Depending on the Index of Refraction
There are two types of optical fiber: single-mode and multi-mode.
- Single-mode fiber transmits a single beam that is nearly straight.
- Multi-mode fiber transmits multiple rays with different angles that bounce off the edge. If the ray is not between the angles, it is rejected.
3. Infrared Waves
Infrared waves have frequencies above 300 kHz. They have a large bandwidth, making them ideal for transmitting large amounts of data. However, these waves are short-range and do not pass through walls. This makes them suitable for connecting devices such as a mouse or keyboard to a remote PC without interference from other rooms.
Infrared waves require line of sight for transmission.
4. Circuit Switching
Circuit switching is a method of communication that establishes a physical connection between two or more devices. It consists of switches with different channels to establish a physical connection.
Circuit switching passes through three stages:
- Establishment phase: Resources are requested and maintained throughout the transmission.
- Data transmission phase: Data is sent out.
- Release phase: When the data transmission is finished, the sender sends a request to release the connection and waits for the receiver to send a confirmation of release.
5. HFC Network
A hybrid fiber-coaxial (HFC) network is a hybrid coaxial cable network that uses fiber for the backbone and coaxial cable for the user. The data that is downloaded is modulated using the 64-QAM technique.
The theoretical speed for data download is 30 Mbps, and the theoretical speed for data upload is 12 Mbps.
6. Diagram of a Cable Network for Data Transmission
To use a cable network for data transmission, you need two key devices: a cable modem (CM) and a cable modem transmission system (CMTS).
The cable modem (CM) is installed on the subscriber’s premises. It is similar to an ADSL modem.
The cable modem transmission system (CMTS) is installed inside the distribution center for the cable company. It receives data from the Internet and passes it to the combiner, which sends it to the subscriber. The CMTS also receives data from the subscriber and passes it to the Internet.
7. Hamming Distance
The Hamming distance between two words is the number of differences between the corresponding bits. The minimum Hamming distance is the smallest Hamming distance between all possible pairs in a set of words.
To ensure the detection of up to s errors in all cases, the minimum Hamming distance of a code block should be dmin = s + 1.
To ensure correction of up to t errors in all cases, the minimum Hamming distance of a code block should be dmin = 2t + 1.
8. Linear Parity and Parity Blocks
Linear parity code adds a parity bit to each word, indicating whether the total number of 1s is even or odd.
Parity blocks take multiple blocks of code words and add, in addition to linear parity, a new parity word.
9. Cyclic Redundancy Check (CRC)
Cyclic redundancy check (CRC) involves taking the data as a polynomial and dividing it by a generator polynomial modulo 2. The remainder is shipped together with the information as the frame check sequence (FCS).
The receiver makes the same division. If the remainder is the same, no errors occurred.
10. Checksums and Their Use for Error Detection
Checksums are used to detect errors in data transmission. They involve adding a few extra bits to the data, which are calculated based on the data itself.
The receiver can then check the checksum to see if it matches the calculated value. If the checksums do not match, it indicates that an error has occurred.
An example of a checksum is the addition of four bits to the data, so that the total number of 1s is even. The receiver can then check if the number of 1s is even. If it is not, an error has occurred.