Basics of Computer Network
A computer network can be described as an interconnected connection of autonomous computers. Two computers are said to be interconnected if they are able to exchange information. Or a network is two devices connected to each other with a physical medium, such as wires or radio signals.
By the term 'autonomous' it is meant that there should not be any master-slave relationship between the computers, i.e., all the computers should have the resources to work independently.
- A network helps to share resources such as a database, processor, hard disc space, scanner, CD-ROM or software.
- A network provides a communication medium so that persons sitting at remote places can exchange messages, etc.
- The network provides high reliability by having alternate resources so that if one processor crashes, another processor may take its place, or if one route fails, another route may become available.
Computer Network Functions
- Information must be delivered reliably without any corruption of data.
- Information must be delivered consistently – the network should be capable of determining where the information is going.
- Multiple computers must be able to identify each other across the network.
- There must be a standard way of naming and identifying the parts of the network.
Basic Elements of a Communication System
Communication is the process of transferring a message from one point to another. The three basic elements of a communication system are
- A sender (source) that creates and sends a message.
- A medium that carries the message.
- A receiver (sink) that receives the message.
Sender (source) 𑁋𑁋𑁋𑁋𑁋⮞ Receiver (sink)
Three basic elements of any communication system are a sender (source) that creates and sends a message, a medium that carries the message, and a receiver (sink) that receives the message.
Data Transmission Modes
Three modes of data transmission are simplex, half-duplex, and full duplex.
- A simplex communication system can transmit data in one direction only.
Sender (source) 𑁋𑁋𑁋𑁋𑁋⮞ Receiver (sink)
- A half-duplex communication system can transmit data in both directions, but in only one direction at a time.
Sender (or Receiver) ⮜𑁋𑁋𑁋(OR)𑁋𑁋𑁋⮞ Receiver (or Sender)
- A full-duplex communication system allows data to flow in both directions simultaneously.
Sender (or Receiver) ⮜𑁋𑁋𑁋 (AND) 𑁋𑁋𑁋⮞ Receiver (or Sender)
Data Transmission Speed
'Bandwidth' of a communication system refers to its data transfer rate (amount of data that it can transfer per unit of time). The higher the bandwidth of a communication system, the more data it can transfer in a given time. Bandwidth is measured in bits per second (bps) (also called baud). Based on data transmission speeds, three basic categories of communication channels (paths) are:
Narrowband
Narrowband or sub-voice-grade channels have speeds in the range of 45 to 300 baud. Low-speed devices and communication systems use narrowband channels for low data volumes.
Voiceband
Voice-band channels have speeds up to 9600 baud. Their major application is in ordinary telephone voice communication; hence, the name "voiceband". Communication systems for data transmission from slow I/O devices to the CPU or vice versa use voice-band channels.
Broadband
Broadband channels have a speed of 1 million baud or more. Communication systems use broadband channels to transmit large amounts of data at high speed (such as high-speed computer-to-computer communication or simultaneous data transmission to multiple devices).
Data Transmission Media
There are several types of physical channels (communication media) used for data transmission from one point to another. Some popular data transmission media are twisted-pair wire (UTP cable), coaxial cable, microwave systems, communications satellites, and optical fibers.
- UTP cables are commonly used for local telephone communications and short distance (up to about 1 km) digital data transmission. Generally, they are used to connect terminals to the main computer, if they are placed a short distance apart. For distances up to 100 meters, they provide data transmission speeds of up to 9600 bps and for longer distances (such as local telephone lines) they provide speeds of 1200 bps.
- Coaxial cables offer much higher bandwidths than UTP cables, and can transmit digital signals at rates up to 10 mega bps. They are used extensively in long distance telephone lines for both voice and data transmission.
- Microwave systems have speed of about 16 giga bps (1 giga = 10^9). They can support about 250,000 voice channels simultaneously. its use repeaters at intervals of about 25 to 30 kms in between transmitting and receiving stations. As they support wireless communication, they do not require laying of the cables and associated cost of land digging.
- Communication satellites are microwave relay stations in other space.
