Basic Elements of a Communication System
The following are the basic requirements for working of a communication system.
1. A sender (source) which creates the message to be transmitted.
2. A medium that carries the message.
3. A receiver (sink) which receives the message.
Data Transmission Modes
There are three ways for transmitting data from one point to another
1. Simplex: In simplex mode the communication can take place in one direction. The receiver receives the signal from the transmitting device. In this mode the flow of information is Uni.-directional. Hence it is rarely used for data communication.
2. Half-duplex: In half-duplex mode the communication channel is used in both directions, but only in one direction at a time. Thus a half-duplex line can alternately send and receive data.
3. Full-duplex: In full duplex the communication channel is used in both directions at the same time. Use of full-duplex line improves the efficiency as the line turn-around time required in half-duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.
Computer Network
A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of types and categories and also presents the basic components of a network.
Purpose of Computer Network
Computer networks can be used for several purposes:
- Facilitating communications- Using a network, people can communicate efficiently and easily via e-mail, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
- Sharing hardware- In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, each user can then access the laser printer on the network, as they need it.
- Sharing files, data, and information- In a network environment, any authorized user can access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
- Sharing software- Users connected to a network can access application programs on the network.
Computer Network Types
Computer Networks may be classified on the basis of geographical area in two broad categories.
1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (LAN)
4. Personal Area Network (PAN)
5. Campus Area Network (CAN)
Local Area Network
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology.
Metropolitan Area Network
A metropolitan
area network (MAN) is a large computer network that usually spans a
city or a large campus. A MAN usually interconnects a number of local area
networks (LANs) using a high-capacity backbone technology, such as
fiber-optical links, and provides up-link services to wide area networks and
the Internet. Wide Area Network
A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies
Personal Area Network
A personal area
network (PAN) is a computer network used for communication among
computer devices, including telephones and personal digital assistants, in
proximity to an individual's body. The devices may or may not belong to the
person in question. The reach of a PAN is typically a few meters. PANs can be
used for communication among the personal devices themselves (intrapersonal
communication), or for connecting to a higher level network and the Internet.
Campus Area Network
A campus area network (CAN) is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc).
Wired technologies
Twisted pair wire is the
most widely used medium for telecommunication. Twisted-pair wires are
ordinary telephone wires which consist of two insulated copper wires
twisted into pairs and are used for both voice and data transmission. The
use of two wires twisted together helps to reduce crosstalk and electromagnetic
induction. The transmission speed ranges from 2 million bits per second to
100 million bits per second.
Coaxial cable is
widely used for cable television systems, office buildings, and other
worksites for local area networks. The cables consist of copper or
aluminum wire wrapped with insulating layer typically of a flexible
material with a high dielectric constant, all of which are surrounded by a
conductive layer. The layers of insulation help minimize interference and
distortion. Transmission speed range from 200 million to more than 500
million bits per second.
Optical fiber cable e consists
of one or more filaments of glass fiber wrapped in protective layers. It
transmits light which can travel over extended distances without signal
loss. Fiber-optic cables are not affected by electromagnetic radiation.
Transmission speed may reach trillions of bits per second. The
transmission speed of fiber optics is hundreds of times faster than for
coaxial cables and thousands of times faster than for twisted-pair wire.
Network topology
Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.
Mesh
networking
is a type of networking wherein each node in the network may act as an
independent router, regardless of whether it is connected to another network or
not. It allows for continuous connections and reconfiguration around broken or
blocked paths by “hopping” from node to node until the destination is reached.
A mesh network whose nodes are all connected to each other is a fully connected
network.
Bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks.
Star networks are one of
the most common computer network topologies. In its simplest form, a star
network consists of one central switch, hub or computer, which acts as a
conduit to transmit messages. Thus, the hub and leaf nodes, and the
transmission lines between them, form a graph with the topology of a star. If
the central node is passive, the originating node must be able to
tolerate the reception of an echo of its own transmission, delayed by the
two-way transmission time (i.e. to and from the central node) plus any delay
generated in the central node. An active star network has an active central
node that usually has the means to prevent echo-related problems.
A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet.
Basic hardware Components for Networking
Network interface cards
A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.
Repeaters
A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI model.
Hubs
A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address. It works on the Physical Layer of the OSI model.
Switches
A network switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC (Media Access Control) addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches
Routers
A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet. In many situations, this information is processed in conjunction with the routing table (also known as forwarding table).
Programming Languages
The language we are using to give instruction to computer in a machine recognizable way is called programming language.
There are two major types of programming languages. These are Low Level Languages and High Level Languages. Low Level languages are further divided in to Machine language and Assembly language.
Low Level Languages
The term low level means closeness to the way in which the machine has been built. Low level languages are machine oriented and require extensive knowledge of computer hardware and its configuration.
Advantage of Low Level Languages
The only advantage is that program of machine language run very fast because no translation program is required for the CPU.
High level Language
Higher level languages are simple languages that use English and mathematical symbols like +, -, %, / etc. for its program construction.
Advantages of High Level Languages
Higher level languages have a major advantage over machine and assembly languages that higher level languages are easy to learn and use. It is because that they are similar to the languages used by us in our day to day life.
Compiler
It is a program translator that translates the instruction of a higher level language to machine language. It is called compiler because it compiles machine language instructions for every program instructions of higher level language. Thus compiler is a program translator like assembler but more sophisticated. It scans the entire program first and then translates it into machine code.
Higher Level Language --> (Compile) ---> Program --> Machine Language Program
Interpreter
An interpreter is another type of program translator used for translating higher level language into machine language. It takes one statement of higher level languages, translate it into machine language and immediately execute it. Translation and execution are carried out for each statement. It differs from compiler, which translate the entire source program into machine code and does involve in its execution.
