Another key element of information technology is computer network. You know the information technology is the merger of computer and communications so that easy and quick information may be provided to the different users for their day-to-day task. Now a network is a source of communicating data or information among a set of computers either using some sort of cable or wireless media. In case of cable media, we will be using the communication channels of fiber optic cables or twisted pair cables (both shielded and unshielded or coaxial cables (including both thin and thick coax) and fiber optic. On the other hand, if wireless media is used for communication, then Satellite transmission, radio waves, infra-red waves, microwaves, mobile communication or any other such medium will be used to provide its channels for the communication of information.
A network may be defined as "the environment in which two or more computers are connected together with the help of certain specific media, which can transmit data and information to each other." As there are differences between data and information, the network that is responsible for the communication of information among a set of computers is called computer network whereas the one with the help of which simple data is communicated among inter-networked computer is called data communication network. As information technology specifically belongs to the delivery of information to users, computer networks are highly associated to this technology. A good example of computer network is the Internet and World Wide Web.
This is belongs to techniques of communication of information across an information network so that users in each section of a business organisation may be benefited. These communication techniques, their fundamentals and uses are discussed in the topic below.
- Technology of Workgroup Computing:
Workgroup Computing is an important technique. It is used for communication of information within the boundaries of some business organisation. Using this technique, different departments of an organisation may have information in time. This technique is used to arrange a set of computers in a logical manner is such a way that this set is identified by a unique name. This unique name may be any name e.g. name of the organisation or some other proposed name. Due to workgroup computing, its members can access resources shared by other computers within the same workgroup.
Each computer in a workgroup is responsible for its own security. An example of workgroup may be a network established among the different departments of an organisation e.g. a bank. One department can get benefit from information stored on workgroup member computer of another department of the same bank. Workgroup computing technology is very helpful in the communication of information through computer network. Thus sharing of information is easy for computer based information system. Some network operating system that are most appropriate for workgroup computing are Windows 95 and Windows 98. - The Benefits of Email;
One of several benefits that workgroup provides to its user is Email, which means electronic mail. Using this facility, the user of a workgroup can send or receive their messages regarding business or other interests of their employer / organisation. It is considerably beneficial when the organisation spread over a large area and direct meetings with one another are time consuming. Special websites of the Internet / World Wide Web servers are Yahoo, Hotmail, Lycos and so on.
Using email facility, the users can:
* Send or receive messages to / from other users of computer networks.
* Attache important document, pictures, audios and videos with their mails and send them to other people living anywhere in the wold through Internet.
* Get the latest information about any topic of interest e.g. jobs, admission, market, sports, stock exchange and what so ever by having membership of specific newsgroup.
There are many more benefits of Email, however using Email services the most important advantage is that information we want to send or receive may be transmitted within seconds across thousands of miles even from one continent to another in the world. The Email facility can be achieved through subscription to an Email server and making an account in it. This subscription takes place through a form that is provided by Email server filling and submitting which grants the user his / her Email account and address.
Email is also called offline communication. The receiving person doesn't need to be online or connected to Internet at the time of Emailing rather he / she can receive the message after days or months as long as his / her email account exists. The Email message remains stored on the specified email server computer. The receiving person gets it as soon as he / she connects the Internet and opens his / her email account. Chatting on the other hand is an example of online communication of information. Both sending and receiving persons must be online during the chatting. It is therefore considered as direct communication among the users of a computer network. - Internet:
A good example of global computer is the Internet i.e. a network of almost all computer networks in the world. It is thus working as a huge computer network. It is considered as the backbone of modern information technology. Now a days it contains World Wide Web (www) which is collection of several millions uploaded websites that exist in the world. These websites contain information about different fields of life. This information can be easily accessed if someone is connected to the Internet. The useful characteristics of Internet and World Wide Web are:
* Latest news about different matters of life may be obtained easily.
* Researchers are capable of reading the up[loaded research papers and other materials of scholars in a particular field to put forward their research work.
* Email and chatting may be used to send or receive instant messages to friends or relatives living far away in the world.
* Business companies are capable of advertising their products and services to the entire world.
There are many more advantages of Internet but in short, Internet is a very cheap source of gaining the latest information about the world. - LAN & WAN:
One of the important considerations of establishing a computer network is that of area in which the network will perform it functions. On the basis of this, there are two different types of computer networks i.e. LAN stands for (Local Area Network) and WAN stands for (Wide Area Network). - Local Area Network (LAN):
A Local Area Network (abbreviated as LAN) is a collection of computers and peripherals that are usually connected together by cables and is confined or bounded to one building, site, campus or a city. A LAN offers a mean of pooling network resources and information between a number of users. A central mini computer or mainframe computer with a number of "dumb" terminals attached to it is one form of LAN, but the term is most frequently used to describe a number of interlinked Personal Computer (PCs), often with a more powerful computer controlling the network.
A Local Area Network has several advantages over a collection of standalone minicomputers with respect to:
* Sharing of resources such as disk storage, printers and possibly a large powerful computer called server.
* Sharing of information held on disk drives that are accessible by all users of network.
* Sharing of installed software.
* Ability to communicate with other users on the network. This is not important when all computer are in the same room but can be very useful in case when the computers are distributed around a large building.
Components of LAN:
All LANs must have at least three basic components that are: - Workstation which are actually PCs or terminals
- File Servers or Disk Servers, which are special PCs or larger computers. Shared software resources are stored on them including networking software for monitoring the entire network operations.
- Cabling and connection hardware link the computers together. A special interface card or printed circuit board has to be inserted into each computer on the network. This card is used to give a unique identity and allow it is interact with other computers of the network. This card is called Network Interface Card (NIC) or LAN Card.
LAN may also have additional hardware such as printers and extra disk storage. Network printers are connected to computer designated as file server if files stored on it are shared by all other workstations. Each workstation on network may have its own processing power and disk storage (Floppy or Hard Disk) and printer but these are additional hardware. - Wide Area Network (WAN):
A Wide Area Network (abbreviated as WAN) is a network of computers over the wide geographical area possible across several continents. The communication may be via microwave or a satellite link. It also takes place through ordinary telephone lines or a computers from sender to receiver.
The use of global networks (including Internet) has increased enormously over the past few years due to:
* Changeover the telephone networks from old-style analogue to high-speed digital-technology.
* Reduction in cost of connecting to and using networks.
* Improved compression techniques for faster transmission of text and graphics.
The implementation of information supper highway is also expected in future. This will use a combination of telephone lines, satellite links, computer networks and multimedia to bring interactive two-way communication to many homes. The distinction between a television, a microcomputer and a telephone may become blurred when we cand ialup and download videos or TV programs on request, send electronic mail and browse the World Wide Web all from the same piece of equipment.
Such a network that is capable to sup[port voice, video and computer data communication is called an Integrated Services Digital Network (abbreviated as ISDN). An ISDN needs high-speed digital connections with a high band width to send video data for example for Video Conferencing or net-meetings in real time. A category of ISDN now a days is a DSL (stands for Digital Subscriber Line) which provides a mean of faster transmission of Audio, Video and Textual data or information. It must be noted that ISDN or DSL connections are provided by Tele-communication organisations of a country such as PTCL in Pakistan on payment of very high charges. Thus these lines are highly expensive. - Networking Concepts:
Following are some of the important networking concepts that must be known for establishment of computer network:
Client:
A client may also be called terminal. It is an application installed on workstation computers which requests for services or resources from the network server. In some network operating system such as Windows NT and Windows 2000, these applications are called clients whereas in some others like UNIX or LINUX, such applications are called terminals.
Server:
A server may also be called console. It is an application used to provide services or resources of computer network to client workstation on their requests. In Windows operating system, such computers on which servers are installed are called servers whereas from UNIX or LINUX point of view the are called consoles. As server computers are having various network resources and centeralised controls over the entire network, the entire client-server networks under the control of servers.
Peers:
Peers are servers as well as clients. The reason behind this is that in some operating systems, like Windows-95 or Windows 98, there is no central control due to absence of client and server applications. In such cases, the computers called peers share their resources in a cooperative manner. For example, if one peer has printer resource and the other one has scanner resource then these resources can be associatively shared between them. - Network Modals:
In the networking concepts we have discussed the different roles computers may play in a network. A network operating system also plays its vital rol to make a computer client, server or peer. Now depending on the types of network operating system and their network applications i.e. clients, servers or peers following are the different networking models: - Client- Server Model:
Different network operating system like Windows-NT, Windows 2000, UNIX and LINUX are used for client-server networks. Higher security measures and a centralised control of server on set of various network resources make the network strongly secure and safe for protection of information. However certain shortcomings also exist in client-server networks as such networks require the services of a network administrator for its proper look after. In case if server of the network fails due to any reason then entire network operations are badly suffered. Such networks are mostly used in a situation where security and privacy of data or information is a critical issue. Each user may have his / her rights of using the network. The network administrator gives these rights so that one user can't get the private data or information from account of another user without his / her permission. - Peer-to-Peer Modal:
Some operating systems like Windows-95 and Window-98 are used for working with such networks. There is a central control due to absence of server and client software. Each computer (peer) is a server with respect to its own resources and a client with respect to resources of another computer. All of administration work is on part of the users. Thus expensive services of a network administrator are not required. However the major shortcoming of peer-to-peer networking is that there is less security and privacy of data or information than client-server architecture. - Hybrid Network Modal:
The word hybrid means a mixture of two opposite qualities in one and the same thing. Now when both the client-server and peer-to-peer networking features exist in a network then such a network will be called hybrid network. The advantages of client-server network cancel the disadvantages of peer-to-peer may cancel the disadvantages of client-server whose services are still required due to the presence of client-server characteristics. Keep a network administrator may be expensive and that is a major drawback. - Networking Standards:
Standards are actually documented agreements containing technical specifications or other precise criteria to be used consistently as rules, guidelines or definition of characteristics in order to ensure that materials, products, processes and services are fit for their purposes. For example the format of credit cards, phone cards and smart cards are derive from International Standard Organisation (ISO). According to the standards for example 0.76mm thickness of card means that these cards can be used worldwide with same thickness. These International standards make life simple; increase the reliability and effectiveness of services and goods that we are using.
Different types of network standards may be used. For example.
* The number of switches in a hub or router.
* Licensing criteria for the number of computers to use a specific network operating system.
* Standards for cable media or bandwidth of communication channels etc.
These standards make networking more successful, efficient and reliable. Two wide categories of standards are: - De Facto Standards:
De fecto means "by fact" or "by convention". These standards are not approved by organised bodies however they have been adopted as standards through their widespread uses. De facto standards are often established originally by manufactures seeking to define the functionality of a new product or technology. - De Jure Standards:
De jure means "by law" or "by regulation" and as its name refers, these standards have been properly legislated by an officially recognised body.
Certain famous standards making bodies or organisation are listed one by one below: - The International Standards Organisation (ISO)
- The International Telecommunication Union-Telecommunication Standards Sector (ITU-T, formerly the CCITT).
- The American National Standards Institute (ANSI).
- The Institute of Electrical and Electronic Engineers (IEEE).
- The Electronic Industries Association (EIA) and
- Telcordia.
- Network Typologies:
The topology of a network may be defined as its physical layout i.e. the way in which computers and other equipment are connected. There are different basic layouts or typologies for networks. Following are the most commonly used typologies. - Star Topology:
Each node (computer or other device in star topology is connected to a central minicomputer which controls the network. Network signals travel from server to the stations along each individual station's cable. There is a polling system involved in which the file server pools each station in turn to see if it has a signal to send. The server then handles the signals as they are received. Star topology may also use a central platform in the form of a hub where cables from different computers are plugged and thus providing a mean of signal transmission.
These individual stations connected to the central platforms are also called node or devices. The topology has following advantages over its other counterparts: - If one cable fails then other stations are not affected by this failure.
- The performance of network is consistent even in case when the network is heavily used.
- There is no problem of collision among data signals as each station has its own individual cable to central platform i.e. server or hub.
- It is very easy to add new station to star network with out disrupting the network.
Few drawbacks may be found in this topology are: - Entire network is badly suffered when central server fails.
- Cable cost increases due to a large number of cables from individual stations to a central server or hub.
- Bus Topology:
A bus topology is that is which all of the devices or computers share a single cable. Information can be transmitted in either direction from any PC to any other. As several stations may want to transmit down the same line simultaneously, a popular scheme called "Ethernet" uses a collision system known as "Garrier Sense Multiple Access with Collision Detection" (abbreviated as CSMA-DC)to aviod collision among data signals. The mechanism of CSMA-CD is that before a station begins to transmit a signal of data, it conforms that the channel is not busy. In case when channel is busy, the station has to wait before transmission can begin. Once it begins transmission, it listens for other nodes which are beginning their transmission. IF the transmitted message collides with another transmitted message, both stations abort and wait for a random period of time before trying again. This all activity is controlled by the CSMA-CD protocol.
The diagrammatic representation of a bus network is in figure below.
In this diagram there are two terminators at the ends of cable connecting computers. These terminators are actually resistors and are used to absorb signal in case of ringing condition. Ringing condition arises when the signal send by a computer does not reach its target and thus creates disturbance in the network by moving here and there. The major advantages of this topology over other typologies are:
- It is very easy and inexpensive to install as it needs and the least amount of cable and is simple too.
- More stations or computer can easily be added without disrupting the network.
The main shortcomings of this topology are given as: - The whole network goes down if main cable fails at any point.
- Cable'e failure is difficult is isolate.
- The network performance degrades under heavy loads.
Ethernet is a famous real world network scheme of this topology. An Ethernet may be physically star or bus logically it is a bus and uses CSMA-CD for its working. Using this scheme only a single user can use the same communication line at a time and if there is a chance of collision then user has to wait till the line becomes clear for his / her data to be communicated. An example of this may be dialing a telephone number. If the phone line is busy mean that required phone number is engaged in communication then user may be to wait until that telephone connection line becomes free. In case when telephone line is engaged in communication there is a chance of collision. This is avoided by specific tone indicating that the phone line is busy in communication with someone else. - Ring Topology:
In ring network there is no central computer or hub. Each computer or station may communicate with any other in the ring with messages being specifically addressed to destination computer. A famous scheme called "token passing" is used in a token ring system. This scheme is used to pass a "message token" from one node to another one. A "message token" is actually a unique character sequence. Each node has a designated time a which it can removed token and adds message with address of the receiving node, sending node and some control bits. A receiving node i.e. computer or device acknowledges the receipt of a message by inverting a 1 bit field i.e. changes the bit from 1 to 0. The diagrammatic representation of ring network is given as under.
The arrows show that flow of takes place in a single anti-clockwise direct in a ring. There is no collision among message tokens passing in a ring.|
Certain advantages of ring network are: - There is no dependence on a central computer or file server and each node controls transmission to / from itself.
- Transmission of messages around the ring is relative simple with messages traveling in a single anti-colckwise direction.
- Very high transmission rates are possible in ring networks.
Few shortcoming that exist in this networking topology are: - The transmission between any two devices in network is disrupted with the breakdown of a single station. The reason is that each station regenerates the signal incase when it is not addressed for it.
- The entire network is disrupted in order to add new stations to the ring network.
Some real world networks based on this topology are Token-Ring and FDDI i.d. Fiber Distributed Data Interface. FDDI is implemented as a dual ring
- Mesh Topology:
Mesh is that topology in which multiple links exist among network computers. Mesh networks may be found into one of the following types: - True Mesh:
In true mesh the total number of links for "n" computers are "n(n-1)2" and every two computers in this network are directly connected to each other. When the total number of computer "n" is 6 then there will be total 15 links among them as demonstrated in the following diagram.
In this diagram representation there is a two-way communication of data across each link. - Hybrid Mesh:
In hybrid mesh total links are less then n(n-1)/2 for "n" computers. Each computer is not directly connected with each other computer in the network. If for example the total number of computers "n" is 6 and there are 9 links instead of 15 then such a network will be hybrid mesh.
This topology is based on multiple links between any two computers in the network and it has the following major advantages over other typologies. - Mesh network has high fault tolerance due to multiple links.
- Due to multiple links mesh network can work fine even under severe loads.
- Troubleshooting of mesh network is easy as compared to other networks. If data is not communicated between any two computers then it means that there is some fault in direct links between them.
Some shortcomings of this topology are given below: - Cable cost is too high due to multiple links. This cable cost may even be more than a star network in case of true mesh network among a large number of computers.
- It is also very difficult to maintain a true mesh for a large number of computers.
Even Mesh networks are rare in real world due to their shortcomings however a good example of Mesh network is the Internet in which every computer can be connected to every other computer directly (if we are connected with Internet). - Data Communication Protocol:
Up till now, we have discussed about the different mechanisms that are used for data communication from one computer to another one. However there are also some software that take an active part in the communication of data. In order to allow equipments from different suppliers to be networked, a strict set of rules (protocols) has been devised covering standards of physical connections, cabling mode of transmission, speed, data format, error detection and correction etc. Any equipment that uses the same communication protocols can be connected together. In other words we can say that the data communication software used to control the transmission of data is called a protocol. Some common examples of protocols are TCP/IP (Transmission Control Protocol/Internet Protocol), FTP (File Transfer Protocol), HTTP (Hyper Text Transfer Protocol) and so on.
Manufactures are gradually incorporating these standards in some of their products however it is unlikely that total standardisation will be achieved for sometime, if ever. Where two devices have different protocols they can sometimes communicate via a protocol conversion computer.
The OSI Reference Model:
The working procedure of data communication protocols and other software can be fully described by OSI seven layers reference model. OSI seven layers reference model. OSI is a non-tangible model and is very useful in understanding how equipments from one manufacturer could be connected with totally different equipments from some other manufacturer. This model is under the process of development since 1977. OSI stands for Open System Interconnection and here the openness means that every detail about the working of the data communication software can be understood by studying this model. This model has devised a hierarchy of the following seven layers so that each layer is a service or procedure according to which the data to be communicated is processed and is forwarded to the lower level layers at the sending point or the higher level layer at the receiving point.
The upper three layers of this model are called high-level layers as they are concerned with the software whereas the lower four layers are called low-level layers because they are concerned with the functions of different networking hardware. These layers are described one by one below in detail: - Application Layer:
It is the first high-level layer and is closest to the users. It is used for providing support to the phenomena of the transfer of information between end-users, application programs and devices. Several types of protocols that exist in this layer are covering specific and general applications such as accounting, entry control and user identification. - Presentation Layer:
This is the second high-level layer and accepts the processed data from application layer for further processing. The purpose of protocols in this layer is to ensure that different devices using data in different formats can communicate with each other for example, handling the conversion between ASCII and EBCDIC codes. It may also be used to carry out encryption to ensure the security of data during its transmission. - Session Layer:
This the third and last high-level layer of the OSI reference model and is actually the user interface to the network. When a user requests for a particular service from the network, this layer handles the dialogue. - Transport Layer:
This layer is the last low-level layer and fourth layer of the OSI reference model. This layer handles the data transmission between host computers by performing addressing and error controls to ensure a high quality data transmission service for the network. - Network Layer:
This the third low-level layer and fifth layer in the OSI reference model which has the function of performing tasks like routing of information around the network, connecting adjacent nodes in the network and also carrying out accounting functions to enable the network's owners to charge the users. - Data Link Layer:
This the second low-level and sixth layer of the OSI reference model. This layer is used to handle the data transmission errors caused by the corruption of data due to different types of interferences that affects physical data transmission media used in the networks. The techniques used for the receipt and acknowledgements of data by a receiver are handled through this layer. - Physical Layer:
This the last layer of OSI reference model and is the first low-level layer as it is closest to the hardware. This layer is concerned with standards for mechanical, electrical and procedural aspects of the interface devices. An example of such standards may be the number of pins contained within a network's connector. This layer is especially concerned with how the binary data is transmitted along the communication channels.
The diagrammatic representation of this layer-by-layer architecture of entirely different networking products and the way data is sent and received by them is given as follows: - OSI reference model gives a clear understanding about the working of communication software and equipments.
- OSI reference model when followed make different networking software capable to transmit their data with each other.
- This model provides a standard for the quality of communication between similar or different networking equipments.