Communications

You have already seen in the module on Local Area Networks how computers can be linked together to form networks, enabling them to communicate, share information and resources. While information requirements within a limited area (like an office building or university campus) can be handled by Local Area Networks (LANs), communication requirements beyond that need Metropolitan Area Networks (MANs) or Wide Area Networks (WANs).

In this session, you will see how the services available on Wide Area Networks help in expanding the usage of a PC. The rapid increase of such networks has been responsible for transforming the PC from an information-processing machine into a communications center.

Wide Area Networks may be commercial networks which anyone can subscribe or they may be run privately by companies for their internal use only. There are international networks with thousands of users as well as smaller ones run by local computer clubs. Computer equipment manufacturers have networks to give their customers the latest information on their products. Customers can also report problems or place orders through them.

Networks like CompuServe offer their users (subscribers) many useful facilities like:

• Communication with other users through E-Mail (Electronic Mail) or FAX (Facsimile).
• Transfer of files from one computer to another. You may want to send a file to a particular user, or you may want to share a game or utility that you have developed with other users. In such a case, you can upload (send) it to the network, from where other users can download it for their use.
• Access to centralized databases. These are like libraries on computers containing business, technical or academic information. They have complete text of publications or abstracts that you can browse through, as in a library. Some well known centralized databases are:
• Dow Jones & Co's Dow Jones News/Retrieval Service.
• Lockheed's Dialog Information Service. It has 518 separate databases covering science, engineering, business and economics.
• Mead Data Central's NEXIS/LEXIS. It offers full text from 15 newspapers like New York Times and 31 magazines like Byte, Newsweek and Business Week, etc.
• West Publishing Co's Westlaw. It allows lawyers to browse through court cases and federal regulations.
• Special Interest Groups (SIGs) or forums where you can ask questions, get responses and exchange information about your specific areas of interest, that could be medicine, cricket or computers.
• On-line services offered by various banks, airlines and shopping centers allow you to transact with them through the network.
• Support forums maintained by various hardware and software companies provide technical expertise and solutions to problems to their customers.
• Computing Time, i.e. allowing you to link to mainframes and utilize their processing capacity.

Wide Area Networks that offer such services are called Bulletin Board Services (BBSs).

Designing the Network's Layout

The term topology, or more specifically, network topology, refers to the arrangement or physical layout of computers, cables, and other components on the network.

A network's topology affects its capabilities. Choosing one topology over the other can impact the:

• Type of equipment the network needs.
• Capabilities of the equipment.
• Network's growth.
• Way a network is managed.

A network's topology implies a number of conditions. For example, a particular topology can determine not only the type of cable used but how the cable is run through floors, ceilings and walls. Topology can also determine how computers communicate on the network. Different topologies require different communication methods, and these methods have a great influence on the network.

The type of network you install will depend on a number of factors, including the:

• Network budget
• Network size
• Level of security required
• Physical layout
• Type of business
• Amount of network traffic

Peer-to-Peer Networks

In a peer-to-peer network, there are no dedicated servers. All the computers are equal and, therefore, are termed as peers. Normally, each computer functions as both a client and a server.

A peer-to-peer network has the advantage of simplicity in design and maintenance. It is usually less expensive to set up as compared to server-based networks. Peer-to-peer networks are also called workgroups. The term workgroup implies a small group of users.

Peer-to-peer networks are suitable for environments where:

• There are limited users (usually 10 or less).
• The users are located in the same area.
• Security is not an important issue.
• The organization and the network have limited growth.
• Users need to freely access data and programs that reside on other computers across the network

In a peer-to-peer network, there is no one assigned to be an administrator responsible for the entire network. Users administer their own computers. All users can share any of their resources.

Note: Network administration involves tasks like managing users and security, making resource available, installing and upgrading software.

Why Networks Exist

During the 80's, the concept of desktop computers working independently was very popular. This was, and still is called the stand-alone environment.

Slowly, businessmen all over the world began to realize that information was useful only when it was communicated between human beings. The process of distributing and processing information among, individuals, each with an independent desktop computer being slow and prone to error, led to the concept of connecting computers together to form computer networks.

Computer Networks

A computer network is a communication system where a group of computers and other devices like printers are connected by cables and other hardware. The data is shared between the computers. A network, besides facilitating data communication, allows resources to be shared among all the systems connected to the network (refer Figure 1.3). Thus, users on the second floor of a building can use the printer on the eleventh floor if their computer and the printer are connected to the network. This concept of connected computers sharing resources is called networking.

Computers that are connected in a network can share:

• Data
• Messages
• Printers
• Hard Disks
• CD-ROMs
• Modems
• Other hardware resources