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).

Electronic Mail (E-Mail)

Sending Electronic Mail, or E-Mail, using computers is similar to sending letters through ordinary mail. When you write a letter, address it and post it, it is collected, transported and delivered at that address.

In a network, each user is given a unique identification, called E-Mail address. If you type the letter and the E-Mail address of the receiver, the E-Mail facility will take care of sending it over the network to the right person. You can send a message to someone in another office, another city or another continent with equal ease, using your computer.

While most WANs like CompuServe also offer E-Mail as one of their services, there are networks set up specifically for this purpose. Examples of such networks are MCl-Mail and Telecom Gold.

Receiving, storing, forwarding and monitoring of mail are handled by dedicated software called E-Mail software. Some well-known E-Mail software are cc:Mail and Microsoft-Mail.

The advantage of E-Mail is that the receiver's machine need not be working when the mail arrives. It is put in the receiver's mailbox, that is essentially a subdirectory that stores all the mail received. When the machine is accessed, the user is informed of the arrival of mail. Since E-Mail is very fast and reliable, many offices and universities have started using it for sending letters, memos and applications, instead of normal mail.

Facsimile or FAX

Facsimile or FAX is another area where computers are taking over. FAX machines have been used for a long time to transfer documents by scanning and sending over telephone lines.

You can plug in an add-on card, called the FAX card, into your PC. This will enable you to send the file on the disk to a FAX machine at the other end, and vice versa.

On a Local Area Network, if the FAX card is installed on one PC, other workstations of the LAN can utilize its services to send FAXs.

FAX Machine

Requirements to Connect your PC to a Network

Unlike a Local Area Network, where the workstations are normally connected through cables, connection to a Wide Area Network is done through telephone lines, and so a telephone connection is a pre-requisite.

To connect to a WAN, you need a device called a modem, and a communication software for dialing and establishing a connection with another PC. ProComm, ProComm Plus, pcANYWHERE, Telix and Crosstalk are some well-known communication packages.

Lastly, you must subscribe and get an account to become a user of a WAN or BBS that you want to use.

The general features provided by a communication package are:

• Operation in host and remote modes: If the communication software is running in the host mode on your computer, other computers can connect themselves to it and utilize its services. Your machine is called the host as it provides its resources to the others. When you connect to another host and utilize its services, you are said to be a remote user. In host mode, the communication software can handle the task of providing services while the host computer can be left unmanned.
• Sending and receiving of files: This could be used to send a file to one or multiple destinations. Files are normally compressed and then transferred to save time on the network.
• Automatic logging of incoming data to printer or disk: You may want to use this when you want messages/files that are received to be saved on disk or printed without prompting and disturbing your other activities on the PC.
• Recording and playback of sessions and calls: This helps you keep track of all the calls made, duration and amount of data transfer for each one of them. You can also re-run a call. This is useful if the transfer of the same data has to be repeated.
• Providing a Process Control Language: This helps you to program repetitive functions such as unattended file transfer to multiple destinations after business hours.

Communication

A Network user can afford to be sociable. We are referring to the facility that helps a LAN user talk to other users by sending short messages on their screen. First of all, how does a user find out who the neighbors are?

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USERLIST Command

The USERLIST command displays the list of other users who have logged into the LAN.

The command, USERLIST when typed at the command prompt displays the list of login ids of users logged in and other details, as given in Figure.

Output of the USERLIST Command

In the above list, the login id with an asterisk is your login id.

The command USERLIST /A gives additional information. It includes the network numbers and node addresses where the users are working. The connection number gives the serial number of the users in the order that they have logged in (refer Figure).

Output of the USERLIST/A Command

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SEND Command

This command allows the user to send brief messages to other users or user groups. The messages can be up to 45 characters. The command,

SEND "How about lunch?" TO USER JOE

will flash the message, How about lunch? on the screen of the workstation where JOE has logged in. You may include more than one user in that command, if you wish.

The command,

SEND "MEETING TODAY AT 3.00 P.M. IN ROOM NO. 5" TO GROUP MKTG

will flash the message on the screen of everyone belonging to the user group MKTG.

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BROADCAST Command

This command flashes a message on the screens of all the users who have logged in. The message can be up to 60 characters and appears on line 25 of the screen. Thus, the command

BROADCAST There is a fire in the office. Head for fire exit.

should have the desired result. Note that the message need not be in quotes. The BROADCAST command can only be used from the server prompt and not from a workstation.

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CASTOFF Command

You can give this command at the command prompt, and any user who sends you a message will get a display on the screen informing him or her that the message was not conveyed. CASTOFF does not block messages that have been flashed by the BROADCAST command.

To do this, the command CASTOFF A can be used.

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CASTON Command

If you have turned off receipt of messages and wish to establish links with other fellow-users again, you use the CASTONcommand.

List the components in a communication process.

Sender, Receiver and Medium.

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