|
The following questions are to be answered while reviewing the following text...
1. What is the name of the computer you are calling and to what mode must it be set?
2. list some of the services that you can call up on a computer (10 items)
3. What is remote computing?
4. What is a null-modem cable used for?
5. What is 'E-mail'?
6. What is meant by "real time" conferencing?
7. What is the advantage of using a packet switching network. '' How does it work'?
SAVE AND ** E-MAIL YOUR "WIDE AREA NETWORK " DOCUMENT FOR GRADING ..... /14
Once you feel confident that you have completed this lesson, e-mail your document as an attachment to Mr. Dunning at the
following address:
dunning_r@fc.sd36.bc.ca
Your document should include the appropriate file extension in order for the formating to remain in transmission.
For sending documents from Apppleworks, use the extension ".cwk". A correct file name and extension would look
similar to:
L3wideareanetworks.cwk
Notice that any spaces in the file name have been removed and an indicator of which lesson (L3) has been added.
The assigned value for this assignment will be returned once it has been graded.
Wide Area Networks
OBJECTIVES
After completing this topic, you will be able to:
Describe wide area networks
List and briefly describe computers that you can call
Explain the purpose of packet switching networks
Many users want to call computers that are not connected into a local network. To do so, they dial up these computers
using their modems, which are connected to the telephone lines. These telephone lines are also referred to as a WIDE AREA
NETWORK Using this network, you can call other computers, information services like CompuServe, or bulletin boards set up
by companies or Individual users. The computer that you call is the host computer. The host computer can be the computer that
runs the information service, a mainframe or minicomputer, a PC running a bulletin board, or another computer running a communications
program.
You can communicate with thousands of computers through telecommunications. They fall into four classes:
* Information services that offer a varied of databases and other services. You must subscribe to the service and are
then billed for the time you are connected to the service.
* Electronic mall services are available for sending messages and mail. Your message is stored by the computer and then
forwarded to the person it is addressed to when he or she logs on (signs on) to the service.
* Bulletin boards are set up by individuals or groups. You can call them without charge.
* Private wide area networks set up by corporations are open only to members of the company.
Calling Other Computers
You can call any other computer that is also equipped with a modem. To do so, the computer you are calling must be on, running
a communications software program, and set to answer mode. Besides calling other computers you can use your computer to answer
incoming calls. This is handy if, for instance, you want to set up your own Internet Web page or Web Page Server, and you
are not sure when your office will call for this month's income statement and you want to go out to lunch.
To use your computer to answer and record incoming calls. You need an auto answer modem: most autodial modems can answer
the phone as well. If your modem allows you to set the number of rings before it answers the phone you may have to adjust
this setting. Some communications programs let you assign passwords. Callers are prompted to enter the password and are usually
given three tries to get it right. If they enter the correct password, communications continue. If not, the modem disconnects
and hangs up the phone.
Remote Computing
What if you are at home and you want to find a file on your computer in the office? You can do so by using remote computing.
With remote computing your home computer can call the office computer, which must be running a remote computing program or
a regular communications program set to host mode, to search for files and even run applications programs. The keys you press
on your keyboard in this mode do not affect your computer: rather, they control the computer you are connected to. The information
displayed on your screen is the same information displayed on the remote computer's screen. These programs were originally
developed by support services that wanted to be able to check a user's computer from a distance. The usefulness of these programs
has led to their being made available as standalone programs and incorporated into many communications program.
Because you can access files and programs on the remote computer, most programs of that kind are designed so that you
can protect your computer from unwanted intruders by assigning passwords. Users without the correct password cannot gain access
to the computer.
Hard Wired Computers
You can also wire two computers together so that they act just like a wide area network. This is useful when you want
to exchange files between two computers that are not part of a network and are located close to each other. To do this you
use a special cable called a null modem cable to connect the two computers. This cable is just like the one you use to connect
a stand alone modem to your computer but two wires have been reversed. When calling a computer connected in this way, you
follow all the same procedures you use to call one over the phone lines but you don't enter a phone number. The other computer
answers automatically when you select it for a call.
Calling Information Services
There are many commercial information services that you can subscribe to. For example, CompuServe, established in 1979, is
a typical information service. Some of the services it offers are:
~ News bulletins from AP and The Washington Post
~ Weather reports for any area of the country
~ Sports scores
~ An electronic encyclopedia
~ Electronic mail
~ Home shopping and banking
~ Discussion forums on various topics
~ Computer games
~ Home management programs (for example, Balancing Your Checkbook)
~ Travel reservations
~ Business news
~ Stock quotations
~ Standard & Poor's analysis
~ Brokerage service
~ Electronic conferencing
~ A business reference library
~ Personal finance programs (for example. Calculating Your Next Raise)
~ Forums for personal computer users
~ Services for professionals in aviation, Legal, medical, engineering. etc.
Calling Electronic Mail Services
One of the major uses of wide area networks is the distribution of electronic mail (also called E-mail). E-mail services
are provided by both commercial and private networks. HOTMAIL and YAHOO! are typical of the commercial electronic mail services
available to microcomputer users.
o Electronic mail is transferred from the originating computer to the service providers Domain Server. There it is routed
using the next available computer to either it's own internal mailing service, for retrieval by the person it is intended,
or to the recipients host service where it is stored until retrieved.
o Bitnet connects many colleges and universities.
o ARPA net connects government researchers in colleges and industry.
o BIX connects serious computer users.
Using these networks users can teleconference. They can leave messages for each other to be read later or if two users
call at the same time they can type messages back and forth. ICQ is a good example of what has become real time conferencing,
that is, instant messages between several people on line all at once. With the advent of video conferencing, the computers
become instant communications forums for many users at once, with the availability to be able to see each other.
Packet Switching Networks
When you call an outside service like CompuServe you do not have to pay a long-distance rates. If you use a service like
Telus or Shaw a monthly charged is assessed for the time you use. The services are designed to connect computers around the
country. They have access ports (also called nodes or ports) in hundreds of cities throughout the world. For example, Telus
and Shaw have 100's of thousands of access points in over 700 cities and 67 countries. To use the service you dial the phone
number of the local access point using a local telephone number. If your town does not have one you may have to place a long-
distance call to the nearest town that does. When you connect with the network you indicate the service you are calling the
network then takes your local call and sends it to that service. These services work only to the computer you are calling
is also on the system.
Packet switching networks transmit digital data. Since they pack a lot more data onto the same lines they are generally
cheaper than placing a long-distance call directly to the computer over any available phone line. When you are connected to
a phone line you use only a small part of its capacity and much of the time you are connected no data is being sent or received.
Packet switching networks use the same kinds of lines but package your data along with that of other users. By time-sharing
the lines more data can be sent, and the lines are used more efficiently, which lowers the cost for all users. Moreover,
the network's charge you based on the amount of data you transmit rather than the time you are connected.
Since packet switching networks generally connect fixed points at the host end packet switching companies have introduced
a type of service that lets you connect with any phone number in a given area. These services like Telus and Shaw, allow you
to dial a local number to access the network. You then dial the area code you want to call. and you are connected to a modem
at that end from which you can dial any number in the remote city. These systems are widely used to connect with out-of-town
servers that are not fixed nodes on the network.
|
