BITNET is an electronic data network which connects several thousand universities, colleges, and research institutions world-wide, with more being added regularly. BITNET also has connections to many other global networks, including the INTERNET, and CSNET. Technically, BITNET refers to the network based in the United States of America, with systems in other countries having their own appellations. However, BITNET is the term most often used for the global system as a whole. The United States sector of the BITNET is controlled by CREN (the Corporation for Research and Educational Networking.)
2. What is BITNET used for?
The purpose of BITNET is to provide a way for researchers, students, and faculty at different universities and research institutions to exchange information with each other in a timely manner. BITNET also serves a variety of recreational purposes. No commercial traffic is permitted on BITNET.
3. How does BITNET/CREN work?
Institutions on the BITNET are connected to one another by what are essentialy heavy duty telephone lines. All BITNET locations (often referred to as sites) are thereby part of an "electronic chain" through which data can flow. A very simplified drawing of a section of BITNET is shown here:
 
In the illustration above, the boxes represent machines connected to the BITNET, and the lines represent the connections between these systems via telecommunications lines.
BITNET is a "store and forward" network. This means that data is sent to the next site that is in the chain between you and the data's destination, and then are held there until the link is clear for it to continue. Using the sample region above, a data file being sent from site A to Site D would first go to site B, and then from there to site D.
A problem can occur if a link is down between machines. If the link between machines B and D is down, the file we just sent would have to wait until the link was restored to continue. If the file was going to site C, however, it would not be affected by the bad link.
For an analogy, the system may be viewed as interconnected data "highways" and a link failure as a "traffic jam."
4. How does BITNET know where to send all this data?
Much like the United States Postal Service, BITNET uses a system of addresses to determine the destination of data. Each address consists of two parts. The first part is the recipients account id at his/her machine. The second is the BITNET id for the recipients machine itself. For example, a sample account could be V1234D (account id) at TEMPLEVM (machine id). The address is usually expressed in one of two ways, depending on the system sending the data:
V5057U@TEMPLEVM
V5057U at TEMPLEVM
Both of these represent the same address.
On an IBM Mainframe (such as TempleVM) running the CMS operating system, the XXXXXX at XXXXXXX format must be used. The @ symbol is sometimes interpreted as a special "delete" character and can change the address.
Also, sometimes machines are set up so that when sending to another user on the same machine, a BITNET address is not necessary. On TEMPLEVM, mail sent to V1234D would be sent to that user's account automatically.
5. What kinds of communications are available via the BITNET?
There are three main kinds of communication avaialbel on the BITNET. These are interactive messaging, electronic mail, and file transfer:
A> Interactive Messaging:
Interactive messages are the fastest form of communication between users. Messages are transmitted immediately to the destination and appear on the target user's screen. Because these data packets are only one or two lines in length, they move through the system very quickly.
There can be several disadvantages to using interactive messaging. One, many systems managers do not like to have messaging used on their system, becuase it is inordinately wasteful of systems resources. Two, the recipient of the message must be logged in to their machine when the message arrives. If not, some form of a USER NOT LOGGED IN MESSAGE will be returned to the sender, and the original message disposed of. Three, if an intermediate link is down, a LINK DOWN message will be returned to the sender, and the original message discarded. Finally, interactive messages are generally limited to 255 characters or less.
The format for sending an interactive message is:
(IBM/CMS users) TELL (Userid) at (Address) Message
(VAX/VMS users) SEND (Userid) at (Address) Message
While fast, interactive messaging is by no means instantaneous. It may take a few moments for your message to arrive. Please be patient.
B> Electronic Mail
Electronic Mail is a slower, but more reliable way of sending messages to other users. Mail has three main advantages. One, mail can (theoretically) be any length. Two, mail is held for a user if that user is not currently connected to the system. Three, the same mail message may be sent to a number of users at one time. There are also some disadvantages. Mail is slower than electronic messaging, and may take more time to arrive at its destination. The larger the mail file is, the longer it will take.
If an intervening node is down, the mail file will be held until the "traffic jam" clears.
For more information on using MAIL check the appropriate chapter. (Additional chapters for different systems will be added later.)
C> File Transfer
File transfer is used to transfer large data files, or files in a non-text format from one user to another. Transfer speed is dependent on the size of the data file. The command to send a file under IBM/CMS is:
SENDFILE (Filename) (Filetype) (Filemode) to (Userid) at (Address)
For example: to send a copy of the LISTSERV BASICS file to the author on an IBM/CMS system, use the command:
SENDFILE LISTSERV BASICS to (account) at (Machine id)
Of course, files may be sent to you over the BITNET. Contact your systems people for more information on how to receive these files.
A note about BITNET II
Many sites are now switching to, or considering using, the newer BITNET II protocol, which allows for BITNET type file/data management over TCP/IP lines, such as are used for Internet connections. This allows for a greater speed of communication, and the dynamic nature of TCP/IP networks, as opposed to the linear arrangement of BITNET links, helps to avoid "traffic jams."
