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Item (3) is of much less importance because the amount of coding in each program is small and
because any given installation will have at most a few programs.
For most systems, the system capability will be inversely proportional to the amount of time
required to service a line, i.e.,
if
the time per line can be reduced 20 per cent with more efficient
programming, then the system has the capability to handle 20 per cent more lines with the same
hardware configuration. Another way of looking at the importance of the operating time used by a
program is this: Presume that system requirements specify that 10 ms are available in which to
service all lines once.
Then a program which requires 11 ms cannot be used unless the 10 ms
specification is changed, the number of lines reduced, or the 11 ms program made more efficient.
Because the amount of operating time
is so important, several special features have been
included in the DATANET-30 hardware to reduce the operating time. Writing the actual
coding at the assembler level is the best way to utilize these special features and attain the neces-
sary efficiency.
The amount of memory used for the instructions and tables in a program will determine how much
memory is left over for data storage.
Decreasing the program memory required will increase
the data storage memory available and help smooth out the peaks in system traffic, thus improving
the store and forward performance. In addition, for those applications which permit giving a busy
signal, more data storage memory will delay or possibly eliminate the point at which a busy signal
will have to be given because of a full memory. For those applications which do not permit giving
a busy signal, decreasing the memory required for the program will decrease the total amount
of memory needed in the system.
The actual coding effort for a system generally will be a small part of the cost of the system
because each piece of the total program is small and the total program will seldom be modified.
Since each piece of the total program is used frequently, the coding cost in obtaining the program
is small when compared to the operating cost of the program over its lifetime.
Message Switching Center
When operating as a message switching center, the configuration of the overall system must be
considered:
1.
Number and type of incoming/ outgoing lines--half duplex, full duplex, etc.
2.
Number of receive-only remote terminals
3.
Number of stations per multipoint line
4.
The speed of transmission on each line, if there are transmission speed differences in
the system.
5.
The handling of priority messages,
if
any
6.
Whether or not another DATANET-30 is included in the system
7.
Routing codes: multiple broadcast or single address
8.
Remote station identification codes
9.
Message format
10.
How communication with other networks will be handled
11.
Control of the system for beginning of day and end of day
12.
The type of remote terminal equipment and all operating characteristics.
The above list only partially covers the considerations necessary. After the characteristics
of each system have been determined, the programming can proceed.
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