FOR COMPUTER-CONTROLLED
MESSAGE SWITCHING SYSTEMS
R. L. SHARMA
Collins Radio Company, Newport Beach, Calif.
(A summary of the paper presented at the IFIP Congress 65 held in New York City
and as published in the Proceedings of the IFIP Congress 65)
At present a great deal of confusion exists in regard to
the evaluation of the capability of a computer-controlled message-switching
system. Such a a confusion prevents one from comparing various complex
systems that are being developed by several industries. This paper attempts
to present a basis for evaluating and comparing complex controlled message-switching
systems.
A computer-controlled message-switching system can be basically specified by the following design parameters: (1) number of input and output lines and their characteristics such as speed and logic; (2) message statistics in regard to length (lm), number of addresses (µ
The capability and the performance of a computer-controlled message switching system can be specified by three basic limits.
1. Processor-Time Limit. This is the maximum number of input messages (NmI) that can be switched per hour as determined by the availability of the computer time. One can evaluate this as follows:
where 3600 = number of seconds per hour
FA = fraction of computer time available to application programs and I/O doperations
TmI = total processor-time spent per input message on account of application and I/O control programs, and character transfers to I/O device
The simplicity of Eq. (1) is in great contrast to the difficulty in obtaining the values of FA and TmI.
2. I/O Device Limit. This is the maximum number of input messages (Nm2) that can be switched per hour as determined by the nature and load on the various I/O devices such as disc file and magnetic tapes. One can evaluate this as follows:
Nm2 = 3600/ Tm2 ................................................................(2)
where 3600 = number of seconds per hour
Tm2 = total time spent per input message on I/O devices such as disc file and/or magnetic tape
The solution of Tm2 requires a generous use of probability theory, statistics, queuing theory, combinatorics, and system logic.
3. Output Channel Limit. This is the maximum number of input messages (Nm3) that can be sent per hour as determined by the the number and types (speed and service logic) of output channels. One can evaluate this limit as
where µ = traffic multiplication factor
lmo = average length of an outgoing message in characters
No = total number of output channels
i = ith channel
fui = fraction of the time an ith output line can be utilized for transmission of messages
tci = character duration on the ith output channel in seconds
Based on the above limits, one can plot the capabiliity and the performance curves. The capability curves can enable the design engineer not only to evaulate the system bottlenects and find means to design improved programs or hardware to extend the capability, but also to compare several complex systems. The performance curves can yield the grade of service a customer is getting at various input-message loads.
A computer-controlled message-switching system can be basically specified by the following design parameters: (1) number of input and output lines and their characteristics such as speed and logic; (2) message statistics in regard to length (lm), number of addresses (µ
The capability and the performance of a computer-controlled message switching system can be specified by three basic limits.
1. Processor-Time Limit. This is the maximum number of input messages (NmI) that can be switched per hour as determined by the availability of the computer time. One can evaluate this as follows:
NmI = 3600 (FA)
/TmI .........................................................(1)
where 3600 = number of seconds per hour
FA = fraction of computer time available to application programs and I/O doperations
TmI = total processor-time spent per input message on account of application and I/O control programs, and character transfers to I/O device
The simplicity of Eq. (1) is in great contrast to the difficulty in obtaining the values of FA and TmI.
2. I/O Device Limit. This is the maximum number of input messages (Nm2) that can be switched per hour as determined by the nature and load on the various I/O devices such as disc file and magnetic tapes. One can evaluate this as follows:
Nm2 = 3600/ Tm2 ................................................................(2)
where 3600 = number of seconds per hour
Tm2 = total time spent per input message on I/O devices such as disc file and/or magnetic tape
The solution of Tm2 requires a generous use of probability theory, statistics, queuing theory, combinatorics, and system logic.
3. Output Channel Limit. This is the maximum number of input messages (Nm3) that can be sent per hour as determined by the the number and types (speed and service logic) of output channels. One can evaluate this limit as
where µ = traffic multiplication factor
lmo = average length of an outgoing message in characters
No = total number of output channels
i = ith channel
fui = fraction of the time an ith output line can be utilized for transmission of messages
tci = character duration on the ith output channel in seconds
Based on the above limits, one can plot the capabiliity and the performance curves. The capability curves can enable the design engineer not only to evaulate the system bottlenects and find means to design improved programs or hardware to extend the capability, but also to compare several complex systems. The performance curves can yield the grade of service a customer is getting at various input-message loads.