Browse Prior Art Database

Automatic SPEED Reduction and Switched Network Back-Up

IP.com Disclosure Number: IPCOM000035137D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 61K

Publishing Venue

IBM

Related People

Bell, RA: AUTHOR [+3]

Abstract

A process is disclosed to automatically put a communication line in back-up speed and to establish a switched network back-up or SNBU connection on the line whenever transmission throughput rates drop to an unacceptable level. The process assumes that IBM LPDA (link problem determination aid) version 2 modems are in use.

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Automatic SPEED Reduction and Switched Network Back-Up

A process is disclosed to automatically put a communication line in back-up speed and to establish a switched network back-up or SNBU connection on the line whenever transmission throughput rates drop to an unacceptable level. The process assumes that IBM LPDA (link problem determination aid) version 2 modems are in use.

The speed of an LPDA 2 line can be changed by an operator request. This is normally done in an effort to improve the transmission quality of the line. The overall throughput will hopefully be greater at the reduced speed because there will be less time wasted on lengthy error recovery procedures (ERPs). The original speed can be restored if the line quality improves.

LPDA 2 modems provide a command for changing line speeds (SET TRANSMIT SPEED) and, as such, have a built-in mechanism for improving line availability and enhancing error recovery. Currently, however, there are no automatic procedures in place that take advantage of this capability. It is up to the operator to manually reduce the speed when it becomes desirable to do so. The disclosed process removes the need for operator intervention in reducing line speeds when the performance of the line warrants such a measure. Any programmable product that supports LPDA 2 modems has configuration definition capability and its own error recovery procedures can take advantage of the new procedure.

A 'speed reduction threshold' must be computed by the configuration definition program for LPDA 2 lines. The threshold is passed to the control program. The threshold will be a percentage of the total retries specified (the suggested threshold is 80%). If the automatic speed reduction process is not to be performed, then a threshold of zero will be passed. Zero will be passed in two cases; the first is when the speed reduction threshold is less than five. It would be premature to reduce the speed of a line because of such a small threshold. The second case is when the user wants to override the function.

The control program will keep a total count of all of the error recovery procedures that are executed on a line during any one cycle (the number of ERPs that are required to recover from a single failure). If the total ERP count reaches the speed reduction threshold, and it is permissible to automatically reduce the speed (the threshold was not zero), then the LPDA 2 automatic speed reduction procedure can be started.

The process will first send a SET TRANSMIT SPEED command to the modem with a request for its backup speed. The control program will remember that backup speed has been invoked (to avoid trying it again later in another ERP cycle). It will also set a special speed reduction timer. The purpose of the special timer is to prevent the backup speed from running forever, and to insure that it continues to run, once invoked, until it is safe to return to a higher speed.

Once backup speed has been invoked, it will...