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Method for Reducing Polling Overhead on Synchronous Data Link

IP.com Disclosure Number: IPCOM000121441D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 5 page(s) / 189K

Publishing Venue

IBM

Related People

Clarke, D: AUTHOR [+9]

Abstract

Disclosed is a method for reducing polling overhead on SDLC links with secondary station controllers that support multiple secondary stations. This method, called Group Poll for Secondary Controllers Supporting Multiple Secondary Stations, is an adaptation of the architected Group Poll for SDLC multi-point loop environments, and is based on the premise that polling overhead is reduced when a secondary station is given a response opportunity prior to its normal turn as defined by the primary station's polling list. When applied to secondary controllers supporting several secondary stations, this accelerated response opportunity results in reduced polling overhead on the T-P link.

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Method for Reducing Polling Overhead on Synchronous Data Link

      Disclosed is a method for reducing polling overhead on
SDLC links with secondary station controllers that support multiple
secondary stations.  This method, called Group Poll for Secondary
Controllers Supporting Multiple Secondary Stations, is an adaptation
of the architected Group Poll for SDLC multi-point loop environments,
and is based on the premise that polling overhead is reduced when a
secondary station is given a response opportunity prior to its normal
turn as defined by the primary station's polling list.  When applied
to secondary controllers supporting several secondary stations, this
accelerated response opportunity results in reduced polling overhead
on the T-P link.  Reduced polling overhead implies that the T-P link
is more available for data transfer, thus reducing transmission delay
and overall network response times.  Fig. 1 illustrates a sample
Group Poll environment.

      The implementation of Group Poll by a secondary controller can
be such as to increase the relative "fairness" of secondary station
response opportunities and improve the consistency of overall network
response times. Normally data is received at the primary station in
the order of the primary station's polling list.  The combination of
Group Poll and FIFO queuing by the secondary controller allows data
to be received at the primary station in an order that more closely
re sembles the order in which the data was received at the secondary
controller for transmission to the primary station.  This increased
ordering of secondary station transmissions reduces the probability
of extremes in end-to-end transmission delays, thereby increasing the
predictability and consistency of overall network response times.

      According to SDLC architecture, a secondary station must wait
for a poll from the primary station before it can transmit data.  In
a T-P environment with multiple secondary stations, a given secondary
station must wait for this response opportunity while the primary
polls the other secondary stations within the same controller.
Typically, the case that polls to these other stations does not
result in data transfer.  The polling opportunity then becomes
unproductive and contributes to the polling overhead of a waiting
secondary station.  However, in this multiple secondary station
controller environment, it is possible for a controller to determine
that a response opportunity for a supported secondary station will
not be used, and whether a poll to another one of its supported
stations would have resulted in productive data transfer.  The use of
Group Poll in this environment provides a mechanism that allows the
secondary controller the opportunity to determine which secondary
station has data to transmit and to transmit that data in response to
the Group Poll.

      In a Group Poll environment, the SDLC primary station is
responsible for determining wh...