Browse Prior Art Database

Dynamic Adjustment of Frame Size Based on Transmission Error Rates

IP.com Disclosure Number: IPCOM000122232D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 90K

Publishing Venue

IBM

Related People

Kiel, HG: AUTHOR [+2]

Abstract

A Work Station Controller (WSC) provides attachment of multiple work stations to a computer system via some type of communication protocol. Transmission error rates can be used to automatically adjust frame sizes on read and write operations to individual work stations. An SNA/SDLC communications implementation is also discussed.

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This is the abbreviated version, containing approximately 52% of the total text.

Dynamic Adjustment of Frame Size Based on Transmission Error Rates

      A Work Station Controller (WSC) provides attachment of
multiple work stations to a computer system via some type of
communication protocol.  Transmission error rates can be used to
automatically adjust frame sizes on read and write operations to
individual work stations.  An SNA/SDLC communications implementation
is also discussed.

      Work stations can include dependent displays, programmable work
stations, printers, or other devices.  In some protocols, work
stations are allowed to cable-through, where multiple work stations
can attach to the same communication cable.  A typical local WSC with
attached work stations is shown in the figure.  This article also
applies to remote WSCs which attach to the host processor via a
communication line instead of system bus.

      This article involves the WSC Licensed Internal Code (LIC)
choosing the frame size based on transmission error rates to the
specific work station.  When transmission errors are frequent, frame
size is reduced.  When transmission errors are infrequent, frame size
is increased to the largest supported size.  The result is large
frame size on good quality communication cables and small frame size
on poor quality communication cables, where adjustment occurs
dynamically.

      For each work station, the WSC stores the current maximum frame
size being used for reads/writes and a count of successful full frame
read/writes.  The layer of LIC which handles the work station
communication protocol will break read or write requests into
multiple reads or writes if the size is larger than the current
maximum frame size being used.  As reads/writes are successful or
unsuccessful, the maximum read/write frame size is adjusted as shown
below.

      When a transmission error occurs requiring retry of a read or
write operation (for example, parity or length check), the following
steps occur:
1.  If the retry count exceeds the retry limit (for example, 16), a
permanent error is logged and the work station is taken off-line;
steps 2 through 5 are skipped below.
2.  The retry count is incremented.
3.  The counter of successful full frame reads/writes is set to zero.
4.  If the current maximum read/write...