Browse Prior Art Database

Equitable, Half-Duplex Polling for SDLC With Priority for Output

IP.com Disclosure Number: IPCOM000101984D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Fisher, ME: AUTHOR [+2]

Abstract

On a half-duplex SDLC multipoint line, when priority is given to polling stations with output, a 'Fair Polling Timer' is used to ensure that all remote stations are polled equitably, even those with no output. When the timer pops, those stations which have not yet been polled will be polled.

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Equitable, Half-Duplex Polling for SDLC With Priority for Output

       On a half-duplex SDLC multipoint line, when priority is
given to polling stations with output, a 'Fair Polling Timer' is used
to ensure that all remote stations are polled equitably, even those
with no output.  When the timer pops, those stations which have not
yet been polled will be polled.

      The details of the polling methodology, when using the fair
poll timer, are as follows:
-  If primary SDLC has no data for any station, all remote stations
will be polled with Receive Ready (or Receive Not Ready) frames in
the sequence in which they were opened.
-  If data becomes available for any remote station, the sequential
polling of stations will be interrupted at the next opportunity (when
a response is received from the last polled station), and primary
will send data to that station.
-  To prevent primary from sending continuous output data to a single
station when primary also has data to send to other stations, an OUT
LIMIT will be used.  The 'out limit' tells primary to send
consecutive, extra sequences of information frames to a remote
secondary station before it stops sending to that station.  When it
stops sending, primary will look for other stations in the poll list
for which it has data and transmit to them using their respective out
limits; if, after checking the other stations, primary finds data for
only one station, primary will continue transmitting data to just
that station.

      For example, with an out limit of zero, primary will send a
number of information frames up to the 'maximum frames outstanding'
count, wait for a response, then check for other stations with
output.  With an out limi...