Browse Prior Art Database

Modem Synchronization Protocol

IP.com Disclosure Number: IPCOM000117215D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Fisk, BE: AUTHOR

Abstract

When a pair of modems first connect, it is not easy to determine exactly when user data starts to flow (as opposed to modem messages and other spurious data generated when modems first connect). In order to establish clearly when user packets of data start to flow some sort of protocol exchange is required.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 54% of the total text.

Modem Synchronization Protocol

      When a pair of modems first connect, it is not easy to
determine exactly when user data starts to flow (as opposed to modem
messages and other spurious data generated when modems first
connect).  In order to establish clearly when user packets of data
start to flow some sort of protocol exchange is required.

      In order to accommodate protocol updates it is also desirable
for a sending modem to be able to establish which version of a
particular protocol is observed by the remote modem.

      The following simple, two byte, protocol may be used to
synchronize a pair of modems observing the same protocol version:
  1.  Send the character 'X' at periodic intervals (say 250
       milliseconds) until an 'X' is received from the remote modem
  2.  Once an 'X' is received send an 'X' followed by a 'Y' then wait
  3.  Once an 'XY' pair is received then the synchronization is
       complete
  4.  If, however, after sending the 'Y' a character other then 'X'
or
       'Y' is received then the protocol reverts back to step 1
  5.  If, after some fixed number of 'X's have been sent (e.g., 100)
       without an 'XY' pair being received then the protocol is
       terminated and is deemed to have failed to synchronize
  6.  In order to extend this to determine what protocol version is
at
       the remote end the protocol is extended as follows
  start:      count = 0
  sendZ:      Send the character 'Z'
                increment count
                Wait for defined period
                If...