Browse Prior Art Database

X21 Automatic Back-Up on Switched Line

IP.com Disclosure Number: IPCOM000116811D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 78K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

Up to now, if it were desirable to install a back-up channel on an existing network, it was necessary to connect an other communication element: DCE2 in parallel of the DCE1, and when the NETWORK LINE 1 was broken, the operator had to manually set the new connection and to start the routed communication. This solution is huge and slow. In addition, this approach needs an operator present to check very often the status of the link.

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This is the abbreviated version, containing approximately 58% of the total text.

X21 Automatic Back-Up on Switched Line

      Up to now, if it were desirable to install a back-up channel on
an existing network, it was necessary to connect an other
communication element:  DCE2 in parallel of the DCE1, and when the
NETWORK LINE 1 was broken, the operator had to manually set the new
connection and to start the routed communication.  This solution is
huge and slow.  In addition, this approach needs an operator present
to check very often the status of the link.

      With the AUTOMATIC X21 SWITCH BACK-UP, it is now possible to
set a backward communication line automatically.  The process is
based upon a box constituted of a hardware state machine analyzing
all the states of the T,C,R and I leads of the X21 leased link
between the DTE and DCE1 in order to detect an eventual break, then
the states between the DTE and the DCE2 for the future connection of
the back-up backward channel.  Finally, the communication is switched
between DTE and DCE2 on the NETWORK LINE 2.

      Timing description - Define a starting point which is the
normal communication link between the DTE and DCE1.  During this
time, C and I leads are 'on'.  This state is state 0 of the state
machine and the state 13 of CCITT.  When the communication is broken,
I = 'off' and the state machine is in state 1.  In this state, a 24
time bit timer is started.  One time bit after state 2 of the state
machine, set the T lead 'on' at DCE2.  It is the state 18 of CCITT.
When tim...