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Mechanism for Bandwidth Adjustment in an ATM Network in Case of Intermittent

IP.com Disclosure Number: IPCOM000116634D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 109K

Publishing Venue

IBM

Related People

Suffern, ES: AUTHOR [+2]

Abstract

The concept of an ATM Inverse Multiplexer (AIM) has been previously presented to the ATM Forum Technical Committee describing a cost effective mechanism to bring ATM network access to users needing bandwidths between T1/E1 and T3/E3. These previous descriptions have centered around definition of multiplexing ATM cells, with requisite ATM processing in the AIM device. To enable users with bandwidth needs less than T3/E3 rates, but greater than T1/E1 rates, and to access ATM networks in a cost effective manner, a T1 inverse multiplexer might be utilized with an enhanced ATM physical layer specification.

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

Mechanism for Bandwidth Adjustment in an ATM Network in Case of Intermittent

      The concept of an ATM Inverse Multiplexer (AIM) has been
previously presented to the ATM Forum Technical Committee describing
a cost effective mechanism to bring ATM network access to users
needing bandwidths between T1/E1 and T3/E3.  These previous
descriptions have centered around definition of multiplexing ATM
cells, with requisite ATM processing in the AIM device.  To enable
users with bandwidth needs less than T3/E3 rates, but greater than
T1/E1 rates, and to access ATM networks in a cost effective manner, a
T1 inverse multiplexer might be utilized with an enhanced ATM
physical layer specification.

      Since each transmission path is physically separate, there is a
very real possibility that one line will degrade in quality or fail
entirely while the others continue to operate.  In this case the user
does not want the transmission to stop when it is possible to have
transmission continue, but at a reduced bandwidth.  Figs. 1 and 2
depict the signal flow to allow the continuity of transmission if one
of the T1 lines either degrades or fails entirely.

      T1 framers automatically monitor the status of all T1 channels
and signal the processor if one or more of the T1 channels should be
dropped due to sub-standard performance, or the detection of a major
alarm.  Any faulty or sub-standard T1 span will 'fallback' out of
service, until it subsequently is observed to be free from defect and
can be restored to service.  When a 'fallback' T1 line is taken out
of service, the remaining T1 lines are realigned to carry the entire
Data Terminal Equipment (DTE) data stream.  Since the inverse
multiplexer sources the clock to the DTE, automatic rate throttling
is provided.

      Fallback can be coordinated between the originating and
receiving ends of the T1 network via in-band signalling, utilizing
the first DS0 time slot of each T1 frame.  This signalling would
override the normal pseudo-random(PN) sequence used for alignment, so
no additional bandwidth is taken away from the payload to provide the
bandwidth adjustment function.  This in-band coordination of T1
fallback/recovery also eliminates the need for additional overhead
definition at the ATM cell level, as identified in previous AIM
presentations to the ATM Forum.

      A fallback management protocol between the two inverse
multiplexers can utilize defined codes to be transmitted in the first
DS0 time slot o...