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Dynamic Segmentation Size for CCITT V.120 Communications

IP.com Disclosure Number: IPCOM000102141D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Henderson, JG, Jr: AUTHOR [+2]

Abstract

CCITT Recommendation V.120 terminal adaptation for ISDN defines segmentation/desegmentation procedures for data sent between two terminal adapters via an ISDN, but a segment size negotiation procedure is not well defined or standardized. This article defines a method that a terminal adapter can use to dynamically determine the optimal V.120 segment size without user intervention. This article has the following attributes which are believed to be unique: - Use of trial and error to determine the optimal V.120 segment size. - Use of a binary split algorithm to reduce the number of successive segment size attempts required. - Use of a table of standard segment size values to further reduce the number of negotiation steps. - Automatic segment upward and downward resizing after initial negotiations.

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Dynamic Segmentation Size for CCITT V.120 Communications

       CCITT Recommendation V.120 terminal adaptation for ISDN
defines segmentation/desegmentation procedures for data sent between
two terminal adapters via an ISDN, but a segment size negotiation
procedure is not well defined or standardized.  This article defines
a method that a terminal adapter can use to dynamically determine the
optimal V.120 segment size without user intervention.  This article
has the following attributes which are believed to be unique:
-    Use of trial and error to determine the optimal V.120 segment
size.
-    Use of a binary split algorithm to reduce the number of
successive segment size attempts required.
-    Use of a table of standard segment size values to further reduce
the number of negotiation steps.
-    Automatic segment upward and downward resizing after initial
negotiations.

      The following defines a method where the TA dynamically adjusts
the segmentation size according to the presence or absence of a LAP-E
FRaMe Reject (FRMR) frame-too-large error condition without user
intervention (V.120 segments are carried over the ISDN connection
using LAP-E protocol).  It is assumed that there is a correlation
between the segment size and the largest acceptable LAP-E frame size.

      After the connection is first established, the TA sends the
largest segment that it is capable of.  On the reception of FRMR
frame-too- large error condition, the TA automatically reduces the
segment by half and retransmits the data.  If the error occurs again,
the segment size is reduced by half again and the data is
retransmitted again. If the segment is accepted, the next segment
size is increased to half way between the last unacceptable segment
size and the last acceptable segment size.  This process is repeated
until the acceptable and unaccept...