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Dynamically Determining the Appropriate Call Back Number for Disconnect And Call Back Schemes

IP.com Disclosure Number: IPCOM000120507D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 113K

Publishing Venue

IBM

Related People

Barclay, AS: AUTHOR [+2]

Abstract

SNA short hold mode (SHM) augments the basic SNA support of switched networks by releasing the switched connection during idle periods to save transmission costs. This disconnect/reconnect process is performed at the Link Service layer without disrupting the end-to-end associations at any higher layer. This support was developed for use with Public Data networks offering the X.21 interface, but it is applicable to any type of switched network in which a disconnect and call back scheme is economically viable.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Dynamically Determining the Appropriate Call Back Number for Disconnect
And Call Back Schemes

      SNA short hold mode (SHM) augments the basic SNA support
of switched networks by releasing the switched connection during idle
periods to save transmission costs.  This disconnect/reconnect
process is performed at the Link Service layer without disrupting the
end-to-end associations at any higher layer.  This support was
developed for use with Public Data networks offering the X.21
interface, but it is applicable to any type of switched network in
which a disconnect and call back scheme is economically viable.

      The initial SHM architecture, which supports SNA PU T2.0 type
nodes, required that the "exact" recall number be included in the
Exchange Identification (XID) frame that is exchanged during the
initialization procedure between the "HOST" and T2.0 nodes.  This
prevented national and international calls from being mixed in the
same port group.

      This limitation was overcome in the SHM architecture for PU
T2.1 nodes by the development of an algorithm for dynamically
determining whether the local or international form of the X.121
address should be used during subsequent recalls.  During the initial
connection and subsequent reconnections, an XID frame is exchanged
containing the X.121 international data number.  The dial digits
contained in the XID are processed to determine the proper number to
be used when recalling the adjacent node following a period of
inactivity.

      The CCITT recommendations X.121 and E.164 define international
numbering plans (phone numbers) for X.21 public data networks (X.121)
and Integrated Services Digital Networks (E.164).  These two plans
provide the basis for the interworking of X.21 public data networks
as well as for Integrated Services Digital Networks (ISDN) on a
worldwide basis.

      The X.121 address (number) consists of a four-digital data
network identification code (DNIC) followed by a network terminal
number (NTN) of up to ten digits.  The ISDN E.164 numbering scheme
has similar provisions, with a country code (CC) followed by a
national destination code (NDC) and a subscriber's number (SN), all
of variable length.

      When making an international call, there is generally a
requirement for a prefix (or access code) in addition to the
international data number to access the appropriate facilities for
international interworking.  This prefix is network spec...