Browse Prior Art Database

Callback Feature for X.21 Shorthold Mode/Port Sharing

IP.com Disclosure Number: IPCOM000061242D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Bentley, AM: AUTHOR [+2]

Abstract

The callback feature for X.21 Shorthold Mode/Port Sharing gives the Host system the capability to return a call to a Remote device when the Host's main ports are busy. To help free the X.21 PDN (Public Data Network) and Host SHM (Short Hold Mode) systems during periods of congestion, the callback feature is introduced. The exchange of a special SHM XID (Exchange Identification Information) between the Host port and the Secondary device allows the Host to call back the Secondary device when a Host port is available for connection. Therefore, during periods when the Host system is congested, the Secondary device trying to establish a connection goes into an answer mode and waits until the Host system is capable of receiving the Secondary.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Callback Feature for X.21 Shorthold Mode/Port Sharing

The callback feature for X.21 Shorthold Mode/Port Sharing gives the Host system the capability to return a call to a Remote device when the Host's main ports are busy. To help free the X.21 PDN (Public Data Network) and Host SHM (Short Hold Mode) systems during periods of congestion, the callback feature is introduced. The exchange of a special SHM XID (Exchange Identification Information) between the Host port and the Secondary device allows the Host to call back the Secondary device when a Host port is available for connection. Therefore, during periods when the Host system is congested, the Secondary device trying to establish a connection goes into an answer mode and waits until the Host system is capable of receiving the Secondary. The Host system has a configurable parameter that selects a maximum number of ports, within a group of ports, that can be physically busy at one particular time. If the number of maximum busy ports is exceeded, such as a remote device calling the Host and no main Host ports are available, the Host system would exchange XIDs with this Remote device informing the Remote that the Host system will call back when a main port is free. The reception of the XID by the Remote would put the Remote device into the answer state waiting for the Host to call when one of the Host's main ports has become available for a connection. The Remote device remains in the answer state for some set time period b...