Callback Feature for X.21 Shorthold Mode/Port Sharing
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
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.