scope:

Scope, Purpose, and Application

This addendum to T1.628-2000 specifies the use of the Connection Hold network capability by the Emergency Calling Service (ECS) to support ECS call hold and ring back. This addendum also specifies the TCAP messages exchanged between a switching node routing ECS calls and a Selective Routing Database (SRDB) that contains information determining the PSAP that should receive the emergency calls originating from a given caller or calling location.

The Connection Hold Network Capability disables a calling user's capability to initiate release of a call. Connection hold also provides a mechanism to indicate that the calling user has requested disconnect (or reconnect) without initiating release procedures.

The procedures described in this addendum supplement the procedures in T1.628-2000, American National Standard for Telecommunications-Emergency Calling Service. In particular the procedures described here take precedence over normal call release procedures when ECS Call Hold is invoked.

The use of connection hold is restricted when the caller has an ISDN user-network interface. Due to existing provisions of the DSS1 protocol it is not possible to prevent an ISDN caller from disconnecting an active call. When call hold is applied to ECS calls originating from an ISDN user-network interface and the caller disconnects, the network will attempt to reconnect to the user's terminal in cases when the network has information that permits it to identify the end user's terminal.

A PSAP using an ISDN access can invoke the network to apply ring back to the caller's terminal using the protocol defined in this addendum.

Following the references clause, the remainder of this addendum specifies changes to the existing text of T1.628-2000 using strikeout to indicate deletions and underlining to indicate insertions.