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CRM/CRA (ANSI)

Definitions

The messages related to circuit reservation are defined in this section.

CRM

Circuit Reservation Message: This message is used to perform continuity procedures on an outgoing SS7 circuit before collecting address digits from the incoming MF circuit. On receiving a seize from the incoming MF agency, a CRM with the required NOC is sent to the succeeding exchange and the timer TCRM (typically 15 seconds) is started. Based on the NOC, a continuity check may or may not be performed.

CRA

Circuit Reservation Acknowledgment: On receipt of a CRA message, the timer TCRM is stopped and further processing continues. If TCRM expires before the receipt of CRA, the CRM is re-attempted on a different CIC.

Circuit Reservation Timer

After sending a CRA in response to the CRM, a Timer TCRA (typically 15 seconds) is started by the terminating node while waiting for an IAM (or COT if a continuity check is to be performed). If neither of the messages is received and the timer expires, an REL message is sent from the terminating node with a cause value of "Temporary Call Flows.

Call Flows

TCRM Timeout

TCRM Expiry

Dual Seizure during CRM Processing

See Signaling System Number Seven.
Multi-Frequency
Network Operation Center
See Circuit Identification Codes.