Continuity Check Request with IAM or CCR

The Continuity Check is a procedure for checking a circuit. It can be requested, when supported by the selected flavor, in an IAM, a CCR or a CRM message. The following sections describe a number of Continuity scenarios.

Continuity Check on this Circuit

A Continuity Check is performed on the current circuit if the continuity check indicator in the IAM message is set to ‘Continuity Check required on this circuit’.

Successful Continuity Check

The outgoing side sends a Continuity message with a successful indication after a correct check of the transmission path (a loop is required on the incoming side, a tone is sent from the outgoing side and is returned in time).




	NOTE: `CONNECT_LOOP_IND` and `SETUP_IND` are handled in parallel by HP OpenCall SS7 ISUP. Therefore, depending on the behavior of the application, the order of the primitives in the diagram below can change. However, `CONNECT_LOOP_IND` and `DISABLE_ECHO_IND` will always be issued to the application sequentially (that is, after the corresponding `ACK`s are sent back by the application).

Figure 18-11 Continuity Check - Outgoing Side

Figure 18-12 Continuity Check - Incoming Side

Continuity Recheck

If the continuity recheck procedure is a success, only the outgoing side sends a REL message to finish the procedure.

Figure 18-13 Continuity Recheck - Outgoing Side

Figure 18-14 Continuity Recheck - Incoming Side

Continuity Recheck - TCCR Expiry at Outgoing Side

If the TCCR timer expires during the continuity recheck phase, either activated after a continuity failure during call setup, or after an explicit continuity recheck request, the following occurs:

On the outgoing side, a reset procedure is activated by HP OpenCall SS7 ISUP, the continuity recheck phase is cancelled. A START_RESET_IND_ACK indicating DCO_LPA_FAIL is issued to the application and an RSC message is sent by HP OpenCall SS7 ISUP when application acknowledges by a START_RESET_IND_ACK.
On the incoming side, the continuity recheck procedure is cancelled by the reset procedure engaged on the outgoing side.

Figure 18-15 Continuity Recheck - Outgoing Side - TCCR Expiry

Continuity Recheck - T24 Expiry at Outgoing Side

If the T24 timer expires during the continuity recheck phase, either activated after a continuity failure during call setup, or after an explicit continuity recheck request, the following occurs.

On the outgoing side, a COT indicating failure is issued to the network, and a MAINTENANCE_SYSTEM_IND primitive indicating DCO_FAIL is issued to the application after the SECOND continuity failure (including the eventual call setup continuity failure). The T26 timer is started to restart a continuity recheck phase at its expiry.

Figure 18-16 Continuity Recheck - Outgoing Side - T24 Expiry

Continuity Check Request with IAM or CCR

Technical documentation

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Continuity Check on this Circuit

Successful Continuity Check

Continuity Recheck

Continuity Recheck - TCCR Expiry at Outgoing Side

Continuity Recheck - T24 Expiry at Outgoing Side