SS7 Host Link Failure Detection Architecture

SS7 Host Link Failure Detection and Handling Logic

An SS7 local host is capable of detecting and managing a host link failure with an SS7 card and take subsystems out-of-service is needed. Previously in a CSP, if the CSP Matrix Series 3 Card detected any host link failure, it would automatically take all spans and channels out-of-service. Host link failure detection is now a separate process on an SS7 card. For more details, see SS7 Host Link Failure Detection and Recovery.

Enhancements to Matrix Host Link Failure Handling

Because of recent enhancements, if the matrix controller local host detects a host link failure, there will be no impact on an SS7 host; no subsystems that reside on an SS7 card will be taken out-of-service. With software enhancements, only those subsystems that have been configured to reside on the matrix host will be taken out-of-service. Also these subsystems will be taken out-of-service only if the host has been configured to take the subsystem out-of-service when a host link failure occurs. In this case, the SCCP/TCAP subsystem out-of-service procedure applies.

SCCP/TCAP Subsystem Out-of-Service Procedure

The SCCP/TCAP module on an SS7 card can be instructed to take a subsystem out-of-service. As part of the SCCP subsystem out-of-service procedure, SCCP sends SSP (SubSystem Prohibited) to all the relevant point codes on the network.

If SCCP/TCAP module has been configured to initiate TCAP restart when a local subsystem is out-of-service (see TCAP TUSI (0x0070)), a TCAP restart procedure will be initiated. In this case, all the active TCAP transactions for this local subsystem are aborted. TCAP Abort messages can be sent to the network when necessary according to the TCAP protocol. Note that the TC-U-Abort indication will not be sent to the host because the host link connection failed.

SCCP/TCAP Subsystem In-Service Procedure

As part of the SCCP subsystem in-service procedure, SCCP sends an SSA (SubSystem Allowed) message to the configured concerned point codes on the network.

Diagram of SS7 Host Link Failure Architecture

In the next diagram, A, B, C, and D are the host link failure detection points where the host link failure detection logic resides. Host link failure detection is set up as two separate processes: one for an SS7 card and one for a Matrix Controller card.

The TCAP and SCCP module is responsible for taking a subsystem out-of-service and initiates the TCAP restart procedure when a host link failure occurs.