Changing the STI-VS Trigger

To optimize processing and reduce unnecessary traffic, enabling the man-compliance option allows the SBC to trigger STI-VS processing after the completion HMR and DoS processing, which includes constraint checks. When configured in this way, if a call attempt is below session-constraints set for the corresponding ingress Session Agent, sip-interface or realm, the STI-VS can be triggered, and processing can continue after receipt of the STI-VS response regardless of constraints status.

By default, the SBC triggers STI-VS processing after ingress Header Manipulation Rules (HMR) processing. Ingress HMR processing occurs immediately after software Denial of Service (DoS) handling, which includes CPU load monitoring, message parsing, access control, and constraints checking. This sequence of operations leads to the system triggering STI-VS exchanges before the session constraints are evaluated, resulting in unnecessary processing on both the SBC and the STI server, and generating additional, often avoidable traffic processing.

Default call processing stages:

1. SIP message parsing
2. Denial of Service (DoS) handling (including CPU load monitoring, message parsing, access control, and constraints)
3. Inbound HMR (Header Manipulation Rules)
4. Load Index (LI) processing
5. STIR-VS processing
6. Check session constraints

Call processing stages after enabling the man-compliance option:

1. SIP message parsing
2. Denial of Service (DoS) handling (including CPU load monitoring, message parsing, access control, and constraints)
3. Inbound HMR (Header Manipulation Rules)
4. Load Index (LI) processing

   (Steps 5 and 6 are reversed.)

5. Check session constraints
6. STIR-VS processing

By moving the STI-VS trigger to occur after complete software DoS processing, you streamline call processing logic and improve efficiency, ultimately reducing unnecessary traffic processing.