The Service-Point-Trigger is the smallest logical atom in the Trigger Point. There are 5 distinct types of SPTs, based on what each of them is used to check in the SIP message:

1. Request-URI equals <value>
2. SIP Method equals <value>
3. SIP Header matches <regular expression>
4. Session Case is one of [originating, terminating, terminating to unregistered user]
5. SDP Line [<line name>] matches <regular expression>

The result of each SPT can be negated, as required. Also it could be specified to each SPT if it applies to the Initial/Re/De-Registration when checking a REGISTER message for triggering a 3rd Party Registration.

The SIP Header SPT can be used to also test the absence of a header by negating it and omitting the regular expression.