Interworking ACM/CPG Parameters for 180 and 183 Messages

When configured for native interworking, the SBC provides a fixed set of responses when presented with SIP to SIP-I and SIP-I to SIP-I calls that include ISUP progress messages, including user-configured ACM and CPG parameters. (The SBC only interworks an inbound-annoucement into a PEM header if it is present in the extract-isup-params list.) The SBC inserts interworked information into 180 and 183 messages.

For both SIP to SIP-I and SIP-I to SIP-I calls, the SBC checks for the presence of an in-band announcement in ISUP progress messages. It also checks to see if the extract-isup-params configuration contains the inband-announcement value. If it finds both these to be true, it interworks PEM headers while generating SIP 180 and 183 messages as follows:

• ACM message—The SBC confirms the presence of an in-band announcement if it finds an optional BCI parameter with the In-band information indicator bit set to 1.
• CPG message—The SBC confirms the presence of an in-band announcement if it finds an Event Information parameter with its Event indicator set to "In-band information" or "an appropriate pattern is now available" (0000011).

If an in-band announcement is present in the ACM/CPG message encapsulated in the received SIP 180 and 183 messages, the SBC may modify it as follows:

• If there is no PEM header, the SBC adds one with a value of sendonly.
• If there is a PEM header that does not have a value of sendonly, the SBC changes the value to sendonly.