Enabling Interworking of SIP and SIP-I Endpoints
The device can interwork between SIP and SIP-I endpoints for SBC calls. SIP-I endpoints are entities that are connected to the SS7 PSTN network, referred to as the ISDN User Part (ISUP) domain. The device supports the SIP-I Application-layer signaling protocol, which is the standard for encapsulating a complete copy of the SS7 ISUP message in SIP messages, according to ITU-T Q.1912.5, Interworking between Session Initiation Protocol (SIP) and Bearer Independent Call Control protocol or ISDN User Part. In other words, SIP-I is SIP encapsulated with ISUP and the interworking is between SIP signaling and ISUP signaling. This allows you to deploy the device in a SIP environment where part of the call path involves the PSTN.
The SIP-I sends calls, originating from the SS7 network, to the SIP network by adding ISUP messaging in the SIP INVITE message body. The device can receive such a message from the SIP-I and remove the ISUP information before forwarding the call to the SIP endpoint. In the other direction, the device can receive a SIP INVITE message that has no ISUP information and before forwarding it to the SIP-I endpoint, create a SIP-I message by adding ISUP information in the SIP body. For SIP-I to SIP-I calls, the device can pass ISUP data transparently between the endpoints.
For the interworking process, the device maps between ISUP data (including cause codes) and SIP headers. For example, the E.164 number in the Request-URI of the outgoing SIP INVITE is mapped to the Called Party Number parameter of the IAM message, and the From header of the outgoing INVITE is mapped to the Calling Party Number parameter of the IAM message.
The ISUP data is included in SIP messages using the Multipurpose Internet Mail Extensions (MIME) body part, for example (some headers have been removed for simplicity):
INVITE sip:1774567@172.20.1.177;user=phone SIP/2.0
Via: SIP/2.0/UDP 172.20.73.230:5060;branch=z9hG4bK.iI
...
Accept: application/sdp, application/isup, applicatio
Content-Type: multipart/mixed; boundary=unique-bounda
MIME-Version: 1.0
Content-Length: 350
...
Content-Type: application/isup; version=FTSSURI; base
Content-Disposition: signal; handling=required
01 00 40 01 0a 02 02 08 06 83 10 71 47 65 07 08
01 00 00
--unique-boundary-1—
D6 SIP-T ISUP/IAM (Initial address message)
(--) len:-- >> Nature of connection indicators
Oct 1 : ---0---- Echo ctrl = Half echo not included
----00-- Cont. check = Not required
------00 Satellite = No circuit
(--) len:-- >> Forward call indicators
Oct 1 : 01------ ISUP pref. = Not req. all the way
--0----- ISUP indic. = Not used all the way
---0---- End-end inf = Not available
----0--- Interwork. = Not encountered
-----00- Method. ind = No method available
-------0 Call indic. = as National call
Oct 2 : -----00- SCCP method = No indication
ISUP data, received in the MIME body of the incoming SIP message is parsed according to the ISUP variant (SPIROU itu or ansi), indicated in the SIP Content-Type header. The device supports the following ISUP variants (configured by the 'ISUP Variant' parameter in the IP Profile table):
| ■ | French (France) specification, SPIROU (Système Pour l'Interconnexion des Réseaux OUverts), which regulates Telecommunication equipment that interconnect with networks in France. For SPIROU, the device sets the value of the SIP Content-Type header to "version=spirou; base=itu-t92+". |
| ■ | ITU-92, where the device sets the value of the SIP Content-Type header to "version=itu-t92+; base=itu-t92+". |
To configure interworking of SIP and SIP-I endpoints, using the IP Profile parameter 'ISUP Body Handling' (see Configuring IP Profiles).
You can manipulate ISUP data, by configuring manipulation rules for the SIP Content-Type and Content-Disposition header values, in the Message Manipulations table (see Configuring SIP Message Manipulation). For a complete description of the ISUP manipulation syntax, refer to the document Syntax for SIP Message Manipulation Reference Guide. In addition, you can use the