7 Control plane interworking

29.4213GPPEndorsement of 3GPP TS 29.162 Interworking between IM CN Sub-system and IP networksNGN Release 1Release 8TISPANTS

7.1 SIP with TISPAN IMS Profile to non-IMS SIP Interworking

ES 283 003 (see bibliography) defines the behaviour of an IMS UE when communicating with SIP terminal with missing SIP capabilities required by the IMS.

7.2 Procedures at the IBCF

7.2.1 IBCF usage of SIP

The IBCF acting as a B2BUA forwards all SIP messages transparently with respect to all methods, result codes, headers with the following exceptions:

  • the IBCF shall include its own SIP URI to the top of the Record-Route header within an initial request for a dialog, to place itself on the path for subsequent requests within the dialog;
  • the IBCF may modify the Contact, Record-Route and Via headers to remove routing information received from an incoming SIP message before forwarding it;
  • the IBCF shall apply any privacy required by RFC 3323 [77] and RFC 3325 [88] to the P-Asserted-Identity header and;
  • if specified by local policy rules, the IBCF may omit or modify any other received SIP headers prior to forwarding SIP messages.

The behaviour of the IBCF regarding SIP message bodies (including SDP) is described in the following clause.

7.2.2 IBCF procedures on SIP message bodies

If IP address translation (NA(P)T or IP version interworking) occurs on the user plane, the IBCF shall modify SDP according to the corresponding clauses 9 or 10;

Additionally, the IBCF may take the followings action upon SIP message bodies:

  • examine the length of a SIP message body and if required by local policy, and take an appropriate action
    (e.g. forward the message body transparently, reject the INVITE, remove the body), and possibly record the event in the CDR;
  • examine the characteristics of the message body (i.e. check the values of any "Content-type",
    "Content-disposition", and "Content-language" headers), take an appropriate action defined by local policy (e.g. transit the body, remove the body, reject the call), and possibly record the event in the CDR;
  • examine the content of SIP bodies, and take appropriate action defined by local policy (e.g. transit the body, remove the body, reject the call), and possibly record the event in the CDR.