5.15 Mobile Terminating session procedure for unknown user

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

5.15.0 General

This clause describes information flows Mobile Terminating procedure for an unknown user. The unknown user cases include those where session requests are made towards Public User Identities that are incorrect, un-issued or have been cancelled/deleted. The determination of unknown user is carried out in the HSS and/or the SLF (for networks that require SLF functionality). The information flows of figures 5.45 and 5.46 illustrate how SIP messages can be used to inform the requesting party that the requested user is not known within the network.

In the case where the destination Public User Identity is an E.164 number in the SIP URI with user=phone parameter format, the I‑CSCF shall first translate it into the Tel: URI format per IETF RFC 3966 [15] prior to sending to the HSS a Cx_LocQuery (or to the SLF a DX_SLF_QUERY). If a failure occurs under these circumstances, the Mobile Terminating user is not an IMS user of this network. In this case, the I‑CSCF may invoke the portion of transit functionality that translates the E.164 address contained in the Request‑URI of the Tel: URI format to a routable SIP URI, or BGCF for further routing as described in clause 5.19.

5.15.1 Unknown user determined in the HSS.

In Figure 5.45 the unknown status of the requested party is determined in the HSS. The I‑CSCF requests information on the user to be reached and the HSS responds back to the I‑CSCF with an indication that the user is unknown. The I‑CSCF uses the indication that the user is unknown returned from the HSS to formulate the correct SIP message back towards the originating party to inform them that the user is unknown. The case where the SLF determines unknown status is in clause 5.15.2. The flows of figure 5.45 could include SLF determination of the HSS, however these are not shown for clarity.

Figure 5.45: HSS determination of unknown user

1) I‑CSCF receives an INVITE.

2) I‑CSCF queries the HSS for current location information.

3) HSS responds with an indication that the user is unknown.

4) The I‑CSCF responds to the origin of the request that the user is unknown.

5.15.2 Unknown user determined in the SLF

In Figure 5.46 the unknown status of the requested party is determined in the SLF. The I‑CSCF requests information on the user to be reached and the SLF responds back to the I‑CSCF with an indication that the user is unknown. The I‑CSCF uses the indication that the user is unknown returned from the SLF to formulate the correct SIP message back towards the originating party to inform them that the user is unknown.

Figure 5.46: SLF determination of unknown user

1) The ICSCF receives an INVITE request and now has to query for the location of the user’s subscription data.

2) The I‑CSCF sends a DX_SLF_QUERY to the SLF and includes as parameter the user identity which is stated in the INVITE request.

3) The SLF looks up its database for the queried user identity.

4) The SLF answers with an indication that the user is unknown.

5) The I‑CSCF responds to the origin of the request that the user is unknown.