1. Essentials Guide
  2. Oracle USM Supporting the IMS Core
  3. Initial Filter Criteria (IFC)
  4. TEL URI Replacement with SIP URI in R-URI to AS

TEL URI Replacement with SIP URI in R-URI to AS

When the USM receives a request containing a TEL URI from the Media Gateway Control Function (MGCF), it sends the TEL URI as an R-URI to the Application Server (AS) to perform services. However, in some implementations, the AS does not accept TEL URI and requires the trigger to be based on SIP URI. This feature, when enabled, causes the USM to replace the TEL R-URI with a SIP URI based on the first SIP user in the implicit set.

In the current implementation of the USM for terminating calls, when the USM receives an R-URI with SIP user=phone (for example, "sip:+359888528650@sip.mtel.bg; user=phone"), the USM replaces the SIP URI with a TEL URI and further uses the TEL URI (for example, "tel:+359888528650") for Location Information Requests (LIR) and Server Assignment Requests (SAR) when the user is not in the registration cache. The Server Assignment Answer (SAA) provides the Public Identity "sip:tel.359888528650@sip.mtel.bg" in the Service Profile as it's part of the implicit registration set and the USM stores it in its registration cache. Then, based on the Service Profile for the TEL URI, the USM triggers the AS using the R-URI "tel:+359888528650". However, in some implementations, for requests coming from the MGCF, the USM receives requests with a TEL URI which is sent as an R-URI to the AS while doing services, but the AS does not accept TEL URIs and requires the trigger to be based on a SIP URI.

To rectify this deficiency, this feature, when activated and when the USM is the assigned Serving Call Session Control Function (S-CSCF), causes the USM to replace the TEL R-URI with the first SIP URI in the implicit set for the TEL user; it then performs services based on the trigger for the user of the first implicit SIP URI. Once a TEL URI is changed to a SIP URI to perform services it will not be changed back to a TEL URI for the entire call flow. When this feature is enabled, the USM uses the first SIP user entry in the implicit set and performs services for the user irrespective of whether the user is in the registration cache.