Emergency Calls from Unregistered Users

Version S-CZ7.2.0 provides compliance with Section 5.1.6.2 of 3GPP TS24.229. This section mandates that unregistered, or roaming User Endpoints (UE) must perform an emergency registration before sending any SIP request (for example, an INVITE) related to the emergency situation.

Version S-CZ7.2.0 adds a new parameter (options reject-unreg-priority-calls) that enforces compliance with Section 5.1.6.2, Initial Emergency Registration, of 3GPP TS24.229, IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP);Stage 3. Section 5.1.6.2 mandates that unregistered, or roaming User Endpoints (UE) must perform an emergency registration before sending any SIP request (for example, an INVITE) related to the emergency situation.

Prior to Version S-CZ7.2.0, the default SBC behavior (acting as a P-CSCF) was not compliant with Section 5.1.6.2 of 3GPP 24.229. Rather, an emergency call from an unregistered or roaming UE was processed and routed in exactly the same way as a similar call from a currently registered UE.

Processing of emergency calls received from an unregistered or roaming UE as specified by 3GPP TS24.229 can be summarized as follows.

First, the emergency call (for example an INVITE) is rejected by the SBC with a 380, Alternative Service response message, which includes

1. a Content-Type header field set to

   application/3gpp-ims+xml

2. a P-Asserted-Identity header set to the value of the SIP URI of the last entry on the path header field value received during registration -- the SIP URI of the P-CSCF. This is the UE-side Service Route that the SBC sends out when sip-ims-feature is enabled.
3. an Alternative Service child element containing a Type element set to "emergency" ;

   emergency-value = %x65.6D.65.72.67.65.6E.63.79 ; "emergency"

   an Action element set to “emergency-registration”

   %x65.6D.65.72.67.65.6E.63.79.2D.72.65.67.69.73.74.72.61.74.69.6F.6E ; "emergency-registration"

   a Reason element set to

   "priority calls not allowed from unregistered UEs"

Second, upon receipt of the 380, Alternative Response, the UE responds with an emergency registration.

Finally, upon receipt of the emergency registration, the SBC processes that registration as it would any other registration request.

Emergency Calls from Unregistered Users Configuration

1. Access the sip-interface configuration element.

   ORACLE# configure terminal
   ORACLE(configure)# session-router
   ORACLE(session-router)# sip-interface
   ORACLE(sip-interface)# 
   

2. Select the sip-interface object to edit.

   ORACLE(sip-interface)# select
   <RealmID>:
   1: realm01 172.172.30.31:5060
   
   selection: 1
   ORACLE(sip-interface)#

3. options +reject-unreg-priority-calls—Add this option to require compliance with Section 5.1.6.2 of 3GPP TS24.229 . If this option is enabled, emergency calls from unregistered or roaming UEs are rejected with a 380, Alternative Service response, and the UE is required to perform an emergency registration prior to sending an emergency message. If this option is not present, emergency calls, by default, are processed and routed regardless of registration status.

   ORACLE(sip-interface)# options +reject-unreg-priority-calls

4. disallow-priority-calls—ensure that this option has not been enabled on the current SIP interface because it summarily rejects all emergency calls on the current SIP interface. Ensure that this option is NOT present to ensure compliance with 3GPP TS24.229.

   ORACLE(sip-interface)# options -disallow-priority-calls

5. options send-380-response—ensure that this option has not been enabled on the current SIP interface. The send-380-response option provides the text for the Reason header. The correct text is supplied by the 380 Alternative Service message. Ensure that this option is NOT present to ensure compliance with 3GPP TS24.229.

   ORACLE(sip-interface)# options -send-380-response

6. Type done to save your configuration.