1. Configuration Guide
  2. External Policy Servers
  3. Network Provided Location Information
  4. NPLI Implementation
  5. Handling NPLI for Unregistered Emergency Calls

Handling NPLI for Unregistered Emergency Calls

Despite the absence of a SIP contact within the context of an unregistered user, the SBC manages network provided location information (NPLI) within call flows for unregistered emergency calls using the same controls it uses for registered flows. There is no additional configuration required to support unregistered calls. Common behavior for registered and unregistered emergency calls include the SBC managing NPLI AVP’s in AARs and using the same timing controls to fine tune this management.

When configured, the SBC creates an AAR to be sent to the PCRF to initiate and establish the session, inserts NPLI AVPs and subscribes the SBC to NPLI changes. The SBC holds the INVITE after sending the AAR, even after the AAA comes from the PCRF.

As is true for registered emergency calls, configuration required for this feature includes:

  • Include the access-network-info-report in the specific-action-subscription parameter in the applicable ext-policy- server.
  • Enable the location-optimization-on-aar option on the applicable ext-policy-server.
  • Disable optimize-aar on the applicable ext-policy-server.

Additional configuration that affects this feature include:

  • Configuring the hold-emergency-calls-for-loc-info parameter to a value greater than zero.
  • Configuring the cache-loc-info-expire parameter to zero. If not set to zero, the SBC adds the default PANI when this location cache timer expires.

    You can configure hold-emergency-calls-for-loc-info and cache-loc-info-expire in an npli-profile applied to the applicable sip-interface and/or the sip-config. The values in the npli-profile take precedence.

When receiving an unregistered emergency call, the SBC generates an AAR with NPLI AVPs and sends it to the PCRF for session initiation/establishment. At this point, the SBC holds the INVITE waiting for a RAR, even if it receives an AAA. When the RAR arrives, the SBC stops the hold timer and constructs its PANI header for inclusion within the subsequent INVITE as follows:

  • If the AAA/RAR includes location information, the system used that to frame the PANI.
  • If the incoming AAA has the RAT-type set to WLAN the SBC includes the value configured in default-vowifi-string in the npli-profile in the PANI.

    Having determined it is using the default-vowifi-string, the system ignores any timers and forwards the INVITE immediately.

  • If either of the following are true, the SBC immediately populates its PANI header with your configured default-location-string or any UE-provided location, and forwards the SIP request without waiting for hold timer expiry:
    • The incoming AAA from the PCRF has the NetLoc-Access-Support AVP set to 0
    • The RAR from the PCRF includes the INDICATION_OF_ACCESS_NETWORK_INFO_REPORTING_FAILURE (specific-action AVP)
  • If the SBC does not receive location information from the PCRF and you have configured a default-location-string, it uses the default-location-string in the PANI.

    Note:

    If you have configured the default location string in both the sip-interface and the realm, the realm configuration takes precedence.
  • If the SBC does not receive location information and there is no default-location-string, it does not include network-provided PANI.
  • The SBC includes any UE-provided in addition to network-provided location information if the UE is trusted, meaning you have enabled the trust-me parameter on the applicable session-agent.

    If the UE is not trusted, the SBC does not include UE-provided location information.

Feature Interactions with S8HR

If an S8HR unregistered emergency call arrives at an SBC with the NPLI feature enabled, the SBC initiates an Rx exchange requesting EPC-level identities (MSISDN, IMEI, IMSI) along with NPLI AVP’s in an AAR. It sends this to the PCRF and waits for the AAA. When the SBC receives the AAA, it validates EPC-level identities and waits for the RAR. When the SBC receives the RAR, it constructs the PANI header and inserts it, along with the P-Asserted-Identity, into the INVITE, and sends the INVITE to the UAS.

CDRs

You can configure the SBC to generate an INTERIM Call Detail Record (CDR) for an unregistered Emergency MO call. This configuration would include CDR generation and NPLI management. When the SBC then receives an unregistered emergency INVITE, the SBC retrieves policy information, including NPLI, from the PCRF during the AAR/AAA and RAR/RAA sequences over the Rx interface.

The SBC includes any NPLI provided by the PCRF in the CDRs, and creates the interim record after the egress INVITE.

High Availability

This feature is supported by high availability (HA) for:

  • MO Call
  • MT Call
  • Registered emergency call
  • Unregistered emergency call

Note:

This feature does not support HA for REGISTER and SMS.

This feature does not require any additional configuration parameter to support HA because the SBC replicates the required configuration on the standby.

When a call is established at the ACTIVE SBC and a switchover occurs, the newly ACTIVE SBC continues to perform NPLI management. If it receives a re-INVITE for this call, the newly active SBC does not send NPLI AVP’s in the AAR initiated for re-INVITE. Also the newly active SBC does not send the network provided PANI header while forwarding the re-INVITE. Additionally, the SBC does not hold the re-INVITE (to wait for RAR). Instead, it sends the re-INVITE to the core immediately after receiving the AAA.