E-CSCF Support

An Emergency Call Session Control Function (E-CSCF) is an IMS core element that aids in routing emergency calls to an appropriate destination, such as a PSAP. E-CSCF functionality can be performed by the Oracle Communications Session Border Controller with appropriate local policy and network management control configuration.

The E-CSCF feature let the Oracle Communications Session Border Controller internally prioritize and route emergency calls to the corresponding Emergency Service Center, based either on the calling party’s request URI, or based on location information retrieved from a CLF (Connectivity Location Function) for wireline/TISPAN networks.

By integrating E-CSCF functionality into the P-CSCF (Oracle Communications Session Border Controller ), networks can satisfy the common local requirement that certain telephony elements be deployed locally, rather than use single, centralized elements. Funcitons like the E-CSCF likely fall into this category.

Service URN Support

To enable E-CSCF functionality, the Oracle Communications Session Border Controller can parse service URNs for local policy lookup keys, and as desitnation identifiers in network management controls (NMC). Ensure that the match-URN is entered correctly as: urn:service:sos” or "urn:service:sos.type or the Oracle Communications Session Border Controller will interpret the URN as a hostname. Please see RFC 5031 for more information on compliant URN construction.

E-CSCF Configuration Architecture

There are four elements which comprise and enable E-CSCF support on the Oracle Communications Session Border Controller :

  • CLF Connectivity
  • NMC Emergency Call Control
  • Local Policy
  • Emergency Local Route Table

CLF Connectivity

The Oracle Communications Session Border Controller must be configured with Diameter-based CLF support. This is accomplished by creating an appropriate external policy server configuration.

When the Oracle Communications Session Border Controller requests authorization from the CLF server, a Line-Identifier AVP which includes a location string is expected to be returned for the call. The returned location string will be used later for an LRT query.

NMC Emergency Call Control

By configuring a Network Management Control (NMC), the Oracle Communications Session Border Controller can flag a call for special priority early after it is received and validated by the system. The destination identifier must be configured in the NMC with the service URN of an incoming emergency call. Also, the NMC configuration must have its next hop parameter left blank. This lets the Oracle Communications Session Border Controller route the emergency call with local policies.

For example, if urn:service:sos is the configured value in the NMC’s destination identifier, and an INVITE arrives on the Oracle Communications Session Border Controller with urn:service:sos in the request URI, the call will be flagged for emergency handling. The next step in call processing is for the INVITE to be evaluated by local policy.

Local Policy

Local policies must be configured to match and then route an incoming emergency call. Once a local policy match is made, the Oracle Communications Session Border Controller looks to the configured policy attributes for where to forward the INVITE. A matching policy attribute’s next hop should be configured to point to an emergency LRT that contains specific destinations for emergency calls. In addition, the elec str lkup parameter must be set to enabled so the Oracle Communications Session Border Controller will perform an LRT lookup based on the location string returned in the CLF response.

The eloc str match parameter identifies the attribute, whose value in the location string will be used as the lookup key in the emergency LRT. For example, if the returned location string is: 

loc=xxx;noc=yyyy;line-code=zzzz

and the eloc str match parameter is set to noc, then when the Oracle Communications Session Border Controller performs a local policy route search, it will search the LRT for yyyy. If the eloc str match parameter left empty or if there is no match when eloc str lkup is enabled, the entire location string is used as the lookup key.

Emergency LRT

The Oracle Communications Session Border Controller needs to be configured with an emergency LRT to route emergency calls to their destination.

As stated in the previous section, when searching an emergency LRT, any user defined parameter within a Location String may be used as the key to look up next-hop routing information.

LRT files support <user type = string> which enables the Oracle Communications Session Border Controller to perform searches on free form attributes that may appear in the returned location-string. The <user type = string> value for an entry in the emergency LRT should be set to a part or whole value returned in the CLF’s location string. For example: 

<?xml version="1.0" encoding="UTF-8" ?>
<localRoutes>
	<route>
		<user type="string">1234</user>
		<next type="regex">!^.*$!sip:911@192.168.200.140:5060!</next>
	</route>
	<route>
		<user type="string">loc=xxx;noc=yyyy;line-code=zzzz</user>
		<next type="regex">!^.*$!sip:911@192.168.1.139:5060!</next>
	</route>
</localRoutes>

Note:

Given that the Location String is not a well-defined string, care should be taken when defining and configuring the LRT tables.

LRTs must be individually uploaded to both the active and standby systems in an HA node; LRTs are not automatically replicated across nodes.

CLF Response Failure

If there is no location string in a CLF’s repsone or the CLF rejects the call, the Oracle Communications Session Border Controller uses the default location string parameter from the ingress SIP interface to populate the PANI header. The emergency call proceeds normally using this location string’s information for emergency LRT lookups.

E-CSCF Configuration

This procedure assumes that the Oracle Communications Session Border Controller is configured to communicate with a CLF. In addition, this procedure assumes an the Oracle Communications Session Border Controller is configured and loaded with an appropriate LRT for E-CSCF Use.

To configure an NMC for E-CSCF use (baseline parameters are not mentioned):

  1. In Superuser mode, type configure terminal and press Enter. 
    ORACLE# configure terminal
  2. Type session-router and press Enter to access the signaling-related configurations. 
    ORACLE(configure)# session-router
  3. Type net-management-control and press Enter. 
    ORACLE(session-router)# net-management-control
  4. name—Enter the name of this network management control rule; this value uniquely identifies the control rule. There is no default for this parameter.
  5. state—Enable or disable this network management control rule. The default value is enabled. The valid values are:

    • enabled | disabled

  6. type—Set this parameter to priority so that the Oracle Communications Session Border Controller will flag incoming calls with a matching destination identifier as a priority calls.
  7. treatment—Set this parameter to divert.
  8. next-hop—Leave this parameter blank so that the call’s processing will go directly to local policy.
  9. destination-identifier—Enter the service URN that endpoints in your network include in their request URIs to identify themselves as emergency calls.
  10. Save your configuration.

    To configure local policy for E-CSCF use (baseline parameters are not mentioned):

  11. In Superuser mode, type configure terminal and press Enter. 
    ORACLE# configure terminal
ORACLE(configure)#
  12. Type session-router and press Enter. 
    ORACLE(configure)# session-router
ORACLE(session-router)#
  13. Type local-policy and press Enter. If you are adding this feature to a pre-existing local policy configuration, you will need to select and edit your local policy. 
    ORACLE(session-router)# local-policy
ORACLE(local-policy)#
  14. to-address—Set this parameter to the lookup key for matching emergency calls. You can now use a service URN as lookup key criteria.
  15. Save your configuration.

    To configure policy attributes for E-CSCF use (baseline parameters are not mentioned):

  16. Type policy-attributes and press Enter. If you are adding this feature to a pre-existing local policy configuration, you will need to select and edit your local policy. 
    ORACLE(local-policy))# policy-attributes
ORACLE(policy-attributes)#
  17. next-hop—Set this parameter to lrt: name-of-elrt-file.gz for this policy attribute to lookup routes in the named lrt file.
  18. eloc-str-lkup—Set this parameter to enabled for the Oracle Communications Session Border Controller to parse the emergency location string, as received in a CLF Line Identifyier AVP, for emergency LRT lookup.
  19. eloc-str-match—Set this parameter to the attribute name found in the location string whose value will be used as a lookup key in the LRT named in the next-hop parameter. Common values include “loc” or noc.
  20. Save and activate your configuration.

Maintenance and Troubleshooting

The show lrt route-entry command displays two entries, if the username 1234 has a "string" type and "E164" type entries.

ACMEPACKET# show lrt route-entry emergency_lrt 1234
UserName <1234>
 User Type= E164
 NextHop= !^.*$!sip:911@192.168.200.139:5060!
 NextHop Type= regexp
UserName <1234>
 User Type= string
 NextHop= !^.*$!sip:911@192.168.200.140:5060!
 NextHop Type= regexp
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