HSS-based P-CSCF Restoration for Trusted/Untrusted WLAN Access (S2a/S2b)
PCRF-based P-CSCF Restoration for LTE (S5/S8) and Trusted/Untrusted WLAN Access (S2a/S2b)
HSS-based P-CSCF Restoration was supported at P-GW for LTE (S5/S8) prior to StarOS release 21.0.
This feature provides support for both basic and extended P-CSCF Restoration procedures.
HSS-based P-CSCF Restoration for WLAN
If the P-CSCF restoration mechanism is supported, gateway indicates the restoration support to AAA server through Feature-List AVP in the Authorization Authentication Request (AAR) message sent over S6b. The Feature-List AVP is part of the Supported-Features grouped AVP. The Bit 0 of the Feature-List AVP is used to indicate P-CSCF Restoration support for WLAN.
During the P-CSCF Restoration, 3GPP AAA server, after having checked that the P-GW supports the HSS-based P-CSCF restoration for WLAN, sends a P-CSCF restoration indication to the P-GW over S6b in a Re-authorization Request (RAR) command. A new Diameter AVP “RAR-Flags” is encoded in the RAR message with the Bit 1 set, would indicate to the gateway that the AAA server requests the execution of HSS-based P-CSCF restoration procedures for WLAN.
The existing CLI command diameter authentication under AAA Group configuration is extended to encode P-CSCF Restoration feature as part of Supported-Features AVP in the AAR message.
Supported-Features will be sent in every AAR message for RAT type WLAN. Feature negotiation is required in every AAR. ReAuth AAR will also do the feature renegotiation.
Emergency PDN HSS based P-CSCF Restoration for S5/S8 will be performed if CLI is configured at P-GW service to support the restoration for emergency PDNs.
PCRF-based P-CSCF Restoration
PCEF supporting P-CSCF restoration mechanism indicates the restoration support in CCR-I message through the Supported-Features AVP. The 24th Bit of the Supported-Feature-List AVP indicates whether this mechanism is supported or not.
The existing CLI command diameter encode-supported-features in Policy Control configuration is extended to allow the negotiation of P-CSCF Restoration feature support with PCRF. A new Diameter AVP “PCSCF-Restoration-Indication” is introduced to indicate to PCEF that a P-CSCF Restoration is requested. This is achieved by setting AVP value to 0.
Supported-Features AVP is negotiated in CCR-I of all access types (eHRPD, P-GW, GGSN); however, Restoration trigger, if received, is ignored in eHRPD and GGSN.
As per the 3GPP standard specification, if S6b re-authorization request is used for P-CSCF Restoration for WLAN, then for extended P-CSCF Restoration the gateway may send authorization request with only mandatory AVPs. However, in the current implementation, ReAuth used for extended P-CSCF Restoration is a common authorization request of normal ReAuth. It will contain all the AVP of ReAuthorization AAR.
For P-CSCF Restoration extension mechanism during P-CSCF ReDiscovery with P-CSCF FQDN, local DNS cache will be queried first. If FQDN is already present in local DNS cache, then DNS query will not be sent out to the DNS server and P-GW will immediately get the DNS response.
Since local DNS cache flush will not be done, operator should configure the cache accordingly.
Use of P-CSCF Restoration requires that a valid license key be installed. Contact your local Sales or Support representative for information on how to obtain a license.