-
Restoration is
supported for IPv4/IPv6/IPv4v6 calls.
-
With extension,
Restoration Support UBR will always go on default bearer.
-
P-GW does not
compare any of the stored values with the new updated P-CSCF IP addresses; it
relies on the DNS provided/discovered values and forwards the P-CSCF IP
addresses as is.
-
P-CSCF
Restoration will be performed for all PDN connections, regardless of APN
configuration of IMS/non-IMS.
-
Upon receiving
P-CSCF Restoration trigger for extended mechanism, P-CSCF address discovery
priority is first for P-CSCF FQDN. If FQDN is already present in DNS cache,
then as per current implementation of HSS based (S5/S8) P-CSCF Restoration, DNS
query will not be sent 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.
-
In case of S6b
RAR, P-GW supports configuration for whether to perform ReAuthentication
Request and Response (AAR/AAA) with extended restoration support.
Authentication
after RAR for restoration is not mandatory as it increases the authentication
signaling flow at AAA Server. In order to maintain backward compatibility with
the existing Diameter Relay Agents (DRA)/AAA servers, which expect
authentication after RAR, authentication can be configured for RAR with P-CSCF
Restoration.
-
If the DNS
resolution for FQDN fails or P-GW does not have P-CSCF address configured in
any other way, P-GW will still send UBR with no P-CSCF address PCO/APCO during
restoration.
-
If the P-CSCF
Restoration is already in progress, then restoration will not be performed
again for any second restoration indication received.
-
For basic P-CSCF
Restoration, call will be cleared with disconnect reason
"ue-pcscf-reselect-not-supported (613)".
-
P-GW does not
expect change in S6b P-CSCF FQDN during ReAuth. In the rare scenario that
P-CSCF FQDN is changed in S6b ReAuth, then the new FQDN will be used in next
P-CSCF Discovery. If P-CSCF FQDN if changed during ReAuth, then it is not
recovered.
-
For S6b, every
AAR supported-feature will be negotiated. ReAuth AAR will also do the feature
renegotiation. It’s expected that S6b AAA server should do the renegotiation in
every AAA. This is specifically applicable to LTE-WiFi and vice versa handoff.
During LTE attachment, supported-feature will not be sent. During WiFi handoff,
however, support for P-CSCF Restoration should be indicated in AAR.
-
Supported-feature on Gx for P-CSCF Restoration will apply to
GGSN/eHRPD calls as well to support handoff scenarios.
-
For S6b RAT type
WLAN, AAA group supports configuration to control when AAR is sent with the
supported-feature to S6b server. If AAA group disables this functionality, then
once the AAA response comes with supported-feature it is considered not
negotiated. Thus, negotiation depends on the CLI configuration of
supported-feature at the time of handling AAA.
-
Supported-feature for P-CSCF Restoration in S6b will only go for
RAT type WLAN.
-
During IPv6
reporting S6b information update, if information update AAA is pending and RAR
for restoration is received, then only the restoration will be handled. In this
case, ReAuth will not be performed again for extended restoration, even if
configured.
-
APCO for Update
Bearer Request (UBRequest) for extended P-CSCF Restoration in ePDG will be sent
at bearer context level itself. APCO is not at message level for UBRequest.
-
If S6b RAR
ReAuth is pending and AAA of ReAuth is not yet received when RAR for
restoration is received, then only the restoration will be handled. In this
case, ReAuth will not be performed again for extended restoration, even if
configured.
-
For PCRF based
P-CSCF Restoration/HSS based (S2a/S2b) P-CSCF Restoration, if UE PDN type and
the PCO requested P-CSCF address do not match (for example, PDN type is IPv4
and PCO P-CSCF requested in IPv6, and vice versa), then basic restoration will
be performed.
-
UE Capability
PCO and P-CSCF Restoration for S5/S8:
P-CSCF
Reselect Support
|
P-CSCF
Address Requested
|
MME-triggered Restoration
|
PCRF-triggered Restoration
|
✓
|
✓
|
Extended Restoration
|
Extended Restoration
|
✓
|
✗
|
Restoration Ignored
|
Basic
Restoration
|
✗
|
✓
|
Basic
Restoration
|
Basic
Restoration
|
✗
|
✗
|
Basic
Restoration
|
Basic
Restoration
|
For S2a only, if
MCM mode/WPMSI flag and UE P-CSCF re-selection support and P-CSCF address
request is received, then only extended P-CSCF Restoration will be performed.
For all other scenarios, if P-CSCF Restoration Indication is received, then
basic P-CSCF Restoration is performed.
If both MCM/SCM
flag are set, then it’s considered SCM.
For S2b only, if
UE P-CSCF re-selection support and P-CSCF address request is received during
establishment or handoff is received, then only extended P-CSCF Restoration
will be performed. For all other scenarios, if P-CSCF Restoration Indication is
received, then basic P-CSCF Restoration is performed.