This feature implements SCC-AS procedures for access transfer of a terminating call in the alerting phase using PS to CS SRVCC .

This page refers to SIP INVITE due to STN-SR or SIP INVITE due to ATU-STI as a "Handover INVITE".

Feature cheat sheet

B2BUA Instance SAS Support Originating / Terminating Points in Session Plan Network Operator Data Subscriber Data Stateful or Stateless POJO Feature or SBB Feature Feature FSM

SCC

Yes

Terminating

SipAccessPartyRequest, SipAccessPartyResponse, and SipMidSession_PartyResponse

No

No

Stateless

POJO

Yes

Statistics

SCCTerminatingPreAnswerSessionTransfer statistics are tracked by the sentinel.volte.sip SBB and can be found under the following parameter set in REM:
SLEE-Usage → sentinel.volte.sip service → sentinel.volte.sip SBB → feature → SCCTerminatingPreAnswerSessionTransfer
or with rhino-stats:
"SLEE-Usage.Services.ServiceID[name=sentinel.volte.sip,vendor=OpenCloud,version=4.1].SbbID[name=sentinel.volte.sip,vendor=OpenCloud,version=4.1].feature.SCCTerminatingPreAnswerSessionTransfer"

Parameter Type Description
Started

Counter

Incremented each time the feature runs.

FailedToStart

Counter

Incremented when Sentinel VoLTE encounters an error while attempting to start the feature.

IssuedWarning

Counter

Incremented when the feature encounters a non-fatal error while executing.

FailedDuringExecution

Counter

Incremented when the feature encounters a fatal error while executing.

TimedOut

Counter

Incremented when the feature does not finish executing within a reasonable time frame.

AccessTransferSuccessful

Counter

Incremented when the ACK to the 2xx-INVITE due to ATU-STI or STN-SR is received by the feature.

AccessTransferAborted

Counter

Incremented when the feature aborts access transfer procedures before the transfer is complete.

AbortedDuringRemoteUpdateUsingUpdate

Counter

Incremented when the feature aborts access transfer procedures while a remote update using a SIP UPDATE request is in progress.

AbortedDuringRemoteUpdateUsingInvite

Counter

Incremented when the feature aborts access transfer procedures while a remote update using a SIP INVITE request is in progress.

SentPost405Update183

Counter

Incremented when the feature sends a 183 response to the MSC after a 405 response is received for an UPDATE.

SentRemoteReInvite

Counter

Incremented when the feature attempts a remote update using a reINVITE.

SentRemoteUpdate

Counter

Incremented when the feature attempts a remote update using an UPDATE.

SentPostUpdate183

Counter

Incremented when the feature sends a 183 response to the MSC following an UPDATE-200 to the originating party.

SentInfoOnNewAccessLeg

Counter

Incremented when the feature sends an INFO to the MSC as part of an Access Transfer.

SentForked183Response

Counter

Incremented when the feature sends a forked 183 response following an UPDATE-200 with different SDP from the access transfer request.

SentImmediate183

Counter

Incremented when an access transfer does not trigger an UPDATE to the originating party and the feature immediately sends a 183 to the MSC.

TermAlertingTransferAttempted

Counter

Incremented when the feature attempts an access transfer from an alerting call state.

TermAlertingTransferSuccessful

Counter

Incremented when the feature successfully completes an access transfer from an alerting call state.

TermAlertingTransferFailed

Counter

Incremented when the feature fails to complete an access transfer from an alerting call state.

MaskedInviteEvent

Counter

Incremented when the feature masks delivery of further INVITE events on the new access leg.

UnmaskedInviteEvent

Counter

Incremented when the feature unmasks delivery of further INVITE events on the new access leg.

Behaviour

This feature implements SCC-AS procedures for access transfer of a terminating call in the alerting phase using PS to CS SRVCC. It includes support for media anchored in the ATGW and media non-anchored.

The behaviour is best described by reading section 12.3.4.2 in 3GPP TS 24.237. The feature implements the full text. A call flow diagram showing the media anchored case is in the Example call flow section of this page.

Removal of superfluous sessions is implemented through the SCCCoordinateSignallingAnchors and SCCRemoveSuperfluousSession features.

The following sections define additional behaviour to cover specification gaps.

UEs with an Allow header that does not include UPDATE

TS 24.237 specification doesn’t explicitly describe procedures at the SCC-AS for the case where a UE has specified an Allows header without including an UPDATE as the value. This feature implements behaviour as though it has received a 405-UPDATE when it receives the handover INVITE if:

  1. the speech media component of the session to transfer is not equal to that in the Handover INVITE, and

  2. the session to transfer has an Allows header without including UPDATE

That is, it creates a new early dialog towards the MSC using a 183 response. The 183 response includes signalling elements described in subclause 6A.4.3A. It includes an SDP answer:

  1. with c-line set to the unspecified address (0.0.0.0) if IPv4 or to a domain name within the ".invalid" DNS top-level domain in case of IPv6 as described in IETF RFC 6157; and

  2. including media of media types received in SDP offer of the SIP INVITE request due to STN-SR, which are also offered in the SIP INVITE request from the served user; and

Error responses other than 405-UPDATE

The specification does not describe behaviour for error responses other than 405-UPDATE. If a necessary SIP procedure fails due to an error response, the feature terminates:

  1. the old access leg

  2. the new access leg

  3. the remote leg

Example call flow

Please refer to 3GPP TS 24.237 appendix A.17.8. It is a single "successful case" for a terminating alerting access transfer where media is anchored in the ATGW.

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Sentinel VoLTE Version 4.1