This feature prepares a signalling anchor such that it is ready to receive and process an access transfer request for the current session .

The preparation takes place during session establishment. The notification is in the form of a SIP request. It includes the ID of the SIP dialog for the access leg to be transferred.

Feature cheat sheet

B2BUA Instance Originating / Terminating Point(s) in Session Plan Network Operator Data Subscriber Data Stateful or Stateless POJO or SBB Feature Other notes

SCC

Both Originating and Terminating

 
SipAccess_SessionCheck, SipAccess_PartyResponse

None

None

Stateless

POJO

Binds a name in ACNaming.

3GPP Rel 10 Packet Switched to Circuit Switched support is implemented as a grouping of features and Sentinel capabilities.

Related features are:

Prerequisite features

  • DetermineCallType

Network operator data

There is none.

Subscriber data

There is none.

Session input and output variables

Session input variables

Variable Type Description

CallType

Enum

Used to determine whether originating or terminating instance behaviour should be invoked.

EnhancedSRVCCBound

boolean

Indicates whether an activity context name has already been bound for this session.

FeatureCapsManager

FeatureCapsManager

Management interface for controlling Feature-Caps header values on outgoing messages.

Session output variables

Variable Type Description

EnhancedSRVCCBound

boolean

This field is set when the access dialog is bound to its activity context name.

FeatureCapsManager

FeatureCapsManager

Management interface for controlling Feature-Caps header values on outgoing messages.

Statistics

SCCBindEnhancedSRVCC statistics are tracked by the volte.sentinel.sip SBB and can be found under the following parameter set:
SLEE-Usage → [volte.sentinel.sip service name] → [volte.sentinel.sip SBB name] → feature.SCCBindEnhancedSRVCC

Statistic Increments when…​ 
Started

The feature is started.

 
FailedToStart

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

 
IssuedWarning

A non-fatal problem is encountered and the feature and issues a warning.

 
FailedDuringExecution

A fatal problem is encountered and the feature cannot execute correctly.

 
BoundACName

The feature binds and activity context name using the full dialog-ID.

 
BoundPartialACName

The feature binds and activity context name using the partial dialog-ID.

 
UnboundACName

The feature unbinds a full dialog-ID activity context name.

 
UnboundPartialACName

The feature unbinds a partial dialog-ID activity context name.

Behaviour

This feature binds an activity context name for the access dialog.

Activity Context Name Binding

The feature binds the access dialog (access leg in 3GPP terminology) to a normalised name in the Activity Context Naming Facility.

The binding takes place once a non-100 provisional or a success response is received for the initial INVITE.

The feature does not attempt to bind more than once per session.

Once the name is bound successfully, the feature sets the session output variable enhancedSRVCCBound to true.

The access dialog is as follows:

  • for an originating B2BUA instance, the access dialog is the dialog from the A party

  • for a terminating B2BUA instance, the access dialog is the dialog towards the B party.

Therefore when acting as an originating anchor, the feature obtains the full SIP Dialog ID from the response in SessionState.latestCallingPartyResponse.

When acting as a terminating anchor, the feature obtains the full SIP Dialog ID from the response in SessionState.latestCalledPartyResponse.

Procedure for normalising the name to use

The normalised name string is comprised of four parts:

  1. the CallID header in string form (for example, me03a0s09a2sdfgjk1491777)

  2. the remote tag parameter value (for example, 774321)

  3. the local tag parameter value (for example, 64727891)

  4. a string to help with readability (for example, esr indicating “enhanced SRVCC”).

Note

For the originating SCC B2BUA instance, the local tag is the from-tag, and the remote tag is the to-tag.

For the terminating SCC B2BUA instance, the local tag is the to-tag, and the remote tag is the from-tag.

These are then normalised into a single string form as follows:

  • CallID value followed by a semi-colon, then

  • r= followed by the value of the remote tag parameter, followed by a semi-colon, then

  • l= followed by the value of the local tag parameter, followed by a semi-colon, then

  • esr;

So, given the following:

  • CallID of me03a0s09a2sdfgjk1491777

  • remote tag parameter value of 774321

  • local tag parameter value of 64727891

We generate the following normalised string:
me03a0s09a2sdfgjk1491777;r=774321;l=64727891;esr;

The rationale for choosing a format like this is so that an administrator can look at the string, and see:

  • esr means it is enhanced SRVCC as opposed to SRVCC (because our BindSRVCC feature uses sr not esr)

  • r and l are easy short hand for remote and local.

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Sentinel VoLTE Version 2.7.0