This feature identifies SIP MESSAGES sent to the AS by E-CSCF to notify the AS that a subscriber has placed an emergency call. The feature records this information in Cassandra where it can be used by MMTel Determine PSAP Callback to identify calls as potential PSAP callbacks. A PSAP callback is a returned call to a subscriber made by a Public Safety Answering Point.

Feature Cheat Sheet

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

MMTel

Yes

Originating

SipAccess_SessionCheck

No

Yes

Stateless

POJO

Prerequisite Features

Cassandra storage

The feature requires access to a Cassandra database to store records of PSAP calls.

Data Schema

If PSAP call are recorded using the SIP MESSAGE mechanism as per MMTel Determine PSAP Callback Configuration then the Cassandra configuration as per the MMTel Determine PSAP Callback Data Schema is required.

Configuration

Configuration for this feature is stored in the MMTelPSAPCallbackConfigProfileTable profile table. Details can be found in the MMTel Determine PSAP Callback feature documentation.

Session Input Variables

Session State variable name Type Comments

SentinelSelectionKey

SentinelSelectionKey

Determines which configuration to use.

Subscriber

String

Subscriber value is used as the primary key in the Cassandra database as determined by SIP Subscriber Determination

RecordPsapCallCassandraSessionACI

ActivityContextInterface

The ACI used to update Cassandra.

RecordPsapCallQueryStartTime

Long

Used to determine and log latency of Cassandra queries.

Session Output Variables

Session State variable name Type Comments

RecordPsapCallCassandraSessionACI

ActivityContextInterface

Stored off so that the feature can detach from the ACI when finished.

RecordPsapCallQueryStartTime

Long

Used to determine and log latency of Cassandra queries.

Statistics

MMTelRecordPSAPCall 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 → MMTelDeterminePSAPCallback
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.MMTelRecordPSAPCall"

Statistic Incremented when…​

Started

The feature runs

FailedToStart

Sentinel VoLTE encounters an error while attempting to start the feature

FailedDuringExecution

A fatal problem is encountered and the feature cannot execute correctly

Misconfigured

The feature doesn’t have any config.

InvalidSipRequest

The feature was started with a SIP request which is not a MESSAGE.

RecordedPSAPCall

A PSAP call has been successfully recorded in Cassandra.

SentCassandraUpdate

The feature has sent an update to Cassandra.

CassandraError

The feature failed to send an update to Cassandra.

CassandraWriteFailed

The feature received an error response from Cassandra.

CassandraWriteSuccess

The feature received a success response from Cassandra.

SipMessageResponseSent

The feature sent a response to the incoming SIP MESSAGE.

SipMessagePassedThrough

The feature allowed the incoming SIP MESSAGE to continue propagating through the network.

CassandraResponseLatency

Time from sending the Cassandra request to receiving the Cassandra result, sampled on receipt of the result

Behaviour

The feature’s behaviour depends on the trigger. There are 3 supported triggers, a SipRequest, CassandraQueryResultEvent, and CassandraErrorEvent.

Invoked by a SipRequest

If invoked by a SipRequest trigger the feature first performs some checks to ensure that the request is a SIP MESSAGE. It then checks the request URI to identify messages notifying PSAP calls. SIP MESSAGEs that identify PSAP calls have a request URI of urn:service:sos.

If the SIP MESSAGE is identified as a PSAP call notification then the feature records that the subscriber has placed a PSAP call in Cassandra using a TTL as configured in the ExpiryTime profile field. The feature then waits for a response from Cassandra. If TerminateMessage is set to true the feature sends a 200 OK response to the incoming SIP MESSAGE otherwise the SIP MESSAGE is allowed to propagate through the rest of the network.

Invoked by a CassandraQueryResultEvent

This event indicates that the PSAP call has been recorded in Cassandra. The feature simply increments the appropriate statistics and sends a SAS log in this case.

Invoked by a CassandraErrorEvent

This event indicates that the PSAP call has not been recorded in Cassandra. The error is logged to SAS and appropriate statistics are incremented but no further action is taken.

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Sentinel VoLTE Version 4.1