1. Configuration Guide
  2. STIR/SHAKEN Client
  3. Per Call Availability of STI Servers
  4. Call Rejection Enhancement

Call Rejection Enhancement

You can configure the SBC can provide more detailed reasons for rejecting a call towards the caller. You configure these reason-code and reason-text entries within your sti-response-treatment-config configurations. This feature applies to the messages sent by the SBC to the caller after it has completed its STI verification process.

By default, the SBC sends generalized reason detail to applicable stations for rejecting a call based on an STI-VS response. You can understand these responses as normalized verstats, presenting a standardized string for both ATIS and 3GPP deployments with the applicable SIP messages. As a result, the verstat information provided by the SBC may not be as specific as desired about the reason a call failed.

For example, without this feature the SBC tags the following call failure scenarios with the same verstat, No-TN-Validation:

  • STI-VS no request
  • STI-VS no answer
  • Answer with no verstat

The SBC, however, allows you to configure your sti-response-treatment-config to more provide more specific reason information for specific call fail scenarios, including:

  • No-TN-Validation-Timeout—STI-VS does not answer
  • No-TN-Validation-StiInvalid—STI-VS answer is meaningless (JSON missing or malformed)
  • No-TN-Validation-IdentityMissing—SIP Identity is missing (no request sent to STI-VS)
  • No-TN-Validation-TNMissing—TN is missing (no request sent to STI-VS)
  • No-TN-Validation-StiConstraints—STI constraints are exceeded (no request sent to STI-VS)
  • No-TN-Validation-Unreachable—STI-VS circuit-breaker is open (no request sent to STI-VS)
  • No-TN-Validation-ClientError—SBC internal failure (no request sent to STI-VS)

No-TN-Validation-Timeout—STI-VS does not answer

When you configure a sti-response-treatment-entry with a verstat of No-TN-Validation-Timeout and a reason-code that is “empty" or "0”, the SBC rejects applicable calls when there is a response timeout on the STI-VS server. However, the SBC adds "No-TN-Validation" (default) in the FROM.

When these requests to STI-VS servers time out, the SBC uses the verstat key “No-TN-Validation-Timeout” to find matches for rejecting these calls.

This first configuration example demonstrates the SBC providing a less accurate response. 

ORACLE(sti-response-treatment-entry)show
verstat No-TN-Validation-Timeout 
reason-code
role STI-VS
sip-reason-code
sip-reason-text

In this case, the SBC rejects the call with:

  • A “403 Forbidden” Response
  • STI-VS-REASON "" (Field left empty)
  • Reason Headers:
    • ATIS SIP Reason header—SIP;cause=403;text=Forbidden
    • 3GPP SIP Reason header—Empty - No reason header included

This second configuration example demonstrates the SBC providing a more accurate response. Here, the system adds "NoValidationTimeout" (your configuration) in the FROM. 

ORACLE(sti-response-treatment-entry)show
verstat No-TN-Validation-Timeout 
reason-code
role STI-VS
sip-reason-code 404
sip-reason-text
sip-reason-text NoValidationTimeout

In this case, the SBC rejects the call with:

  • “404 NoValidationTimeout” Response
  • STI-VS-REASON empty
  • Reason Headers:
    • ATIS SIP Reason header—SIP;cause=403;text=Forbidden
    • 3GPP SIP Reason header—Empty - No reason header included

No-TN-Validation-StiInvalid/No-TN-Validation-MalformedStiResponse—STI-VS answer is meaningless (JSON missing or malformed)

When you configure a sti-response-treatment-entry with a verstat of No-TN-Validation-StiInvalid and a reason-code that is “empty" or "0”, the SBC rejects applicable calls when there is a malformed response or missing JSON body from STI-VS server.

Again however, the SBC adds "No-TN-Validation" (default) in the FROM.

This first configuration example demonstrates the SBC providing a less accurate response. 

ORACLE(sti-response-treatment-entry)show
sti-response-treatment-entry
verstat No-TN-Validation-MalformedStiResponse
reason-code
role STI-VS
sip-reason-code
sip-reason-text

In this case, the SBC rejects the call with:

  • A “403 Forbidden” Response
  • STI-VS-REASON, composed of the HTTP status code plus status text
  • Reason Headers:
    • ATIS SIP Reason header—SIP;cause=403;text=Forbidden
    • 3GPP SIP Reason header—SIP;cause=HTTP status code;text=HTTP status phrase

Unlike the other cases in this section, you enable the man-compliance option in the sti-config to establish this more accurate behavior.

This second configuration example demonstrates the SBC providing a more accurate response. Here, the system adds "No-TN-Validation" in the FROM. 

(sti-response-treatment-entry)show
sti-response-treatment-entry
verstat No-TN-Validation- MalformedStiResponse
reason-code
role STI-VS
sip-reason-code 404
sip-reason-text NoValidationStiInvalid

In this case, the SBC rejects the call with:

  • A “404 NoValidationStiInvalid” Response
  • STI-VS-REASON includes http reason code + reason text
  • Reason Headers:
    • ATIS SIP Reason header—SIP;cause=403;text=Forbidden
    • 3GPP SIP Reason header—SIP;cause=403;text="4xx/5xx"

No-TN-Validation-IdentityMissing—SIP Identity is missing (no request sent to STI-VS)

Consider this scenario to be the same as the second configuration examples above, differing in your sip-reason-text and verstat configurations, which the SBC uses to find matches for rejecting these calls. 

verstat No-TN-Validation-IdentityMissing
sip-reason-text NoValidationIdentityMissing

Here, the system provides a “404 NoValidationIdentityMissing” Response, and a adds "No-TN-Validation" in the FROM.

No-TN-Validation-TNMissing—TN is missing (no request sent to STI-VS)

Consider this scenario to be the same as the second configuration examples above, but differing in your sip-reason-text and verstat configurations, which the SBC uses to find matches for rejecting these calls. 

verstat No-TN-Validation-TNMissing
sip-reason-text NoValidationTNMissing

Here, the system provides a “404 NoValidationTNMissing” Response, and a adds "No-TN-Validation" in the FROM.

No-TN-Validation-StiConstraints—STI constraints are exceeded (no request sent to STI-VS)

Consider this scenario to be the same as the second configuration examples above, but differing in your sip-reason-text and verstat configurations, which the SBC uses to find matches for rejecting these calls. 

verstat No-TN-Validation-StiConstraints
sip-reason-text NoValidationStiConstraints

Here, the system provides a “404 NoValidationStiConstraints” Response, and adds "No-TN-Validation".

No-TN-Validation-Unreachable—STI-VS circuit-breaker is open (no request sent to STI-VS)

Consider this scenario to be the same as the second configuration examples above, but differing in your sip-reason-text and verstat configurations, which the SBC uses to find matches for rejecting these calls. 

verstat No-TN-Validation-Unreachable
sip-reason-text NoValidationStiUnreachable

Here, the system provides a “404 NoValidationStiConstraints” Response, and adds "No-TN-Validation".

No-TN-Validation-ClientError—SBC internal failure (no request sent to STI-VS)

Consider this scenario to be the same as the second configuration examples above, but differing in your sip-reason-text and verstat configurations, which the SBC uses to find matches for rejecting these calls. 

verstat No-TN-Validation-ClientError
sip-reason-text NoValidationClientError

Here, the system provides a “404 NoValidationStiConstraints” Response, and adds "No-TN-Validation".