SIP Codes for Call Blocking Scenarios: 603, 607, and 608
You may have noticed an increase in the appearance of certain response codes in failed call attempts, and wondered, "What do these new codes mean?"
In the SIP protocol, response codes are used to convey the status or outcome of a SIP Invite back to the SIP client originating the call. When a call attempt fails, the SIP response code explains the reason the call failed.
Three codes are being used more frequently to give you more insight into failed call attempts. The increased frequency does not mean calls are failing more often. There is no decrease in call completion rate due to this change. The change is only to provide more granular visibility into why calls did not complete.
Due to the large volume of calls that are spam or fraud, the major wireless networks use analytic engines to identify—and in some cases, block—suspicious traffic. Unfortunately, the analytic engines sometimes flag legitimate traffic causing those calls to be inappropriately blocked.
If a voice network blocks a call based on analytics, the blocking network returns one of three SIP response codes:
| SIP Response Code | Explanation |
|---|---|
|
603 |
General-purpose code that could mean the call was blocked by a voice network or by the call recipient |
|
607 |
The call recipient did not want the call and rejected it |
| 608 | The call was blocked by the terminating voice network or an upstream network |
Frequently Asked Questions
How are these SIP response codes treated by non-IP voice networks?
If a call is blocked by a non-IP voice network, ISUP code 21 is used.
If a blocked call transits both SIP and non-IP networks, then:
-
603/607/608 SIP codes are mapped into ISUP 21
-
ISUP 21 is mapped into 603 SIP code
How do these SIP response codes relate to spam warnings displayed as part of the caller ID?
These codes are used only when the call is blocked. If analytics result in a spam warning, that could have a negative influence on the call outcome (for example, the call recipient may ignore a mislabeled call), but these codes are used only if the call outcome is blocking.
What actions can a legitimate enterprise take if failed call attempts have these SIP response codes?
Businesses and other organizations can register their phone numbers with the three major analytic engines (powering the three major US wireless carriers) at the Free Caller Registry.
IntelePeer also offers more advanced Reputation Management services to address call blocking and mislabeling issues.