New SIP 603+ regulation effective date set
The effective date for the FCC’s new rule mandating the use of SIP 603+ for immediate notification of calls blocked by analytics has been set. Let’s have a look.
The rule
The new rule was adopted on February 27, 2025, by the Commission in the Eighth Report and Order on robocalls. Here’s the rule:
Any terminating provider that blocks calls based on any analytics program, either itself or through a third-party blocking service, must immediately return, and all voice service providers in the call path must transmit, an appropriate response code to the origination point of the call. For purposes of this rule, an appropriate response code is:
- In the case of a call terminating on an IP network, the use of Session Initiation Protocol (SIP) code 603+, as defined in ATIS-1000099, adopted August 16, 2022;
- In the case of a call terminating on a non-IP network, the use of ISDN User Part (ISUP) code 21 with the cause location “user”;
- In the case of a code transmitting from an IP network to a non-IP network, SIP code 603+ must map to ISUP code 21; and
- In the case of a code transmitting from a non-IP network to an IP network, ISUP code 21 must map to SIP code 603 or 603+ where the cause location is “user.”
Effective date
This rule is effective March 25, 2026.
DNO Do-Not-Originate blocking
The Eighth Report and Order also mandates that all providers in the call path use Do-Not-Originate (DNO) blocking.
The final rule states that the effective date of this requirement will be 90 days after the publication of a notice of approval by the Office of Management and Budget in the Federal Register. (The OMB is required to review some regulations by the Paperwork Reduction Act.)
We’ll be on the lookout for this notice, which will set the exact effective date for DNO blocking. Stay tuned.
More information
- Final rule published in the Federal Register
- Eighth Report and Order on robocalls CG Docket No. 17-59
- ATIS-1000099, Standard on Robocall Call Blocking Notification

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