Call blocking notification—old technology or new?

The FCC asked for comment on its Sixth Further Notice of Proposed Rulemaking (FNPRM) on immediate notification of call blocking. Here’s our review and recap of recurring themes.

You may recall that the FCC had ordered providers to send SIP 607 or 608 beginning January 1, 2022. The FCC changed this rule on December 10, 2021, with an order on reconsideration and call for comments on proposed rules. Here’s the first round of comments.

Here’s a list of the commentors with links to their comment summaries.

Recurring themes

Nine entities filed 58 pages of comments. Here are the recurring themes that we noticed:

  • Commenters representing callers and some industry associations say that SIP 603 does not provide actionable information for redress. Therefore, it doesn’t satisfy the TRACED Act.
  • Commenters representing carriers and an analytics firm say that SIP 603 is adequate, or at least the most pragmatic choice.
  • A few pro-603 commenters also mentioned discussions to improve 603. It’s an awkward bit of mixed messaging: 603 is fine, but just in case it isn’t, we’re talking about making it better. This is explained with a claim that improving 603 might take less time than rolling out 607/608.
  • There was a flurry of comments filed on this topic throughout 2021. It’s notable that many who participated in those comment cycles are sitting on the sidelines for this round.


Here are quick summaries of each comment filing. You can read the entire filing by clicking the heading above each comment section.

ABA and Joint Trade Associations

  • Terminating providers should eventually use only SIP 607 or 608 to provide immediate notification of blocking.
  • The Commission should request that ATIS submit a projected time for finalization of operational standards for these codes.
  • The FCC should set a firm deadline for mandatory use of SIP 607 and 608.
  • SIP 603 does not satisfy the redress standard mandated by the TRACED Act.

First Orion Corp

  • The Commission should not further define what constitutes “reasonable analytics” for the purpose of call blocking authorizations. Further definitions could potentially reveal methodologies, stifle innovation and inhibit the flexibility needed to adjust to illegal tactics being used.

INCOMPAS and the Cloud Communications Alliance

  • The Commission should retain SIP 607 and 608 as the ultimate form of immediate notification, seek input from standards setting bodies on a reasonable deadline for implementation and ask industry to submit periodic progress reports.
  • The Commission should reject efforts to make SIP 603 a permanent solution. It doesn’t provide actionable information. Time and effort would be better spent finalizing standards on SIP 607 and 608.
  • Since SIP 603 doesn’t indicate why a call was blocked, typical network architecture dictates that the rejected call be retried along a different path. These retries consume network capacity.

National Opinion Research Center

  • The Commission should direct the adoption and use of only SIP 607 and 608.
  • The NORC really needs immediate knowledge of any calls blocked and actionable information about who blocked the call.
  • SIP 603 could not meet the notice and transparency standards articulated in the TRACED Act.
  • Callers receiving SIP 603s are in no better position than they were before the immediate notification requirement.
comment bubble

NCTA - The Internet & Television Association

  • The Commission should reevaluate reliance on SIP 607 and 608 after the June 30, 2023 STIR/SHAKEN implementation deadline for small facilities-based providers.
  • SIP 603 provides sufficient information for legitimate callers to seek redress.
  • Standards work on SIP 607 and 608 is ongoing. Open issues should be resolved before they are used.
  • SIP 607 and 608 could give bad actors visibility into robocall mitigation efforts and enable them to circumvent those efforts.

Professional Association for Customer Engagement

  • SIP 603 is an inadequate form of blocking notification. SIP 607 and 608 provide a superior level of detail.
  • The Commission should set a deadline for use of SIP 607 and 608.
  • The Commission should require those providers who can send SIP 607 and 608 to do so and stop sending SIP 603 in situations that require blocking notification.

Transaction Network Services, Inc.

  • The Commission should not sunset use of SIP 603 as a notification method. It should be allowed indefinitely.
  • SIP 603 provides actionable information for redress.
  • TNS is a participant in discussions about enhancing SIP 603.
  • TNS asks if the additional information provided by SIP 607 and 608 is necessary to seek redress? Would it materially affect the caller’s actions? If the additional information is not meaningful and the caller is likely to seek redress anyway, then any of the SIP 6xx codes would be sufficient.
  • The jCard should not be made required by the Commission; it should be optional.

USTelecom – The Broadband Association

  • SIP 603 is currently the best and most pragmatic solution to provide callers with actionable information.
  • It is likely that SIP 603 can be modified to include information to distinguish analytics-based blocking from other call declinations. This modification could likely be deployed sooner than it would take to deploy SIP 607 and 608.
  • If SIP 603 can meet callers’ needs more quickly and at lower complexity and cost than SIP 607 and 608, then it would be unreasonable for the Commission to require SIP 607 and 608.

Voice on the Net Coalition

  • SIP 603 does not provide any useful information to the originating carrier. Use of this code makes redress cumbersome and ineffective and drives up costs for consumers.
  • Near-term implementation of SIP 607 and 608 is necessary to recognize the benefits of STIR/SHAKEN, promote competition, and reduce consumer costs.
  • Some callers must pay a third-party service to temporarily whitelist their calling numbers to avoid call blocking. The process is cumbersome and expensive.
  • Redress with SIP 603 requires placing a ticket with the originating provider. They place a ticket with the next downstream provider, who in turn places a ticket with the next one until they find who blocked the call. This is cumbersome, difficult, and time consuming.
  • Failure to implement SIP 607 and 608 will leave smaller originating providers behind. They can’t compete with larger carriers who can afford third-party number management programs.
  • The Commission should establish a December 31 deadline for use of SIP 607 and 608.

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