Industry comments for robocall blocking report

In December 2019, the FCC issued a call for comments on robocall blocking. These comments were due January 29, 2020. Twenty-eight responses were filed. Don’t have time to read them all? We’ve provided a brief summary of each response.

We noticed a few recurring themes across these comments:

  1. Several carriers are using SHAKEN/STIR call authentication and call analytics for robocall prevention in their production networks.
  2. Representatives of high-volume callers commented that their outbound calls continue to be mislabeled and blocked. They asked for technology to inform the caller when their call is blocked and provide a way to challenge and remove inappropriate labeling and blocking.
  3. Several groups representing small and mid-sized carriers were concerned over their inability to participate fully in SHAKEN/STIR call authentication. They asked the FCC to address these barriers to industry-wide adoption.
  4. A group of consumer advocates joined together and asked the FCC for more robust, detailed reporting to accurately assess whether consumers are getting the protection they need.
  5. There were signs of confusion in some filings between call authentication and call analytics:
    • STIR/SHAKEN provides call authentication to determine whether caller ID is legitimate. It does not identify the intent or legality of a call. It does not identify nuisance calls.
    • Call analytics use call information and traffic patterns to identify calls that might be nuisance robocalls. Analytics don’t work as well when the caller spoofs caller ID, especially with valid phone numbers, i.e., neighbor spoofing.
    • Robocall prevention is more effective when both call authentication and call analytics are used together.

Here are summaries of the comments filed. If you’d like to read the full document, click the company name or document type in the header above each summary.

ACA International

  • Members continue to see lawful, legitimate calls blocked and mislabeled
  • Urges FCC to provide more uniform requirements for disclosure and unblocking
  • Asks FCC to require voice service providers to give notice when it places a derogatory label on a business’s outbound calling number
  • Criticizes use of terms “unwanted” and “illegal” calls—grouping these together complicates efforts to eliminate fraudulent calls
  • FCC should mandate that:
    • Carriers blocking a call provide caller with both an audio intercept and SIP error code informing them that their call was blocked
    • Carriers report the number of instances that callers report problems regarding blocked calls
  • Asks FCC to clarify that, as a result of the Pallone-Thune TRACED Act becoming law, voice service providers may no longer rely on “reasonable analytics” to block “unwanted” “robocalls” on an opt-out basis

American Bankers Association

  • Banks’ outbound calling numbers continue to be mislabeled and calls blocked. This increased after the Declaratory Ruling
  • Banks initiate a large volume of outbound calls in a short period of time. This causes call analytics to identify the calling number as spam.
  • Banks are not notified when their calls are blocked. Instead, they receive a busy signal.
  • When a bank resolves the blocking and labeling issues with a voice service provider, the problem soon reappears. Feels like playing “whack-a-mole.”
  • The ABA encourages the FCC to require voice service providers to notify callers when it places a derogatory label on its outbound calling numbers and to send an intercept message when a call is blocked
  • FCC should require voice service providers to provide a robust challenge mechanism that removes an inaccurate label or improper block promptly, permanently, and without cost to the caller

AT&T Services

  • Overview of call blocking services offered
  • Began offering opt-out blocking in July 2019
  • Began offering call validation display in December 2019 using SHAKEN/STIR. Tested 11 labeling options, and Valid Number conveyed the most accurate information with less chance of confusion.
  • Surveys and lab simulations estimate answer rates and trust levels increase by 16-26 percent, with no negative effects on non-marked calls
  • Estimate false positives of less than one percent in its global fraud program
  • SHAKEN/STIR will be even more useful as it becomes broadly deployed and when used in conjunction with other tools to address illegal and unwanted calls.


  • In response to questions about possible disruption of emergency service, ATIS noted that a new draft is being considered by the IETF to enable signing of 911 origination and callback calls. The new technique could be used to prioritize emergency calls for treatment by local policy among providers.

Charter Communications

  • Has implemented STIR/SHAKEN with residential customers, is exchanging signed calls with Comcast and testing with other carriers
  • Plans to offer robocall blocking by default
  • Using DNO request from Industry Traceback Group to block calls with those calling numbers
  • Beginning data collection for the reassigned number database.
  • Plans to combine call pattern data analytics with STIR/SHAKEN call authentication to identify and block known nuisance and fraud callers.

Comcast Corporation

  • Blocking calls from DNO, invalid or unallocated numbers
  • Has implemented STIR/SHAKEN with residential customers

Competitive Carriers Association

  • SHAKEN/STIR will not be the cure-all solution for robocall abuse
  • Many carriers continue to exchange TDM voice traffic, which presents challenges for SHAKEN/STIR
  • Members are exploring user app and network blocking approaches

Consumer group comments

A group of consumer advocates joined together to provide comments on robocall blocking. These groups include:

  • Consumer Reports
  • National Consumer Law Center
  • Consumer Action
  • Consumer Federation of America
  • National Association of Consumer Advocates
  • Public Citizen

This group says the FCC should:

  1. Require voice service providers to report specific information rather than simply request the information
  2. Require the information include a description of each program for call authentication and opt-in/opt-out
  3. Require every voice service provider to provide the dates by which call authentication and call blocking will partially and fully implemented
  4. Require every voice service provider that does not use STIR/SHAKEN to explain how calls will be handled, whether STIR/SHAKEN limitations are for inbound and/or outbound calls, and what alternative mechanisms the providers will provide
  5. Require every voice service provider to give a description of call blocking and labeling mechanisms provided on an opt-in and opt-out basis, along with an analysis of the number and percentages of customers who use them
  6. Require all providers to evaluate the efficacy of anti-robocall measures used
  7. Ask callers and call-blocking companies to provide information that would be useful for this report

Cox Communications

  • Blocks calls with DNO, invalid and unallocated calling numbers
  • Offers anonymous call blocking and Nomorobo as an option
  • Blocks 14.6% of incoming call attempts to residential customers
  • Blocking tools will be aided by call authentication frameworks such as SHAKEN/STIR
  • Will have SHAKEN/STIR available when IMS network transition is finished in Q1 2020

Credit Union National Association

  • Cautions against call blocking without the ability of legitimate callers to remove blocking or mislabeling of their calls
  • Says the FCC has no authority to authorize the blocking of legal calls


  • Difficult to assemble reliable data for statistical measure of blocking effectiveness—FCC should define terms and metrics to be collected
  • CTIA consumer survey showed increased appetite for call blocking
  • Ask for broad safe harbor for carrier call blocking

Encore Capital Group

  • Concerned that carriers are over-blocking and mislabeling calls
  • Debt collectors typically attempt to reach debtors 17 times before resorting to litigation. If these calls are blocked, more debtors will end up in litigation.
  • Callers need instant notification that their call is being blocked and why
  • Ask for a way to white list calling numbers used by large-scale callers

First Orion Corp

  • Since there are no standards for data collection, cautioned against comparing apples to oranges
  • Ask for broad safe harbor for carrier call blocking. Lack of safe harbor slows down deployment of call treatment tools.
  • Approximately 25-30% of traffic is identified as scam calls
  • Only a fraction of 1% of subscribers have chosen to turn off “scam likely” labeling
  • Only a third of false positives/negatives turn out to be misidentified
  • No central DNO list exists


  • Some members have had legal calls blocked
  • Encourages FCC to include false positives in measuring effectiveness of call blocking
  • Urges FCC to provide clarity on what call-blocking treatments are “reasonable”
  • Recommends FCC report on standardized response codes for rejected calls
  • Urges the FCC consider concerns expressed by NTCA about barriers to industry-wide adoption of SHAKEN/STIR from lack of IP interconnection availability

National Association of Federally Insured Credit Unions (NAFCU)

  • STIR/SHAKEN framework must ensure that calls that legitimate businesses, including credit unions, place to their customers are not blocked
  • Credit unions place thousands of calls to their members related to data breach, fraud alerts, loan servicing and collections. Currently these calls are delayed or blocked due to an unclear and inconsistent call blocking environment.
  • Described problems with calls that transit TDM networks not being signed or receiving only a gateway attestation as it enters the SIP network
  • Recommends that the FCC:
    • Direct service providers not to block unsigned calls until STIR/SHAKEN is fully implemented
    • Authorize service providers to block only calls that have been properly authenticated with full attestation
    • Require service providers to notify the calling party of blocks and remove erroneous blocks within 24 hours as a requirement for safe harbor protection
    • Fully authenticated calls should not be blocked using analytics

National Opinion Research Center

  • Conducts the CDC’s National Immunization Survey to gather public health info, primarily by telephone
  • Call completion rate has eroded. Calls are being labeled as spam by call analytics
  • NORC has been unable to get this situation addressed. No party in the call blocking ecosystem appears to be accountable.
  • NORC would support a national white list program that would include critical calls, such as the CDC’s NIS
  • “Reasonable analytics” must be subject to objective criteria
  • Federal government callers should be able to demonstrate qualification for any white-list program
  • FCC cannot adopt safe harbor provision for call blocking until call authentication and analytics frameworks demonstrate transparency and have adequate immediate redress for false positives

NCTA – The Internet & Television Association

  • Encourage the FCC to adopt a broad safe harbor and establish a centrally compiled and maintained Critical Calls list

NENA: The 9-1-1 Association

  • Public Safety Answering Points (PSAPs) have themselves been victims of robocalls. These are at least a nuisance and at worst an interruption that leads to delays in responder dispatch
  • PSAPs attempt to call back a caller when a 9-1-1 call is dropped without resolution. There is little that differentiates these call backs from any other call. NENA is aware of some of these calls being blocked only on an anecdotal scale.
  • Given the life-threatening implication of such calls being blocked, NENA urges the FCC and voice service providers to ensure these calls don’t get blocked
  • NENA has developed a secure database, web portal and map that contains info about PSAPs through the U.S. They call this the NENA EPRC. It offers export and API functions. It is scheduled to launch mid-February 2020. It may need several months to be fully populated with all PSAP outbound lines in the U.S.
  • NENA says this system may help the robocall blocking services avoid blocking PSAP calls

Noble Systems Corporation

  • The FCC should:
    • Define criteria for defining when call analytics can be used to block illegal robocalls
    • Define circumstances that would justify a carrier using analytics to block a fully authenticated call
    • Ensure that carriers do not over-block legitimate calls
    • Make call blocking transparent to the caller by mandating an audio intercept and a SIP error code
  • A fully authenticated call should be presumed to be a legitimate call
  • Proposals for a Critical Calls List (CCL) should be cautiously and skeptically considered by FCC, and only after experience with call authentication is obtained
    • If fully authenticated calls are considered legitimate, then there’s no need for a CCL
  • Analytics should rarely, if ever, be used to block fully authenticated calls
    • Use traceback to investigate bad actors instead

NTCA – The Rural Broadband Association

  • There is a severe risk of a “reverse call completion” problem, where calls from rural areas cannot be authenticated with STIR/SHAKEN
  • The primary barrier to SHAKEN/STIR is the lack of IP interconnection agreements available to rural carriers
  • Even if RLECs are all IP and invest in the SHAKEN/STIR infrastructure within their own networks, the end-to-end-all-IP nature of this standard will render that investment useless
  • It is quite possible that ill-intentioned spoofers will migrate to rural telephone numbers
  • The increased use of call blocking applications could result in legitimate calls from rural areas being blocked
  • For the first time ever, the costs of transport for voice traffic to and from rural service areas would be foisted solely onto small rural customer bases without any additional universal service support to cover such costs
    • The FCC should adopt a simple default rule that maintains existing interconnection points and transport responsibilities whether a call is exchanged in TDM or IP
  • The FCC should seek comment on and encourage industry cooperation on call authentication alternatives that could function with the continued presence of TDM facilities, such as Out-of-Band STIR
  • The NTCA urges the FCC to:
    1. Adopt basic rules of the road with respect to interconnection for the exchange of voice traffic between IP-enabled networks
    2. Encourage industry cooperation in alternative call authentication methods due to the continued presence of TDM
    3. Require that providers implement guardrails, such as intercept messages to tell blocked callers why their call was blocked and a rapid redress process to correct mistakenly blocked calls


  • Has observed inconsistencies across analytics in identifying the risk rating of numbers that Numeracle has vetted
  • Although customer complaints can be useful in evaluating a number’s reputation, number reassignment and customer confusion make scoring problematic
  • Current practices incentivize callers to change and or rotate through a pool of numbers when a number acquires a bad rating
  • The FCC should ensure that carriers provide a redress mechanism for improper labeling and blocking

Professional Association for Customer Engagement

  • Carriers should:
    • Implement intercept announcements and SIP error/cause codes to alert callers whose calls are blocked and improve processes to rectify erroneous blocking
    • Disclose on their website a toll-free number and email address that will connect a caller to an error resolution team
    • Respond to error resolution claims within one business day after receiving all requested information from the caller
    • Report complaints of erroneous call blocking to the FCC


  • Has installed SHAKEN/STIR in its network and is testing with select carriers
  • Has launched a call screening application
  • There is no reliable means of quantifying illegal calls. For example, a carrier cannot know whether a customer consented to receive a call, whether a call is perpetrating a scam or whether a call is legal but unwanted.
  • Sprint blocks calls when the calling number is invalid, unallocated or on a DNO list. However, they do not block unassigned numbers, since they don’t know whether an allocated number has been assigned.
  • Sprint has not observed evidence of 911 calls being blocked
  • Sprint does not support efforts to create a list of emergency numbers, as that would create a list for bad callers to spoof. Instead, Sprint supports efforts to identify all callers accurately using SHAKEN/STIR.

T-Mobile USA

  • Were the first wireless provider to fully implement STIR/SHAKEN. Are currently capable of signing and authenticating 100% of SIP traffic that both originates and then terminates on their network.
  • Use call display Caller Verified for calls verified using STIR/SHAKEN
  • The effectiveness of call blocking cannot be measured by any one or two metrics. Instead, they should focus on overall results.
  • T-Mobile suggested a few statistics that might be useful:
    1. Percentage of calls analyzed
    2. Number of customers that have call blocking tools available to them as a percentage of total customers
    3. Percentage and accuracy of calls that appropriately receive various scam and other call treatments. This is heavily reliant on customer input, so carriers need to provide easy ways to collect feedback.
  • The FCC should encourage providers to develop new tools and innovations
  • The Commission should develop a robust safe harbor that is technology agnostic and allows both reasonable analytics and STIR/SHAKEN
  • To ensure calls from emergency call centers back to customers are not blocked, T-Mobile disables scam identification and blocking for 911 callers for a period of time.

Transaction Network Services

TNS provided comments and results of a survey.

TNS comments

  • Estimates that 30% of intercarrier calls are either nuisance or high risk
  • Only 12% of negatively scored traffic originates with tier 1 carriers, even though they originate over 70% of all calls
  • Bad actors are originating calls on networks other than those of tier 1 carriers
  • Bad actors are shifting from spoofed VoIP numbers to spoofed toll free numbers
  • Increase in neighbor spoofing and spreading illegal calls across a larger set of numbers
  • SHAKEN/STIR will help respond to these tactics
  • Encourage a broad safe harbor for blocking
  • Not aware of any instances of call blocks to 911.
  • Has seen a few instances of outbound calls from emergency centers blocked. This can be avoided by using a valid telephone number that can receive inbound calls, even if different from the number placing the call
  • Supports Critical Calls List

TNS survey

  • Shared results of a survey conducted in late June 2019
  • Majority of consumers do not want carriers to block calls from callers not in their contact list
  • Majority of consumers want carriers to automatically block high risk calls
  • Majority of consumers want nuisance calls sent to voicemail automatically
  • Slight majority of consumers prefer to screen their own calls rather than carrier doing it for them


  • We commented on the availability of call-blocking tools, effectiveness of these tools, the impact of FCC actions and the impact of call blocking on 911 services and public safety
  • In addition, we urged the FCC to support Out-of-Band STIR, which would enable STIR/SHAKEN to be used regardless of the type of network segments used to route the call
  • Availability of tools
    • Dynamic traffic analysis
    • Phone number reputation lookup
    • Blacklisting – especially helpful to thwart neighbor spoofing
    • Database of high risk numbers
    • SHAKEN/STIR – not a robocall prevention tool per se, but makes other tools more effective
  • Effectiveness
    • Neighbor spoofing undermines the effectiveness of analytics
    • Carrier blacklisting of inbound calls with their own calling number coming from outside their network is very effective in thwarting neighbor spoofing
  • Impact of FCC actions
    • Carriers are more aggressive in blocking invalid numbers and calls using their calling numbers coming from outside their network (neighbor spoofing)
    • Carriers still ask their customers to block other calls, such as with phone number reputation lookup services
  • Impact on 911 services and public safety
    • Our service provider customers do not inspect 911 calls for possible blocking
  • Other relevant information
    • We encouraged the FCC to support Out-of-Band STIR to extend the benefits call authentication to all consumers


  • The FCC should allow flexibility in measuring the effectiveness of call blocking, since providers use different methods, which are constantly evolving
  • FCC should provide broad safe harbor for call blocking
  • USTelecom’s Industry Traceback Group (ITG) stands ready to traceback illegal spoofing of emergency numbers and partner with law enforcement to go after callers placing such calls
  • In 2018, USTelecom conducted about 20 tracebacks/month; in 2019, 110/month
  • Traceback time has dropped from weeks to days—sometimes even hours
  • USTelecom maintains the government DNO list


  • Using STIR/SHAKEN for wireless customers
  • Are using STIR/SHAKEN status of incoming calls in their analytics engine.
  • Enhanced call blocking to use STIR/SHAKEN verification status. For example, if a bad actor spoofs a legitimate customer number, the spoofed calls are blocked, but calls from the legitimate customer are not.
  • Has a feedback website, which invites legitimate callers and consumers to tell Verizon about calls they believe were treated incorrectly
  • Runs a honeypot program to identify mass calling campaigns with a high degree of certainty
  • Advocates know your customer policies be adopted by all carriers so they can take bad actors out of their networks

Robocall blocking comments