Fixing 911 Overload

Every year, NENA – The National Emergency Number Association – estimates that there are over 240 million calls into 911 call centers (known as Public Safety Answer Points or PSAPs). A common problem among all PSAPs continues to be non-emergency calls arriving into the center on Their specialized 911 trunks that exist specifically for emergency calls. The quantity of these trunks is typically limited in each center and and the amount has been carefully engineered to handle the normal volume of 911 calls from the community served by that agency along with a few spares and diverse CO routing where available. The problem is that when they become flooded with non-emergency traffic, legitimate emergency calls could be blocked.

This design also makes the PSAP more susceptible to SWATTING and DDoS attacks by practically anyone and from anywhere. In some areas, emergency calls into a center that is busy may overflow to an adjacent PSAP. While this seems like a logical idea from a backup perspective, let’s examine the bigger picture here.

Not only does this expand the attack face from a SWATTING and DDoS perspective, it is actually quite useless unless there is a Mutual Aid and MOU agreement in place with the other agency. Without the proper authority and the radio comms infrastructure, as well as access to the CAD, there really isn’t much that those agencies can do other than answer the call and write down the information. They then need to figure out a way to get that incident to the agency that can provide service. Typically, if there is no access to the radio network of the adjacent community, or no visibility to the computer-aided dispatch or CAD system, there is little they can actually do with the information they have. Also, remember that if the call has overflowed to them in the first place, they might not even have a way of reaching the original agency using conventional methods, Where is the problem?

The Core Problem: Dedicated 911 Trunks

The existing 911 network in the US is dependent on specialized CAMA trunks. Queries for location use the Automatic Number Identification (ANI) received with the call to determine the location of the caller, and a direct peer-to-peer relationship exists between the PSAP and the local exchange carrier 911 Central Office using these single-purpose trunks.

Since these trunks are limited in number, when a non-emergency call arrives on an emergency trunk, that line becomes tied up for the duration of that call, even if the resource that handles the call is a non-emergency resource. This creates a traffic engineering problem, because now the number of trunks reserved to handle emergency calls are taking the additional non-emergency traffic, something that totally Skews the Erlang calculations used to engineer the number of circuits.

311 to the rescue?

Many believe, and cities like NYC and Philadelphia have implemented, a localized 311 non-emergency service designed to offload non-emergency calls from 911 Call centers and call takers. The call handling technology used to deliver a 311 service is similar to that in the 911 center. This allows the 311 facility itself to become a natural choice for a disaster recovery location or if a facility is needed to house a temporary relief workforce for the 911 center due to capacity or physical damage.

The fact that a 311 center exists though, does not itself provide a solution to the problem, a little more is required. The root cause of the overload issue noted earlier is that people dial 911 when they should have dialed 311. In other words, their call is arriving on the wrong network, and that wrong network has limited resources from a trunking perspective.

Are rubber bands the fix?

While fixes for critical emergency communications from the public should never use duct tape and rubber bands, “elasticity” does bring significant value. Looking back on legacy trunking, of nearly any kind, there is the limitation of a physical circuit on a pair of copper wires. If I need one, I order one. If I need 10, then I order 10. If I need 10, but I only can get 8, then I am short by 2, and there is not much I can do about it. SIP trunking, on the other hand, is delivered over a data facility. The actual bandwidth on that facility can often be dynamic and Is commonly referred to as “a pipe.”

When thinking about the characteristics of data, often it equates very nicely to water. If I need to deliver more water, I need to get a bigger pipe; if I need to deliver more data, the same concept applies. That being said, an inherent benefit of a “data pipe” is that often the delivery medium is the same regardless of the capacity or size. Now a request to the carrier can turn-up or turn-down service capacities through software or configuration. Because of this, the size of the pipe becomes elastic and flexible to my current trends and needs.

Re-engineering with new capabilities

With this new elasticity capability in our network, let’s re-engineer things a little bit to take advantage of its capabilities.

Modern NG-911 Network on Dynamic Trunks

With all of these circuits moved to intelligent SIP trunking, I now have flexibility and sizing capabilities that allow me to be more dynamic with emergency and non-emergency call center call routing. The initial overall pipe capacity reflects best guess estimations for ALL TRAFFIC, and a new control layer of communication between my premise and the carrier networks exists to communicate any changes Required in the specific trunk route sizing required.

Sending these real-time statistics and state changes to the carrier allows real-time elasticity of IP trunking size to realize the most efficient use of resources. Calls to 911 are automatically flagged as such and routed to the 911 CPE where call takers answer. Similarly, calls to 311 are automatically flagged as such and routed to the 311 CPE, where call-takers also answer those calls. By doing this, the number of simultaneous calls to each type of service is controlled by the CPE.

Should a 911 call end up being a non-emergency situation, and the call gets transferred to the 311 center for assistance, a signal is sent to the carrier to add additional bandwidth to the inbound 911 trunk group to compensate for the non-emergency call.

How bandwidth is calculated and allocated is something that now becomes totally under the control of the receiving agency. For example, let’s go back to our disaster recovery scenario. A significant natural event is impacting the local area. An anticipated  20% increase of 911 call taker staff will require 15 additional call-taker seats. In the 311 Center, 15 seats get flagged as auxiliary 911 positions and get staffed by 911 personnel. An increase in carrier bandwidth allows for the additional call volume expected.

This scenario is just another example of why the nation needs to move to NG 911 quickly. The Legacy 911 network in the US uses analog CAMA trunks that are special-purpose and fixed in their capacity. Increases must be pre-engineered and may take weeks or months to implement or sit idly unused, causing unnecessary charges to stack up to municipalities. The technology to accomplish this architecture already exists in nearly every commercial market in existence today. We should heed the lessons learned over many years and provide the same level of innovation to our most essential call centers, ones that save lives.

Follow me on Twitter @Fletch911
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© 2020, All Rights Reserved, Mark J. Fletcher, ENP
Reuse and quote permitted with attribution and URL


  1. Mark, the headline misses the mark a bit. You give a fair explanation on the limitations of CAMA trunks but it is missing several of the moving parts & pieces on overload issues. First, implementing the mentioned NG911 ESINET ‘Provider’ requires regional if not statewide coordination. The provider routes the calls based upon location data embedded within the call frame. This requires a huge amount of database work to move from address concentric data to spatial. Not that it won’t occur in the future, but it is usually beyond the resources of the typical PSAP provider.

    Second, simply increasing the incoming call capability to a particular PSAP does not necessarily allow the processing of more calls. That is a byproduct of the number of telecommunicators on duty. With selective routed CAMA trunks, calls are routed to alternate PSAPs when trunks are busied-out, taking advantage of additional personnel. With SIP based trunking, it becomes a factor of logged in phones. Do you set the phones to provide a visual or audible indicator when the +1 call arrives? Or, is the call auto-routed to an alternate center and then re-routed by transfer? During overload periods, it does not matter if the caller gets a busy signal, continuous ringing or ends up on hold. The caller will hang up and dial again.

    Not every incoming 9-1-1 call is at the incident’s location. Questions must be asked and calls redirected when necessary. NG911 does not change that scenario. Neither will it eliminate the potential for DDOS or SWATTING, especially with burner phones, SMS and fake video. IP is IP.

    As far as the fusion of 9-1-1 and 3-1-1 routing, a bit more thought is required. Most states require the documented competence of 9-1-1 telecommunicators to answer 9-1-1 calls. Overload and transfer calls can only be routed to another ‘certified’ PSAP. That would imply that 3-1-1 operators would require 9-1-1 certification or, 9-1-1 telecommunicators would do 3-1-1 in their ‘spare time’, NOT!

    The best practical cure is consolidation of the PSAP function into larger, regional organizations which have the personnel capacity to absorb incident based overload generated at the local level i.e.: weather, vehicular collisions, etc. Also, regional coverage limits the number of inter-PSAP transfers. While it will not eliminate overload in catastrophic conditions, it buffers the routine spikes. Perhaps future auto-attendant AI will help in screening duplicate reporting.

    As witnessed over a period of 48 years in ‘the business’, technology improvements rarely ‘fix’ operation issues. I’m with you in the move to NG911, just don’t forget that adding text and video into the mix has it’s own workload requirements. Without a different approach to workload distribution, NG911 will make overload worse. Technology + approach + people is needed to address 9-1-1 overload. Even then, when the hurricane or earthquake hits, overload is a fact of life.


  2. Hi Mark, we read your article and the comments of Richard Tucker with interest. All good points, but there are other ways to solve this issue. Have a look at Below is the E! News version:

    FailSafe Offers Patented Solution for Unanswered 911 Calls

    Who is calling 911 right now but not getting through? Dallas-based FailSafe Communications believes it has the answer. FailSafe is the first licensee of technology that uses Signaling System 7 (SS7) to find the people most in need when disaster strikes. Until now SS7 has been used almost exclusively by phone companies and it has changed little in decades. Today U.S. Patent No. 10,812,663 was issued and it changed all that. The trade name for the service is TeleSentient.TM

    Most people do not realize that the wireless and landline networks we use every day are really two networks. One is the voice network that carries our speech. The other is the SS7 network that tells the voice network what to do. Leo A. Wrobel, inventor of TeleSentientTM and longtime disaster recovery expert, uses the SS7 network to reveal the impact of disasters and outages on real people, in real time.
    To put it another way, dialing every phone in America to look for people in trouble or locate outages would clearly be annoying and impractical. Wrobel has patented a process to do basically the same thing, but in seconds, and without having to call anyone’s phone. According to Leo:

    “It’s easy to spot a disaster. Anyone can turn on weather radar. The problem is knowing exactly WHO the disaster is affecting before it’s too late to help them.”

    TeleSentientTM data can be displayed on a Network Operations Center display, personal computer or smart phone. It can operate in both stand alone mode or in combination with external data. Imagine a tornado on a weather radar screen that also displays every 911 caller in the vicinity at that moment.
    The Pacific Disaster Center produces a variety of products that assess impacts of a disaster on lifelines, including power, communication, and transportation. Knowing where the power is on and where the phones are working are vital components of effective planning and response.
    – Ray Shirkhodai, Executive Director Pacific Disaster Center

    Available tools such as the DisasterAWARE® application by the Pacific Disaster Center provide real-time threat monitoring capabilities that stand well alone, but can be enhanced with TeleSentient.TM Using TeleSentientTM in its “passive observation” mode, combined with tools like these, users can spot problems as they happen. “Hey, Tulsa just turned red on the display. I wonder what happened there?”

    In some cases the “red” area might not be a disaster at all. It could just as easily be a mass calling event due to a riot or a large swing in financial markets. TeleSentientTM spots these events as well, opening up even more possibilities for this technology. After all, who would not want to know when all of Wall Street’s lines turn red or when a dozen 911 calls just originated from a grade school?

    About the Inventor: Leo A. Wrobel was the first in the U.S. to build a Disaster Recovery Center in a telephone office and first to run phone traffic on the Dallas cable system. He has consulted on disaster recovery for hundreds of Fortune companies. He founded the first 50-state CLEC and serves as an Expert Witness in high-stakes technology disputes. See the Leo A. Wrobel Companies at or visit for more information on his patent.


  3. Valid point for TODAY’s network, but SIP based NG911 is being rolled out, and that will be the demise of the legacy analog networks with their SS7 signalling. The question becomes, “Do we spend money fixing an end-of-life technology, or do we accelerate the evolution of NG911?” For me, I vote on the latter. Thanks for the comments! Best of luck on your patent and technology.



  4. NG911 or not, as long as there is one landline left on the planet, SS7 and H.323 /SIP will need to communicate with each other and any other conceivable technologies. By the way we were just awarded our second patent. Thanks for the kind words and good wishes.

    Liked by 1 person

    1. That is true, and the FE (Funtional Element) designed to handle that conversion is the LNG (Legacy Network Gateway). That box will sit in the central office. Converting the SS7 to a NENA i3 compliant IP protocol to be sent into the ESI Net. SS7 signalling will be contained to a patch cable between the CO’s cage and the ESI Net cage. 🙂

      Thanks for the comments, though, and congrats on your patent.


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