The popular belief is:

[When you dial 911, your call ends up in a massive modern control room like environment that could be easily mistaken for NASA with all the latest bells and whistles that tells the 911 call taker exactly who you are, what you’re calling about, and your precise location]


Well, that might be the way it works on TV and in the movies, but the fact of the matter is the majority of 911 centers or PSAPs in the United States (about 80% of them in fact according to NENA) are only 2 to 4 answering positions. While the large “mega-centers” do exist in cities like New York, Chicago, and Los Angeles, they are certainly the smallest percentage.

Likewise there’s a mass misperception by the general public on the technology that a 911 call taker has at their fingertips. To those of my readers that are in the industry, it’s no great secret that the only “information” that is received on a 911 call is a telephone number, and the local equipment uses that phone number to query the telephone company database for the subscriber information resulting in the address. While that’s technology that is useful for residential fixed endpoints such as land lines where a telephone number equals a physical street address, that method of location discovery is completely useless for a device that is mobile by nature such as a cellular telephone.

Since cellular phones can be used anywhere in the country, when they make a 911 emergency call the number that is displayed initially at the 911 center, is a special number that is actually representative of the tower that is handling the call. This is known as “Phase I” location reporting. This number is called a pANI (pseudo Automatic Number Identification). While this provides the 911 call taker with a very general area that the call is coming from, it is initially used for determining what 911 center needs to get the call. All cellular calls, that’s right ALL OF THEM, initially arrive at the 911 center with Phase I location information.

While the call taker is working the call, about 8 to 15 seconds later, the 911 equipment makes a second query on the pANI number received, and by this time the cellular network should have been able to determine a more precise location of the caller, and returns that information along with subscriber data in what is called Phase II location information. Depending on the technology used to locate the device, the information is also assigned a reliability or accuracy score.

When the planets are all in alignment, and the 911 gods are shining down upon the network, this can produce fairly accurate location information, and in fact the FCC mandates that carriers provide this level of location accuracy on a certain percentage of calls. Now that you have the background information, here’s the earth shattering news that was published earlier this week in a letter to Acting FCC Chairwoman Mignon Clyburn by CalNENA president Danita L. Crombach, ENP.

The letter cites several alarming factors that came to light after a study of real-time data over a two-year period by public safety analytics company Public Safety Network. The data focused on the amount of cellular phone calls that had received Phase II data by the completion of the call.

The report focused on four areas within the state, San Francisco, San Jose, Bakersfield and Ventura County and noted that statewide, 45% of wireless 911 calls lacked Phase II data, with some areas such as Ventura County lacking that critical location information on more than 50% of the calls. Was it a particular carrier worse than the others? Not really, although some were better and some were worse the problem was consistent across all five major carriers (AT&T, Metro PCS, Sprint, T-Mobile and Verizon) and the report shows that even under the best scenario accuracy never surpassed 64% in December 2012.

Public Safety Networks Report

There’s quite a bit of speculation why these numbers indicate the problem is getting worse. While no specific hard analytical data was collected to define the root cause of the problem, it’s generally accepted among experts in the industry that to specific phenomena contribute to the problem. The first is the fact that cellular device saturation in the United States is estimated to be at 103%, meaning a device for every person in the country, plus a little. That first factoid directly leads to the second, where people are using their devices more and more inside of buildings and what the report calls “urban canyons”.


The urban canyon actually has two negative effects on cellular location discovery. The first is the fact that GPS signals typically need to be what’s called “line of sight” and therefore do not penetrate steel and concrete rendering them ineffective indoors. The second problem affects the backup location discovery mechanism typically used known as TDOA (Time Delay on Arrival). In layman’s terms, this is the time it took for the signal to travel between the transmitter (the cell phone) and the receiver (the cell tower). Given that radio waves travel at the speed of light, the distance between the two becomes a simple mathematical calculation. Using this information from two or more cellular towers, and old-fashioned radio triangulation can be used to pinpoint a transmitter’s location with surprising accuracy. Unfortunately cellular radio waves “bounce” off of buildings and do not travel in a direct line. These signal reflections, if severe enough, can actually increase the distance traveled skewing the calculation.

Bottom line, more people are carrying cell phones, therefore more people are making 911 calls from their cell phones, and people are within buildings during the work day. Add all of that together, and you come up with a decrease in accuracy statistic. Not because the problem got worse, but because more people are using the problematic method.

Now while this specific report covers California, one would imagine that this same phenomenon exists in every major metropolitan city across the US. So while communication habits have drastically changed with the multitude of smart devices now available at our fingertips, if we’re going to continue to enjoy an accurate level of public safety communications, the Federal Communications Commission is going to need to step in, and as the report states, “issue all necessary orders” to correct this problem.

So just bring this into full circle, if you have an enterprise PBX, and you feel that your cellular phone is a suitable replacement to addressing E911 within the enterprise, based on the information in this report you may want to think that over again.