Aswath Weblog: An Overlooked E911 Requirement?

June 10, 2005

An Overlooked E911 Requirement?

Recently FCC issued a ruling on E911, requiring qualified VoIP providers to comply with the ruling within 120 days. All the discussions in the media and blogs have focused on location determination and how to accurately report that information to the emergency operator. If I remember correctly there are other requirements that have received scant attention, of which one may be difficult to implement within the required period.

There are three requirements related to “premature” call clearing initiated by the caller:

If, during the exchange of information the caller does not respond, the operator must be able to generate a high pitched tone (I forget the technical term for this tone).
If the caller disconnects the call abruptly, the operator must be able to call back the caller.
If the caller hangs up the phone but picks up the phone within 45 minutes, then the caller must be reconnected to the same operator as long as the operator has not disconnected.

It is straight forward to see that the first two requirements are easily met. But VoIP clients require additional intelligence to meet the third requirement:

The client should recognize that an emergency call has been initiated.
The client should not initiate call clearing procedure on its own, but wait for the operator to initiate it.
If the user requests clearing anyway, the client should store the session ID (or equivalent) till the operator clears the call or for 45 minutes, whichever comes first.
During this period, if the user wants to initiate a session, then the client should not follow the standard session setup procedure (dial-tone, digit collection etc) but directly issue reInvite (or equivalent) using the stored session ID.

This means that the ATAs deployed in the field need to be upgraded to meet this particular E911 requirement. So the question is whether this has to be done within the stipulated deadline? Or we will collectively ignore it because this covers an unlikely event?

Posted by aswath at June 10, 2005 03:07 AM

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Comments

HiHi, good luck!

This is an very old requirement and was used in step-by-step systems in addition to trace back malicious calls (MCI) manually. It was also available on request on every normal extension to trace back malicious call via hook-flash, with the execption that the call was hold only until the end-office of the caller. This was already a lot of fun to implement in digital switching systems.

But we should leave "the church in the village", as we say in German. You simply cannot implement each feature of an old technology 1:1, even if you consider VoIP as fixed line replacement. This is also true for an other requirement: remote power-feed from the local exchange. This is also gone with ISDN-NT1 and DECT-phones. And I do not think that you requirement is available on cellular phones used by more than 50% of emergency calls already.

Posted by: Richard Stastny at June 10, 2005 05:54 AM

Since this is a social policy, the political forces will prevail over the technical difficulties. It is very difficult to predict how the public debate will shape up. As you indicate the public seem ready to accept restricted application for cellular phones; so the question is will they accept it for VoIP. The next lawsuit will generate the public debate.

Posted by: Aswath at June 10, 2005 07:22 AM