The animated tutorial is available at: http://blog.tmcnet.com/cross-talk/

This is an introduction not an indepth analysis of NENA-National Emergency Number Association (www.nena.org) recommendations regarding IP/SIP and E911.  There are many open issues to be resolved such as:

- Users - stationary (fixed location), nomadic (user who can move) and mobile (user who is moving), etc.

- Media - wireline, wireless, infrared, game box, zigbee, etc.

- Format - voice, text/email, IM-Instant Message, SMS-Short Message Service (SS7), TTY, other data formats, language identifier, etc.

- Security - encryption, digital certificates, etc.

- Functional support - overflow ACD-Automatic Call Distribution to PSAP agents and other PSAP sites and transfer back, PSAP VPN-Virtual Private Network access and security, conference call, database queries, muting, etc.

Before reviewing next-generation E911 systems via IP, let's explore one potential benefit.  Here is an example of IMS-IP Multimedia Subsystem application for public safety using SIP-Session Initiation Protocol used for enhanced, multi-user, multi-media conferencing.  Internet access or VXML-Voice eXtensible Markup Language applications can be directed based on an exception-triggered instant conference such as a disaster.

In planning new SIP/VoIP systems, there are many new considerations.  For example, the NIST Report on VoIP, indicated "special consideration should be given to E-911 emergency services communications because E-911 automatic location service is not available with VoIP in some cases."  That is, SIP and VoIP systems are, for the most part, designed to be location-independent.   

1 - LIS-Location Information Service distributes Location Object to user

2 - Call Origination -  sos@company.com from callback tel.enum

3 - Submit Query -  sos@company.com from callback tel.enum

4 - Query Response - valid, routing, ESQK-Emergency Services Query Keys

5 - Call Routing Call Server to ESGW-Emergency Services GateWay

6 - Call Routing - ESGW to E-911 SR-Selective Router

7 - Deliver Call to PSAP

8 - ALI-Automatic Location Identifier Query to ESQK

9 - Submit Query ESPOS-Emergency Service Point of Service for ESQK

10 - Query Response - Callback, LO-Location Object

11 - ALI Response - Callback, LO-Location Object

12 - VPC-VoIP location Positioning Center clears call for new call

There are too many places where hackers can attack this process to mention.  However, spoofing LO-Location Objects via LIS-Location Information Servers, redirecting (intercepting) packets between the Call Server and the ESGW seem likely places for attacks and DOS-Denial Of Service attacks on any of the routers will also be prime targets.

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