1. Proposal for a Generic Emergency Call Support
July 2006
doc.: IEEE /0917r0
July 2006
Proposal for a Generic Emergency Call Support
Date:
Authors:
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Anne-Laure Selignan, Alcatel
Anne-Laure Selignan, Alcatel

2. July 2006
doc.: IEEE /0917r0
July 2006
Abstract
This proposal addresses requirement R11I1: Define IEEE functionality which would be required to support and Emergency Call service as part of an overall, multi-layer solution.
Anne-Laure Selignan, Alcatel
Anne-Laure Selignan, Alcatel

3. July 2006
Scope
This paper describes a solution for the provision of emergency services to terminals entering the customer premises that are not and will never be known / registered.
Note: Throughout the document, Call Manager encompasses MLTS, Media Gateway, Call Server, IP PBX, …
Anne-Laure Selignan, Alcatel

4. July 2006
Basic Principles
It is an unknown terminal therefore it cannot register to the Call Manager; the emergency call will be handled without registration.
The protocol for call setup of the terminal is not known (e.g. SIP, H.323, proprietary,…); we propose to make use of a specific port:
The Call Manager listens to this particular port incoming traffic from a terminal making an emergency call
The terminal directly sends RTP packets to the Call Manager on this port
Capability Negotiation cannot take place (H.245, SDP, …)
We make a priori choice which is to use G.711 since it is a mandatory codec in all VoIP standards.
Supporting such terminals implies open authentication/association and therefore security barriers are considered
Anne-Laure Selignan, Alcatel

5. July 2006
Solution Components
Following the Emergency Call Problem Statement, the solution contains the following key components:
Network Selection
Network Join
Admission Control and Traffic conditioning
Anne-Laure Selignan, Alcatel

6. Network Detection and Join
July 2006
Network Detection and Join
WLAN
LAN
PSTN
DHCP Server
AP/WLAN controller
Call Manager
PSAP
Beacon (Emergency Capability)
Icon or any information on the phone: Emergency enabled facility
Action of the end-user: dial Emergency Service number or press softkey
Open Authentication and Association to the Emergency Network
Access Granted to the Call Manager via this AP (Limited)
Anne-Laure Selignan, Alcatel

7. July 2006
Architecture
The terminal does not know a priori the IP address of the Call Manager. Higher layers have to handle this. Several options :
Get the Call Manager IP address via a new DHCP Emergency option
With destination-NAT on the LAN side to redirect packet to the Call Manager
Use of a new “well-known multicast address”: the terminal sends emergency packets to this multicast address.
We need to choose only one for interoperability purpose
Anne-Laure Selignan, Alcatel

8. Routing PSAP July 2006 WLAN LAN PSTN
DHCP Server
AP/WLAN controller
Call Manager
PSAP
Solution 1: The terminal retrieved the Call Manager Address with DHCP
Start of the G.711 RTP flow with the destination address and port given in the DHCP option
Call Setup to the PSAP
Solution 2: Destination NAT
G.711 RTP Flow with any IP address as destination address for the flow from the phone to the Call Manager
Call Setup to the PSAP
RTP Flow with Call Manager as destination
Solution 3: Multicast
Call Setup to the PSAP
G.711 RTP Flow with multicast address as destination
Anne-Laure Selignan, Alcatel

9. July 2006
Security Issue
The use of an open authentication is required, several attacks can be performed:
Denial of Service
Man In The Middle
Etc..
Different security mechanisms can be used to avoid or tackle attacks at the LAN side
Bandwidth contract
Dedicated VLAN
Destination NAT
Firewall Rules
Etc…
Up to the manufacturer and security strategies
No impact on the emergency call setup
Anne-Laure Selignan, Alcatel

10. July 2006
Motion
This proposal has no impact on existing proposals (ref: u-e911-support-normative-text.doc, …). This solution can be part of the future standard.
Motion: Proposal to include the description of this solution as an informative annex
Anne-Laure Selignan, Alcatel

11. References [1] 802.11-06/616r0 Emergency Call Problem Statement
July 2006
References
[1] /616r0 Emergency Call Problem Statement
[2] /681r0 Proposal for E911 support
[3] /290r0 Proposal for Emergency Services Support
Anne-Laure Selignan, Alcatel