Internet E-911 System Henning Schulzrinne and Knarig Arabshian Department of Computer Science Columbia University

Overview How E-911 works Emergency call using SIP Internet E-911 Architecture Location Resolution SIPc and SIP-CGI functionality Conclusion

E-911 service Four components needed 1) Universal number such as 911 2) Call routing to an emergency response center-PSAP CEPSR, Columbia University 3) Caller Identification Who is calling? caller-id to avoid prank call 4) Caller Location Where is he calling from? Address for speedy response

E-911 service How it works? SRDB Prefix Emergency Service Number xxxx  Selective routing database Central office Telco DB  613 CEPSR, 120 th st Broadway and Amsterdam Ave Emergency Service Primary PSAP Number  Secondary PSAP

Emergency call using SIP (Legacy PSAP sees the gateway) SRDB Telco DB  606 CEPSR IP network SIP-PSTN gateway (switch room) x (multimedia lab) Sends fire-fighters to the switch room. Central office PSAP PSTN ESR DB

Emergency call using SIP (IP-enabled PSAP is aware of IP telephony) LAN Outbound Proxy (multimedia lab) Richer Communication Envorinment: video to instruct caller in first aid or use sign language, text-based messaging, etc. PSAP IP Network

Architecture for IP telephony INVITE SIP/2.0 Location: Rm. 523, 123 Main Street Centerville, NY Outbound Proxy EPAD 302 Moved Temporarily Contact: tel: INVITE Location: Rm. 523, 123 Main Street Centerville, NY Use local switch tables to get the address of the caller PSAP

DB sipd Sends Location: 613 CEPSR Caller Internet Location Some phones may not know the location. Some phones may have address configured. Proxy server invokes location resolution module (LRM)

DB sipd Caller Internet Location User dials 911 or Sipd knows IP address of the caller

DB sipd Caller Internet Location Pings and traceroutes to caller’s IP address to locate last router R1 R2 R3

Using switch’s CAM table and recursive query, locate the last port (using CDP). DB sipd Caller Internet Location Uses SNMP to query the ARP table on R1 to know the MAC address of caller. R1 R2 R3

DB sipd Internet Location Administrative SQL database lookup to map the switch and port to physical address.

Location resolution module The program is capable of identifying CDP participating ports, but SNMP-CDP querying the router for the ARP table (for MAC address) hasn’t been implemented. Unable to test cascading infrastructure or remote vlan scenario. All code in perl, intended to be used within sip-cgi script SNMP-walk program is used to query various CAM tables Traceroute and SNMP query take time Pre-fetch and cache this information for all registered users Can also be used with modification at caller’s user agent (in sipc)

Location resolution algorithm

SIPc functionality Click on SOS icon and Call 911 Check to see if home address is configured Location Resolution Module If not, then call Location Resolution Module and insert Location into SIP INVITE

DB sipd Sends Location: 613 CEPSR Internet SIP-CGI Once sipd knows physical address, either using LRM or from INVITE message itself Queries to get the longitude and latitude information

DB sipd Internet SIP-CGI Pass longitude/ latitude into to intrado DB to get the nearest PSAP phone. Intrado DB

DB sipd Internet SIP-CGI Place the call to the PSAP

Summary Internet E-911 system gives us a flexible and robust environment Next generation devices will be interoperable with SIP Location resolution still a topic of research Currently working with Intrado (provider of 911 services and systems) database to implement this system.