Internet E-911 SystemInternet E-911 System

Henning Schulzrinne and Knarig Arabshian

Department of Computer ScienceColumbia University

{hgs,knarig}@cs.columbia.edu

OverviewOverview

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

E-911 serviceE-911 serviceFour components neededFour components needed

1) Universal number such as 911

2) Call routing to an emergency response center-PSAP

1-212-9397063613 CEPSR,Columbia University

3) Caller IdentificationWho is calling? caller-id to avoid prank call4) Caller LocationWhere is he calling from? Address for speedy response

E-911 serviceE-911 serviceHow it works?How it works?

SRDB

Prefix Emergency Service Number212939xxxx 2345

1-212-9397063

Selective routing database

Central office

TelcoDB

2129397063 613 CEPSR, 120th st Broadway and Amsterdam Ave

Emergency Service Primary PSAPNumber 2129119345

2345 Secondary PSAP

2129119456

2129119345

Emergency call using SIPEmergency call using SIP(Legacy PSAP sees the gateway)(Legacy PSAP sees the gateway)

SRDB

128.59.19.61

TelcoDB

2129397130 606 CEPSR

IP network

SIP-PSTN gateway(switch room)

939713x

(multimedia lab)

Sends fire-fighters to the switch room.

Central office

PSAP

PSTN

ESRDB

Emergency call using SIPEmergency call using SIP(IP-enabled PSAP is aware of IP telephony)(IP-enabled PSAP is aware of IP telephony)

128.59.19.61

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 Architecture for IP telephonytelephony

INVITE sip:sos@example.com SIP/2.0Location: Rm. 523, 123 Main Street

Centerville, NY

Outbound Proxy

EPAD

302 Moved TemporarilyContact: tel:+1-212-911-1234

INVITE sip:1-212-911-1234@gw-r-us.comLocation: 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

InternetLocationLocation

Some phones may not know the location.

Some phones may have address configured.

Proxy server invokes location resolution module (LRM)

DB

sipd

Caller

InternetLocationLocation

User dials 911 or sos@cs.columbia.edu

Sipd knows IP address of the caller

DB

sipd

Caller

InternetLocationLocation

Pings and traceroutes to caller’s IP address to locate last router

R1R2

R3

Using switch’s CAM table and recursive query, locate the last port (using CDP).

DB

sipd

Caller

InternetLocationLocationUses SNMP to query the ARP table on R1 to know the MAC address of caller.

R1R2

R3

DB

sipd

InternetLocationLocation

Administrative SQL database lookup to map the switch and port to physical

address.

Location resolution Location resolution modulemodule 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 Location resolution algorithmalgorithm

Process DNS/IPentry. NSLookup

the entry

Is the entrypingable?

Traceroute to thesource and save

the last hopaddress

SNMP query for theARP entry of the

source. Determine thenext hop layer-2

device using CDP.

SNMP query theswitch to determine ifthe MAC exists in the

CAM table.

Determine if staticdatabase contains the

information.

Is the MAC entrylearned via local portor via CDP/bridge/

VTP/ISL/STP enabledports?

Determine thenext hop layer-2

device using CDP.

Is the next hopswitch orrouter?

SQL Lookup theswitch and port

info to get physicalinformation.

Return to output

If yes, returnthe information

If no,return the

info.

Return theoutput toscreen.

DirectlyLearned

Indirectlylearned

Nextdevice is a

switch

Nextdevice is a

router

If noIf yes

SIPc functionalitySIPc functionalityClick on SOS icon and

Call 911

Check to see if homeaddress is configured

Location ResolutionModule

If not, then callLocation ResolutionModule and insertLocation into SIP INVITE

DB

sipd

Sends Location: 613 CEPSR

InternetSIP-CGI SIP-CGI

Once sipd knows physical address, either using LRM or from INVITE message itself

Queries www.geocode.com to get the longitude and latitude information

DB

sipd

InternetSIP-CGISIP-CGI

Pass longitude/ latitude into to intrado DB to get the nearest PSAP phone.

IntradoDB

DB

sipd

InternetSIP-CGISIP-CGI

Place the call to the PSAP

SummarySummary 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.