Internet E-911 Internet E-911 System System Henning Schulzrinne and Knarig Arabshian Department of Computer Science Columbia University {hgs,knarig}@cs.columbia.edu
Jan 15, 2016
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:[email protected] SIP/2.0Location: Rm. 523, 123 Main Street
Centerville, NY
Outbound Proxy
EPAD
302 Moved TemporarilyContact: tel:+1-212-911-1234
INVITE sip:[email protected]: 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 [email protected]
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.