Internet%20E-911%20System

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Internet E-911 System

• Henning Schulzrinne and Knarig ArabshianDepartmen
  t of Computer ScienceColumbia University
• hgs,knarig_at_cs.columbia.edu

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Overview

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

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E-911 serviceFour components needed
2) Call routing to an emergency response
center-PSAP
1) Universal number such as 911
3) Caller Identification Who is calling?
caller-id to avoid prank call 4) Caller
Location Where is he calling from? Address for
speedy response
1-212-9397063 613 CEPSR, Columbia University
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E-911 serviceHow it works?
Selective routing database

• Emergency Service Primary PSAP
• Number 2129119345
• ? Secondary PSAP
• 2129119456

Prefix Emergency Service
Number 212939xxxx ? 2345
SRDB
2129119345
Central office
2129397063 ? 613 CEPSR, 120th st Broadway and
Amsterdam Ave
1-212-9397063
Telco DB
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Emergency call using SIP(Legacy PSAP sees the
gateway)
ESRDB
SRDB
SIP-PSTN gateway (switch room)
PSAP
PSTN
939713x
Central office
2129397130 ? 606 CEPSR
IP network
Sends fire-fighters to the switch room.
Telco DB
128.59.19.61
(multimedia lab)
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Emergency call using SIP(IP-enabled PSAP is
aware of IP telephony)
PSAP
Outbound Proxy
IP Network
LAN
Richer Communication Envorinment video to
instruct caller in first aid or use sign
language, text-based messaging, etc.
128.59.19.61
(multimedia lab)
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Architecture for IP telephony
Use local switch tables to get the address of the
caller
PSAP
EPAD
302 Moved Temporarily Contact tel[phone]
INVITE sipsos_at_example.com SIP/2.0Location Rm.
523, 123 Main Street Centerville, NY
INVITE sip1-212-911-1234_at_gw-r-us.comLocation
Rm. 523, 123 Main Street Centerville, NY
Outbound Proxy
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Location
Internet
Proxy server invokes location resolution module
(LRM)
Some phones may have address configured.
Some phones may not know the location.
Sends Location 613 CEPSR
Caller
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Location
Internet
Sipd knows IP address of the caller
User dials 911 or sos_at_cs.columbia.edu
Caller
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Location
Internet
Pings and traceroutes to callers IP address to
locate last router
R3
R2
R1
Caller
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Location
Internet
Uses SNMP to query the ARP table on R1 to know
the MAC address of caller.
Using switchs CAM table and recursive query,
locate the last port (using CDP).
R3
R2
R1
Caller
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Location
Internet
Administrative SQL database lookup to map the
switch and port to physical address.
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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) hasnt
  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 callers
  user agent (in sipc)

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Location resolution algorithm
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SIPc functionality
Click on SOS icon and Call 911
Check to see if home address is configured
If not, then call Location Resolution Module and
insert Location into SIP INVITE
Location Resolution Module
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SIP-CGI
Internet
Once sipd knows physical address, either using
LRM or from INVITE message itself
Queries www.geocode.com to get the longitude and
latitude information
Sends Location 613 CEPSR
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SIP-CGI
Internet
IntradoDB
Pass longitude/ latitude into to intrado DB to
get the nearest PSAP phone.
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SIP-CGI
Internet
Place the call to the PSAP
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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.