Transcript Providing Emergency Services in Internet Telephony

Internet E-911 System
Henning Schulzrinne and Knarig Arabshian
Department of Computer Science
Columbia University
{hgs,knarig}@cs.columbia.edu
Overview
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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
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
E-911 service
How it works?
Selective routing database
Prefix
Emergency Service
Number
SRDB
212939xxxx  2345
Emergency Service
Number
2345

Primary PSAP
2129119345
Secondary PSAP
2129119456
2129119345
Central office
1-212-9397063
2129397063 
613 CEPSR,
120th st Broadway
Telco and Amsterdam Ave
DB
Emergency call using SIP
(Legacy PSAP sees the gateway)
SIP-PSTN gateway
(switch room)
ESR
DB
SRDB
PSAP
PSTN
939713x
Central office
2129397130 
606 CEPSR
IP network
Sends fire-fighters
to the switch room.
128.59.19.61
(multimedia lab)
Telco
DB
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)
Architecture for IP telephony
Use local
switch tables
to get the
address of
the caller
PSAP
EPAD
INVITE sip:[email protected] SIP/2.0
Location: Rm. 523, 123 Main Street
Centerville, NY
302 Moved Temporarily
Contact: tel:+1-212-911-1234
INVITE sip:[email protected]
Location: Rm. 523, 123 Main Street
Centerville, NY
Outbound Proxy
Location
Internet
sipd
DB
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
Location
Internet
sipd
DB
Sipd knows IP
address of the
caller
User dials 911 or
[email protected]
Caller
Location
Internet
sipd
DB
Pings and traceroutes
to caller’s IP address to
locate last router
R3
R2
R1
Caller
Location
Internet
Uses SNMP to
query the ARP
table on R1 to
know the MAC
address of caller.
sipd
DB
Using switch’s
CAM table and
recursive query,
locate the last
port (using CDP).
R3
R2
R1
Caller
Location
Internet
sipd
DB
Administrative
SQL database
lookup to map
the switch and
port to physical
address.
Location resolution module
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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
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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
Process DNS/IP
entry. NSLookup
the entry
Return to output
Is the entry
pingable?
If yes
Traceroute to the
source and save
the last hop
address
If yes, return
the information
If no
Determine if static
database contains the
information.
If no,
return the
info.
SNMP query for the
ARP entry of the
source. Determine the
next hop layer-2
device using CDP.
SNMP query the
switch to determine if
the MAC exists in the
CAM table.
Next
device is a
switch
Next
device is a
router
Is the next hop
switch or
router?
Return the
output to
screen.
Is the MAC entry
learned via local port
or via CDP/bridge/
VTP/ISL/STP enabled
ports?
Indirectly
learned
Determine the
next hop layer-2
device using CDP.
Directly
Learned
SQL Lookup the
switch and port
info to get physical
information.
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
SIP-CGI
Internet
sipd
DB
Sends
Location: 613 CEPSR
Once sipd knows
physical address,
either using LRM
or from INVITE
Queries www.geocode.com to
message itself
get the longitude and latitude
information
SIP-CGI
Intrado
DB
Internet
sipd
Pass longitude/
latitude into to
intrado DB to get
the nearest PSAP
phone.
DB
SIP-CGI
Internet
sipd
DB
Place the call to
the PSAP
Summary
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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.