Emergency Calling

1
Emergency Calling Summary and Open Issues

• Henning Schulzrinne
• Columbia University

2
Emergency Calling Components

• Sub-problems
• Universal identifier
• Call routing
• User location
• Differs depending on whether local gateway,
  remote gateway or IP-enabled PSAP

3
Universal identifier

• Proposal sipsos_at_local-domain local tel
  numbers (911, 112, )
• Thus, resolution in outbound proxy
• Difficulty obtaining local domain
• Works if client uses home domain, but longer
  resolution path and international issues
• Special identifier, e.g., sipsos_at_localhost?

4
Call routing

• Need to find appropriate emergency call center
• Local gateway
• Just use appropriate emergency number
• Remote gateway
• need to dial 10-digit number
• IP ECC
• need to find appropriate ECC

5
Call routing proposal
EPAD
REGISTER sipsos Location 07605
302 Moved Contact sipsos_at_psap.leonia.nj.us Conta
ct tel[phone]
SIP proxy
INVITE sipsos Location 07605
INVITE sipsos_at_psap.leonia.nj.us Location 07605
6
Call routing

• Requires no changes to proxy or SIP
• Allows multiple EPAPs to REGISTER for redundancy

7
Call routing open issues

• EPAD realistic?
• database of 10-digit ECC numbers needed for
  telematics
• EPAD needs to be told about proxy
• rare fill out web form
• provide secret ensures that only SIP proxy
  owner can (usefully) do this
• How to authenticate EPAD?
• Shared secret works for standard proxy
• Certificate with credential (requires proxy
  knowledge)

8
Call routing - alternatives

• Configure proxy manually to route emergency calls
  to designated address
• anycast?
• Service discovery
• SLP

9
User location

• Rely on geopriv output architecture not clear
  (special protocol with GML?)
• Insert into SIP request by
• UA (manual configuration, GPS, )
• Outbound proxy (MAC backtracking, database, )