Emergency services for SIP
Henning Schulzrinne
31 July 2017
Emergency services
 Two types of emergency services:
– emergency calls ("911", "112")
– emergency notification ("inverse 911")
 emergency calls are hard:
– PSTN gateway dialing 911 may be located
anywhere, far away from IP phone
– VPNs  IP address may not reveal
network location
31 July 2017
Emergency services
 More than just replicating PSTN:
– multimedia
• video monitoring of accident scene or victim
• video instruction in first aid
– better than TTY for hearing-impaired
– transmit biometric data
 Easier to create multiple backup PSAPs
31 July 2017
PSTN emergency calling
 Basic 911: call number, get routed to one
Public Safety Answering Point (PSAP)
– since 1968 in the United States
– 93% of population covered by 911
 Enhanced 911:
– route based on CLID (cannot be suppressed)
– provide user location
– started in 1970s, now 95%
 see Bellcore SR4163 for details
 see 47 USC 251 for legal mandate
31 July 2017
Wireless emergency calling
 FCC Phase I: caller ID, cell site
 FCC Phase II mandates user location:
– Handset-based:
• 50 meters for 67 percent of calls
• 150 meters for 95 percent of calls
– Network-based:
• 100 meters for 67 percent of calls
• 300 meters for 95 percent of calls
31 July 2017
VoIP emergency calls
Work for both "legacy" PSAPs and IP-based
PSAPs
 Define "sos" universal emergency address
1. find location of phone based on

–
–
street address  geocoding  long/lat, or
mobile: longitude, latitude
2. find appropriate jurisdiction and PSAP

use national database: long/lat  PSAP
3. find ESR (routing number)  call appears
like 911 call
–
31 July 2017
convey location to PSAP
Emergency identifier
 Requirements:
– dialable from all SIP devices
– universally recognized
– note: SOS  "save our souls"!
not quite unassigned – consider 112@ and 911@?
 Also allow "sos.fire" and others for specialized
emergency services
 Use sip:sos@home-domain to make
handling predictable
– intermediate proxies may deflect
31 July 2017
Routing emergency calls
EPAD
302 Moved
Contact: sip:[email protected]
Contact: tel:+1-201-911-1234
REGISTER sip:sos
INVITE sip:sos
Location: 07605
Location: 07605
INVITE sip:sos
Location: 07605
SIP
proxy
INVITE sip:[email protected]
Location: 07605
31 July 2017
Where is the phone?
 Regular GPS doesn't work well
–
–
–
–
doesn't work indoors
long time to first fix: 30"-15'
assisted GPS (A-GPS)
HDTV-based
 Landline and 802.11 phones:
– LAN jack tracing via traceroute, ARP, Cisco Discovery
Protocol (CDP) and SNMP vLAN tables
– 802.11 field strength triangulation (e.g., Microsoft, VTT)
– hardware identification:
• IR/RF tags
– user data entry
31 July 2017
911 deployment
"Bergen County"
400 Broad Avenue
Leonia, NJ
SIP
010
c1.leonia.us
IP
UDP, TCP
IP
"sos"
A@
B@
C@
Leonia
c2.leonia.us
Alice
ISDN B
"911"
ISDN D
SS7 ISUP
Bob
SIP call setup
audio (IP or circuit)
SIP registration
c1.fortlee.us
IP
Fort Lee
010
RTP
UDP
IP
Bergen County
analog phone
IP phone
31 July 2017
Open issues
 What needs to be standardized?
 Are there any other UA behaviors?
– prevent accidental disconnect
– bypass carrier authentication
• e.g., 3G requirement of REGISTER before calls?
 Myth: During PSTN 911 calls, certain
features (three-way calls, hang-up) are
unavailable
– true only for Basic 911
31 July 2017
Emergency notification
 notify public officials and citizens of
emergencies:
– "tornado coming"
– "fugitive alert"
 current systems are typically single-mode
(fax, telex, phone, TV, loudspeaker)
 don't scale well
 very limited information content
 don't reach citizens outside calling area
– people at work
 hard to authenticate
31 July 2017
SIP-based emergency
notification
 SIP has scalable event notification feature
 use for hierarchical notification reflecting civil lines of
authority
 use XML/WSDL message bodies to semantically
describe emergency:
–
–
–
–
location
type of emergency
instructions
...
 allow automated reaction:
– routing to legacy systems (pagers, police radios)
– translation
31 July 2017
Emergency notification
United States
Federal Govt.
NJ
State Govt.
Alabama
Alaska
New Jersey
Wisconsin
NOTIFY
SUBSCRIBE
Atlantic
31 July 2017
Bergen
Wyoming