1. 911 services: wireline, wireless and VoIP
Prof. Henning Schulzrinne
Dept. of Computer Science
Columbia University, New York
FCC Solutions Summit
March 18, 2004

2. Overview E911 for wireline E911 for wireless (Phase II)
Short-term 911 service for VoIP
Differences between PSTN and VoIP
Objectives
Internet standardization efforts

3. Components of emergency calling
Three core components that need to be replicated – everything else are implementation details
identifying emergency calls (“911”)
determining the right PSAP for current caller location
coarse-grained location
currently, ALI and MSAG
deliver caller location to PSAP
fine-grained location

4. E911 for wireline MSAG ALI verify address validity PSAP #1 CAMA or PRI
delivers ANI
( )
CO Switch
CAMA or SS7
Tandem Switch
(911 Selective Router)
313 Main St
LEC
network
 PSAP #1
ANI:
 313 Main
MSAG
ALI
private
data link
Main Street  ESN 1789
 PSAP #1, 313 Main St
provisioned
updates
verify address
validity

5. Wireless 911 Phase I (April 1998) Phase II (October 2001)
Route all call to the appropriate PSAP based on call sector
Provide cell/sector location data to PSAP
Provide call back number to PSAP
Phase II (October 2001)
Phase I + latitude and longitude
67%
95%
handset
50m
150m
network
100m
300m

6. Wireless 911: Phase 2 pANI E2 ALI ESRK or ESRD  coordinates
MSC
pANI
ISUP y N e t r s i r l i t
LEC
selective router
Wireless Tower
PDE
MPC/SCP E2
ALI
A-GPS, UTDOA, … S
dynamic
updates t
ESRK or ESRD 
coordinates
callback number w . a p . c o
ESRK = unique for call
ESRD = unique for location

7. Problems with existing 911 system
1970s technology:
CAMA trunks induce long call setup delays
limited in ability to transfer information (10 digits)
gets complicated if multiple providers
ILEC vs. CLEC
multiple wireless providers
tied to ILEC rate centers and other PSTN routing artifacts
hard to move PSAPs on short notice (e.g., emergency evacuation)
can’t just plug into any network termination

8. PSTN vs. Internet Telephony
Signaling & Media
Signaling & Media
China
Internet
telephony:
With a few exceptions, in Internet telephony, end systems are the only entities where signaling and media flows converge. Thus, any service that requires interaction with user media is likely to be easier to implement in the end systems.
More seperately
Signaling
Signaling
Media
Belgian customer,
currently visiting US
Australia

9. How does VoIP differ from landline and wireless PSTN?
All devices are nomadic
new location, but same identifier
Telephone companies are no longer needed
there are still carriers for DSL and cable “IP dial tone”
but unaware of type of data carried (voice, web, IM, …)
VSP may be in another state or country
Corporations and universities don’t have carriers, either
voice service provider
(TCP, RTP, SIP)
Yahoo
ISP
(IP)
MCI
dark fiber
provider
(λ)
NYSERNET

10. The role of phone numbers and identifiers
Wireline  line, device, subscriber & location
Wireless  device, but not location
VoIP (phone number and URIs):
mostly identifies person, not device
multiple devices located in different states can share the same number
however, may not have a phone number
if it does, area code may be from different state than customer billing address
multiple devices
device can move, while number stays the same
not related to ISP

11. Why is VoIP ≠ wireless?
VoIP devices may not have phone numbers as lookup keys
e.g.,
Location information for devices is civil, not longitude/latitude
e.g., service address for VSPs
GPS not available (nor functional) on indoor devices
plus, accuracy of 50 m (67%) or 150 m spans many buildings…
no floor information
Cell phones don’t work in our building…
so A-GPS is unlikely to work there, either
Plus, wireless E911 complexity due to old signaling mechanism
expensive and complicated to connect to multiple wireless operators
proposals to use IP-based solutions
50m

12. Objectives for IP-based 911
International
devices must work anywhere
independent of local emergency number
Multimedia
Integrate alternate modalities such as text (TDD) and video (sign language)
COTS
avoid repeat of CAMA trunks
Resilient
easily re-route calls to any number of backup PSAPs
Testable
users can test operation without tying up operator resources
Secure
integrity, confidentiality, protection against denial-of-service attacks
Technology-independent
do not depend on (e.g.,) specific wireless or link technology
Pro-competitive
does not require carriers or gatekeepers

13. VoIP and 911 – Two stages Short term: Longer term:
work with existing PSAPs
may not support nomadic devices
Longer term:
upgrades in PSAP CPE
opportunity for improved overall architecture
support nomadic devices
support multimedia
provide framework for simpler & cheaper circuit-switched landline and wireless architecture

14. Short-term solutions Emulate wireline Emulate wireless
every subscriber has phone number
capture VoIP subscriber address and enter into ALI DB
gateway calls 10-digit number and provides ANI
Emulate wireless
VoIP provider = another wireless carrier
use similar dynamic updates for ALI DB

15. IETF standardization efforts
IETF = Internet Engineering Task Force = international open standardization body
“911”
include
civil and/or geo
911  sos
112  sos
provide location (civil or geo)
DHCP
cn=us, a1=nj, a2=bergen

16. Conclusion Existing 911 system closely tied to PSTN history
number as universal identifier
close affiliation with PSTN switches
incremental, constrained evolution
VoIP offers opportunity to increase robustness and decrease costs
Initial international standardization efforts in progress