1. 911 services: wireline, wireless and VoIP
Prof. Henning Schulzrinne
Dept. of Computer Science
Columbia University, New York
VoIP Roundtable, Washington, DC
June 24, 2004

2. Overview E911 for wireline E911 for wireless (Phase II)
Differences between phone system and VoIP
Requirements and opportunities
Internet standardization efforts
Funding and regulation challenges

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 emergency call center (PSAP) for current caller location
coarse-grained location
currently, two main databases: ALI for number-to-location mapping and MSAG for address verification
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 (ESRD or ESRK) E2 ALI ESRK or ESRD 
MSC
pANI
(ESRD or ESRK)
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 (8-10 digits)
sometimes, 2,400 baud modems for database access
increases call setup delays
gets complicated if multiple providers
ILEC vs. CLEC
multiple wireless providers in one state
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
Internet
telephony:
China
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
anybody can be their own “VSP”
Corporations and universities don’t have carriers, either
voice service provider
[VSP]
(TCP, RTP, SIP)
Yahoo
ISP
(IP, DHCP)
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
international roaming
Multimedia
integrate alternate modalities such as text (TDD) and video (sign language)
COTS (commercial off-the-shelf)
re-use standard protocols (SIP, DNS, DHCP, HTTP, XML, …)
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, privacy and 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. Opportunities for I911 More robust Additional services
multiple networks and interfaces increase disaster resiliency
operations can be moved easily to any network-connected location
Additional services
multimedia
text chat replacing TTY
video and images for situational awareness and instructions to civilians at scene of accident
additional data
hazmat data
accident data (impact velocity, airbags, fuel spill, …)
Better integration with first responders and public safety
integration with telematics providers
general awareness of call volume, origin and type
information flow back to PSAP
see 9/11 evacuation
hand off call data, not just remote printing of address
alerts and notifications to public safety and the public
Cheaper to build and operate
currently, small niche  expensive equipment, specialized circuits, slow upgrades
should be able to leverage almost existing technology  lower risk

14. Three stages to VoIP 911: I1  I2  I3
may use administrative line to deliver call
no location delivery
I1 & I2:
no modification to PSAP
calls delivered to PSAP via existing technology
delivers location information
I3:
deliver calls to PSAP via VoIP
including circuit-switched calls
I1, I2 and I3 will likely co-exist for some time
design to allow local upgrades, without national or state-wide coordination

15. Three stages to VoIP 911 I1 I2 I3 when deployable?
use 10-digit admin. number?
mobility
caller
location conveyed to PSAP?
PSAP
modification
ALI (DB)
new services I1
now
allowed
stationary no
none I2
December 2004
nomadic
yes
no (10-digit) I3
specified by late 2004
mobile
IP-enabled
replaced by DNS
global number portability
multimedia
international calls

16. IETF and NENA I3 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

17. Regulatory challenges
Uniform technology
but avoid things that don’t work internationally
Distributed responsibility:
VSP does not know location
Residential user may have any number of VSPs
like prepaid calling cards
and may use any one of them for calling 911
ISP does not know VSP and whether call is voice or not
 ISP needs to provide location information to end user  regulatory mandate!

18. Funding challenges Existing line/number model does not work
longer term, no more “lines” and numbers
every person may have multiple identifiers
Short-term vs. long-term options
Even small VSPs have a national footprint
number assigned may not match location of customer
VoIP has built-in global number portability
can’t require to keep track of 6,000 different county 911 fees and recipients
Funding collector should
have direct customer relationship
know accurately where customer lives
have regional footprint
have modest collection and distribution costs
Some options:
facilities-based (broadband) ISP
local & state taxes
non-telecom utilities (water, gas, electric) that reflect residency
collect directly from household
like home owners insurance

19. Conclusion Existing 911 system closely tied to phone system history
number as universal identifier
close affiliation with telephone switches
incremental, constrained evolution
VoIP offers opportunity to increase robustness, offer new services and decrease costs
Initial international and US standardization efforts in progress
IETF and NENA collaboration combines 911 and Internet expertise
Initial prototypes and demonstration systems in development

20. Additional I1 and I2 information

21. Example I1 solution #1 CLEC # 1 Customer POP CLEC # 2 Example: VoxPathSS 7
Example: VoxPath
End Office
Switch
LAN
IP Phone
Customer
Signaling
Gateway
PSAP
Softswitch
End Office
Selective
Switch
Router 1 2 3 4 5 6 7 8 9 * #
Broadband
Media
Network
Gateway
Call Taker
POP
CLEC # 2
Mark Lewis

22. Level 3 911 Softswitch Network
I1 Solution #2
Level3
Customer
Softswitch
Dedicated
911 trunks
PSTN
E911
Tandem
Public Internet or
Private IP Network
End Users
E911
Tandem
IP Phones
ALI DB
PBX
(emergency lines)
ACD
Level Softswitch Network
PSAP
Mark Lewis

23. Possible I2 architectureIP
PSTN
Selective Router
INVITE sos MG
ISUP
CAMA
ESRK, DN  loc
ALI
PAM
ALI-FE
SIP
PUBLISH
E2+ ESP
Local
ALI
National
Voice N/Ws
Emergency Services N/W
based on slide
by Martin Dawson