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911 services: wireline, wireless and VoIP. Prof. Henning Schulzrinne Dept. of Computer Science Columbia University, New York FCC Solutions Summit March 18, 2004. Overview. E911 for wireline E911 for wireless (Phase II) Short-term 911 service for VoIP Differences between PSTN and VoIP
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911 services: wireline, wireless and VoIP Prof. Henning Schulzrinne Dept. of Computer Science Columbia University, New York FCC Solutions Summit March 18, 2004
Overview • E911 for wireline • E911 for wireless (Phase II) • Short-term 911 service for VoIP • Differences between PSTN and VoIP • Objectives • Internet standardization efforts
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
Tandem Switch (911 Selective Router) CO Switch E911 for wireline PSAP #1 CAMA or PRI delivers ANI (555-1234) CAMA or SS7 555-1234 313 Main St LEC network 555-1234 PSAP #1 ANI: 555-1234 313 Main MSAG ALI private data link 100-500 Main Street ESN 1789 555-1234 PSAP #1, 313 Main St provisioned updates verify address validity
Phase I (April 1998) 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 Wireless 911
Wireless 911: Phase 2 MSC pANI (ESRD or ESRK) ISUP y N e t r s i l r i t LEC selective router Wireless Tower PDE MPC/SCP E2 ALI S A-GPS, UTDOA, … dynamic updates t ESRK or ESRD coordinates callback number w . a p . c o ESRK = unique for call ESRD = unique for location
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
PSTN vs. Internet Telephony PSTN: Signaling & Media Signaling & Media China Internet telephony: Signaling Signaling Media Australia Belgian customer, currently visiting US
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 email carriers, either voice service provider (TCP, RTP, SIP) Yahoo ISP (IP) MCI dark fiber provider (λ) NYSERNET
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
Why is VoIP ≠ wireless? • VoIP devices may not have phone numbers as lookup keys • e.g., sip:hgs@cs.columbia.edu • 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
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 • 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
1 2 3 4 5 6 7 8 9 8 # * Example I1 solution #1 CLEC # 1 Example: VoxPath SS 7 End Office Switch LAN IP Phone Signaling Customer Gateway PSAP Softswitch Selective End Office Router Switch Broadband Media Network Gateway Call Taker POP CLEC # 2 Mark Lewis
ALI DB ACD PBX (emergency lines) I1 Solution #2 Level3 Customer Softswitch Dedicated 911 trunks PSTN E911 Tandem Public Internet or Private IP Network End Users E911 Tandem IP Phones Level 3 911 Softswitch Network PSAP Mark Lewis
Possible I2 architecture IP PSTN Selective Router MG INVITE sos CAMA ISUP ESRK, DN loc PAM ALI ALI-FE SIP PUBLISH E2+ ESP Local ALI National Voice N/Ws Emergency Services N/W based on slide by Martin Dawson
IETF I3 standardization efforts • IETF = Internet Engineering Task Force = international open standardization body “911” sip:sos@ include civil and/or geo 911 sos 112 sos sip:psap@leonia.nj.gov provide location (civil or geo) DHCP cn=us, a1=nj, a2=bergen
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 and US standardization efforts in progress • IETF and NENA collaboration combines 911 and Internet expertise