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 1. identifying emergency calls (“911”) 2. determining the right PSAP for current caller location coarse-grained location currently, ALI and MSAG 3. deliver caller location to PSAP fine-grained location

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

Wireless 911 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 67%95% handset50m150m network100m300m

Wireless 911: Phase 2 y Netrs r t i i l S t w.ap.co Wireless Tower ALI PDE A-GPS, UTDOA, … MPC/SCP ESRK or ESRD  coordinates callback number pANI (ESRD or ESRK) ISUP LEC selective router MSC E2 ESRK = unique for call ESRD = unique for location dynamic updates

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 Signaling & Media Signaling Media PSTN: Internet telephony: China Belgian customer, currently visiting US Australia

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) ISP (IP) dark fiber provider (λ) Yahoo MCI 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., 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

Three stages to VoIP 911 when deployable ? use 10- digit admin. number? mobilitycaller location conveyed to PSAP? PSAP modification ALI (DB) modification new services I1 nowallowedstationaryno none I2 December 2004 nostationary nomadic yesno (10-digit)yesnone I3 specified by late 2004 nostationary nomadic mobile yesIP-enabledreplaced by DNS GNP multimedia international calls

Example I1 solution #1 Mark Lewis Broadband Network LAN IP Phone End Office Switch SS7 End Office Switch Selective Router PSAP Media Gateway Signaling Gateway Softswitch Customer POP CLEC#1 #2 Call Taker Example: VoxPath

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

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

IETF I3 standardization efforts IETF = Internet Engineering Task Force = international open standardization body provide location (civil or geo) include civil and/or geo “911” 911  sos 112  sos cn=us, a1=nj, a2=bergen DHCP

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