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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
    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
                                                               CAMA or PRI             PSAP #1
                                                               delivers ANI
                            CAMA or SS7                        (555-1234)



 555-1234     CO Switch                   Tandem Switch
313 Main St                           (911 Selective Router)
              LEC
              network                            555-1234                      ANI: 555-1234
                                                  PSAP #1                      313 Main


                                                                               private

                                MSAG                           ALI             data link




               100-500 Main Street  ESN 1789     555-1234  PSAP #1, 313 Main St


                                                                     provisioned
                                                                     updates


                                           verify address
                                           validity
Wireless 911
   Phase I (April 1998)                     67%    95%
       Route all call to the      handset   50m    150m
        appropriate PSAP based     network   100m   300m
        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: Phase 2
                           MSC

                                                                                     pANI
                                                                                     (ESRD or ESRK)
                                          ISUP
                                                     y N et   r s




                                                                         i
                                                                         i l
                                                 r




                                                                         t
  Wireless Tower                                                    LEC
                                                                    selective router

                    PDE   MPC/SCP

                    S
                                                                               E2
 A-GPS, UTDOA, …                    dynamic
                                                 ALI
        t




                                    updates
    w .a p   .c o




                                                                                    ESRK or ESRD 
ESRK = unique for call                                                              coordinates
ESRD = unique for location                                                          callback number
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
         Belgian customer,                              Australia
         currently visiting US
How does VoIP differ from
landline and wireless PSTN?
   All devices are nomadic




                                               Yahoo
       new location, but same identifier                 voice service provider
                                                           (TCP, RTP, SIP)
   Telephone companies are no
    longer needed
                                                                  ISP




                                               MCI
       there are still carriers for DSL and
                                                                  (IP)
        cable “IP dial tone”
       but unaware of type of data carried
                                                              dark fiber




                                               NYSERNET
        (voice, web, IM, …)
                                                               provider
       VSP may be in another state or                           (λ)
        country
   Corporations and universities
    don’t have email carriers, either
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…   50m
             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
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         use 10-   mobility     caller     PSAP            ALI (DB)       new services
     deployable   digit                  location   modification    modification
     ?            admin.                 conveyed
                  number?                to PSAP?

I1   now          allowed   stationary   no         no              no             none


I2   December     no        stationary   yes        no (10-digit)   yes            none
     2004                   nomadic

I3   specified    no        stationary   yes        IP-enabled      replaced by    GNP
     by late                nomadic                                 DNS            multimedia
     2004                   mobile                                                 international
                                                                                   calls
           Example I1 solution #1
                                      CLEC #1
                               SS7
                                                  Example: VoxPath
                                     End Office
                                      Switch
              LAN
IP Phone

                       Signaling
Customer               Gateway

                                                                              PSAP
                       Softswitch
                                     End Office   Selective
                                      Switch       Router
           Broadband    Media                                     1
                                                                  4
                                                                  7

                                                                  *
                                                                      2
                                                                      5
                                                                      8
                                                                      8
                                                                          3
                                                                          6
                                                                          9
                                                                          #




            Network    Gateway
                                                                Call Taker

                        POP           CLEC #2

                                                   Mark Lewis
             I1 Solution #2
                                                                                            Level3
                Customer
                                         Dedicated
                Softswitch
                                         911 trunks   PSTN


                                                                              E911
                                                                             Tandem

              Public Internet
 End                or
Users           Private IP                                E911
                                                         Tandem
                Network
 IP Phones

                                                                                      ALI
                                                                                      DB



                                                               PBX
                                                         (emergency lines)
                                                                             ACD
                                Level 3 911                                  PSAP
                                Softswitch
                                 Network



                                                                         Mark Lewis
 Possible I2 architecture
                    IP          PSTN



INVITE sos                               ISUP
                                                            Selective   CAMA
                         MG
                                                             Router


             ESRK, DN  loc


                                                    ALI           PAM

       SIP               ALI-          E2+          Local
       PUBLISH            FE           ESP

                                                    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
911  sos                  civil and/or geo
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

				
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posted:5/9/2010
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