Introduction to Telephony _ VoIP

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Introduction to Telephony _ VoIP Powered By Docstoc
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Introduction to Telephony &
VoIP

Henning Schulzrinne
Columbia University



                                                      1




                   Overview

   !  The Public Switched Telephone System (PSTN)

   !  VoIP as black phone replacement ! interactive
     communications enabler

   !  Presence as a service enabler

   !  Peer-to-peer VoIP




                                                      2




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             Name confusion

!  Commonly used interchangeably:
   !  Voice-over-IP (VoIP) – but includes video
   !  Internet telephony – but may not run over Internet
   !  IP telephony (IPtel)

!  Also: VoP (any of ATM, IP, MPLS)

!  Some reserve Internet telephony for transmission
     across the (public) Internet

!  Transmission of telephone services over IP-based
     packet switched networks

!  Also includes video and other media, not just voice


                                                              3




                A bit of history

!    1876 invention of telephone
!    1915 first transcontinental telephone (NY–SF)
!    1920’s first automatic switches
!    1956 TAT-1 transatlantic cable (35 lines)
!    1962 digital transmission (T1)
!    1965 1ESS analog switch
!    1974 Internet packet voice (2.4 kb/s LPC)
!    1977 4ESS digital switch
!    1980s Signaling System #7 (out-of-band)
!    1990s Advanced Intelligent Network (AIN)
!    1992 Mbone packet audio (RTP)
!    1996 early commercial VoIP implementations (Vocaltec);
     PC-to-PC calling

                                                              4




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                   Phone system

!  analog narrowband circuits to “central office”
   !  48 Volts DC supply

!  64 kb/s continuous transmission, with compression across ocean

!  !-law: 12-bit linear range ! 8-bit bytes

!  everything clocked at a multiple of 125 !s

!  clock synchronization ! framing errors

!  old AT&T: 136 “toll”switches in U.S.
   !  interconnected by T1 and T3 digital circuits ! SONET rings (AT&T: 50)

!  call establishment “out-of-band” using packet-switched signaling
   system (SS7)



                                                                              5




                  Circuit diagram




  ringing: 25 Hz, 50 V AC                                                     6




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                    WE 2500 diagram




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        Transatlantic cable systems
System   Year      technology            cost ($M)    circuits        $/circuit   $/minute
         (use)
TAT-1    1956-78   Coax + tubes               $49.6              40    213,996       2.443
TAT-2    1569      Coax                       $42.7              44    167,308       1.910
TAT-3    1963      Coax                       $50.6              79    111,027       1.267
TAT-4    1965      Coax                       $50.4              62    140,238       1.601
TAT-5    1970      Coax                       $70.4         648          18,773      0.214
TAT-6    1976-94   Coax                        $197       3,200          10,638      0.121
TAT-7    1978-94   Coax                        $180       3,821           8,139      0.093
TAT-8    1988-02   Fiber (20 Mb/s)             $360       6,048          10,285      0.117
TAT-9    1992-04   Fiber                       $406      10,584           6,628      0.076
TAT-10   1992-03   Fiber (2x565 Mb/s)          $300      18,144           2,857      0.033
TAT-11   1993-04   Fiber (2x565 Mb/s)          $280      18,144           2,667      0.030
TAT-12   1996-08   Fiber ring (5 Gb/s)         $378      60,480           1,080      0.012
TAT-13   1996-08   Fiber (2x5 Gb/s)            $378      60,480           1,080      0.012 8




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         Transatlantic cable systems
System   Year   technology   cost ($M)      circuits    $/circuit   $/minute

TAT-13   1996 Fiber                  $378      60,480       1,080      0.012
Gemini 1998 Fiber                    $520    214,920          371      0.004
AC-1     1998   120 Gb/s             $850    483,840          304      0.003
TAT-14   2001   WDM
                16xOC-192
                                   $1,500     4x2.5M          <75      0.001




                                                                                9




          Call load over the week




                                                                               10




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Signaling System #7




                      11




   SS7 network




                      12




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                           Typical signaling network
                                                                                                      Gateway STP

                                                                                                      Local STP
                                                                     A-                                  AIN SCP
                                                                     Links                               LNP SCP
                                                      A-Links                                         LTF/800 SCP
                                                                                                          SSP (CO)




                                                                         D-Lin
           NOTE: ‘C’ Links

                                             A-
                                                                                                       Tandem
           exist between

                                                Li
                                                                                                      Low Speed Link (56 kb/s)

                                                 nk




                                                                              k
           each mated
                                                                                                      High Speed Link (1.544 Mb/s)
           STP pair
                                                            B-Link                               A-Link

                                                                                  B-
                                                                                    Lin
                A-Link                      nk                                         k             A
                                        i
                                    B -L
                           D-Link




                                                                                           ‘A’

                                                                     D


                                                                                                                                 13
D. Finn (BellSouth 2006)




                      Types of switching entities

                  !  Class 5 End Office (or C. O.)
                     !  Connects subscribers’ telephone lines to the telecommunications
                        network
                     !  Provides BORSCHT functionality (Battery, Overvoltage protection,
                        Ringing, Supervision, Codec, Hybrid and Testing)
                     !  Provides line and trunk concentration
                     !  Serves as a “Host” for Remote Offices
                     !  Serves as an ‘SSP’ - Connects to SS7 for signaling and AIN functions

                  !  Tandem Central Office
                     !  Serves as a ‘hub’ for connecting voice trunks from numerous Class 5 end
                        offices
                     !  Provides voice trunk connections to Long Distance carriers and Wireless
                        providers
                     !  Provides E9-1-1 Routing to PSAPs
                     !  Types include LATA/Access Tandem, Toll Tandem, E911 Tandem, TOPS
                        Tandem



                                                                                                                                 14
D. Finn (BellSouth 2006)




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            Types of switching entities: STP

                  !  Signaling Transfer Points (STPs)
                           !  Provide efficient, fast call setup and teardown of
                              telephone calls
                           !  Provide routing for database lookups (AIN, LNP,
                              800, etc.)
                           !  Are the primary switches used in a “packet-based”
                              network as opposed to the circuit based network
                           !  Provide Gateway Screening for Customer Access
                              (IXCs, ITCs, CLECs, Wireless)
                           !  Serve as the PSTN entry point into the VoIP Network




                                                                                    15
D. Finn (BellSouth 2006)




                                 Example: BellSouth

                  !  32 Analog 1AESS COs (SSPs)
                  !  856 Lucent 5ESS COs
                           !  355 5ESS “Hosts’ and 501 Remotes
                  !  581 Nortel DMS COs
                           !  285 DMS “Hosts” and 283 Remotes and 10 DMS-10
                  !  138 Siemens COs (includes 85 Remotes)
                  !  1607 Total COs with approx. 20.3 million NALs
                           !  hosts ~ 24,000 lines
                           !  remotes ~ 3,500 lines
                  !  109 tandems


                                                                                    16
D. Finn (BellSouth 2006)




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                           CO picture

  copper wires:
  home ! cable
  vault ! distribution
  frame




                                                   17
D. Finn (BellSouth 2006)




                           CO picture




                              distribution frame



                                                   18




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                                          CO pictures

                                                                     fiber cross connect
                                                                     point: fiber leaves
                                                                     CO




                                                                                           19
D. Finn (BellSouth 2006)




                                                     SS7

                  !  SSP: service switching point = voice switch + adjunct

                  !  STP: signal transfer point            router

                  !  SCP: service control point = interface to databases
                           !  call management service database
                           !  line information database
                           !  home location register (cellular)
                           !  visitor location register (cellular)

                  !  traditionally, connected by 64 kb/s & T1 leased lines
                           !  future: IP (! IETF Sigtran WG)

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           SS7 protocol stack




                                                                       21




           SS7 protocol stack

!  Level 1 (physical)
   !  DS0A = 56/64 kb/s in DS1 facility

!  Level 2 (data link)
   !  error detection/correction, link-by-link

!  Level 3 (network)
   !  routing message discrimination      “point codes” distribution

!  Level 4 (user parts)
   !  basic signaling (ISUP)
   !  Transaction Capabilities Application (TCAP)
   !  Operations, Maintenance, Administration (OMAP)
   !  Mobile Application Part (MAP)


                                                                       22




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             SS7 call




                                             23




         Reliability
#9’s   reliability   outage/      example
                     year
1      90%           36.5 days
2      99%           3.65 days
3      99.9%         8.8 hours    good ISP
4      99.99%        53 minutes
5      99.999%       5 minutes    phone
                                  system
6      99.9999%      32 seconds




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                     Reliability

!  FCC incidents: " 90,000 customers, > 30 minutes
   (972 between 1992 and 1997)
!  FCC ARMIS (Automated Reporting Management
   Information System)
!  ANSI T1A1: logarithmic outage index = f(duration,
   # affected, time, functions, ...)
!  call defects per million (e.g., AT&T 173 ppm)
                            http://fjallfoss.fcc.gov/eafs7/PresetMenu.cfm




                                                                            25




                     Outages

!  median outage lasts 2.9 hours
   !  (natural disasters: 13.4 hours)
   !  causes:
     !  facilities (45%)
     !  local switches (18%), CCS (13%), CO power (7.3%)
   !  facility failures:
      !  dig-ups (“back-hoe fade”, 58%)
      !  cable electronics (8%)

!  ARMIS example:
   !  Bell Atlantic 1998: 180 switches, combined
      downtime of 628 minutes, or 6.6 ·10-6

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        The phone works – why bother with VoIP



    user perspective                                       carrier perspective
    variable compression: tin can to broadcast quality !   better codecs + silence suppression – packet header
    no need for dedicated lines                            overhead = maybe reduced bandwidth

    security through encryption                            shared facilities simplify management, redundancy


    caller & talker identification                         advanced services

    better user interface (more than 12 keys, visual       cheaper bit switching
    feedback, semantic rather than stimulus)

    no local access fees (but dropping to 1c/min for       fax as data rather than voiceband data (14.4 kb/s)
    PSTN)

    adding video, application sharing is easy




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                                     Old vs. new
               old reality                  new idea                    new reality
service        ILEC, CLEC                   email-like, run by          E.164-driven; MSOs, some
provider                                    enterprise, homes           ILECs, Skype, European SIP
                                                                        providers, Vonage, SunRocket

media          4 kHz audio                  wideband audio,             4 kHz audio
                                            video, IM, shared
                                            apps, …

services       CLASS (CLID, call            user-created                still CLASS
               forwarding, 3-way            services
               calling, ...)                (web model)
                                            presence


user IDs       E.164                        email-like                  E.164
                                                                        IM handles


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                                       Evolution of VoIP

                                                                                       “Can it really
                                                                                       replace the
                                                                                       phone
                                                            “How can                   system?”
                                                            I make it
long-distance calling,                                      stop                  replacing the
ca. 1930                               “does it do          ringing?”
                                                                                  global phone system
                                       call transfer?”    going beyond
     “amazing
     – the                                                the black phone
     phone                      catching up
     rings”                     with the digital PBX



  1996-2000                        2000-2003                 2004-2005                   2006-

                                                                                                        29




              VoIP Signaling Protocols

 !  H.323                                                !  MGCP
      !     ITU standard, ISDN-based,                       !     IETF RFC 2705
            distributed topology                            !     Centralized call control
      !     early on, used to be 90%+ of all                      architecture
            Service Provider VoIP networks                  !     Call-Agents (MGC) & Gateways
      !     video conferencing (Microsoft                         (MG)
            NetMeeting, room units [Polycom,
                                                         !  SIP
            Tandberg, …])
                                                            !     IETF RFC 2543 and RFC 3261
 !  Skinny
                                                            !     Distributed call control
      !     Centralized call control
            architecture                                    !     Used for more than VoIP…SIMPLE:
                                                                  Instant Messaging / Presence
      !     CallManager controls all features
      !     over 1 mio. IP Phones deployed –
            probably most popular corporate
            IP-PBX



   Brian Gracely, Cisco, 2001 (mod.)
                                                                                                        30




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                                  IETF VoIP & presence efforts
                                                                      XMPP                                 P2PSIP
                                                                     (presence)                        (DHT protocol)
                                     ECRIT
                             (emergency calling)
                                                                                     SIMPLE
                                                                                  (presence)                               ENUM
                                                                                                                       (E.164 translation)

                                    uses
                                                        GEOPRIV                                                   uses
                                                       (geo + privacy)
                                                                                       may use          uses                  SPEERMINT
                                                                                                                                  (peering)
                            XCON
                         (conf. control)
                                                                                                                                         uses

                                                                  SIPCORE                          DISPATCH
                                 BLISS                            (protocol)                     (spin off mini-WGs)
                                (services)                                                                                               DRINKS
                                                                                                                                             (registry)

                                                                           usually
                                                                           used
                                                                           with
                                                                                                                                   MEDIACTRL
                                                                                             MMUSIC                               (media servers)
                                                       AVT                                 (SDP, RTSP, ICE)
                                                (RTP, SRTP, media)
                                                                                                                             SPEECHSC
                                                                                                                          (speech services)
                              IETF RAI area
                                                                                                                                                     31




                                                             PBX features
                                                                                                                            boss/admin features
                         call waiting/multiple calls   RFC 3261                            simultaneous ringing            RFC 3261

                         hold                          RFC 3264                            basic shared lines              dialog/reg. package

                         transfer                      RFC 3515/Replaces                   barge-in                        Join
centrex-style features




                         conference                    RFC 3261/callee caps                “Take”                          Replaces

                         message waiting               message summary package             Shared-line “privacy”           dialog package

                         call forward                  RFC 3261                            divert to admin                 RFC 3261

                         call park                     RFC 3515/Replaces                   intercom                        URI convention

                         call pickup                   Replaces                            auto attendant                  RFC 3261/2833

                         do not disturb                RFC 3261                            attendant console               dialog package

                         call coverage                 RFC 3261                            night service                   RFC 3261




                                                                                                                attendant features

                                                                                                                                              32
                                                                                                                   from Rohan Mahy’s VON Fall 2003 talk




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RTP                                   33




                   RTP stack

   RFC 3550
(RTP, RTCP) pair
                               RTCP




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                                               RTP

        !  Real-Time Transport Protocol (RTP) = data + control
             !  data (media):
                !  timing
                !  loss detection
                !  content labeling
                !  talkspurts & video frames
                !  encryption
             !  control (RTCP):
                !     periodic with T population
                !  QoS feedback
                !  membership estimation in multicast
                !  loop detection


                                                                                                 35




                                  RTP Packet Header                           RFC 3551
                                                                          audio-video profile


        padding (for fixed
         size block), last
        byte of pkt is the
            pad count



ver 2             # contributor


                                    static or dynamic



                                                        granularity determined by payload type
  1 = first pkt of a talkspurt,
     after a silence period


                                                               if this RTP stream is mixed




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                RTP timestamp

!  +1 per sample (e.g., 160 for 20 ms packets @
   8000 Hz)
!  random starting value
!  time per packet may vary
!  different fixed rate for each audio PT
     !  typically, 20 – 100 ms / packet
!  90 kHz for video
   !  several video frames may have same timestamp
!       gaps      silence
     !  split video frame (carefully. . . ) across packets


                                                             37




        RTP mixer & translator

!  mixer:
     !  several media stream      one new stream (new
       encoding)
       !  e.g., audio/video conferencing
     !  appears as new source, with own identifier

!  translator:
     !  single media stream
     !  may convert encoding
     !  e.g., protocol translation (IPv4 ! IPv6)
     !  all packets: source address = translator address

                                                             38




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         RTP mixer & translator




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                                   RTCP

stackable packets, similar to data packets
!  sender report (SR)
    !    bytes send    estimate rate
    !    timestamp     synchronization
!  reception reports (RR):
    !    number of packets sent and expected       loss, interarrival jitter, round-trip
         delay
!  source description (SDES):
    !    name, email, location,…
!  canonical name (CNAME) = user@host
    !    identifies user across media
!  explicit leave (BYE): in addition to time-out
!  extensions (APP): application-specific (none yet)



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                                RTCP




                                                                             41




                       RTCP (detail)
Value   Abbreviation   Name                                     Document

194     SMPTETC        SMPTE time-code mapping                  RFC 5484

195     IJ             Network interarrival jitter              RFC 5450

200     SR             Sender report                            RFC 3550

201     RR             Receiver report                          RFC 3550

202     SDES           Source description                       RFC 3550

203     BYE            Good bye                                 RFC 3550

204     APP            Application-defined                      RFC 3550

205     RTPFB          Generic RTP feedback (loss)              RFC 4585

206     PSFB           Payload-specific feedback                RFC 4585

207     XR             Extended report (RLE, delay, R factor)   RFC 3611

208     AVB            Audio-video bridging                     IEEE 1733

209     RSI            Receiver summary information             ietf-avt-rtcpssm


                                                                             42




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 RTCP SR packet example




                                                 43




  RTCP bandwidth scaling




!  next packet = last packet + max(5 s, T ) #
  random(0.5. . . 1.5)

!  randomization prevents “bunching”

!  to reduce RTCP bandwidth, alternate between
  SDES components

                                                 44




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RTCP intermedia synchronization

 !  = sync different streams (audio, video, slides, . . .)
 !  timestamps are offset with random intervals
 !  may not tick at nominal rate
 !  SRs correlate “real” time (wallclock time) with
   RTP timestamp




                                                             45




 Round-trip time estimation
    compute round-trip time between sender and receiver




                                                             46




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SIP overview

 Internet services – the missing entry

     Service/   synchronous          asynchronous
     delivery
     push       instant messaging    messaging
                presence
                event notification
                session setup
                media-on-demand

     pull       data retrieval       peer-to-peer file
                file download        sharing
                remote procedure
                call




                                                         48




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           Filling in the protocol gap

    Service/              synchronous      asynchronous
    delivery
    push                  SIP              SMTP
                          RTSP, RTP
    pull                  HTTP             (not yet standardized)
                          ftp
                          SunRPC, Corba,
                          SOAP




                                                                    49




           SIP as service enabler

!  Rendezvous protocol
   !  lets users find each other by
      only knowing a permanent
      identifier

!  Mobility enabler:
   !  personal mobility
      !  one person, multiple terminals
   !  terminal mobility
      !  one terminal, multiple IP
         addresses
   !  session mobility
      !  one user, multiple terminals in
          sequence or in parallel
   !  service mobility
      !  services move with user



                                                                    50




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                   What is SIP?
        "    Session Initiation Protocol ! protocol that
             establishes, manages (multimedia) sessions
             "    also used for IM, presence & event
                  notification
             "    uses SDP to describe multimedia sessions
        "    Developed at Columbia U. (with others)
        "    Standardized by
             "    IETF (RFC 3261-3265 et al)
             "    3GPP (for 3G wireless)
             "    PacketCable
        "    About 100 companies produce SIP
             products
        "    Microsoft’s Windows Messenger ("4.7)
             includes SIP
                                                             51




                     Philosophy

!  Session establishment & event notification

!  Any session type, from audio to circuit emulation

!  Provides application-layer anycast service

!  Provides terminal and session mobility

!  Based on HTTP in syntax, but different in protocol
  operation
!  Peer-to-peer system, with optional support by proxies
   !  even stateful proxies only keep transaction state,
     not call (session, dialogue) state
  !  transaction: single request + retransmissions
  !  proxies can be completely stateless

                                                             52




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Basic SIP message flow




                                                                  53




              SIP trapezoid
                                         destination proxy
          outbound
                                         (identified by SIP URI domain)
          proxy
1st request


                             SIP
                             trapezoid
                2nd, 3 , … request
                           rd




                 a@foo.com
                 :
                 128.59.16.1



              registrar
                                                         voice traffic
                                                         RTP
                                                                  54




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                          SIP message format
request line                        request                                       response
                  INVITE sip:bob@there.com SIP/2.0                 SIP/2.0 200 OK

                   Via: SIP/2.0/UDP here.com:5060                  Via: SIP/2.0/UDP here.com:5060
  header fields




                   From: Alice <sip:alice@here.com>                From: Alice <sip:alice@here.com>
                   To: Bob <sip:bob@there.com>                     To: Bob <sip:bob@there.com>
                   Call-ID: 1234@here.com                          Call-ID: 1234@here.com
                   CSeq: 1 INVITE                                  CSeq: 1 INVITE
                   Subject: just testing                           Subject: just testing
                   Contact: sip:alice@pc.here.com                  Contact: sip:alice@pc.here.com
                   Content-Type: application/sdp                   Content-Type: application/sdp
                   Content-Length: 147                             Content-Length: 134
message body




                   v=0                                             v=0
                   o=alice 2890844526 2890844526 IN IP4 here.com   o=bob 2890844527 2890844527 IN IP4 there.com
                   s=Session SDP                                   s=Session SDP
                   c=IN IP4 100.101.102.103                        c=IN IP4 110.111.112.113
                   t=0 0                                           t=0 0
                   m=audio 49172 RTP/AVP 0                         m=audio 3456 RTP/AVP 0
                   a=rtpmap:0 PCMU/8000                            a=rtpmap:0 PCMU/8000

                                    SDP
                                                                                                                  55




                                                                                                     RFC
                                                          SDP                                        2327
                                                                                                     4566



!  Format description (payload), not a protocol

!  Used in MGCP and SIP to describe media characteristics
                  !  Type of stream (audio, video, real-time text, …)
                  !  Codec type
                  !  IP address & port

!  Sent within a SIP message as a message body
                  !  Content-Type: application/sdp

!  Originally designed for multicast sessions (SAP)
                  !  limited extensibility
                  !  capability (“can”) vs. request (“want”)
                  !  media alignment problems


                                                                                                                  56




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                            SDP example
                    v=0
                    o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
                    s=SDP Seminar
                    i=A Seminar on the session description protocol
     send           u=http://www.example.com/seminars/sdp.pdf
    data to         e=j.doe@example.com (Jane Doe)
                    c=IN IP4 224.2.17.12/127
                    a=recvonly                                        session
RTP audio           m=audio 49170 RTP/AVP 0                        description
 with PT 0                                                          (mainly for
(!-law) on
                    m=video 51372 RTP/AVP 99                         multicast)
port 49170          a=rtpmap:99 h263-1998/90000

              RTP video
              with PT 99,               RTP
              defined in            timestamp
                  a=                frequency
                                      = 90 kHz




                                                                                  57




                            Offer/Answer                                 RFC
                                                                         3264




      !  = the process of negotiating codecs using SDP

      !  SDP can be sent in SIP INVITE, 18x/200 responses,
             and ACK

      !  The first SDP sent in either direction is considered
             to be an offer

      !  An SDP consequently sent in the reverse
             direction is an answer




                                                                                  58




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                SDP offer/answer
                              INVITE(sdp)
Caller                                                        Callee
                                   180

                                 200(sdp)
                                                              Let me see you !
                                  ACK




                          INVITE(sdp + video)
                              200(sdp)

                                  ACK




                                                                                 59




           PSTN vs. Internet Telephony
    PSTN:


                    Signaling & Media               Signaling & Media

                                                    China
   Internet
   telephony:
                        Signaling                     Signaling



                                            Media
         Belgian customer,                                        Australia
         currently visiting US

                                                                                 60




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                   SIP addressing
  !  Users identified by SIP or tel URIs
     !  sip:alice@example.com
  !  tel: URIs describe E.164 number, not
     dialed digits (RFC 2806bis)
  !  tel URIs ! SIP URIs by outbound proxy tel:110                        sip:sos@domain
  !  A person can have any number of SIP
     URIs
  !  The same SIP URI can reach many
     different phones, in different networks
     !    sequential & parallel forking
  !  SIP URIs can be created dynamically:
     !    GRUUs                                                              domain !
     !    conferences                                                        128.59.16.17
     !    device identifiers (sip:foo@128.59.16.15)                          via NAPTR + SRV
  !  Registration binds SIP URIs (e.g., device
     addresses) to SIP “address-of-
     record” (AOR)

                                                                                           61




3G Architecture (Registration)

                                      mobility management
                                           signaling




              serving                 interrogating              interrogating
               CSCF

               proxy                                        home IM domain

                                                       registration signaling (SIP)_



                       visited IM domain



                                                                                           62




                                                                                                      '!&
                                                                         !"#"$#$%&




Presence & events

               Event notification

  !  notify (small) group of users          with NATs
     when something of interest
     happens                    !  Lots of research (e.g., SIENA)
     !  presence = change of
        communications state         !  IETF efforts starting
     !  email, voicemail alerts         !  SIP-based
     !  environmental conditions        !  XMPP
     !  vehicle status
     !  emergency alerts

  !  kludges
     !  HTTP with pending response
     !  inverse HTTP --> doesn’t work


                                                                    64




                                                                               '"&
                                                                                         !"#"$#$%&




               Context-aware communication

            !  context = “the interrelated conditions in which
               something exists or occurs”

            !  anything known about the participants in the
               (potential) communication relationship

            !  both at caller and callee


        time                              CPL
        capabilities                      caller preferences

        location                          location-based call routing
                                          location events

        activity/availability             presence
        sensor data (mood, bio)           privacy issues similar to location data


                                                                                    65




                The role of presence

!  Guess-and-ring                               !  Presence-based
   !  high probability of failure:                 !  facilitates unscheduled
       !    “telephone tag”                           communications
       !    inappropriate time (call during
            meeting)
                                                   !  provide recipient-specific
       !    inappropriate media (audio in             information
            public place)                          !  only contact in real-time if
   !  current solutions:                              destination is willing and able
      !  voice mail ! tedious, doesn’t             !  appropriately use
          scale, hard to search and                   synchronous vs. asynchronous
          catalogue, no indication of
          when call might be returned                 communication
      !  automated call back ! rarely              !  guide media use (text vs.
          used, too inflexible                        audio)
   !  ! most successful calls are now              !  predict availability in the near
       scheduled by email                             future (timed presence)



                   Prediction: almost all (professional) communication
                   will be presence-initiated or pre-scheduled
                                                                                    66




                                                                                               ''&
                                                                                                                          !"#"$#$%&




                GEOPRIV and SIMPLE architectures


                DHCP
                                                                          rule
                                                                          maker
                                                       XCAP
                                                       (rules)

                          publication             location       notification         location
       target             interface                              interface                          GEOPRIV
                                                  server                              recipient

                                                                 SUBSCRIBE
                                                  presence                                          SIP
       presentity                                                                     watcher
                         PUBLISH                  agent                                             presence
                                                                  NOTIFY


       caller                                                                         callee        SIP
                             INVITE                              INVITE                             call

                                                                                                                67




                  Presentity and Watchers

           Bob’s
                                                             Presence            SUBSCRIBE
         Presentity                        PUBLISH             Server                                Watchers
                                                                                                    Watchers
                                                                                                    Watchers
                                                                (PS)                NOTIFY
                                    Bob’s
                                   status,
                                  location                    Bob’s
                                                              Filters
                                                             (Rules),                                          wife
                       PUBLISH                               PIDF *)


                                                                                                               son
                             R u there ?             *) - PIDF = Presence Information Data Format


Cell
                            BUZZ                                                                               friend
          Phone              Bob’s play station
                  PC-IM Client

       Bob’s Presence User                                                                                     external
       Agents (PUA)                                                                                            world
                                                                                                                68




                                                                                                                                '(&
                                                                                                     !"#"$#$%&




               Basic presence

!  Role of presence
   !  initially: “can I send an instant message and expect a
      response?”
   !  now: “should I use voice or IM? is my call going to interrupt
      a meeting? is the callee awake?”
!  Yahoo, MSN, Skype presence services:
   !  on-line & off-line
   !  useful in modem days – but many people are (technically)
      on-line 24x7
   !  thus, need to provide more context
   !  + simple status (“not at my desk”)
!  entered manually ! rarely correct
!  does not provide enough context for directing interactive
   communications


                                                                                                69




         Presence data architecture


   presence sources

      PUBLISH

                                  raw
           create
           view                   presence                                   privacy
           (compose)              document                                   filtering


                    XCAP                                    depends on watcher     XCAP
                               select best source
                               resolve contradictions


            composition                                                      privacy
            policy                                                           policy

           (not defined yet)
                                                        draft-ietf-simple-presence-data-model

                                                                                                70




                                                                                                           ')&
                                                                                        !"#"$#$%&




         Presence data architecture


  candidate                              raw
                                                                 post-processing
  presence                    watcher    presence                composition
  document                    filter     document                (merging)




                                   SUBSCRIBE
         remove data not of
         interest                         difference
                                          to previous notification


                                                              final
                                                              presence
              watcher                                         document
                                         NOTIFY


                                                                                   71




                  Rich presence

!  Provide watchers with better information about the
   what, where, how of presentities

!  facilitate appropriate communications:
   !  “wait until end of meeting”
   !  “use text messaging instead of phone call”
   !  “make quick call before flight takes off”

!  designed to be derivable from calendar information
   !  or provided by sensors in the environment

!  allow filtering by “sphere” – the parts of our life
   !  don’t show recreation details to colleagues

                                                                                   72




                                                                                              '*&
                                                                        !"#"$#$%&




                     Rich presence

    !  automatically derived from
       !  sensors: physical presence, movement
       !  electronic activity: calendars

    !  Contains:
       !  multiple contacts per presentity
          !  device (cell, PDA, phone, …)
          !  service (“audio”)
       !  activities, current and planned
       !  surroundings (noise, privacy, vehicle, …)
       !  contact information
       !  composing (typing, recording audio/video IM, …)

                                                                  73




    The role of presence for call routing
                                                PUBLISH
!  Two modes:
   !  watcher uses presence
      information to select                              PA
      suitable contacts
     !  advisory – caller may not
        adhere to suggestions and                              NOTIFY
        still call when you’re in a          translate
        meeting                              RPID
  !  user call routing policy
     informed by presence
     !  likely less flexible – machine
        intelligence                         CPL          LESS
     !  “if activities indicate
        meeting, route to tuple
        indicating assistant”
     !  “try most-recently-active
        contact first” (seq. forking)

                                                              INVITE

                                                                  74




                                                                              '+&
                                                                                        !"#"$#$%&




                 Presence and privacy

!  All presence data,
  particularly location, is   <tuple id="sg89ae">

  highly sensitive              <status>
                                  <gp:geopriv>
                                     <gp:location-info>

!  Basic location object               <gml:location>

  (PIDF-LO) describes                    <gml:Point gml:id="point1“
                                          srsName="epsg:4326">
  !  distribution (binary)                  <gml:coordinates>37:46:30N 122:25:10W
                                        </gml:coordinates>
  !  retention duration                    </gml:Point>
                                       </gml:location>

!  Policy rules for more
                                     </gp:location-info>
                                    <gp:usage-rules>
  detailed access                     <gp:retransmission-allowed>no
  control                           </gp:retransmission-allowed>
                                       <gp:retention-expiry>2003-06-23T04:57:29Z
  !  who can subscribe to           </gp:retention-expiry>
     my presence                    </gp:usage-rules>

  !  who can see what
                                  </gp:geopriv>
                                </status>
     when                       <timestamp>2003-06-22T20:57:29Z</timestamp>
                              </tuple>




                                                                                   75




                    Privacy rules

 !  Conditions                 !  User gets maximum of
    !  identity, sphere            permissions across all
    !  time of day                 matching rules
    !  current location            !  privacy-safe
                                        composition: removal of
    !  identity as <uri> or
       <domain> + <except>
                                        a rule can only reduce
                                        privileges
 !  Actions
                               !  Extendable to new
    !  watcher confirmation        presence data
 !  Transformations                !  rich presence
    !  include information
                                   !  biological sensors
                                   !  mood sensors
    !  reduced accuracy


                                                                                   76




                                                                                              ',&
                                                                                            !"#"$#$%&




                                  Example rules document
                <conditions>      <rule id=1>

                                  <identity><id>user@example.com</id></identity>
            <actions>




                                  <sub-handling>allow</sub-handling>
<ruleset>




                                   <provide-services>
              <transformations>




                                     <service-uri-scheme>sip</service-uri-scheme>
                                     <service-uri-scheme>mailto</service-uri-scheme>
                                   </provide-services>
                                   <provide-person>true</provide-person>
                                   <provide-activities>true</provide-activities>
                                   <provide-user-input>bare</provide-user-input>



                                                                                       77




Location-based
services

                                                                                                  '%&
                                                                                                                          !"#"$#$%&




                     Location-based services

                                                                         Using location to
             Finding services
                                                                              improve
                based on
                                                                             (network)
                 location                                                     services




 physical services          electronic
      (stores,          services (media I/
                                             communication     configuration            awareness         security
restaurants, ATMs,          O, printer,
         …)                display, …)




                                                incoming                               others are     proximity grants
                                                              devices in room
                                             communications                           (selectively)     temporary
                                                               adapt to their
                                             changes based                           made aware of    access to local
                                              on where I am    current users          my location        resources




                                                                                                                     79




             Location-based SIP services

              !  Location-aware inbound routing
                     !  do not forward call if time at callee location is [11 pm,
                         8 am]
                     !  only forward time-for-lunch if destination is on campus
                     !  do not ring phone if I’m in a theater

              !  outbound call routing
                     !  contact nearest emergency call center
                     !  send delivery@pizza.com to nearest branch

              !  location-based events
                     !  subscribe to locations, not people
                     !  Alice has entered the meeting room
                     !  subscriber may be device in room ! our lab stereo
                         changes CDs for each person that enters the room

                                                                                                                     80




                                                                                                                                ($&
                                                                                                         !"#"$#$%&




             GPS
                       Location delivery



                                         HELD
                                                      HTTP

                                                                              wire
                                                                              map
                                                       DHCP




                                                    LLDP-MED
                                                                                                 81




        Location determination options
Method       CDP or LLDP-           DHCP           HELD             GPS              manual entry
             MED
Layer        L2                     L3             L7 (HTTP)        -                user
advantages   •  simple to           •  simple to   •  traverses     •  accurate      •  no
                implement              implement      NATs          •  mobile           infrastructure
             •  built into switch   •  network     •  can be           devices          changes
             •  direct port/room       locality       operated by   •  no carrier    •  no carrier
                mapping                               L2 provider      cooperation      cooperation
problems     may be hard to         mapping MAC    mapping IP       •  indoor        •  fails for
             automate for large     address to     address to          coverage         mobile
             enterprises            location?      switch port?     •  acquisition      devices
                                                                       time          •  unreliable for
                                                                                        nomadic
Use          Ethernet LANs          Enterprise     DSL, cable       mobile devices   fall back
                                    LANs
                                    Some ISPs




                                                                                                 82




                                                                                                               (!&
                                       !"#"$#$%&




Program location-based services




                                  83




                                  84




                                             ("&
                                                                         !"#"$#$%&




P2P

 Defining peer-to-peer systems
Each peer must act as both a client and a server.

Peers provide computational or storage resources for other peers.

Self-organizing and scaling.



         1 & 2 are not sufficient:
             DNS resolvers provide services to others
             Web proxies are both clients and servers
             SIP B2BUAs are both clients and servers




                                                                    86




                                                                               ('&
                                                                   !"#"$#$%&




         P2P systems are …
                               P2P




                         NETWORK ENGINEER’S WARNING
                   P2P systems may be
                   !  inefficient
         vs.
                   !  slow
                   !  unreliable
                   !  based on faulty and short-term
                      economics
                   !  mainly used to route around copyright
                      laws

                                                              87




  Motivation for peer-to-peer
           systems
!  Saves money for those        !  Networks without
  offering services               infrastructure (or system
   !  addresses market            manager)
     failures
!  Scales up automatically !  New services that can’t
  with service demand             be deployed in the
                                  ossified Internet
!  More reliable than client-     !  e.g., RON, ALM
  server (no single point of
  failure)

!  No central point of
  control
   !  mostly plausible
     deniability

                                                              88




                                                                         ((&
                                                                                                 !"#"$#$%&




     P2P traffic is not devouring the Internet…

                                   AT&T backbone


                                      Other;
steady percentage
                                       14%                     HTTP web;
               P2P; 20%                                           33%



                                         HTTP audio/
                                         video; 33%




                                                                                            89




             Energy consumption


                                                                           Monthly cost =
                                                                               $37
                                                                           @ $0.20/kWh




                    http://www.legitreviews.com/article/682/                                90




                                                                                                       ()&
                                                                       !"#"$#$%&




                Bandwidth costs




!  Transit bandwidth: $40 Mb/s/month ~ $0.125/GB

!  US colocation providers charge $0.30 to $1.75/GB
   !  e.g., Amazon EC2 $0.17/GB (outbound)
   !  CDNs: $0.08 to $0.19/GB
                                                                91




               Economics of P2P
!  Service provider view
   !  save $150/month for single rented server in
      colo, with 2 TB bandwidth
   !  but can handle 100,000 VoIP users

!  But ignores externalities
   !  home PCs can’t hibernate ! energy usage
     !  about $37/month
  !  less efficient network usage
  !  bandwidth caps and charges for consumers
                                              charge ($)




     !  common in the UK
     !  Australia: US$3.20/GB

!  Home PCs may become rare
   !  see Japan & Korea                                    bandwidth

                                                                92




                                                                             (*&
                                                                                !"#"$#$%&




 Which is greener – P2P vs. server?

    !  Typically, P2P hosts only lightly used
       !  energy efficiency/computation highest at full load
       !  ! dynamic server pool most efficient
       !  better for distributed computation (SETI@home)

    !  But:
       !  CPU heat in home may lower heating bill in winter
          !  but much less efficient than natural gas (< 60%)
       !  Data center CPUs always consume cooling energy
          !  AC energy $ server electricity consumption

    !  Thus,
       !  deploy P2P systems in Scandinavia and Alaska


                                                                          93




                        Reliability
!  CW: “P2P systems are more reliable”
                                                     Some of you may be
                                                     having problems
!  Catastrophic failure vs. partial failure          logging into Skype. Our
                                                     engineering team has
   !  single data item vs. whole system              determined that it’s a
                                                     software issue. We
   !  assumption of uncorrelated failures            expect this to be
                                                     resolved within 12 to 24
      wrong                                          hours. (Skype, 8/12/07)


!  Node reliability
   !  correlated failures of servers (power,
      access, DOS)
   !  lots of very unreliable servers (95%?)

!  Natural vs. induced replication of data
  items

                                                                          94




                                                                                      (+&
                                                          !"#"$#$%&




          Security & privacy

!  Security much harder
   !  user authentication and credentialing
     !  usually now centralized
  !  sybil attacks
  !  byzantine failures

!  Privacy
   !  storing user data on somebody else’s machine

!  Distributed nature doesn’t help much
   !  same software ! one attack likely to work
      everywhere

!  CALEA?

                                                     95




                        OA&M

!  P2P systems are hard to debug

!  No real peer-to-peer management systems
   !  system loading (CPU, bandwidth)
     !  automatic splitting of hot spots
  !  user experience (signaling delay, data path)
  !  call failures

!  Later: P2PP & RELOAD add mechanisms to query
  nodes for characteristics

!  Who gathers and evaluates the overall system
  health?
                                                     96




                                                                (,&
                                                                            !"#"$#$%&




P2P for VoIP                                                           97




          The role of SIP proxies

                                                tel:1-212-555-1234
                                                    REGISTER

sip:alice@example.com


                                               sip:line1@128.59.16.1


                         Translation may
                        depend on caller,
                        time of day, busy
                            status, …

                                            sip:6461234567@mobile.com
                                                               98




                                                                                  (%&
                                                                                                           !"#"$#$%&




                                    P2P SIP
!  Why?                                                  generic DHT service

   !  no infrastructure available: emergency                                   p2p network
      coordination
   !  don’t want to set up infrastructure: small
      companies                                                                P2P provider B
   !  Skype envy :-)

!  P2P technology for
   !  user location                                                                       DNS

       !    only modest impact on expenses
       !    but makes signaling encryption cheap         P2P
   !  NAT traversal                                      provider A
      !  matters for relaying
   !  services (conferencing, transcoding, …)
                                                                                    traditional provider
      !  how prevalent?


!  New IETF working group formed
   !  multiple DHTs                                                                zeroconf
   !  common control and look-up protocol?
                                                           LAN
                                                                                                 99




      More than a DHT algorithm
           Tree
   Finger table                    Routing-table stabilization
Periodic recovery                                                      Lookup correctness

                                                                          Prefix-match
                                           Modulo addition
  Routing-table size
                                    Parallel
        Recursive routing           requests
                                                                 Bootstrapping
  Updating routing-table from lookup requests
                                                                         Leaf-set
                  XOR          Proximity neighbor selection
 Lookup performance
                                                   Reactive recovery
                             Successor
  Hybrid                                               Proximity route selection
            Strict vs. surrogate routing
                                                              Routing-table exploration
                                                                                                100




                                                                                                                 )$&
                                                                               !"#"$#$%&




            P2P SIP -- components
  !  Multicast-DNS (zeroconf) SIP
     enhancements for LAN
     !  announce UAs and their
        capabilities

  !  Client-P2P protocol
     !  GET, PUT mappings
     !  mapping: proxy or UA

  !  P2P protocol
     !  get routing table, join, leave, …
     !  independent of DHT
     !  replaces DNS for SIP and basic
        proxy

                                                                         101




                P2PSIP architecture
Bootstrap & authentication server
                                      alice@example.c
                                      om
                                       Overlay 2
                                                                 SIP
            NAT
       bob@example.com ! 128.59.16.1
                                                         P2P           STUN
                  INVITE bob@128.59.16.1
                                                           TLS / SSL
                                NAT
                                                        peer in P2PSIP

bob@example.comOverlay 1                                client



                                                                         102




                                                                                     )!&
                                                                        !"#"$#$%&




        IETF peer-to-peer efforts

    !  Originally, effort to perform SIP lookups in p2p network

    !  Initial proposals based on SIP itself
       !  use SIP messages to query and update entries
       !  required minor header additions

    !  P2PSIP working group formed
       !  now SIP just one usage

    !  Several protocol proposals (ASP, RELOAD, P2PP)
       merged
       !  still in “squishy” stage – most details can change


                                                                  103




                           RELOAD
!  Generic overlay lookup (store & fetch) mechanism
  !  any DHT + unstructured

!  Routed based on node identifiers, not IP addresses

!  Multiple instances of one DHT, identified by DNS name

!  Multiple overlays on one node

!  Structured data in each node
  !  without prior definition of data types
  !  PHP-like: scalar, array, dictionary
  !  protected by creator public key
  !  with policy limits (size, count, privileges)

!  Maybe: tunneling other protocol messages

                                                                  104




                                                                              )"&
                                                    !"#"$#$%&




Typical residential access




                                              105
                    Sasu Tarkoma, Oct. 2007




         NAT traversal

                  get public IP address


          media


                      P2P

  peer




                                              106




                                                          )'&
                                                                               !"#"$#$%&




              ICE (Interactive Connectivity
                      Establishment)




                                        offer &
gather        prioritize   encode                   check      complete
                                        answer




                                                                        107




          OpenVoIP snapshots




     direct                    call through a NAT       call through a relay
                                                                         108




                                                                                     )(&
                                                 !"#"$#$%&




     OpenVoIP snapshots

!  Google Map interface




                                           109




     OpenVoIP snapshots
!  Tracing lookup request on Google Maps




                                           110




                                                       ))&
                                                               !"#"$#$%&




Emergency calling

   Modes of emergency communications


                          emergency call
 information
 “I-am-alive”
                emergency alert               dispatch
                (“inverse 911”)



                         civic coordination


                                                         112




                                                                     )*&
                                                                                         !"#"$#$%&




                  Background on 9-1-1

        !  Established in Feb. 1968
            !    1970s: selective call routing
            !    late 1990s: 93% of population/96% of area covered by 9-1-1
            !    95% of 9-1-1 is Enhanced 9-1-1
            !    US and Canada

        !  Roughly 200 mio. calls a year (6 calls/second)
            !  1/3 wireless

        !  6146 PSAPs in 3135 counties
            !  most are small (2-6 call takers)
            !  83.1% of population have some Phase II (April 2007)

        !  “12-15 million households will be using VoIP as either
            primary or secondary line by end of 2008” (NENA)

                                                          http://www.nena.org/   113




                                         Local Switch




Automatic
Number
Identification


                        Automatic
                        Location
                                                          Collaboration between
                        Identification
                                                          local phone providers and
                                                          local public safety agencies



                                                                                 114




                                                                                               )+&
                                                                                               !"#"$#$%&




          E9-1-1 Call flow elements -
                   wireline
                      E9-1-1
End                   Tandem
                                                           Public Safety
office
          ES Trunks   w/SRDB            EM Trunks          Answering Point



                                                                PSAP ALI Data Links
 Loop                                               PSAP
 Acces
 s
 Contr       The
 ol          Local
 ie DLC      Loop
 Syste                                                                       ALI
 m
                                             Recent
                                             Change
                                             Links
                           SCP                                   Update
                           GATEWAY                               Links
                           (Firewall)                  DBMS
                                                                    Service Providers
                               ALI Database Elements                                     115




     Wireless 911 Phase II - TDOA




                                                                                         116
                                                                             BellSouth




                                                                                                     ),&
                                                                                      !"#"$#$%&




        Wireless 911 Phase II accuracy
              Accuracy               67%        95%
              Handset-based         50m       150m
              Network-based        100m       300m




                                                                                117




E9-1-1 CALL FLOW ELEMENTS - WIRELESS

                                                               ALI/SR
PDE                                                 8          DBASE
                                        E2                                      7
                         MPC
        3      4
                                                        9
                                              L’s
                                           TD                  6
                         5
                    E9-1-1                                     Public
    2               Tandem                                     Safety
        MSC
                    w/SRDB                                     Answering
                                                        PSAP   Point


                          #9 is only applicable in a CAS-Hybrid architecture,
                          such as BellSouth’s WLS911 Solution
1


                                                                                118




                                                                                            )%&
                                                                        !"#"$#$%&




        What makes VoIP 112/911 hard?
POTS                    PSTN-emulation VoIP     end-to-end VoIP
(landline) phone        landline phone      no phone number or
number limited to       number anywhere in phone number
limited area            US (cf. German 180) anywhere around
                                            the world
regional carrier        national or             enterprise “carrier”
                        continent-wide          or anybody with a
                        carrier                 peer-to-peer device
voice provider = line   voice provider % ISP    voice provider % ISP
provider (~ business
relationship)
national protocols      probably North          international
and call routing        America + EU            protocols and
                                                routing
location = line         mostly residential or   stationary, nomadic,
location                small business          wireless         119




            Emergency numbers
!  Each country and region
   has their own
   !  subject to change

!  Want to enable
   !  traveler to use familiar home
      number
   !  good samaritan to pick up
      cell phone

!  Some 3/4-digit numbers are
   used for non-emergency
   purposes (e.g., directory
   assistance)
                                                   Emergency number
                                                                  120




                                                                              *$&
                                                                                      !"#"$#$%&




                           Service URN

       !  Idea: Identifiers to denote emergency calls
          !  and other generic (communication) services

       !  Described in IETF ECRIT RFC 5031

       !  Emergency service identifiers:
           sos                General emergency services
           sos.animal-control Animal control
           sos.fire           Fire service
           sos.gas            Gas leaks and gas emergencies
           sos.marine         Maritime search and rescue
           sos.mountain       Mountain rescue
           sos.physician      Physician referral service
           sos.poison         Poison control center
           sos.police         Police, law enforcement

                                                                                121




      LoST: Location-to-URL Mapping
         VSP1
                 cluster serving VSP1
                                                                 replicate
                                                 cluster         root information
123 Broad Ave                                    serves VSP2
Leonia
Bergen County
NJ US
                              LoST
                                        NJ               NY             root
                                        US               US             nodes
          sip:psap@leonianj.gov
                                                  search
                                                  referral
                                             Bergen County
                                             NJ US
                                                               Leonia
                                                               NJ US
                                                                                122




                                                                                            *!&
                                                                                                                         !"#"$#$%&




Cellular
                                LoST
       9-1-1
       9-1-
       9-
       9-1-1




                     SIP




                     RTP



Access Network
                                                                                                                   123




                  The POC system is deployed in 5 real PSAPs and 3 labs across the USA.
                        PSAP: Public Safety Answering Point (=Emergency call center)




King County, WA

                           Bozeman, MT
                                                         St. Paul, MN

                                                                                       Rochester, NY




                                                                                                       Columbia
                                                                                                       Univ. Lab
                                                         Fort Wayne, IN




                                                                                          BAH Lab


                                         TAMU Lab




                                                                                                                   124




                                                                                                                               *"&

				
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