VoIP

Document Sample
VoIP Powered By Docstoc
					Internet Telephony (VoIP)

            Henning Schulzrinne
            Dept. of Computer Science
            Columbia University
            Fall 2003
Overview

   new Internet services: “telephone”, “radio”,
    “television”
   why Internet telephony?
   why not already?
   Internet telephony modalities
   components needed:
    –   audio coding
    –   data transport
    –   quality of service – resource reservation
    –   signaling
    –   PSTN interworking: gateway location, number translation
Name confusion

   Commonly used interchangeably:
    –   Internet telephony
    –   Voice-over-IP (VoIP)
    –   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
New Internet services

   tougher: replacing dedicated electronic
    media vs. new modes (web, email)
   distribution media (radio, TV): hard to beat
    one antenna tower for millions of $30
    receivers
   typewriter model of development
   radio, TV, telephone: a (protocol)
    convergence?
The phone works – why bother with
VoIP

user perspective                                   carrier perspective
variable compression: tin can to broadcast         better codecs + silence suppression – packet
quality  no need for dedicated lines              header 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       fax as data rather than voiceband data (14.4
for PSTN)                                          kb/s)

adding video, application sharing is easy
Emergency Calling
   911 in North America, 112 in Europe, others elsewhere
   First implemented 1968 in US, now roughly 95% of US
    population
   Basic 911 service: route emergency call to nearest emergency
    call center (public safety answering point – PSAP)
   Later, enhanced 911 (E-9-1-1) for selective routing and
    conveying caller location information to PSAP
   Roughly, 150 million 911 calls per year (2000)
     –   45 million wireless
   For wireless: Phase I and Phase II
     –   Phase I conveys call back number + Pseudo-ANI (cell face
         identifier) to PSAP
     –   Phase II provides caller location (e.g., via GPS or TOA)
Wireless 911 Phase II - TDOA




                               BellSouth
Wireless 911 Phase II - EOTD




                               BellSouth
Wireless 911 Phase II

        Accuracy        67%    95%
        Handset-based   50m    150m
        Network-based   100m   300m



   Example: Sprint PCS and Nextel use GPS
   Implementation just starting
   VolP has similar problems as wireless:
    –   devices change “network attachment point”
   E9-1-1 Call flow elements - wireline
                       E9-1-1
End
office
          ES Trunks
                      Tandem       EM Trunks
                                                       Public Safety
                                                       Answering Point
                      w/SRDB
                                                            PSAP ALI Data Links
  Loop
 Acces
                                               PSAP
    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
E9-1-1 CALL FLOW ELEMENTS - WIRELESS

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


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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:40
posted:9/18/2012
language:Unknown
pages:11