internet telephony (voip) henning schulzrinne dept. of computer science columbia university fall...
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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 quality no need for dedicated lines
better codecs + silence suppression – packet 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 feedback, semantic rather than stimulus)
cheaper bit switching
no local access fees (but dropping to 1c/min for PSTN)
fax as data rather than voiceband data (14.4 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
Example: Sprint PCS and Nextel use GPS Implementation just starting VolP has similar problems as wireless:
– devices change “network attachment point”
Accuracy 67% 95%
Handset-based 50m 150m
Network-based 100m 300m
E9-1-1 Tandemw/SRDB
PSAP
Endoffice
Loop Acce
ss Controlie
DLC System
Update Links
The Local Loop
EM TrunksES Trunks
Public Safety Answering Point
PSAP ALI Data Links
Recent Change Links
DBMS
Service ProvidersALI Database Elements
SCP GATEWA
Y(Firewall)
E9-1-1 Call flow elements - wireline
ALI
ALI/SRDBASE
PSAP
Public Safety Answering Point
MSC
MPCPDE
E2
E9-1-1 Tandemw/SRDB
1
2
3 4
56
78
E9-1-1 CALL FLOW ELEMENTS - WIRELESS
TDL’s9
#9 is only applicable in a CAS-Hybrid architecture, such as BellSouth’s WLS911 Solution
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