1. Internet Telephony (VoIP)
Henning Schulzrinne
Dept. of Computer Science
Columbia University
Fall 2003

2. 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

3. 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

4. New Internet services
tougher: replacing dedicated electronic media vs. new modes (web, )
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?

5. 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

6. 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)

7. Wireless 911 Phase II - TDOA
BellSouth

8. Wireless 911 Phase II - EOTD
BellSouth

9. Wireless 911 Phase II Example: Sprint PCS and Nextel use GPS
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”

10. E9-1-1 Call flow elements - wireline
E9-1-1 Tandem w/SRDB
End
office
Public Safety Answering Point
ES Trunks
EM Trunks
Recent Change Links
PSAP ALI Data Links
PSAP
Loop Access Control
ie DLC System
The Local Loop
ALI
Update Links
SCP GATEWAY
(Firewall)
DBMS
Service Providers
ALI Database Elements

11. E9-1-1 CALL FLOW ELEMENTS - WIRELESS
MPC
ALI/SR
DBASE 8
PDE E2 7 4 3 9
TDL’s 6 5
PSAP
Public Safety Answering Point
E9-1-1 Tandem w/SRDB 2
MSC
#9 is only applicable in a CAS-Hybrid architecture, such as BellSouth’s WLS911 Solution 1