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