Internet Telephony – Internet Telephony – completing the completing the transition to IP-based transition to IP-based communicationscommunications

Henning SchulzrinneDept. of Computer Science and Dept. of Electrical

Engineering

Columbia University"World Wide Web Redux" -- November 8, 2002

OverviewOverview Communications modes What makes IP telephony different? How long will it take to displace

POTS? Events as new service enabler Making services programmable IP telephony for emergency

communications

Communications servicesCommunications services

traditional Internetsynchronous, one-way

TV, radio streaming media

synchronous, interactive

telephone Internet telephony

"plesiosynchronous" trunked radio? instant messaging + presence

asynchronous, sender-directed

fax, mail email

asynchronous,reeceiver-directed

library, CD ROM, phone announcement

web

What is Internet What is Internet telephony?telephony?

soft phones PSTN phones

Ethernet phones

VoIP protocol architectureVoIP protocol architecture

IP

TCP

IP

TLS

SIP

TCP

IP

TLS

SIP

TCP

IP

TLS

SIP

UDP

IP

RTP

G.711

UDP

IP

RTP

G.711

TCP

IP

TLS

SIP

audio

signaling

foo@example.com foo@128.59.16.3

SIPproxy

VoIP as natural evolutionVoIP as natural evolution through 1980s: signaling and voice in

same circuit special signaling tones toll fraud, very limited services, slow

1987--: special-purpose packet switched signaling network (SS7) out-of-band signaling separate physical circuits (64 kb/s to 1.5 Mb/s)

1996--: packet signaling + packet media physically in-band higher speed logically out-of-band

VoIP motivationsVoIP motivations Bypass LEC charge

17c/min in 1984, 0.5c in 2002 (17c in China 2002…) cheaper international calls

VoIP most often invisible as prepay calling cards effect: Panama outlaws IP telephony similar to call back in the 1990s

cheaper trunks between PBXs aggregation into single PSTN termination

new services multimedia conferencing integration with Internet services (web, email,

presence) user programmability

Two philosophies for Two philosophies for voice-over-IPvoice-over-IP carry existing voice services without

anybody noticing Ethernet is cheaper switching fabric can share same data pipe at best, subset of PSTN services

make telephone services just another Internet service integrated with email (forward call to email) web ("click-to-dial") end system intelligence same identifier (alice@example.com and sip:alice@example.com)

IETF VoIP architecture IETF VoIP architecture choiceschoices Mobility is not just for wireless:

terminal mobility: change network location personal mobility: change devices, keep name session mobility: move sessions to new device service mobility: services migrate across devices

SIP identifiers are flexible: one identifier, many devices one person (or function), one or more identifiers identifiers are plentiful, cheap and permanent

independent of provider, device or geographic location authentication, not identifiers used for privacy

Proxies are service-transparent new services can be introduced at the edges

e.g., IM & presence added without proxy changes

Technology evolution of Technology evolution of PSTNPSTN

0

10

20

30

40

50

60

70

80

90

100

1980 1985 1987 1990 1995 2000 2001

electromechanalogdigital

SS7: 1987-1997

VoIP statisticsVoIP statistics

Some perspective…Some perspective… Data volume >> voice volume

AT&T: data passed voice in 1998 now 5x the volume not true for local calls (LANs?)

Netflix DVD rental: 1,500TB/day Internet: 2,000TB/day

Total US revenue (in $B):

local service 121

wireless 65

long distance 109

Internet (consumer+business)

13

Two views of the future:Two views of the future:

IP everywhere (Vo)IP on cell phones 3G/4G Internet-based radio and TV core transport: IP over optical

IP at the edge (Wireless) Ethernet in LANs and home edge routers meshed with optical

wavelengths

Programming servicesProgramming services Web success dynamically generated content, not

(just) static pages Content creation: small set of specialists people with

other things to do similar to audio and video recording

Service creation for IP telephony from few thousand Lucent & Nortel programmers to every

sys-admin often uses XML as framework for programming languages

dubious, but designed to be written by machines from higher-level specifications

examples: sip-cgi for using scripting languages (Perl, Tcl, Python, …) Java SIP servlets VoiceXML for voice services CPL and LESS for call routing and handling

Event notificationEvent notification Missing service glue:

network management alarms – "water in level 2" email alert geographic proximity alert

"friend Alice is in the area" see geopriv work in the IETF location object with embedded

security and privacy policy media interaction DVR

"start of show postponed by 30 minutes" "semantic SMS"

have (ab)used email and polling email also incurs polling delay events are typically infrequent overhead (wireless)

can build services one-by-one generic platform for quick service creation

Event notificationEvent notification

100 10 1 0.1 0.011000 eventinterval

alarms IR detector temperatureprocesscontrol

audio

video

emailpolling

SIP eventsRTP

Controlling devicesControlling devices

VoIP for emergency VoIP for emergency communicationscommunications Easier to re-route calls to gateways far

away from disaster area

can quickly set up wireless point-to-point links

gradual degradation: 64 kb/s voice 5.3 kb/s voice signaling only ("Subject: We're ok")

work in progress to grant priority to government emergency communications

IPNYC Yale U.

ChallengesChallenges QoS as classical topic since 1990's

but almost no deployment technical and business complexity

really, just the short-term version of reliability Reliability

Internet: 471 min/year (Labovitz et al.) does not count numerous long-loss episodes

PSTN: 5 min/year (Kuhn) BGP routing recovery time often several minutes, up to

15' SONET = 50 ms fail-over

Emergency services ("911") Complexity due to interworking, address shortage Walled gardens – 3G no service competition Security (privacy, DDOS attacks, spam)

ConclusionConclusion

Not just an efficient & cheap means of transporting the same old voice bits but different spreading mechanism

than web (displacement!) from vendor/carrier services to

user-created services transition time of 1-2 decades