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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
[email protected] [email protected]
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 ([email protected] and sip:[email protected])
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