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May 25, 2004 CITI VoIP Workshop 1 VoIP – early adulthood Henning Schulzrinne Dept. of Computer Science Columbia University

VoIP – early adulthood – early adulthood ... ENUM H.350 directories RTP transport provide URI provide ... Challenge: Global interconnect zCurrently, each VoIP “network”

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May 25, 2004 CITI VoIP Workshop 1

VoIP – early adulthood

Henning SchulzrinneDept. of Computer Science

Columbia University

May 25, 2004 CITI VoIP Workshop 2

OverviewVoIP componentsWhat is different about VoIP?Emerging technologies

integration of presence, IM and event notificationlocation-based serviceswireless VoIPmultimedia

Challenges remaininguser-programmable servicesemergency callingCALEAinter-domainspam prevention

May 25, 2004 CITI VoIP Workshop 3

VoIP componentsRe-uses whole Internet protocol architecture and transmission infrastructure

IP, UDP for transportTLS and S/MIME for securityHTTP for configuration









address codecs(G.7xx,H.26x)

May 25, 2004 CITI VoIP Workshop 4

SIP trapezoid

SIP trapezoid

outbound proxy

[email protected]:


1st request

2nd, 3rd, … request

voice trafficRTP

destination proxy(identified by SIP URI domain)

May 25, 2004 CITI VoIP Workshop 5

Earlier PSTN changesstarting in 1980s:

analog digital transmissionin-band out-of-band (SS7) signaling

end systems relatively unaffectedfew additional services

800#CLASS services (caller ID, call waiting)

customer relationship largely unaffectedexcept CLECs and reselling

May 25, 2004 CITI VoIP Workshop 6

Technology evolution of PSTN


1980 1985 1987 1990 1995 2000 2001


SS7: 1987-1997

May 25, 2004 CITI VoIP Workshop 7

Some differences: VoIP vs. PSTN

Separate signaling from media data pathBut, unlike SS7, same network lower call setup delayAvoid CTI complexity of "remote control"Mobile and wireline very similarAny media as session:

any media quality (e.g., TV and radio circuits)interactive games

No need for telephone company

voice service provider(RTP, SIP)


dark fiberprovider






May 25, 2004 CITI VoIP Workshop 8

PSTN vs. Internet Telephony

Signaling & Media Signaling & Media

Signaling Signaling





Belgian customer,currently visiting US


May 25, 2004 CITI VoIP Workshop 9

(Early) Adulthood“fully developed and mature”

Not quite yet, but no longer a teenagerprobably need another 6 years to be grown up…

Responsibilities:Dealing with elderly relatives POTSFinancial issues payments, RADIUSFamily emergencies 911

May 25, 2004 CITI VoIP Workshop 10

Why has it taken so long?VoIP technology development since 1995Web: worked on dial-up, motivated broadband

deployment from 1992 to 2000VoIP: not usable on dial-up, spurred by residential broadbandMore than just protocols needed:

eco-system (management, configuration, OSS, …)interoperabilityspectrum of products – low to high endinteroperation with legacy equipment

May 25, 2004 CITI VoIP Workshop 11

Transition to broadbandNumbers still small, but moving beyond exploratory trials to real deploymentsNovember 2003: 38% of U.S. home Internet users connect via broadband (Nielsen/NetRatings)

May 25, 2004 CITI VoIP Workshop 12

Emerging technologiesCore VoIP technology largely finished

deployment largely due to cost savings, not new servicestoll and fee bypassintegrated infrastructure (LAN & WAN)extend “PBX” reach to home and branch offices

Presence from “polling” to “status report”special case of event notificationevents as common infrastructure for serviceslocation-based services

Integration of IM and VoIPoften used in same conference (side channel)IM as initiator of real-time voice/video

May 25, 2004 CITI VoIP Workshop 13

Near future: Location-based services

Finding services based on locationphysical services (stores, restaurants, ATMs, …)electronic services (media I/O, printer, display, …)not covered here

Using location to improve (network) servicescommunication

incoming communications changes based on where I amconfiguration

devices in room adapt to their current usersawareness

others are (selectively) made aware of my locationsecurity

proximity grants temporary access to local resources

May 25, 2004 CITI VoIP Workshop 14

Near future: MultimediaWideband audio

“better than phone quality” lectures, discussions,

speaker phonebetter codecs same bandwidth as existing NB codecs

Video phone itself remains niche application

given low incremental cost, may be viableuseful for sign language

Video for group meetingscapture whiteboard

Shared applications(WebEx, etc.)

still requires standardizationInstant messaging

side channelBetter means of coordination (floor control)

wideband audio

May 25, 2004 CITI VoIP Workshop 15

Near future: VoIP over WiFiNot fundamentally different from landline VoIP

combination cellular + WiFi = wide-area + “cordless” phone

Small packet sizes make VoIP over WiFi far less efficient than nominal data rateHand-off delay between different base stations interruptions CU modified hand-off algorithmDelay jitter with high loads new scheduling algorithmsL3 hand-off across different network types

May 25, 2004 CITI VoIP Workshop 16

Challenge: Global interconnectCurrently, each VoIP “network” largely isolated

interconnect via PSTN even if both endpoints are on IPinterconnect via few peering points even if neighbors

Long-term solution: ENUM DNS listing

administration appears difficultShort-term for pure-IP (FWD, etc.): special number prefixes



Enterprise B

May 25, 2004 CITI VoIP Workshop 17

Challenge: Emergency calling911 calling system largely unchanged since 1980s

call routing to appropriate destinationdeliver caller location information

Fundamental differences for VoIP:may not have phone numbermay be no “phone company”identifier does not describe locationlocation determination more difficult

Also use solution for “311” and other location-based call routing systems

May 25, 2004 CITI VoIP Workshop 18

Three stages to VoIP 911




callbacknumber to PSAP?


no (8 or 10 digit)



GNPmultimediainternational calls

ALI not neededMSAG replaced by DNSlocation in-band


nolate 2004I3


noDec. 2004I2


new servicesALI (DB)modification

callerlocation to PSAP?

mobilityuse 10-digit admin. number?

spec. available?

May 25, 2004 CITI VoIP Workshop 19

Challenge: CALEA (lawful intercept)

Existing models assume congruence of signaling and voice flowsChallenges:

voice service providers outside the USsignaling-only providers or no voice providersend-to-end media and signaling encryption (Skype, SRTP)Intercept IP traffic, not application

Assume that long-term, all application traffic (except browsing of public web pages) will have strong encryption

May 25, 2004 CITI VoIP Workshop 20

Challenge: User-programmable and context-aware services

Universal reachability control reachability in time and space by context

allow callee to decide reachability (defer and decline communication)choose appropriate media (text, automated data response)

presenceactivity/availabilitynot yet, but similar to location datasensor data (mood, bio)

location-based call routinglocation events


caller preferencescapabilitiesCall Processing Language (CPL), sip-cgi, …time

May 25, 2004 CITI VoIP Workshop 21

Challenge: Spam preventionCurrently, telemarketing restricted to in-country calling

With VoIP, few economical constraints on automated calls from anywhereAlso, SPIM (instant message spam)

Cannot use content-based filteringPublic key infrastructure (PKI) for individual verification has never scaled

provide domain-level verification (~ TLS) in signalingblacklists and whitelists

may depend on local domain policies for user verificationreputation-based systems

May 25, 2004 CITI VoIP Workshop 22

Challenge: Service reliability“QoS” service availability

loss of network connectionloss of infrastructure components

DNS, SIP servers, DHCP, …bursts of packet loss cannot be repaired at end systemsustained high packet loss (> 10-15%)

Current service availability probably around 99.5%realistic goal: 99.9% (10h/year) to 99.99% (1h/year)

May 25, 2004 CITI VoIP Workshop 23

ConclusionVoIP on cusp of widespread deployment:

commercial-grade VoIP productsmature standards for key componentswidespread broadband availabilitybetter Internet QoS

Focus may shift from “bare-bones” VoIP to context-aware communicationsOperational and technical challenges

911, CALEA, network reliability, user-defined services, multimedia

Thus, roughly where PSTN was in 1980 ☺