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
SIP/SDPH.248MGCPH.323
signaling
ENUMH.350
directories
RTP
transport
provideURI
providedestination
address codecs(G.7xx,H.26x)
May 25, 2004 CITI VoIP Workshop 4
SIP trapezoid
SIP trapezoid
outbound proxy
[email protected]: 128.59.16.1
registrar
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
0102030405060708090100
1980 1985 1987 1990 1995 2000 2001
electromechanalogdigital
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)
ISP(IP, DHCP, DNS)
dark fiberprovider
Yaho
oM
CIN
YSER
NET
May 25, 2004 CITI VoIP Workshop 8
PSTN vs. Internet Telephony
Signaling & Media Signaling & Media
Signaling Signaling
Media
PSTN:
Internettelephony:
China
Belgian customer,currently visiting US
Australia
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
GW
GWVSP A
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
yes
yes
no
callbacknumber to PSAP?
IP-enabled
no (8 or 10 digit)
no
PSAPmodification
GNPmultimediainternational calls
ALI not neededMSAG replaced by DNSlocation in-band
yesstationarynomadicmobile
nolate 2004I3
noneupdateyesstationarynomadic
noDec. 2004I2
nonenonostationaryallowednowI1
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
location
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 ☺