200 likes | 216 Views
Learn about the transition from traditional telephony to IP-based communications, including the unique features and benefits of Internet telephony. Explore the role of events as service enablers and the potential for programmable services. Discover how IP telephony can be used for emergency communications.
E N D
Internet Telephony – completing the transition to IP-based communications Henning Schulzrinne Dept. of Computer Science and Dept. of Electrical Engineering Columbia University "World Wide Web Redux" -- November 8, 2002
Overview • 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
What is Internet telephony? PSTN phones soft phones Ethernet phones
G.711 G.711 RTP RTP SIP SIP SIP SIP UDP UDP TLS TLS TLS TLS IP IP TCP TCP TCP TCP IP IP IP IP IP VoIP protocol architecture foo@example.com foo@128.59.16.3 SIP proxy signaling audio
VoIP 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 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 voice-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 choices • 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 PSTN SS7: 1987-1997
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):
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 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 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 notification video process control temperature IR detector alarms audio 1000 100 10 1 0.1 0.01 event interval email polling SIP events RTP
IP VoIP for emergency communications • 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 Yale U. NYC
Challenges • 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)
Conclusion • 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