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Overview of SIP: Current Status, Challenges, and Future Applications

This document provides an overview of Session Initiation Protocol (SIP) development as of 2002, highlighting its current status, applications in VoIP, challenges in uptake, and implications for services like instant messaging and emergency calling. It explores the tensions between existing circuit-switched systems and the emergence of SIP-based solutions, examining topics such as security, interoperability with legacy systems, and the potential of SIP in both consumer and enterprise environments. The document reflects on the slow adoption rates and presents insights from the SIP community, emphasizing the need for robust security and integration with existing telecommunication services.

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Overview of SIP: Current Status, Challenges, and Future Applications

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  1. SIP in 2002 Henning Schulzrinne Dept. of Computer Science Columbia University

  2. Overview • Where are we? • Uses of SIP – new and old • Challenges • IM • 3GPP • Security • Emergency calling

  3. Where are we? • SIP as the signaling protocol for future applications • 3GPP • Cable modems (DOCSIS DCS) • IM: AOL interworking, Windows Messenger • but: H.323 dominates videoconferencing, trunk replacement • Proprietary protocols dominate for Ethernet phones • Slow uptake of VoIP

  4. Where are we? • Not quite what we had in mind • initially, for initiating multicast conferencing • in progress since 1992 • still small niche • even the IAB and IESG meet by POTS conference… • then VoIP • written-off equipment (circuit-switched) vs. new equipment (VoIP) • bandwidth is (mostly) not the problem • “can’t get new services if other end is POTS’’  “why use VoIP if I can’t get new services”

  5. Where are we? • VoIP: avoiding the installed base issue • cable modems – lifeline service • 3GPP – vaporware? • Finally, IM/presence and events • probably, first major application • offers real advantage: interoperable IM • also, new service

  6. SIP in the Enterprise • Greenfield • save on wiring and admin expenses • per-seat cost similar ($500+) • Existing installations • small PBX (< 8 lines) cheap • can’t beat $80 phones • move towards multi-cordless (Gigaset, etc.)

  7. Where are we? • Number of robust SIP phones • not yet in Wal-Mart • SIP carriers terminate LAN VoIP • number portability? • 911 • 50+ vendors at SIPit • Building blocks: media servers, unified messaging, conferencing, VoiceXML, …

  8. SIP at Home • Lifeline (power) • Multiple phones per household • expensive to do over PNA or 802.11 • BlueTooth range too short • need wireless SIP base station + handsets • PDAs with 802.11 and GSM? (Treo++) • Incentives • SMS & IM services

  9. SIP phones • Hard to build really basic phones • need real multitasking OS • need large set of protocols: • IP, DNS, DHCP, maybe IPsec, SNTP and SNMP • UDP, TCP, maybe TLS • HTTP (configuration), RTP, SIP • user-interface for entering URLs is a pain • see “success” of Internet appliances • “PCs with handset” cost $500 and still have a Palm-size display

  10. SIP developments in 2001 • SIP revision (“RFC2534bis”) almost done: • semantically-oriented rewrite • layers: message, transport, transaction, transaction user • SDP extracted into separate draft • UA and proxy have the same state machinery • better Route/Record-Route spec for loose routing • no more Basic authentication • few optional headers (In-Reply-To, Call-Info, Alert-Info, …) • Integration of reliable provisional responses and server features • DNS SRV modifications

  11. SIP developments in 2001 • SIP revision backwards compatible • “new” messages work with RFC 2543 implementations • some odd allowed RFC 2543 behavior no longer allowed • CPL almost finished – merger with iCal • sip-cgi published • IM & presence mostly done, except for IM sessions (over TCP) – IMTP, BEEP

  12. SIP developments in 2001 • Work continues on staples: • early media (announcements) • resource reservation (COMET) • SIP security • SIP events • User identification • Call transfer and call control • Now three SIP working groups: • SIP for protocol definition and extensions • SIPPING for applications and “vetting” • SIMPLE for IM & presence

  13. SIP security • Bar is higher than for email – telephone expectations (albeit wrong) • SIP carries media encryption keys • Potential for nuisance – phone spam at 2 am • Safety – prevent emergency calls

  14. SIP security • Exposes weak state of general Internet security tools • Attempt to re-use existing mechanisms: • HTTP digest authentication, with additions to protect crucial headers (e.g., Contact in REGISTER) for e2e and proxy authentication • TLS and IPsec for hop-by-hop authentication and confidentiality • S/MIME for end-to-end

  15. SIP security • Security with random strangers is hard! • Identities are cheap – can’t use for filtering bozos • often only need to verify that same “good” person as before – see ssh • Symmetric (secret) key doesn’t scale • Public key cryptography only modest help • need certification authorities • what is being certified? • CRLs • hard to move keys to new devices – smartcard? • Kerberos needs extensions for interdomain

  16. SIP security – longer term • EAP for authentication (used in 3GPP) • Third-party signatures • “this caller is an employee of Visa” • REFER authentication • Alice (verifiable) asked Bob to call Carol

  17. Other SIP standardization projects • Call history – where has this request been? • Emergency calling (911/112) • universal number: sip:sos@domain • finding the emergency call center • PSTN interoperation • Emergency preparedness • priority access to PSTN and IP resources

  18. Instant message & presence • SIMPLE: MESSAGE, SUBSCRIBE, NOTIFY • Also for various SIP-related events, e.g., in REFER and conferences • Just a special case of event notification: “tell me if something happened” – something happened!

  19. Event notification • Missing new service in the Internet • Existing services: • get & put data, remote procedure call: HTTP/SOAP (ftp) • asynchronous delivery with delayed pick-up: SMTP (+ POP, IMAP) • Do not address asynchronous (triggered) + immediate

  20. Event notification • Very common: • operating systems (interrupts, signals, event loop) • SNMP trap • some research prototypes (e.g., Siena) • attempted, but ugly: • periodic web-page reload • reverse HTTP

  21. SIP event notification • Uses beyond SIP and IM/presence: • Alarms (“fire on Elm Street”) • Web page has changed • cooperative web browsing • state update without Java applets • Network management • Distributed games

  22. SIP doesn’t have to be in a phone

  23. SIP longer-term issues • SDPng? • XML-based generalization • better negotiation and grouping • API standardization • JAIN – servlets • APIs for IM and presence • Operational issues • How to configure 10,000 phones without editing config files?

  24. Conclusion • SIP technology vibrant, with large developer community • Deployments and awareness lag • VoIP as replacement technology – conversion from analog to digital PSTN took decades • Not XML, but will soon be on every desktop

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