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SIP in 2002. Henning Schulzrinne Dept. of Computer Science Columbia University. Overview. Where are we? Uses of SIP – new and old Challenges IM 3GPP Security Emergency calling. Where are we?. SIP as the signaling protocol for future applications 3GPP Cable modems (DOCSIS DCS)

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SIP in 2002

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SIP in 2002

Henning Schulzrinne

Dept. of Computer Science

Columbia University


Overview

  • Where are we?

  • Uses of SIP – new and old

  • Challenges

    • IM

    • 3GPP

    • Security

    • Emergency calling


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


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”


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


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.)


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, …


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


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


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


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


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


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


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


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


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


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


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!


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


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


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


SIP doesn’t have to be in a phone


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?


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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