SIP and the Future of Internet Telephony

Transcription

1 hgs/sprint 1 SIP and the Future of Internet Telephony Henning Schulzrinne Dept. of Computer Science Internet Real-Time Laboratory (IRT) Columbia University New York, New York schulzrinne@cs.columbia.edu Sprint (Burlingame, California) December 8, 2000 With Jonathan Rosenberg, Adam Roach and other participants in the SIP WG

2 hgs/sprint 2 Overview VoIP service models the IETF VoIP architecture the Session Initiation Protocol (SIP) programming Internet telephony services challenges on the horizon: emergency services instant messaging & presence generic event notification integration with 2G mobile (GSM, CDMA) next-generationwireless(3gpp,3gpp2,mwif,...)

3 hgs/sprint 3 Internet Telephony Service Models Internet PBX Internet Centrex Internet Carrier same basic equipment, but size of gateway varies

4 hgs/sprint 4 Internet PBX SIP proxy server ISP IP 00 1 Ethernet T1, ISDN (BRI/PRI) or analog lines

5 hgs/sprint 5 IP Centrex Chatterbox Cafe ISP PSTN Ralph s Pretty Good Grocery IP Heads Up Barber Internet

6 hgs/sprint 6 IP Carrier SS7 SIP MGCP H IP Montreal GW Bell Canada San Francisco GW PacificBell LA GW PacificBell Denver GW Qwest El Paso GW Chicago GW MCI Dallas GW BellSouth New York GW Verizon BellSouth

7 hgs/sprint 7 IETF VoIP Protocol Architecture Languages/APIs JAIN CPL voicexml Parlay servlets sip cgi Directory/Discovery DNS/enumLDAP TRIP SLP peer to peer Signaling SIP MGCP PINT H.248 SPIRITS master slave RTSP DiffServ QoS IntServ RTP Transport TLS SCTP

8 hgs/sprint 8 IETF Protocol Reuse protocol designed for VoIP use RTSP streaming media voic DNS name lookup E.164 mapping SCTP reliable transport ISUP transport PGP call authentication MIME signaling info SDP multicast sessions SIP, MGCP

9 hgs/sprint 9 Protocol Holes tight session control for conferences admission control multicast key distribution advanced capability negotiation scalable authentication for individuals cross-provider QoS: primarily a business problem

10 hgs/sprint 10 IETF VoIP Architecture Characteristics universal identifier SIPURL= = NAI separation of transport of services media-neutral, including beyond audio and video emphasis on user-programmable services web integration: content, mutual referral integration with IM and presence

11 hgs/sprint 11 SIP Overview protocol for establishing, modifying, tearing down (multimedia) sessions IETF Proposed Standard since March 1999 multimedia = audio, video, shared applications, text,... also used for click-to-dial (PINT wg) and possibly Internet call waiting (SPIRITS wg) to be used for PacketCable Distributed Call Signaling to be used for Third-Generation Wireless (3GPP, 3GPP2)

12 hgs/sprint 12 SIP Components entity does examples proxy server forward calls firewall controller, call router redirect server application server user agent end system SIP phone, gateway, softswitch registrar location mgt. mobility support Roles are changeable, on a request-by-request basis

13 hgs/sprint 13 SIP Example: Redirection ieee.org? location server tu-berlin.de 4 1 INVITE henning@ieee.org 302 Moved temporarily Contact: hgs@columbia.edu 2 henning columbia.edu ACK henning@ieee.org INVITE hgs@columbia.edu columbia.edu OK ACK hgs@columbia.edu hgs

14 hgs/sprint 14 SIP Example: Proxying cs.tu-berlin.de 1 INVITE 200 OK 7 2 henning? cs.columbia.edu location server hgs@play 3 4 INVITE hgs@play 200 OK 6 5 play 8 ACK henning@columbia.edu tune 9 ACK hgs@play 10 media stream

15 hgs/sprint 15 SIP forking proxies macrosoft.com a.wonderland.com INVITE INVITE CANCEL INVITE ACK 200 OK BYE 200 OK

16 hgs/sprint 16 SIP advanced features forking extensibility: new headers, methods, bodies security: web-like, PPP/CHAP or PGP multicast-capable support for personal, session, terminal, service mobility caller preferences: direct calls based on properties

17 hgs/sprint 17 Design choices and alternatives Alternative but... XML instead of RFC822 space overhead? parsing? RPC model higher message count More restrictive syntax implementation creativity

18 hgs/sprint 18 What is SIP good for (and not) Good for... messaging application-layer routing endsystem abstraction low-overhead Not good for... general RPC mechanism (mostly) high-volume messaging (proxies) UDP large message bodies Megaco stimulus replacement

19 hgs/sprint 19 SIP mobility terminal cross-provider REGISTER, re-invite personal different terminals, same address REGISTER service different terminals, same services upload session move sessions across terminals REFER

20 hgs/sprint 20 SIP personal mobility (also used by yahoo.com tel: columbia.edu tel:

21 hgs/sprint 21 Example SIP system LDAP server sipconf conferencing server (MCU) rtspd RTSP media server PC NT Sun Solaris PC Linux/FreeBSD/NT RTSP analog FXO RTP SIP sipgw sipd proxy/redirect server unified messaging server sipum T1/E1 RTP SIP sipgw MySQL user database PhoneJack interface e*phone sipc SIP H.323 converter sip h323

22 hgs/sprint 22 SIP-Based telephony services conferencing forwarding ACD call transfer DTMF transport billing dial-in, dial-out basic SIP proxy, no protocol extensions REFER extension in RTP, not SIP in resource reservation, (mostly) not SIP

23 hgs/sprint 23 Current SIP efforts SIP to Draft Standard QoS and security preconditions inter-domain AAA and billing session timer for liveness detection early media (PSTN announcements) SIP for presence / instant messaging reliable provisional responses DHCP configuration for finding SIP servers SIP for firewalls and NATs caller preferences services (transfer, multiparty calls, home) ISUP carriage SIP-H.323 interworking

24 hgs/sprint 24 SIP emergency services emergency address need find nearest PSAP PSAP determines caller location cannot just rely on gateway calling 911 generally, allow devices to be location-aware ( what time is it where I m about to call? call pizza parlor ) offers new opportunities: database access, video, measurements, accessibility,...

25 hgs/sprint 25 SIP emergency services GPS customer database (names, addresses) geo < > civil translation database RADIUS or private protocol INVITE sip:911 GPos: N W INVITE sip:911 GPos: N W GL: S3.US location announcement for each wire INVITE sip:911 GL: S3.US first hop switch user database (location, room number,...)

26 hgs/sprint 26 SIP bake-off takes place every four months, 5th at Pulver.com August organizations from 11 countries about implementations: IP telephones and PC apps proxy, redirect, registrar servers conference bridges unified messaging protocol analyzers first IM/presence interop test emphasis on advanced services (multi-stage proxying, tel URLs, call transfer, IVR,...)

27 hgs/sprint 27 The dangers of VoIP focus on single service: voice, fax,... PSTN: service orientation ψ! Internet: neutral transport APIs as least common denominator across POTS, ISDN, SS7! 100-year old functionality carbon-copy replication of existing services terminology overload

28 hgs/sprint 28 Differences: Internet telephony $ POTS separate control, transport (UDP) no triangle routing separate connectivity from resource availability separate services from bit transport datagram service less bootstrapping in-band signaling higher speed features network! end system: distinctive ringing, caller id, speed dialing, number translation,... scaling features: intra-pbx = inter-lata and general protocols: user-network = network-network signaling

29 hgs/sprint 29 PSTN legacies to avoid E.164 numbers might as well wear bar codes tones (e.g., failure indications) in-band signaling (DTMF) systems with user interface knowledge (12 keys, voice) voice-only orientation (e.g., MGCP/Megaco) integration of bit transport and services service-specific billing trigger model for service creation trusted networks without crypto authentication confine PSTN knowledge to edge of network!

30 hgs/sprint 30 Replication of existing services user is familiar with PSTN services but how many users actually know how to use call transfer or directed pick-up? user interface is often just legacy of key systems or other ancient technology avoid binding of identifiers to devices call person or group of people, regardless of location instead, model desired behavior single-server features don t need standardization find general mechanisms (e.g., REFER for three-party calls and various call transfers)

31 hgs/sprint 31 Terminology overload Invasion of the meaningless technical-sounding terms, attempting to familiar mimic PSTN boxes: CO switch! soft switches = gateway + SIP UA +? SCP! application servers = proxy? web server? media server? PBX! Internet PBX = proxy? + gateway?... Temptation: new name! newprotocols,apis,... theoldboxboundaries don t necessarily make sense!

32 hgs/sprint 32 It s that simple... We really only have a few basic components: PSTN gateway, with some combination of FXO/FXS SIP proxy/redirect/registrar servers (or H.323 gatekeepers) SIP user agents (or H.323 terminals): PCs, phones media storage servers DNS,directory,web, ,news,...servers

33 hgs/sprint 33 Invisible Internet telephony VoIP technology will appear in... Internet appliances home security cameras, web cams 3G mobile terminals fire alarms chat/im tools interactive multiplayer games

34 hgs/sprint 34 The largest signaling network is not running SS7 AT&T: 280 million calls a day AOL: 110 million s/day, total about 18 billion/day total > 1 billion instant messages a day (AOL: 500 million) signaling effort of call ß IM

35 hgs/sprint 35 Signaling and events sessions events INVITE, BYE SUBSCRIBE, NOTIFY VoIP conferencing MESSAGE INFO presence appliance status Signaling: do this (push) Events: this just happened

36 hgs/sprint 36 Commonalities between signaling and events presence is just a special case of events: Alice just logged in ß temperature in boiler 300 exceeds F ffi need to locate mobile end points may need to find several different destinations ( forking ) same addressing for users presence often precursor to calls may replace call back and call waiting likely to be found in same devices events already in VoIP: message alert, call events

37 hgs/sprint 37 SIP as a presence & event platform requires minimal extensions to SIP: SUBSCRIBE toasktobealerted,notify when event occurs MESSAGE for sending text messages ( IM ) with forking, can easily register MESSAGE recorder true chat is voice (+ video) services such as reaching mobile phone while in meeting types of events: inside existing call leg within call, but outside call leg unrelated to call leg

38 hgs/sprint 38 SIP and WAP WAP proxy server WAP proxy CU SIP UA library MESSAGE MESSAGE INVITE/BYE REGISTER (with config. info) MESSAGE digital sensor input (optically iso stereo input/output (also for 4 line, 16 character screen configurable keypad RTP audio data (PCMU, DVI, at 8 to 48 khz sampling rate)

39 hgs/sprint 39 SIP presence architecture macrosoft.com presence server presentity bob PUA example.com SUBSCRIBE PA REGISTER UA NOTIFY PUA registrar PUA NOTIFY PA

40 hgs/sprint 40 SIP presence components Presentity: logical entity being subscribe to, e.g., with several agents Registrar: receives REGISTER requests Presence user agent (PUA): generates REGISTER, but no SUBSCRIBE or NOTIFY any non-presence-aware SIP software Presence agent: receive SUBSCRIBE, generate NOTIFY Presence server: SIP proxy + PA Presence client: SIP UA + PA

41 hgs/sprint 41 SIP presence protocol subcriber alice presentity, PA bob SUBSCRIBE bob Event: presence From: alice To: bob 200 OK NOTIFY alice bob available 200 OK NOTIFY alice bob not available 200 OK

42 hgs/sprint 42 SIP SUBSCRIBE example SUBSCRIBE SIP/2.0 Event: presence To: From: Contact: Call-ID: CSeq: 1 SUBSCRIBE Expires: 3600 Content-Length: 0 Forked to all PUAs that have REGISTERed with method SUBSCRIBE. 200 (OK) response contains current state.

43 hgs/sprint 43 SIP NOTIFY example NOTIFY To: From: Call-ID: CSeq: 1 NOTIFY Content-Type: application/xpidf+xml <?xml version="1.0"?> <!DOCTYPE presence PUBLIC "-//IETF//DTD RFCxxxx XPIDF 1.0//EN" "xpidf.dtd"> <presence> <presentity uri="sip:alice@wonderland.com;method="subscribe"> <atom id="779js0a98"> <address uri="sip:alice@wonderland.com;method=invite"> <status status="closed"/> </address> </atom> </presentity> </presence>

44 hgs/sprint 44 Events: SIP for appliances SUBSCRIBE SIP user agent NOTIFY DO INVITE SIP proxy (RGW) (Work with Telcordia)

45 hgs/sprint 45 Programmable Internet telephony APIs servlets sip-cgi CPL Language-independent no Java only yes own Secure no mostly no, but can be yes End user service creation no yes power users yes GUI tools w/portability no no no yes Call creation yes no no no Multimedia some yes yes yes Example: integration with ical! automatically export personal calendar to call handling

46 hgs/sprint 46 Conclusion basic IETF-based architecture in place SIP as foundation for services see extensions to mobility, emergency services,...inprogress first (and last?) chance to recover from 120 years of legacy avoid replication of PSTN on packets most VoIP applications won t look like a telephone opportunities in emergency services, mobile, event notification