sip: status and directions1 sip: status and directions henning schulzrinne dept. of computer science...
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SIP: Status and DirectionsHenning Schulzrinne
Dept. of Computer ScienceColumbia UniversityNew York, New York
Bell Atlantic
January 26, 2000
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Overview� SIP overview/review
� SIP services
� SIP standardization status
� SIP bake-off
� Columbia Internet telephony activities
� SIP for notification
� SIP for mobility
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Architecture
Megaco/MGCP/MDCP
SIP
RTP
circuit-switched voice
H.323
proxy
MGC
MG
GK GK
proxy
PSTN
gateway
circuit-switched voice (POTS, ISDN)Internet
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SIP 101� SIP = signaling protocol for establishing
sessions/calls/conferences/. . .
� session = audio, video, game, chat, . . .
1. called server may map name touser@host
2. callee accepts, rejects, forward (! new address)
3. if new address, go to step 1
4. if accept, caller confirms
5. . . . conversation . . .
6. caller or callee sendsBYE
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SIP Operation in Proxy Mode
10 media stream
4
8
7
1
9
6
5
3
?
henn
ing
hgs@
play
tune
play
cs.columbia.edu
200 OK
location server
ACK hgs@play
cs.tu-berlin.de INVITE hgs@play2
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SIP Operation in Redirect Mode
1
4
32
6
7
8
5
?
henn
ing
INVITE [email protected]
302 Moved temporarily colu
mbi
a.ed
u
locationserver
columbia.edu
hgs
tu-berlin.de
INVITE [email protected]
200 OK
ieee.org
Contact: [email protected]
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SIP Advanced Features� operation over UDP or TCP
� multicast invitations➠ basic ACD
� “interactive web response” (IWR)
� UA $ proxy = proxy/redirect$ proxy/redirect
� stateless proxies: self-routing responses
� forking proxies: call several in sequence and/or parallel
� security: basic (password), digest (challenge/response), PGP
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More SIP Internet Telephony Services� camp-on without holding a line
� short message service (“instant messaging”)
� schedule call into the future
� call with expiration date
� add/remove parties to/from call➠ mesh
� “buddy lists”
� can support CLASS features (see tech report)
� call transfer under discussion
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Internet Telephony – as Part of Internet
� email address = SIP address
� SIP URLs in web pages
� forward to email, web page, chat session, . . .
� include web page in invitation response (“web IVR”)
� RTSP: choose your own music-on-hold
� include vCard, photo URL in invitation
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SIP Security� signaling re-uses existing implementations and protocols�!
bugs less likely:
IPsec hop-by-hop
SSL hop-by-hop
basic SIP plaintext password authentication
p
digest SIP challenge-response
p
pgp SIP PGP encryption/authentication for parts/all
p
� media:
IPsec negotiation via SDP
RTP key in SDP (“k=”)
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Interdomain Communications and Security
� no difference in protocol betwen intra/inter domain
� any proxy server can insist onProxy-Authentication
� intermediaries can sign requests and responses (e.g., “thisphone belongs to a Bell Atlantic employee”)
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SIP Extensibility
� headers that receiver may ignore, e.g.,Photo
� new methods and inquire about those supported (OPTIONS)
� features that receivers needs to understand:Required �!
Unsupported
� e.g.,Required: com.sylantro.feature
� proposed: features supported viaSupported header
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An IETF VoIP Architecture
serveraccountingRADIUS
COPS?
sip-cgi
DIAMETER?
firewall
RTSP
MGCP/MEGACOP
LDAP
RTPMG
CPL
RTSP server
record
SIP
SIP server
message
promptsvoice
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SIP Voice Mail
SIPRTSP
create URL entry for
email URLor media
voice
recordmessage
prompts
voice message
media playerRTSP server
SIP server
RECORD msgPLAYSETUP
ogm
PLAY
INVITE
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IP Centrex
Internet Heads Up Barber
IP
PSTNISP
Ralph’s Pretty Good Grocery
Chatterbox Cafe
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SIP Standardization Status
� Feb. 2, 1999: IETF Proposed Standard
� March 17, 1999: IETF RFC 2543
� eligible for Draft Standard: 6 months, 2 implementations
p
� new SIP working group (move frommmusic)
� working on updated draft based on implementation experience
� mostly clarifications + optional headers, no new version
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SIP Work Items� sip-cgi
� call processing language(CPL)
� reliable provisional (1xx) re-sponses
� caller preferences
� third-party call control
� SIP for subscribe/notify
� server feature negotiation
� SIP–ISUP interworking
� SIP–H.323 interworking
� billing
� reverse channel setup for callprogress tones
� pre-ringing resource reserva-tion
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SIP Bake-Off
� 3 bake-offs: April, August, December
� from 15 to 33 groups
� hardware, PSTN gateways, proxy/redirect servers, clients, testinstrument, . . .
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SIP Bake-Off Participants
3Com dynamicsoft Mitel
8x8 Ellemtel Netspeak
Agilent Ericsson Nortel
Alcatel Facet Nuera
Broadsoft Helsinki Univ. OZ.com
British Telecom Hewlett-Packard Pingtel
Catapult Indigo Radcom
Cisco IPcell Telogy
Columbia University Lucent Vovida
Dialogic MCI Worldcom VTEL
Mediatrix
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SIP Bake-Off Goals
� basic call set-up
� registration, user location
� proxies and redirect server operation
� advanced features: security
� identify implementation bugs and robustness issues
� identify spec ambiguities
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SIP Bake-Off Results� almost all implementations could establish basic calls – either
on arrival or after minor on-site fixes
� tested redirection, proxying, security, registration, . . .
� generated interoperability test cases and tools
� will fold clarifications into Draft revision of RFC and webpage athttp://www.cs.columbia.edu/˜hgs/sip
� install public testing mechanisms (Pulver OpenTestNet,www.siphappens.com)
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On-Going Columbia IP Telephony Projects� e*phone: Ethernet SIP phone
� sipc SIP user agent for Windows, Linux, Solaris, . . .
� sipd SIP server
� SIP-H.323 translation
� SIP/RTSP unified messaging
� SIP gateways to the telephone network (T1 E&M, ISDN,. . . )
� SIP mobility
� programming servers: CPL, sip-cgi
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On-Going Columbia IP Telephony Projects
� light-weight resource reservation: YESSIR
� resource-reservation aggregation: BGRP
� charging for resource reservations: RNAP
� TRIP telephony gateway routing
� QOS fault detection
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Planned Internet Telephony Projects� detailed security evaluation/implementation
� caller preferences implementation
� service creation environments for end users and admins
� SIP for notification (“buddy lists”)
� interaction of signaling and QOS
� SIP and ISUP
� 911 services
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e*phone
stand-alone Ethernet phone will full SIP implementation
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sipc
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sipd
SIP registrar, proxy and redirect server:
� user registration
� forking proxy capability: one call, many destinations
� security mechanisms (basic, digest, pgp) for authentication
� sip-cgi: interface to scripting languages
� caller preferences
� CPL in progress
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Integrating Signaling and Instant Messaging: Some Ideas� “reverse” signaling: callee indicates availability
� buddy lists = special case ofevent notification
� other events: “sensor 17 smells smoke”, “Beanie Babies are onsale”, “(voice) mail has arrived”, . . .
� subscribe – notify – set up call
� useful for call parking
� many SIP mechanisms apply: security, redirection, proxying,content negotiation, . . .
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SIP for Event Notification
� add two methods:SUBSCRIBE andNOTIFY
� proxy server may interceptSUBSCRIBE
� use message body for event description
� default: presence, indicated byREGISTER
� one ofmanyproposals for presence (IETF WG!)
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SIP for Event Notification
SUBSCRIBE
SUBSCRIBE
NOTIFYNOTIFY
REGISTER
SUBSCRIBECarol
publisher
subscriber
Alice
Bob
proxy
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Mobility� new network ➠ new
IP address (DHCP)
� mobile IP hides addr.changes
� but: little deployment
� �: encapsulationoverhead
� �: dog-legged routing
� �: IP address filtering
CN
CH
HA
FAtunnelleddatadata
data
data
home network
foreignnetwork
mobile hostcorrespondent hostrouter with home agentfunctionalityrouter with foreign agentfunctionality
MH
CH
HA
HA
MH
MH
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SIP Mobility Overview
� pre-call mobility➠ SIP proxy, redirect
� mid-call mobility ➠ SIP re-INVITE, RTP
� recovery from disconnection
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SIP Mobility: Pre-call� MH acquires IP ad-
dress via DHCP
� optional: MH findsSIP server via multi-castREGISTER
� MH updates home SIPserver
� optimization: hierar-chical LR (later)
CH
redir
3
1
2
5
foreignnetwork
homenetwork
4
mobile hostcorrespondent host
SIP redirect server
MH
CH
redir
3
1
2
5
4
SIP INVITE
SIP 302 moved temporarily
SIP INVITE
SIP OK
dataMH
MH
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SIP mobility: mid-call
� MH!CH: new IN-VITE, with Contactand updated SDP
� re-registers with homeregistrar
CH
13
2
foreignnetwork
homemobile hostcorrespondent host
SIP redirect server
MH
CH
redir
3
1
2
SIP INVITE
SIP OK
data
redir
network
MH
MH
MH
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SIP mobility: multi-stage registration
Don’t want to bother home registrar with each move
Contact: alice@CAFrom: alice@NY
Contact: 193.1.1.1
REGISTERINVITE
Los Angeles
San Francisco
Contact: 192.1.2.3From: alice@NY
CA NY
From: alice@NY
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Conclusion� SIP basic standard stable
� multiple interoperating implementations
� backward-compatible features:
– interoperation with legacy signaling systems
– mobility
– caller preferences
– call transfer
– . . .
� programming of services: cgi, CPL, applets
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For more information. . .
SIP: http://www.cs.columbia.edu/sip
RTP: http://www.cs.columbia.edu/˜hgs/rtp
Papers: http://www.cs.columbia.edu/IRT