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1
SIP: Status and DirectionsHenning Schulzrinne
Dept. of Computer ScienceColumbia UniversityNew York, New York
Bell Atlantic
January 26, 2000
2
Overview� SIP overview/review
� SIP services
� SIP standardization status
� SIP bake-off
� Columbia Internet telephony activities
� SIP for notification
� SIP for mobility
3
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
4
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
5
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
6
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]
7
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
8
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
9
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
10
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=”)
11
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”)
12
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
13
An IETF VoIP Architecture
serveraccountingRADIUS
COPS?
sip-cgi
DIAMETER?
firewall
RTSP
MGCP/MEGACOP
LDAP
RTPMG
CPL
RTSP server
record
SIP
SIP server
message
promptsvoice
14
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
16
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
17
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
18
SIP Bake-Off
� 3 bake-offs: April, August, December
� from 15 to 33 groups
� hardware, PSTN gateways, proxy/redirect servers, clients, testinstrument, . . .
19
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
20
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
21
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)
22
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
23
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
24
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
27
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
28
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, . . .
29
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!)
30
SIP for Event Notification
SUBSCRIBE
SUBSCRIBE
NOTIFYNOTIFY
REGISTER
SUBSCRIBECarol
publisher
subscriber
Alice
Bob
proxy
31
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
32
SIP Mobility Overview
� pre-call mobility➠ SIP proxy, redirect
� mid-call mobility ➠ SIP re-INVITE, RTP
� recovery from disconnection
33
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
34
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
35
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
36
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