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SIP Musings. Henning Schulzrinne SIP Summit – Las Vegas May 8, 2002. Outline. Where is SIP in 2002? challenges: multimedia conferencing binding SIP to other protocols privacy and identity emergency services SIP tenets challenged by the real ($) world. Where in the world is SIP?. - PowerPoint PPT Presentation
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OutlineOutline
Where is SIP in 2002? challenges:
multimedia conferencing binding SIP to other protocols privacy and identity emergency services
SIP tenets challenged by the real ($) world
Where in the world is SIP?Where in the world is SIP? SIP as the signaling protocol for future
applications 3GPP Cable modems (DOCSIS DCS) IM: AOL interworking (eventually...),
Windows Messenger but: H.323 dominates videoconferencing,
trunk replacement Proprietary protocols dominate for Ethernet
phones Slow uptake of VoIP
How did we get there?How did we get there? 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”
How did we get here?How did we get here?
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 developments in SIP developments in 2001/022001/02 SIP revision (“RFC2543bis”, RFC3261) 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 SIP developments in 2001/022001/02 SIP revision backwards compatible
“new” messages work with RFC 2543 implementations
some odd allowed RFC 2543 behavior no longer allowed
CPL finished – merger with iCal sip-cgi published IM & presence mostly done, except for
IM sessions (over TCP) separate message stream
SIP developments in SIP developments in 2001/022001/02 Work continues on staples:
early media (announcements) resource reservation (COMET) SIP security SIP events User identification: "network asserted identity",
privacy 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
ConferencingConferencing SIP designed for (multicast) multimedia
conferences most conferences are small (~5)
central-server ("star") conferences may be star of stars single-source multicast (SSM)
need supporting infrastructure: conference management user management floor management user management
ConferencingConferencing Conference management
create, delete properties (visibility, duration, ...)
User management mass invitation automated and manual user admission join and leave notification membership lists
Floor control request and release floor re-order queue
Binding SIP to other Binding SIP to other protocolsprotocols SIP not a universal data transport
protocol connect SIP to other protocols via URLs get more data
Call-Info, Error-Info, Alert-Info NOTIFY: pointer to message content obtain configuration information signed (long) version of SDP
publish data presence document buddy lists CPL, sip-cgi, servlet conference (user, floor) management
Binding SIP to other Binding SIP to other protocolsprotocols
Sometimes needed for address-of-record REGISTER addresses AOR
sometimes for particular UA only OPTIONS addresses endpoint(s)
clients need to obtain URIs & set them service mobility
Identity and privacyIdentity and privacy Conflicting goals:
caller may want privacy callee wants real identity SIP as telemarketer's
dream? FBI wants CALEA
Traditional "caller-ID" doesn't work well in SIP: user, not device identity iffy notion of trusted providers SIP direct no need for carrier
Proposal in SIP* WG: asserted identity without authentication signed identity based on first-hop authentication
Emergency servicesEmergency services Two types of emergency services:
emergency calls ("911", "112") emergency notification ("inverse 911")
emergency calls are hard: PSTN gateway dialing 911 may be
located anywhere, far away from IP phone
VPNs IP address may not reveal network location
Emergency servicesEmergency services Work for both "legacy" PSAPs and IP-
based PSAPs1. find location of phone based on
street address geocoding long/lat longitude, latitude
2. find appropriate PSAP for jurisdiction3. find ESR (routing number) call
appears like 911 call convey location
911 deployment911 deployment
SIP registration
Leonia
Fort Lee
"sos"
"911"
Bergen County
ISDN B
SIP call setup
audio (IP or circuit)
ISDN DSS7 ISUP
c1.leonia.us
c2.leonia.us
c1.fortlee.us
SIP
IP
UDP, TCP
IP
0
0
0
10
1
IP
Leonia, NJ400 Broad Avenue
"Bergen County"
Bob
IP phone
Alice
analog phone
C@B@A@
UDP
RTP
IP
Emergency notificationEmergency notification notify public officials and citizens of
emergencies: "tornado coming" "fugitive alert"
current systems are typically single-mode (fax, telex, phone, TV, loudspeaker)
don't scale well very limited information content don't reach citizens outside calling area
people at work hard to authenticate
SIP-based emergency SIP-based emergency notificationnotification SIP has scalable event notification feature use for hierarchical notification reflecting civil
lines of authority use XML/WSDL message bodies to
semantically describe emergency: location type of emergency instructions ...
allow automated reaction: routing to legacy systems (pagers, police radios) translation
Emergency notificationEmergency notification
Bergen
Wisconsin WyomingAlaska
Atlantic
Alabama New Jersey
NJState Govt.
United StatesFederal Govt.
NOTIFY
SUBSCRIBE
Domesticating SIP Domesticating SIP Temptation to make it look like SIP on the
wire, but lacks core SIP design properties SIP is designed as a common carrier
protocol: content-neutral application-neutral plausible deniability in proxies
proxy as minimally aware entities: pass unknown SIP headers handle any method don't touch bodies
SIP design principlesSIP design principles
SIP design: extensibility in all elements
methods, headers, content types disclosure of message handling to
user Via user influence over message handling
Require, caller preferences
SIP: mind-changingSIP: mind-changing
"network" services end-system services proxies as willing helpers, not service
disablers trusted network or network
federations PKI, distributed trust, "tunneled" trust
media-neutrality
3G: Falling into the WAP 3G: Falling into the WAP trap?trap? "3G adopts SIP" "3G adapts SIP" if just another IP transport, should not
need to explicitly do anything wireless-specific: bandwidth scarcity
compression overspecified no need for C/S/P-CSCF as
standard just one of many possible architectures
allow roofed + walled garden with customed characters and "forever wild" national park
The fallacy of topology The fallacy of topology hidinghiding "don't reveal server structure" infinite ways to leak to a determined
"spy" proxies don't reveal IP-layer connectivity
or bandwidths knowing proxy addresses doesn't reveal
proxy capacity security through obscurity? costs of hiding:
lack of diagnosability of faults extensibility decreases