Henning%20Schulzrinne

1

Global Ubiquitous Computing

• Henning Schulzrinne
• Columbia University
• (KAIST KNSS)

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Agenda

• SIP overview
• SIP for ubiquitous computing
• Location-based services
• Emergency calling
• Services, carriers and service creation
• Security issues

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SIP Overview
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Internet services the missing entry
Service/delivery synchronous asynchronous
push instant messaging presence event notification session setup media-on-demand messaging
pull data retrieval file download remote procedure call peer-to-peer file sharing
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Filling in the protocol gap
Service/delivery synchronous asynchronous
push SIP RTSP, RTP SMTP
pull HTTP ftp SunRPC, Corba, SOAP (not yet standardized)
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SIP as service enabler

• Rendezvous protocol
• lets users find each other by only knowing a
  permanent identifier
• Mobility enabler
• personal mobility
• one person, multiple terminals
• terminal mobility
• one terminal, multiple IP addresses
• session mobility
• one user, multiple terminals in sequence or in
  parallel
• service mobility
• services move with user

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What is SIP?

• Session Initiation Protocol ? protocol that
  establishes, manages (multimedia) sessions
• also used for IM, presence event notification
• uses SDP to describe multimedia sessions
• Developed at Columbia U. (with others)
• Standardized by
• IETF (RFC 3261-3265 et al)
• 3GPP (for 3G wireless)
• PacketCable
• About 60 companies produce SIP products
• Microsofts Windows Messenger (4.7) includes SIP

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Philosophy

• Session establishment event notification
• Any session type, from audio to circuit emulation
• Provides application-layer anycast service
• Provides terminal and session mobility
• Based on HTTP in syntax, but different in
  protocol operation
• Peer-to-peer system, with optional support by
  proxies
• even stateful proxies only keep transaction
  state, not call (session, dialogue) state
• transaction single request retransmissions
• proxies can be completely stateless

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Basic SIP message flow
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SIP trapezoid
destination proxy (identified by SIP URI domain)
outbound proxy
1st request
SIP trapezoid
2nd, 3rd, request
a_at_foo.com 128.59.16.1
registrar
voice traffic RTP
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SIP message format
SDP
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RFC 3261

• Backward compatible with RFC 2543 no new
  version
• Major changes
• specification behavior-oriented, not
  header-oriented
• e.g., separation into layers
• mandate support for UDP and TCP
• formal offer/answer model for media negotiation
• uses both SRV and NAPTR for server location, load
  balancing and redundancy
• much more complete security considerations
• sips for secured (TLS) path
• PGP removed due to lack of use
• Basic authentication removed as unsafe
• S/MIME added for protecting message bodies (and
  headers, via encapsulation)
• Route/Record-Route simplified

13
PSTN vs. Internet Telephony
PSTN
Signaling Media
Signaling Media
China
Internet telephony
Signaling
Signaling
Media
Australia
Belgian customer, currently visiting US
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SIP addressing

• Users identified by SIP or tel URIs
• sipalice_at_example.com
• tel URIs describe E.164 number, not dialed
  digits (RFC 2806bis)
• tel URIs ? SIP URIs by outbound proxy
• A person can have any number of SIP URIs
• The same SIP URI can reach many different phones,
  in different networks
• sequential parallel forking
• SIP URIs can be created dynamically
• GRUUs
• conferences
• device identifiers (sipfoo_at_128.59.16.15)
• Registration binds SIP URIs (e.g., device
  addresses) to SIP address-of-record (AOR)

tel110
sipsos_at_domain
domain ? 128.59.16.17 via NAPTR SRV
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3G Architecture (Registration)
mobility management
signaling
serving
interrogating
interrogating
CSCF
proxy
home IM domain
registration signaling (SIP)_
visited IM domain
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SIP is PBX/Centrex ready
boss/admin features
call waiting/multiple calls RFC 3261
hold RFC 3264
transfer RFC 3515/Replaces
conference RFC 3261/callee caps
message waiting message summary package
call forward RFC 3261
call park RFC 3515/Replaces
call pickup Replaces
do not disturb RFC 3261
call coverage RFC 3261
simultaneous ringing RFC 3261
basic shared lines dialog/reg. package
barge-in Join
Take Replaces
Shared-line privacy dialog package
divert to admin RFC 3261
intercom URI convention
auto attendant RFC 3261/2833
attendant console dialog package
night service RFC 3261
centrex-style features
attendant features
from Rohan Mahys VON Fall 2003 talk
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Example SIP phones
about 85
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SIP architecture biases

• International ? no national variants
• Internet intranet
• separation of data and signaling
• signaling nodes can be anywhere
• end-to-end security where possible, hop-by-hop
  otherwise
• S/MIME bodies
• TLS (sips)
• end system control of information

• proxies can
• inspect, modify and add headers
• may be able to inspect the message body (if not
  encrypted)
• should not modify the message body ? may break
  end-to-end integrity
• no security by obscurity
• dont rely on address or network hiding

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SIP, SIPPING SIMPLE 00 drafts
includes draft-ietf--00 and draft-personal--00
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Ubiquitous computing ?Location-based services
?Emergency calling
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What is ubiquitous computing?

• Ubiquitous computing has as its goal the
  enhancing computer use by making many computers
  available throughout the physical environment,
  but making them effectively invisible to the
  user. (Weiser, 1993)
• Ubiquitous computing is not virtual reality, it
  is not a Personal Digital Assistant (PDA) such as
  Apple's Newton, it is not a personal or intimate
  computer with agents doing your bidding. Unlike
  virtual reality, ubiquitous computing endeavers
  to integrate information displays into the
  everyday physical world. It considers the nuances
  of the real world to be wonderful, and aims only
  to augment them. (Weiser, 1993)

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Ubiquitous computing aspects

• Also related to pervasive computing
• Mobility, but not just cell phones
• Computation and communications
• Integration of devices
• borrow capabilities found in the environment ?
  composition into logical devices
• seamless mobility ? session mobility
• adaptation to local capabilities
• environment senses instead of explicit user
  interaction
• from small dumb devices to PCs
• light switches and smart wallpaper

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Context-aware communications

• Traditional emphasis communicate anywhere,
  anytime, any media ? largely possible today
• New challenge tailor reachability
• Context-aware communications
• modify when, how, where to be reached
• ? machine context-dependent call routing
• ? human convey as part of call for human usage
• context-aware services
• leveraging local resources
• awareness of other users
• sources of location information
• voluntary and automatic
• location-based services ? privacy concerns
• applies to other personal information
• activity, reachability, capabilities, bio sensor
  data,
• emergency services as a location-based service

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Context

• context the interrelated conditions in which
  something exists or occurs
• anything known about the participants in the
  (potential) communication relationship
• both at caller and callee

time CPL
capabilities caller preferences
location location-based call routing location events
activity/availability presence
sensor data (mood, bio) not yet, but similar in many aspects to location data
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Location-based services

• Finding services based on location
• physical services (stores, restaurants, ATMs, )
• electronic services (media I/O, printer, display,
  )
• not covered here
• Using location to improve (network) services
• communication
• incoming communications changes based on where I
  am
• configuration
• devices in room adapt to their current users
• awareness
• others are (selectively) made aware of my
  location
• security
• proximity grants temporary access to local
  resources

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GEOPRIV and SIMPLE architectures
rule maker
rule interface
target
location server
location recipient
notification interface
publication interface
GEOPRIV
SUBSCRIBE
presentity
presence agent
watcher
SIP presence
PUBLISH
NOTIFY
caller
callee
SIP call
INVITE
INVITE
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SIP URIs for locations
location beacon

• Identify confined locations by a SIP URI, e.g.,
  siprm815_at_cs.columbia.edu
• Register all users or devices in room
• Allows geographic anycast reach any party in the
  room

siprm815
Contact bob
Contact alice
Room 815
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Location-based SIP services

• Location-aware inbound routing
• do not forward call if time at callee location is
  11 pm, 8 am
• only forward time-for-lunch if destination is on
  campus
• do not ring phone if Im in a theater
• outbound call routing
• contact nearest emergency call center
• send delivery_at_pizza.com to nearest branch
• location-based events
• subscribe to locations, not people
• Alice has entered the meeting room
• subscriber may be device in room ? our lab stereo
  changes CDs for each person that enters the room

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Presence policy
SUBSCRIBE
subscription policy
subscriber (watcher)
for each watcher
event generator policy
subscriber filter rate limiter
change to previous notification?
NOTIFY
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Example user-adaptive device configuration
all devices that are in the building RFC 3082?
802.11 signal strength ? location
SLP
device controller
HTTP
PA
tftp
REGISTER To 815cepsr Contact alice_at_cs
SUBSCRIBE to each room

1. discover room URI
2. REGISTER as contact for room URI

SIP
room 815
SUBSCRIBE to configuration for users currently in
rooms
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Location-based services in CINEMA

• Initial proof-of-concept implementation
• Integrate devices
• lava lamp via X10 controller ? set personalized
  light mood setting
• Pingtel phone ? add outgoing line to phone and
  register user
• painful needs to be done via HTTP POST request
• stereo ? change to audio CD track based on user
• Sense user presence and identity
• passive infrared (PIR) occupancy sensor
• magnetic swipe card
• ibutton
• BlueTooth equipped PDA
• IRRF badge (in progress)
• RFID (future)
• biometrics (future)

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Location-based IM presence
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Emergency (911) services

• Old wireline and wireless models dont work any
  more
• All wireline systems are potentially mobile
  (nomadic)
• device bought in Belgium
• place call in Canada
• with VSP in Mexico
• and maybe a VPN for extra excitement
• Customer may not have a traditional voice carrier
  at all
• corporate
• residential ? VSP in a different country

• Needs to work internationally
• same standards
• no custom configuration
• Components
• universal identifier ? sos
• configure local emergency numbers
• find right PSAP
• identify and verify PSAP
• On-going effort in IETF and NENA

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Location-based call routing UA knows its
location
GPS
INVITE sipssos_at_
40.86N 73.98E CNus A1NJ A2Bergen
leonia.nj.us.sos.arpa POLY 40.85 73.97 40.86
73.99 NAPTR firedept_at_leoniaboro.org
outbound proxy server
provided by local ISP?
40.86N 73.98E Leonia, NJ fire dept.
DHCP
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DHCP for locations

• modified dhcpd (ISC) to generate location
  information
• use MAC address backtracing to get location
  information

8020abd5d
DHCP server
CDP SNMP 8020abd5d ? 458/17
DHCP answer staDC locRm815 lat38.89868
long77.03723
458/17 ? Rm. 815 458/18 ? Rm. 816
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Location-based call routing network knows
location
TOA
outbound proxy
include location info in 302
INVITE sipssos_at_
INVITE sipssos_at_paris.gendarme.fr
48 49' N 2 29' E
map location to (SIP) domain
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Service creation
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PSTN vs. VoIP and the role of carriers

• PSTN only carriers can get full signaling
  functionality (SS7)
• UNI vs. NNI signaling
• VoIP same signaling, same functionality
• Application-layer service providers (VSP) ?
  network-layer service provider
• enterprise may run its own services
• Columbia doesnt use an email service provider

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Network vs. end system services

• Really two meanings
• services implemented in user agent (instead of
  proxy)
• services implemented in server run by end user
  (instead of carrier) ?
• business
• residential
• Variation on old Centrex vs. PBX argument
• except that media routing no longer an issue
• Often, services require or can use both
• e.g., the history of speed dial
• CLASS service translation in CO
• (semi)intelligent end systems locally, possibly
  with hotsync to PC
• intelligent end system, but network-synchronized

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Call routing services

• Outsourcing allows temporarily disconnected end
  users
• Staged service

carrier proxy
user proxy
personal preferences
basic call routing
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Carrier services Identity management

• Identity assertion (notary) services
• best done by larger organization
• server certificates
• name recognition
• recourse
• Anonymity services
• needs to have large user population to provide
  effective hiding
• Portable services
• high availability and universal reachability

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Service creation

• Tailor a shared infrastructure to individual
  users
• traditionally, only vendors (and sometimes
  carriers)
• learn from web models

programmer, carrier end user
network servers SIP servlets, sip-cgi CPL
end system VoiceXML VoiceXML (voice), LESS
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Call Processing Language (CPL)

• XML-based language for processing requests
• intentionally restricted to branching and
  subroutines
• no variables (may change), no loops
• thus, easily represented graphically
• and most bugs can be detected statically
• termination assured
• mostly used for SIP, but protocol-independent
• integrates notion of calendaring (time ranges)
• structured tree describing actions performed on
  call setup event
• top-level events incoming and outgoing

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CPL

• Location set stored as implicit global variable
• operations can add, filter and delete entries
• Switches
• address
• language
• time, using CALSCH notation (e.g., exported from
  Outlook)
• priority
• Proxy node proxies request and then branches on
  response (busy, redirection, noanswer, ...)
• Reject and redirect perform corresponding
  protocol actions
• Supports abstract logging and email operation

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CPL example
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CPL example

• lt?xml version"1.0" ?gt
• lt!DOCTYPE call SYSTEM "cpl.dtd"gt
• ltcplgt
• ltincominggt
• ltlookup source"http//www.example.com/cgi-bin
  /locate.cgi?userjones"
• timeout"8"gt
• ltsuccessgt
• ltproxy /gt
• lt/successgt
• ltfailuregt
• ltmail url"mailtojones_at_example.comSubjec
  tlookup20failed" /gt
• lt/failuregt
• lt/lookupgt
• lt/incominggt
• lt/cplgt

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Service creation environment for CPL and LESS
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Security issues
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Security issues Threats

• Fraud
• authentication (Digest)
• VSP-provided customer certificates for S/MIME
• authenticated identity body
• SIP spam
• domain-based authentication
• trait-based authentication (future)
• return calls
• reputation systems

• DOS attacks
• layered protection
• User privacy and confidentiality
• TLS and S/MIME for signaling
• SRTP for media streams
• IPsec unlikely (host vs. person)
• Needs to work across domains and administrations

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DOS attack prevention
port filtering (SIP only) address-based rate
limiting
return routability
authentication
UDP SIP TCP SYN attack precautions needed SCTP
built-in
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Denial-of-service attacks signaling

• attack targets
• DNS for mapping
• SIP proxies
• SIP end systems at PSAP
• types of attacks
• amplification ? only if no routability check, no
  TCP, no TLS
• state exhaustion ? no state until return
  routability established
• bandwidth exhaustion ? no defense except filters
  for repeats
• one defense big iron fat pipe
• danger of false positives

• unclear number of DOS attacks using spoofed IP
  addresses
• mostly for networks not following RFC 2267
  (Network Ingress Filtering Defeating Denial of
  Service Attacks which employ IP Source Address
  Spoofing)
• limit impact of DOS require return routability
• built-in mechanism for SIP (null
  authentication)
• also provided by TLS
• allow filtering of attacker IP addresses
  (pushback)

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TLS

• End-to-end security ? S/MIME
• but PKI issues
• proxy inspection of messages
• TLS as convenient alternatives
• need only server certificates
• allows inspection for 911 services and CALEA
• hop-by-hop

home.com
Digest
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TLS performance
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TLS performance
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TLS performance
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Conclusions

• SIP missing piece for
• session-based services
• general event notification ? presence
• Location-based and context-aware services
• e.g., emergency calling
• Service creation ? from global to local killer
  app
• challenge automated configuration and deployment
• Security layered approach
• email and web approaches apply
• can hopefully offer stronger caller
  authentication
• TLS as deployable version of PKI