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SIP Session Mobility Project Status

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Motivation: Mobile devices continue to be limited in bandwidth, power and display capability. They can ... New systems are advertised using SLP. Two models ... – PowerPoint PPT presentation

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Title: SIP Session Mobility Project Status


1
SIP Session Mobility Project Status
  • Henning Schulzrinne and Ron Shacham
  • Columbia University
  • Collaboration Meeting
  • DoCoMo Eurolabs, Munich
  • July 28, 2005

2
Project Overview
  • Motivation Mobile devices continue to be limited
    in bandwidth, power and display capability. They
    can greatly benefit from the capabilities of
    other devices.
  • Project goal A mobile user should be able to
    discover nearby devices, then easily and
    seamlessly include them in his ongoing multimedia
    session, with the use of only standard internet
    protocols
  • Elements
  • Location-based Service Discovery
  • SIP signaling for session transfer

3
Publications
  • Two current IETF Internet Drafts
  • draft-shacham-sipping-session-mobility-01
  • draft-shacham-sip-media-privacy-00
  • The Virtual Device Expanding Wireless
    Communication Services through Service Discovery
    and Session Mobility to be presented at WiMob
    05 in Montreal
  • Technical Reports submitted at both Docomo
    Eurolabs and Columbia University

4
Requirements
  • Allow users to automatically discover local
    devices
  • Allow users to transfer sessions from mobile to
    local device and later return them to their
    mobile device
  • Allow splitting of session onto multiple devices
  • Provide option of maintaining signaling on mobile
    device or complete handoff
  • Require no special capabilities of Correspondent
    Node
  • Support existing devices in environment, while
    developing enhanced devices
  • Make transfer invisible to the Correspondent Node
  • Use existing standards whenever possible

5
Architectural Overview
Local Devices
Transcoder
Internet
SLP DA
SLP UA
SLP SA
SIP SM
SIP UA
SIP UA
Correspondent Node (CN)
SLP SIP RTP
SIP SM
SIP UA
SLP UA
Mobile Node (MN)
6
Service Discovery
  • Architecture is not dependent on a single
    protocol
  • Low-power wireless protocols find close devices
    without knowing location
  • Query-based protocols (eg. Service Location
    ProtocolSLP) allow different granularities and
    other locations to be searched
  • Integration of both types of protocols may be
    useful
  • We use SLP in our publications and implementation
  • Location discovered in a variety of ways
  • Direct Through Bluetooth, DHCP, GPS or other
    means, the device receives its own location
  • Device subscribes to user presence, presence
    updated when user walks into a room with his
    swipe card, the device receives location update
    and treats it as its own

7
Service Discovery with SLP
  • SLP Directory Agent (DA) keeps track of devices
    based on location, media attributes
  • SLP Service Agent (SA), either co-located with
    SIP UA or on separate host, advertises the device
    and its attributes (Service Registration)
  • SLP User Agent (UA) on users mobile device
    discovers DA (multicast), queries for devices
    available in a given location (Service Request),
    then queries for attributes of each (Attribute
    Request)

8
ExampleSLP Discovery of display
SLP SA
SrvRqst sip-device room102/ SrvRply URI-list
SLP UA
2
SrvReg/ SrvAck
1
AttrRqst display_at_example.com/ AttrRply attr-list
3
SLP DA
Available Devices display_at_example.com video
9
Session TransferOptions
  • Media that may be transferred
  • Real-time media (eg. audio, video)
  • Text messaging
  • Transfer modes
  • Mobile Node Control Mode
  • Session Handoff Mode
  • Whole or Split Session Transfer
  • Transfer in mid-session or on incoming call

10
Session TransferMobile Node Control Mode
  • Third-party call-control usedmobile node
    establishes a separate session each local device
    while retaining session with CN, setting up
    session media to be transmitted directly between
    them
  • Useful for retaining part of session media (eg.
    audio) on mobile device, while adding or
    transferring another media (eg. video)
  • Easy to support existing devices (they must only
    support INVITE request)
  • To transfer to multiple devices, MN simply
    establishes session with each one, updating
    session with CN accordingly

11
ExampleMNC Transfer to two devices
SIP RTP
Correspondent Node (CN)
12
Session TransferHandoff Mode
  • REFER sipav_at_local_device.example.com SIP/2.0
  • To ltsipav_at_local_device.example.comgt
  • From ltsipmn_at_example.comgt
  • Refer-Toltsipcn_at_host1.macrosoft.comaudiovideo?
  • Replaces1_at_mob.example.com
  • to-tagbbbfrom-tagaaagt
  • Referred-By ltsipmn_at_example.comgt
  • S/MIME authentication body
  • REFER message sent by MN to local device
  • Requests it to initiate a session with CN
    (Refer-To) which CN will regard as replacement
    of its current session with MN (Replaces
    header)
  • MN includes S/MIME body so that local device may
    authenticate with CN
  • Original session is torn down once new session is
    established
  • Completely hands off session to local device, no
    continued involvement by MN
  • Useful if battery runs low or wireless
    connectivity becomes spotty

13
Handoff to multiple devices
  • Sending Multiple REFER messages does not provide
    seamless transfer, since they are not assocated
    together
  • Preferred Approach Multi-device systems
  • One device controls anotherwhen invited into a
    session, it acts as a Back-to-Back UA
  • Devices discover each other, create new systems
    according to all possible combinations in a given
    location
  • New systems are advertised using SLP
  • Two models
  • Dedicated B2B UA for all multi-device systems
    (necessary for existing devices)
  • Distributed model (preferred for enhanced
    software-driven devices

14
ExampleMulti-device system creation and transfer
SLP Directory Agent
CN
A
V
dev2.example.com
dev1.example.com
15
ExampleMulti-device system creation and transfer
SLP Directory Agent
CN
A
V
dev2.example.com
dev1.example.com
16
ExampleMulti-device system creation and transfer
SLP Directory Agent
CN
A
V
9 200 OK
dev2.example.com
dev1.example.com
17
ExampleMulti-device system creation and transfer
SLP Directory Agent
CN
A
V
dev2.example.com
dev1.example.com
18
ExampleMulti-device system creation and transfer
SLP Directory Agent
CN
A
V
SIP
SIP
Audio
dev2.example.com
dev1.example.com
Video
19
Retrieval of a handed-off session
  • Need to replace the current session as was done
    for original handoff
  • Correspondent Node will only replace if referred
    by current call participant (local device)
  • Local device may not have an interface for
    requestion this
  • Our solution Send a REFER to local device that
    requests it to send it a REFER, referring it to
    the CN (nested REFER)
  • Once the MN receives the requested REFER, it will
    initiate a session with the CN, as the local
    device did above
  • REFER sipav_at_local_device.example.com SIP/2.0
  • To ltsipav_at_local_device.example.comgt
  • From ltsipmn_at_example.comgt
  • Refer-Toltsipmn_at_host1.macrosoft.commethodREFER
  • ?Refer-Toltsipcn_at_host1.macrosoft.comaudio
  • video?Replaces1_at_local_device.example.comto-
    tagaaafrom-tagbbbgtgt

20
Incoming Call Transfer
  • Part of session is immediately transferred to
    another device upon receiving a call request
  • Examples
  • Use PC for video and desk IP phone for audio
  • Users PDA discovers local video camera and
    projector, registers itself to the proxy as
    having video capabilities, then transfers video
    to the devices upon receiving video-call request
  • Two models
  • Invite local device before completing call setup
    with caller
  • Complete call setup, then immediately invite
    local device, update call

21
Transfer of messaging
  • Three types of messaging
  • Real-time (RTP) text
  • SIP Message Request
  • Message Session Relay Protocol (MSRP)
  • Real-time text is identical to other real-time
    media
  • SIP Message requests may be forwarded to local
    devices (MNC mode) or are automatically
    transferred (SH mode)
  • MSRP is similar to real-time media, but uses TCP
    to transport messages
  • When relay agents are used, endpoints need not
    create TCP connections between them

22
Reconciling Device Capabilities
  • When the local device and CN have no common
    codecs, session transfer must go through a
    transcoder (may be located through SLP)
  • MN maintains sessions with transcoder, CN, and
    local device, using 3pcc to create media sessions
    between them
  • Transcoder translates between CN and local device
    media
  • Other capabilities, such as bandwidth and display
    resolution, may be negotiated in SDP, using
    existing specifications for H.263

23
Transcoding Example
A
B
RTP
5
Transcoder
INVITE A and B SDP/ 200
1
camera
RTP
5
ACK
ACK CN and camera SDP
3
3
INVITE Transcoder B SDP/ 200 camera SDP
2
ORIGINAL SESSION
ORIGINAL SESSION
SESSION TERMINATED
4
MN
ACK
3
CN
INVITE Transcoder A SDP/ 200 CN SDP
2
24
Security/Privacy Considerations
  • Limiting Usage
  • Trait-based authentication to identify users as
    belonging to an authorized group
  • Preventing remote control of devices for
    surveillance
  • Authentication with a local token (available
    through Bluetooth or display) ensures that the
    user is present in the room
  • Visual indicator (eg. LED) when device is in use
  • Output devices may allow unwanted users to view
    video or text messages or hear audio

25
Privacy of Output Devices
  • Concern not only for session mobility, but
    anywhere output devices are used, or recording
    may be done
  • Speakerphone
  • Video display
  • Specify in call messaging the privacy
    capabilities and privacy requirements
  • E.g. My device will not let anyone hear what you
    say, and I require the same of yours and This
    conversation may not be recored
  • Three levels of privacy
  • 1 Only the device user has access to the media
  • 2 Those in the device users organization (eg.
    company, circle of friends) have access
  • 3 Anyone has access the device is public
  • Though a user may disregard requests, the
    messages provide legal evidence
  • We have specified our model in an Internet Draft

26
Applications
  • Have the proxy server only route the call to a
    device that has the right level of privacy
  • Disallow the other call participant from
    transferring the call to a public device, turning
    on his speakerphone, or recording the call
  • Force the other participants device to retrieve
    the session from a public device when the
    conversation becomes more private

27
Protocol Extensions
  • SIP Caller Preferences
  • The header Accept-Contact privacy1require
    causes the proxy server to only route the call to
    a device on which only the user can view or hear
  • SDP attributes
  • arequired-privacyuser demands that the other
    device not make media available to anyone besides
    the user
  • aprovided-privacyuser expresses that no other
    user has access to the media
  • anorecord disallows recording of the session
  • These may be updated in mid-call

28
Implementation
  • Columbia Universitys SIPC has been enhanced to
    provide the major elements described
  • Both Mobile Node Control Mode and Session Handoff
    Mode supported
  • Multi-Device Systems
  • Incoming Call Transfer

29
Implementation
The location of the device, after being updated,
may be viewed
30
Implementation
  • The user may choose to transfer the current
    session, or set the devices to which new sessions
    should be transferred
  • When transferring a session, the user may
    choose between transfer modes
  • In Mobile Node Control Mode, more than one
    device may be chosen for multiple media

31
Implementation
  • In Session Handoff Mode, only a single device
    may be used for transfer
  • One of the devices in the room acts as a
    Multi-Device System. It supports video locally,
    and audio through one of the IP phones in the room

32
Implementation
The user may set devices to which incoming calls
should be transferred
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