Session Initiation Protocol SIP Session Mobility draftshachamsippingsessionmobility00

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Session Initiation Protocol (SIP) Session
Mobilitydraft-shacham-sipping-session-mobility-00

• Ron Shacham
• Henning Schulzrinne
• Srisakul Thakolsri
• Wolfgang Kellerer

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Motivation

• Session mobility move active sessions from one
  (mobile) terminal to one or more (stationary)
  terminals
• audio on hardware phone, video on PC
• move conference to conference room facilities
• Move active sessions back to controlling device
• i.e., not just call transfer
• Service examples
• requires no new SIP protocol mechanisms
• Real system also requires discovery mechanism
• we use SLP

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Local Devices
Transcoder
Internet
SLP DA
SLP SA
SLP UA
SIP SM
SIP UA
SIP UA
Correspondent Node (CN)
SLP SIP RTP
SIP SM
SIP UA
SLP UA
Mobile Node (MN)
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Requirements

• Interoperability
• Only require CN to support RFCs and mature IDs
• Backward Compatibility
• Support local devices with basic functionality
• Flexibility
• Discover and reconcile device capability
  differences
• Seamlessness
• Limit disruption of media

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Session mobility options

• Transfer and retrieve an active session
• Retrieval not only of a session previously
  transferred
• Transfer all media to a single device or split
  over multiple devices
• Privacy keep audio on handset, watch video on
  large screen
• Take advantage of benefits of different devices
• Includes division of full-duplex media into
  half-duplex streams

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Session mobility modes

• MN may retain control of or relinquish session
  signaling
• Mobile node control mode
• 3pcc (call control flow I)
• Session handoff mode
• REFER, Replaces header, Referred-By mechanism
  for security

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Session Handoff Mode

• Retrieval of session not controlled by MN
• Use Nested REFER for MN to retrieve
• Handoff to multiple devices
• Cant currently bind multiple sessions at CN into
  one
• Devices discover each other and form
  Multi-device systems where B2B UA receives
  REFER and controls other devices

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Handoff to a Multi-Device System
RTP
5
MDSM
INVITE, Replaces/ 200 OK/ ACK
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INVITE / 200
2
ACK (CN SDP)
4
CN
RTP
5
INVITE / 200
BYE/ 200 OK
2
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REFER
1
ORIGINAL SESSION
ORIGINAL SESSION
INVITE / 200
2
ACK (CN SDP)
4
ORIGINAL SESSION
ACK (CN SDP)
4
SESSIONS TERMINATED
7
MN
RTP
5
RTP
5
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Device Capability Differences

• Local device does not support any codec supported
  by CN
• Transfer carried out through transcoder using
  3pcc
• Local device has higher bandwidth and may receive
  media at a higher framerate
• Local device includes such information in
  response, as is done for H.263

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Open issues

• Can we avoid the B2BUA for SH mode?
• Integration of text sessions (MSRP)

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Service Discovery

• Architecture is not dependent on a single
  protocol
• Low-power wireless protocols find close devices
  without knowing location
• Query-based protocols (eg., SLP) allow larger
  areas and other locations to be queried
• Integration of both types of protocols could
  prove useful