Transcript Application Layer (SIP

Application-Layer Mobility
Using SIP
Henning Schulzrinne, Elin Wedlund
Mobile Computing and Communications Review, Volume 4,
Number 3
Presenter: 許啟裕
Date: 2005/5/10
Outline
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Introduction to SIP
Classification of Mobility
Network Layer Mobility
Application Layer (SIP-based) Mobility
Conclusion
Introduction to SIP (1/9)
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A powerful alternative to H.323
More flexible, simpler
Easier to implement advanced features
Better to support of intelligent user
devices
Transport independence (UDP, TCP, or
SCTP)
Introduction to SIP (2/9)
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Developed in SIP working Group in
IETF
– Work began 1995
– Sep. 1999 split from MMUSIC
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Multiparty Multimedia Session Control
– Proposed standard RFC 2543, February
1999
– New version of SIP – RFC 3261, June
2002
Introduction to SIP (3/9)
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SIP is an application-layer signaling
protocol
HTTP-like, “request-response”
– Establish, modify, and terminate
multimedia sessions.
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SIP+(Session Description Protocol)SDP
Introduction to SIP (4/9)
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Separate signaling and media streams
Introduction to SIP (5/9)
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SIP addressing and naming
– The entities addressed by SIP are users at hosts
(SIP URI: Uniform resource identifier)
– Email-like identifier of the form user@host
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User: user name or telephone number
Host: domain name or numeric network number
– For example,
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[email protected]
[email protected]
[email protected]
Introduction to SIP (6/9)
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SIP defines a number of logical
entities, namely
– User agents
– Redirect servers
– Proxy servers
– Registrars
Introduction to SIP (7/9)
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User agent
– User Agent Client - Initiate SIP request
– User Agent Server - Accepts or rejects call
Introduction to SIP (8/9)
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Redirect Server
– Redirect server uses a database or location
service to look up a user
Introduction to SIP (9/9)
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Proxy Server
– Handle requests or forward requests to other
servers
– Can be used for call forwarding, time-of-day
reouting, or follow-me services
Classification of Mobility
Layers Application
Layer
Range
Transport
Layer
Macromobility
SIP
TCP-Migrate
Micromobility
HMSIP
Network
Layer
MIP
HAWAII
CIP
IDMP
TIMIP
Network Layer Mobility
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Advantage
– Retain home IP address while changing
attachment point of the network
– Keep tracking host location
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Disadvantage
– Difficult to deploy, ISP has to provide home
agent
– Need to modify convention IP stack
– Add 8-20 bytes overhead each packet
– Cannot support session, service and personal
mobility
Application Layer (SIPbased) Mobility (1/16)
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Advantage
– Ease to deploy
– Support session, service, personal, and
terminal mobility
– Network transparent
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Disadvantage
– A large amount of signaling overhead
– RTP does not support QoS
Application Layer (SIPbased) Mobility (2/16)
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In this paper, four types mobility have
been defined.
– Terminal Mobility
– Session Mobility
– Service Mobility
– Personal Mobility
Application Layer (SIPbased) Mobility (3/16)
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Terminal Mobility
– Terminal alters the attachment point of
the network.
– Two scenarios have to been concerned
Pre-call: Mobile host (MH) acquires a new
address prior to receiving or making a call
 Mid-call: MH is moving and sending another
INVITE request to the correspondent host
(CH)
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Application Layer (SIPbased) Mobility (4/16)
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Pre-call
Application Layer (SIPbased) Mobility (5/17)
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Pre-call Mobility
– The MH simply re-registers with its home
registrar each time it obtains a new IP address
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A large amount of the register signaling overhead
Waste of the network bandwidth
– The only difficult part there is the ability to
detect, at the application layer, when IP has
changed.
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The client simply polls the OS every few seconds
Power consumption
Application Layer (SIPbased) Mobility (6/16)
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Paging, for MH power conservation,
can also be implemented in SIP
This work assumes that proxies are
organized hierarchically
E.g.
– With a proxy for each wireless network,
region, cell cluster and base station
Application Layer (SIPbased) Mobility (7/16)
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Mid-call
Application Layer (SIPbased) Mobility (8/16)
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The location update takes one one-way
delay after the application in the MH
recognizes that it has acquired a new IP
address
For wideband access, the delay is probably
equal to propagation delay plus a few
milliseconds
For narrowband systems, it may impose
delays of several tens of milliseconds
Application Layer (SIPbased) Mobility (9/16)
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RTP translator intercepts the media
packets and directs them to the
current location of the MH
Insertion of an RTP translator reduces
handoff delay to the one-way between
the MH
Application Layer (SIPbased) Mobility (10/16)
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Session Mobility
It allows a user to maintain a media session
even while changing terminals
For example,
– A caller may want continue a session begun on a
mobile device on the desktop pc when enter her
office
– A user may also want to move parts of a session,
e.g., if he has specialized devices for audio and
video, such as a video projector, video wall or
speakerphone
Application Layer (SIPbased) Mobility (11/16)
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Session mobility using SIP can be
supported in at least three ways
– In the simplest approach, using new
INVITE request.
– One mechanism for such configuration
could be MGCP or Megaco
– Two better solutions, namely third-party
call control or the REFER mechanism
Application Layer (SIPbased) Mobility (12/16)
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Third-party call control
Application Layer (SIPbased) Mobility (13/16)
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REFER method
Application Layer (SIPbased) Mobility (14/16)
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Personal Mobility
It allows to address a single user
located at different terminals by the
same logical address
Both 1-to-n (one address many
potential terminal) and m-to-1 (many
addresses reaching one terminal)
mapping are useful
Application Layer (SIPbased) Mobility (15/16)
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Personal Mobility
Application Layer (SIPbased) Mobility (16/16)
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Service Mobility
It allows users to maintain access to
their services even while moving or
changing devices and network service
providers
For instance, users will likely want to
maintain include their speed dial lists,
address books, and so on in Voiceover-IP environment.
Conclusion
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Application-layer mobility can either
partially replace or complement
network-layer mobility
SIP-based mobility can be used to
provide all common forms of mobility,
including terminal, personal, service,
and session mobility
Thank you for your
attention