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
Introduction to SIP
Classification of Mobility
Network Layer Mobility
Application Layer (SIP
-
based) Mobility
Conclusion
Introduction to SIP (1/9)
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)
Developed in SIP working Group in
IETF
–
Work
began 1995
–
Sep. 1999 split
from
MMUSIC
M
ultiparty
Mu
ltimedia
S
ess
i
on
C
ontrol
–
Proposed standard
RFC 2543
,
February
1999
–
New version of SIP
–
RFC 3261,
June
2002
Introduction to SIP (3/9)
SIP is an
application
-
layer
signaling
protocol
HTTP
-
like
,
“
request
-
response
”
–
Establish
,
modify
, and
terminate
multimedia sessions.
SIP+
(Session Description Protocol)
SDP
Introduction to SIP (4/9)
Separate
signaling
and
media
streams
Introduction to SIP (5/9)
SIP addressing and naming
–
The entities
addressed
by SIP are
users at hosts
(SIP
URI
:
U
niform
r
esource
i
dentifier)
–
Email
-
like
identifier of the form user@host
User
:
user name
or
telephone number
Host
:
domain name
or
numeric network number
–
For example,
m9356020
@npust.edu.tw
0944168888
@
npust.edu.tw
Charles@
140.127.1.200
Introduction to SIP (6/9)
SIP defines a number of logical
entities, namely
–
User agents
–
Redirect servers
–
Proxy servers
–
Registrars
Introduction to SIP (7/9)
User agent
–
User Agent
Client
-
Initiate
SIP
request
–
User Agent
Server
-
Accepts
or
rejects
call
Introduction to SIP (8/9)
Redirect Server
–
Redirect server
uses
a
database or location
service
to
look up a user
Introduction to SIP (9/9)
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
Range
Application
Layer
Transport
Layer
Network
Layer
Macromobility
SIP
TCP
-
Migrate
MIP
Micromobility
HMSIP
HAWAII
CIP
IDMP
TIMIP
Network Layer Mobility
Advantage
–
Retain
home
IP address
while
changing
attachment point
of the network
–
Keep tracking
host location
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 (SIP
-
based) Mobility (1/16)
Advantage
–
Ease to deploy
–
Support
session, service, personal, and
terminal mobility
–
Network transparent
Disadvantage
–
A
large amount
of
signaling overhead
–
RTP
does
not
support
QoS
Application Layer (SIP
-
based) Mobility (2/16)
In this paper,
four types mobility
have
been defined.
–
Terminal
Mobility
–
Session
Mobility
–
Service
Mobility
–
Personal
Mobility
Application Layer (SIP
-
based) Mobility (3/16)
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)
Application Layer (SIP
-
based) Mobility (4/16)
Pre
-
call
Application Layer (SIP
-
based) Mobility (5/17)
Pre
-
call Mobility
–
The MH
simply re
-
registers
with its home
registrar each time it obtains a new IP address
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
.
The client simply
polls
the
OS
every few seconds
Power consumption
Application Layer (SIP
-
based) Mobility (6/16)
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 (SIP
-
based) Mobility (7/16)
Mid
-
call
Application Layer (SIP
-
based) Mobility (8/16)
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 (SIP
-
based) Mobility (9/16)
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 (SIP
-
based) Mobility (10/16)
Session Mobility
It
allows
a
use
r 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 (SIP
-
based) Mobility (11/16)
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 (SIP
-
based) Mobility (12/16)
Third
-
party call control
Application Layer (SIP
-
based) Mobility (13/16)
REFER method
Application Layer (SIP
-
based) Mobility (14/16)
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 (SIP
-
based) Mobility (15/16)
Personal Mobility
Application Layer (SIP
-
based) Mobility (16/16)
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 Voice
-
over
-
IP environment
.
Conclusion
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
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