Application-Layer Mobility Using SIP Henning Schulzrinne, Elin ...

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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

Thank you for your
attention