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

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