Download IMS

IP Multimedia
Subsystems
By
Vamsee K Pemmaraju
Agenda
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IMS Example
Overview
Basic Principles
Architecture
Access, Core Networks and User databases
Call and Session Control
Service Interoperability
Migrating Application to IMS
SIP Architecture
Advantages
Issues
Conclusion.
IMS Example
ANNA
ANDREW
COLLEAGUES
OVERVIEW
The
IP Multimedia Subsystem (IMS) standard defines a generic
architecture for offering Voice Over IP (VoIP) and Multimedia services
It
uses a Voice-Over -IP (VoIP) implementation based on a 3GPP
standardized implementation of SIP, and runs over the standard
Internet Protocol (IP). Existing phone systems (both packet switched
and circuit switched are supported.
The
aim of IMS is not only to provide new services but all the
services, current and future, that the Internet provides.
To
achieve these goals, IMS uses open standard IP protocols, defined
by the IETF
Designed
for both wireless and wire line networks.
BASIC PRINCIPLES
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Access independence: IMS will eventually work with any network
(fixed, mobile or wireless) with packet switching functions, such as
GPRS, UMTS, CDMA 2000, WLAN, WiMAX, DSL cable. Older circuit
switched phone systems (POTS, GSM) are supported through
gateways. Open interfaces between control and service layers allow
elements and calls/sessions from different access networks to be mixed.
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Different network architectures: IMS allows operators and service
providers to use different underlying network architectures.
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Extensive IP-based services: IMS should make it easier to offer just
about any IP-based service. Examples include voice over IP (VOIP),
Push to talk over Cellular(POC), multiparty gaming, video conferencing,
Messaging, community services, Presence Information and content
sharing.
IMS Network (Access Independent Service Enabled)
In Release 6 of the 3GPP specifications, the IMS has been specified to be access
independent. This means that the access technology used to transport user SIP
messages to the IMS network does not impact the functionality of the IMS network
itself. Consequently, any access can be used, examples being DSL, Cable, WLAN,
GPRS, etc. This is obviously a key step in the move towards converged network
architectures
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IMS Services Examples
•Presence (Is the user available)
• Voice and Video Telephony
• Instant Messaging
• Push to talk, push to see
• Conferencing
• Gaming
• Convergence of all of the above
Architecture
AL comprises of
application and content
servers to execute value
added services to the
user.
SCL comprises network
control servers for
managing call or session
set-up. It contains CSCF
(Call Session Control
Function) also know as
SIP server.
CL comprises of routers,
and switches.
IMS Access Network
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The user can connect to an IMS network using various
methods, all of which are using the standard Internet
Protocol(IP). Direct IMS terminals (mobile phones,
computers, ...), can register directly into an IMS network,
even when they are roaming in another network or country
(the visited network).
Fixed access (e.g., DSL, Cable Modems, Ethernet ...),
mobile access (W-CDMA, CDMA, GSM, GPRS ...) and
wireless access (WLAN, WiMAX ...) are all supported.
Other phone systems like the POTS (the old analogue
telephones), and non IMS-compatible VoIP systems are
supported through gateways.
Control Network
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The HSS (Home Subscriber Server) is the master user database that
supports the IMS network entities that are actually handling the
calls or sessions.
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It contains the subscription-related information (user profiles),
performs authentication and authorization of the user, and can
provide information about the physical location of user. It's similar
to the GSM .
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An SLF (Subscriber Location Function) is needed when multiple HSSs
are used. Both the HSS and the SLF implement the DIAMETER
protocol (Cx, Dx and Sh interfaces).
Call or Session Control
Functions
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P-CSCF: Proxy Call Session Control Function: This is
the first point of contact within the IMS for a User Element
(UE). It ensures that the registration of the user is passed to
the correct home network and that SIP session messages are
passed to the correct Serving CSCF (S-CSCF) once
registration has occurred
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PDF (Policy Decision Function): This function takes a
service level policy request from the application layer (for
example P-CSCF) and translates it into IP QoS parameters.
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IBCF Interconnect Border Control Function: This
standard is to specify the detection of failure of interconnect
points.
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I-CSCF Interrogating Call Session Control Function: This is
the function that is able to determine the S-CSCF (Serving-Call
Session Control Function) with which a user should register. This is
achieved by querying the Home Subscriber Server (HSS).
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Serving Call Session Control Function: This is the function that
registers the user and provides service to them even though these
services may be on separate application platforms.
Service interoperability
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IMS enables the reuse of inter-operator relations. Rather
than develop different interconnect relations and
agreements for each service, IMS enables a single interoperator relationship to be established and built upon for
each service.
Many functions can be reused for fast service creation
and delivery.
IMS services are hosted by an Application Server, they
are implicitly placed in the IMS application layer.
IMS defines how service requests are routed, which
protocols are supported etc.
Service Architectures
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Migrating applications to IMS.
SIP (Session Initiation Protocol)
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SIP is an application layer protocol that can
establish, modify and can terminate multimedia
sessions and conferences over the internet.
SIP messages could contain session descriptions
such that participants can negotiate with media
types and other parameters of the session.
SIP provides its own mechanisms for reliability and
can run on top of several different transport
protocols such as TCP, UDP and SCTP (Stream
Control Transmission Protocol)
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Establish a session between the originating and target end
point—If the call can be completed, SIP establishes a
session between the end points. SIP also supports mid-call
changes, such as the addition of another end point to the
conference or the changing of a media characteristic or
codec.
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Handle the transfer and termination of calls—SIP
supports the transfer of calls from one end point to
another. During a call transfer, SIP simply establishes a
session between the transferee and a new end point
(specified by the transferring party) and terminates the
session between the transferee and the transferring party.
At the end of a call, SIP terminates the sessions between
all parties.
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SIP
Elements
User Agent Client / Server
user agent client and server are logical entities, whose roles last
only for the duration of the transaction
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Proxy Server
forward SIP requests and responses
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Redirect Server
receive requests and then return the location of another SIP user
agent or server where the user might be found
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Registrar
accept REGISTER requests and places the information into the
location service for the domain it handles.
SIP Architecture
SIP Request through a Proxy Server
If a proxy server is used, the caller UA sends an INVITE
request to the proxy server, the proxy server determines
the path, and then forwards the request to the cal lee
SIP Response through a Proxy Server
The cal lee responds to the proxy server, which in turn,
forwards the response to the caller
SIP Session through a Proxy Server
The proxy server forwards the acknowledgments of both
parties. A session is then established between the caller and
callee. Real-time Transfer Protocol (RTP) is used for the
communication between the caller and the cal lee
Interfaces
Click here Interfaces.htmfor Different
Interfaces and their Description
Advantages
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The core network is independent of a particular access technology
Integrated mobility for all network applications
Easier migration of applications from fixed to mobile users
Faster deployment of new services based on standardized
architecture
An end to unique or customized applications, leading to lower
CAPEX and OPEX
New applications such as presence information, videoconferencing,
Push to talk over cellular (POC), multiparty gaming, community
services and content sharing.
Evolution to combinational services, for example by combining
instant messaging and voice
User profiles are stored in a central location
The architecture is designed for easy scalability and redundancy
Issues
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Benefits need to be further articulated in terms of actual savings.
IMS is "operator friendly" which means that it provides the operator with
comprehensive control of content at the expense of the consumer.
IMS uses the 3GPP variant of SIP, which needs to interoperate with the
IETF SIP.
IMS is an optimization of the network, and investments for such
optimization are questionable.
Some IMS proponents are trying to push it as the total solution for IP-based
systems such as IPTV, which is causing push-back from companies wanting a
much richer experience in land-line environments that don't have mobile
constraints;
There are no products available other than paper machine;
The new services are the same of ISDN services, i.e, voice calls, video calls,
etc. All the supposed new services already exists;
QoS is not a problem for voice calls. Skype's revenue shows that;
Subscribers won't accept that service providers controls what application they
are running;
It's a useless control-layer.
Conclusion
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Thus IMS plays a vital role in transferring
multimedia messages easily.
References
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http://en.wikipedia.org/wiki/IP_Multime
dia_Subsystem
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http://www.cisco.com/univercd/cc/td/doc/pr
oduct/voice/sipsols/biggulp/bgsipov.htm
www.empirix.com
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Questions
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What is IMS and explain different elements in
IMS?
What SIP? How call is initiated using SIP?
Differences between IMS and pre-IMS?