[SIPForum-discussion] IMS Diagram

Tue May 13 23:31:11 UTC 2008

Hello group,

This is my first post on this forum. A bit about myself, I am based in
Melbourne Australian and I am the head of an IMS systems engineering
group.

Firstly IMS is a big subject which involves a number of standards groups
3GPP, TISPAN, IETF, ITU-T and so on and so on. There are a considerable
number of standards and recommendation documents to wade through, most
of which are pretty detailed, I would start with TS 23.002 Network
Architecture and TS 23.228 IP Multimedia Subsystem (IMS) - Stage 2, use
the following link I think it is a little easier than the 3GPP site.

http://www.tech-invite.com/Ti-ims-standards.html

Regarding your questions 
a. You will find a diagram of the IMS Architecture as Figure 6 in
TS23.002 (get one of the Release 8.2 documents). This diagram is a bit
confusing at first and there is a simpler, clearer one on such sites as
Wikipedia.

The CSCF is Call Session Control Function, there are actually a number
of theses defined the Proxy (P-CSCF), Interrogating (I-CSCF), Serving
(S-CSCF) and the Emergency (E-CSCF) they are defined in the two
documents I mentioned but basically they are SIP Proxies which handle
Security, Registration, SIP routing, header and number management and a
lot of other tasks, there has been a considerable amount of change in
this area between the earlier releases and the later IMS 7 and 8
releases.

The MRF is the media resource function and it provides such things as
announcements, conferencing (mixing), DTMF management and LI, there are
two separate functions for media functions the Media Resource Function
Controller (MRFC) and the Media Resource Function Processor (MRFP) the
first is the resource management function and the other is the Media
recouse function itself.

Very good IMS Blog spot is: http://theimslantern.blogspot.com/

IMS is not complex, it is just defined in a degree of detail most
Softswitch or VoIP guys are unused to and it addresses issues which are
not normally a problem in fixed networks.

I am not sure I understand your "IMS box contain SMSC, IN and MMSC
already?" question, yes there is nothing preventing you from
implementing all of that in one box, however the first two are really
apps as far as IMS is concerned and IMS is basically the MSC, but with
SIP end points some of the service logic moves out from the core, read
TS23.002 and TS.23.228 and you will see what I mean.

Best regards

Cliff Wignell
Alcatel-Lucent 
Director: NSA, CBG, APAC
Phone:   +61 3 9664 3847
Cell:       +61 419 747 373

-----Original Message-----
From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Eric Burger
Sent: Tuesday, 13 May 2008 9:12 PM
To: Agonias, Richard L. (Digitel-GSM)
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] IMS Diagram

Check out the 3GPP web site. It is ALL there.

On May 13, 2008, at 6:41 PM, Agonias, Richard L. (Digitel-GSM) wrote:

> Hi Guys,
>
> Do you have any IMS complete diagram? We are planning to implement  
> this in the near future. Also, hope you can help me on the following:
>
> 	* Can IMS box contain SMSC, IN and MMSC already?
> 	* What does CSCF, MRF means? What are their functions?
>
> Regards,
>
> -chad
>
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