[SIPForum-discussion] Relation b/w SIP and IMS

Neill Wilkinson neill.wilkinson at quortex.com
Sun Nov 25 20:25:13 UTC 2007



OK - IMS is an evolution of the softswitch model and has evolved from the
UMTS standards.


The scenario you refer to below is what would occur in a Release 4/5


Let me expand - as I think you are probably aware of the stages of
architecture from "standard" GSM what is now called release 2 and with GPRS
added on called release 2.5 or also known as release 99. All these are the
ETSI/3GPP standards releases. Beyond 2.5 we move in to release 3, then 4,
then 5. Through releases 3-5 we start to decompose the normal switching
functions of the of the Radio Network Controllers, MSCs, HLRs etc. into a
softswitch architecture and introduce the Soft-MSC or MSC server and
Media/Signalling Gateways to replace the circuit-switched core (CS Domain)
and put either ATM or IP in its place.


Once release 6 of the standards is reached, we decompose this further, to
fully introduce IMS. IMS is first introduced in release 5.


So to expand further on your example if you have Media Gateways and
MCGP/MEGACO in the architecture then the call is originating in a release 4
network. Release 4 networks connect to the IP world via the GPRS (GGSN), and
to the TDM world via the Media Gateways. The media gateways controlled by
some for of Media Gateway Control Protocol. The MSCs Servers are also acting
as Protocol Interworking functions to translate between SIGTRAN, MEGACO,
BICC, SIP etc. This allows us to utilise the existing SS7 protocols inherent
in the earlier mobile networks whilst interworking to the newer SIP
protocols of the IP world.


So why do I go to such lengths to point all this out? Two things:

1.	up to release 5 we're dealing with an Interworking scenario where we
still have some "old-world" equipment and interworking to GSM devices, and
the PSTN. The idea up to Release 5 is that the core of the Mobile network
can be transformed to and IP core (although ATM is still allowed and
prevalent in a number of operators networks), whilst giving the external
impression of still being a circuit switched core (CS Domain).
2.	IMS relies on the whole of the environment being IP based.
Signalling from the mobile device (UE in UMTS terms) is SIP, no interworking
is required from SIP-to-SIP connections directly from Mobile devices to say
softphones. The network is simpler and requires less interworking and
translation, since MGCP/MEGACO is gone and BICC is gone. It allows
connections and roaming across Network boundaries to be pure IP all the way
without the need for media gateways between Networks. The Circuit Switched
core (CS Domain) is gone an only the GPRS function remains in the mobile
elements at release 5 onwards.


Value added services are enabled in IMS through the Application Server. The
Application Servers in turn provide a secure "sandbox if you will" for 3rd
Party developers to communicate to the IMS subscribers and add applications.
Adding applications in this way through APIs was impossible in the "old"
mobile world (up to release 5). With IMS the ability to construct and add
value-added services is much easier and should enable carriers to open up
their networks to 3rd parties for new and exciting applications, without
having to rely on the manufacturers features.


Hope that all makes sense and is of use.


Anyone else on the discussion group want to add/correct my thoughts?





Aeonvista Ltd



From: aditya kumar [mailto:adityaakumar at hotmail.com] 
Sent: 23 November 2007 09:26
To: neillw at quortex.com; discussion at sipforum.org
Subject: RE: [SIPForum-discussion] Relation b/w SIP and IMS


Thanks Neil..for giving a clear cut idea on IMS and SIP.

Could you please share your thoughts on the following scenario:

1.One Call is from mobile to IP phone.[As per my knowledge by using
MGCP/MEGACO, we can successful establish the call b/w these 2 different
Then what's the need of IMS architecture,if we need then How it plays the
value added services?



> From: neillw at quortex.com
> Subject: Re: [SIPForum-discussion] Relation b/w SIP and IMS
> To: adityaakumar at hotmail.com; discussion at sipforum.org
> Date: Thu, 22 Nov 2007 16:03:30 +0000
> IMS is a whole platform/Architecture Framework. The 
> session control protocol (signalling protocol) is SIP with 
> a number of extensions.
> The IMS architecture uses the inherent features that SIP 
> brings and combines those with the features of Mobile 
> networks and adds the ability to construct external 
> applications through SIP Application Servers and the 
> Neill...;o)
> On Thu, 22 Nov 2007 15:00:55 +0000
> aditya kumar <adityaakumar at hotmail.com> wr
> >Hi guys,
> > 
> >1.If IMS is working on SIP protocol then what's the 
> >disadvantage/doesn't support the features by SIP, so that 
> >we have to go for IMS?
> >2.How IMS brings a great flexibility in our near feature?
> > 
> >Please guide me.
> > 
> >Thanks,
> >Adi
> >_________________________________________________________________
> >Tried the new MSN Messenger? It's cool! Download now.
> >http://messenger.msn.com/Download/Default.aspx?mkt=en-in


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