Let's first dissect the name IMS - IP Multimedia Subsystem. What does it mean. First lets look at IP. Everyone knows that IP stands for Internet Protocol. IP is that bases for the Internet today. So by using the term IP, those who have created IMS have decided to use IP as the bases of IMS. Second lets examine the word Multimedia. I remember when I first started in the business and IP was just gaining momentum, Vinton G. Cerf, VP and Chief Internet Evangelist at Google wore a shirt to an IETF meeting that read "IP on Everything". Well in IMS that might become a reality. The term Multimedia was chosen because IMS was created to run anything over IP. That would include, voice, video, IM, Gaming and what ever else we have not even thought about yet. Okay far we have determined that the creators of IMS want to use IP and be able to run any service over it. The final word is Subsystem. This is a key word to understanding IMS. It took me a couple of tries to understand the importance of Subsystem. The definition of Subsystem is Something that is part of a larger system. So if IMS is part of a larger system what is IMS and what is the larger system. This is were I have seen people get confused about IMS. So get ready, here is the first important step to understand what IMS is. IMS is a network Architecture. IMS does not define applications or services, but provides an architecture that allows applications and services to be provided. an analogue that I like to use is a PC. The PC is not the application, it allows applications like Excel, Word or Internet browser to run.
So if IMS is just a network Architecture designed for IP multimedia applications, then you might ask what is all the fuss about IMS and don't networks today allow that. And the answer would be Yes they do. The difference is that today the networks are individual networks. The MSO network, the Telco network and the wireless networks. What IMS brings to the table is the ability to be network independent. So no matter were you are you should have access to any service or application. This is also called mobility and presences. I will dive into more details about the applications and the market timing in a later post.
To keep on track the purpose of this post is just to get a basic understanding of IMS. So let's take a look at an IMS diagram. As you can see in the diagram below there are a lot of blocks and lines in the diagram.
When I first looked at this diagram, I was totally confused and thought that IMS was the most complicated thing I had ever seen. This is because I did not understand the basics concepts of IMS and the philosophy that went into the design of IMS. First thing that we must understand is that IMS was created to be scalable. Since it is meant to be scalable the design and the diagram to the left is done on a function level. For me when I first looked at the IMS diagram, I just immediately assumed that all the boxes were actual Network Elements/hardware. That is not correct. There is nothing to say that you could not have multiple functions in a single piece of hardware. Another thing that has help me in understanding IMS is this, there are really only two components of IMS.
They are the Core and the peripherals. As you can see from the diagram that the core is actually made up of some basic components. The components are the Call/Session Control function (CSCF) and the Home Subscriber Server (HSS) and SLF(Subscription Locator Function) databases. This is the foundation in which the IMS architecture is created around.
So that is all for today. Hopefully the following points have been made through this posting.
1) IMS is an architecture. It is not a single product, application or service. The architecture is based on IP.
2) IMS provides a means for mobility and presence and is network access independent.
3) IMS diagrams call out functions and not individual devices or pieces of hardware.
4) A simplified look at IMS is that there are two components. The Core and the peripheral.
In upcoming post we will start to dissect the architecture and the communication/protocols between functions in more details and we will also start talking about applications and the market drivers.
Until next time have a good one.
