Rajesh, I can give you one possible view, but as I said, it varies quite a bit. Hope the below helps your understanding around some of the possible roles and processes.
Generally, unless you have a massive company, or are very well outfitted, you don’t normally have one person doing each of these roles, you tend to have people who are multi-disciplinary.
So for instance you might just have one UX designer who does the IA, UX, IxD, visuals and UI. Then you have the front end (also known as UI) developers. This is the most common scenario that I have come across, although you generally can also have a UX designer, a Designer and the UI developer, but in this case the Designer normally works in the marketing department.
Development of a webpage or application depends on what process your company uses, and what technologies. For instance an Agile environment might be different to a FDD environment (Feature Driven Design). There are also slightly different processes that can be followed, such as the one in Luke & Matt’s “Get started in UX” which follows Strategy, Research, Analysis, Design, Production, Beta Launch, Evaluation, and then after iteration, Launch.
UX involves the 5 w’s . What problem are you trying to solve, who are you solving it for, why, when, where and normally how. So they’re involved in all of the beginning research, and strategy. Sometimes they are involved in opportunities, and whether the the problem you are trying to solve is actually a problem for users, and other times you are given direction of a product idea and it is your job to help the vision and direction of the project. UX should be throughout the whole process, testing your designs as you go, and getting input from actual end-users.
Information Architecture (IA) can be completed alongside, in the beginning, or after you have an idea around your project. It depends on how the process works. For instance, before any UI or design is done, you might come up with ideas around the possible structure, from the knowledge of what needs to be in your web pages, or application. You may then test this with card sorting or tree testing, iterating as you go.
As a UI Designer you tend to be involved in sketching, then completing low fidelity wireframes in programs like Balsamiq, and then later on higher fidelity wireframes in Illustrator or Axure which can be turned into prototypes to test with. UI designers are more focused on the elements in the design, consistency, hierarchy of elements etc rather than the usability and psychology behind them (which is more UX related). but again if you have someone who’s role is UX designer, they tend to do both UX and UI.
Interaction Design (IxD) is generally done after you have your basic UI designs. You need to know how a user is going to move from one place to another, and how the webpage/application is going to behave.
If you are in an Agile environment, you may have a team who works closely with the UI Developer and Backend developers throughout the process. They can help with possible designs, as well as helping weed out the designs that are definitely not possible with your given timeframe and technology. They are awesome to involve early on, as they can help come up with designs you may not even have thought of. If you are lucky enough, you can also have someone who codes up your designs in a prototype, so you have a functional prototype to test with users along the way. It helps you to see what behaviours and designs won’t actually work, as sometimes what you design on paper turns out a bit differently in an actual website or application.
Once you have launched the application or website, it is generally also good for the UX team to follow up on it’s progress, statistics and getting feedback. If certain parts are underperforming or are obviously not sitting well with the users, they can then complete more research around why people are struggling, and then iterate some more.
Generally these things are never finished, as improvements can always be made (depending on budget and time constraints).