N-Tier And N-Layer Architecture

N-Tier and N-Layer are entirely different concepts. People generally use this term during the design of the application architecture. N-Tier refers to the actual N-system components of your application. On the other hand, N-Layers refer to the internal architecture of your component.

N-Tier architecture usually has at least three logical parts, each located on a separate physical server. Each tier is responsible for a specific functionality. Communication between tiers is typically asynchronous in order to support better scalability.
N-Layers of application may reside on the same physical computer (same tier) and the components in each layer communicate with the other layer’s components by well-defined interfaces. Layered architecture focuses on grouping related functionality within an application into distinct layers stacked vertically on top of each other.

Pros and Cons of Tier and Layered Architecture

• Tiers indicate a physical separation of components, which may mean different assemblies on the same server or multiple servers. Layers refer to a logical separation of components, such as having distinct namespaces and classes for the Database Access Layer (DAL), Business Logic Layer (BLL) and User Interface Layer (UIL).
• Tiers could be on different machines, so they communicate by Value only — as serialized objects. Multi-layered design is suitable for small to mid-size projects only.
• Tiers could be on different machines, so they communicate by Value only — as serialized objects. Layer communicates with each other either by Value or by Reference.
• Tiered Architecture has all advantages of Layered Architecture + scalability as the application will be deployed in different machines so the load will be shared among the tiers and scalability will increase. Layered Architecture will improve readability and reusability

In Tier Architecture ASP.NET Web Services or .NET Remoting can be used in place of the Database Access Layer and Business Logic Layer. In .NET 3.0 & above Windows Communication Foundation (WCF) Services can be used, which will be great, it seems like Web Services but more powerful, secure and flexible than Web Services.