Lecture-1 (Client-Server Model)

Client Server Model

The client–server model of computing is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requests, called clients. Often clients and servers communicate over a computer network on separate hardware, but both client and server may reside in the same system. A server host runs one or more server programs which share their resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.

 Examples of computer applications that use the client–server model are Email, Network Printing, and World Wide Web.

When a bank customer accesses online banking services with a web browser (the client), the client initiates a request to the bank's web server. The customer's login credentials may be stored in a database, and the web server accesses the database server as a client. An application server interprets the returned data by applying the bank's business logic, and provides the output to the web server. Finally, the web server returns the result to the client web browser for display.

In each step of this sequence of client–server message exchanges, a computer processes a request and returns data. This is the request-response messaging pattern. When all the requests are met, the sequence is complete and the web browser presents the data to the customer.

The main basic communication modes:

- RPC (Remote Procedure Call)

- Message-based

Types of Client Server architecture

Basically client server model have three parts: client, business logic and Data Source. Based on this there are two types.

Two Tier

Three Tier

Two Tier Architecture

The direct communication takes place between client and server. There is no intermediate between client and server. Because of tight coupling a 2 tiered application will run faster.

The Two-tier architecture is divided into two parts:

1) Client Application (Client Tier)
2) Database (Data Tier)

On client application side the code is written for saving the data in the SQL server database. Client sends the request to server and it process the request & send back with data. The main problem of two tier architecture is the server cannot respond multiple request same time, as a result it cause a data integrity issue.

Advantages:

1. Easy to maintain and modification is bit easy.
2. Communication is faster.

Disadvantages:

1. In two tier architecture application performance will be degrade upon increasing the users.
2. Cost-ineffective.

Three Tier Architecture

Three-tier architecture typically comprises a presentation tier, a business or data access tier, and a data tier. 

 

Three layers in the three tier architecture are as follows:

1) Client layer
2) Business layer
3) Data layer

1) Client layer

It is also called as Presentation layer which contains UI part of our application. This layer is used for the design purpose where data is presented to the user or input is taken from the user. For example designing registration form which contains text box, label, button etc.

2) Business layer

In this layer all business logic written like validation of data, calculations, data insertion etc. This acts as a interface between Client layer and Data Access Layer. This layer is also called the intermediary layer helps to make communication faster between client and data layer.

3) Data layer

In this layer actual database is comes in the picture. Data Access Layer contains methods to connect with database and to perform insert, update, delete, get data from database based on our input data.

Advantages

1. High performance, lightweight persistent objects
2. Scalability – Each tier can scale horizontally
3. Performance – Because the Presentation tier can cache requests, network utilization is minimized, and the load is reduced on the Application and Data tiers.
4. High degree of flexibility in deployment platform and configuration
5. Better Re-use
6. Improve Data Integrity
7. Improved Security – Client is not direct access to database.
8. Easy to maintain and modification is bit easy, won’t affect other modules
9. In three tier architecture application performance is good.

Disadvantages

1. Increase Complexity/Effort

Summary for Client-Server Architecture

Client-server is a computing architecture which separates a client from a server.

It is almost always implemented over a computer network

The most basic type of client-server architecture employs only two types of nodes: clients and servers.

->This type of architecture is sometimes referred to as two-tier.

->It allows devices to share files and resources.

Server provides the service.

Client is considered as the customer requesting the service.

The server service can be shared among a number of clients.

Clients must request or initiate the service.

The location of the server in the network is transparent to clients.

Transaction between C/S is message-passing based.

C/S architecture is scalable.

->Horizontally (more clients can added)

->Vertically (more servers can be added)

The server is centrally maintained where as clients are independent of each other.