Client-server Shopping
Client-server 		Articles about
Client-server 		 

Information About

Client-server
  CATEGORIES ABOUT CLIENT-SERVER
   
network architecture
   
mobile
   
mobile phones
   
mobile computer
   
mobile software
   
APPAREL
BABY
BEAUTY
BOOKS
CAR TOYS
CELL PHONES
DVD'S
ELECTRONICS
GOURMET FOOD
GROCERIES
HEALTH & PERSONAL
HOME & GARDEN
JEWELRY
MUSIC
MUSIC INSTRUMENTS
OFFICE PRODUCTS
SOFTWARE
SPORTING GOODS
TOOLS & HARDWARE
TOYS
VIDEO GAMES
SHOPPING HOME
MORE SHOPPING...



Each Instance of the client software can send data Request s to one or more connected ''server''s. In turn, the servers can accept these requests, process them, and return the requested information to the client. Although this concept can be applied for a variety of reasons to many different kinds of Applications , the architecture remains fundamentally the same.

These days, clients are most often Web Browser s, although that has not always been the case.
Servers typically include Web Server s, Database Server s and Mail Server s.

The interaction between client and server is often described using Sequence Diagram s. Sequence diagrams are standardized in the Unified Modeling Language .


CHARACTERISTICS


;Characteristics of a client:

:Initiates requests
:Waits for and receives replies
:Usually connects to a small number of servers at one time
:Typically interacts directly with end-users using a Graphical User Interface
;Characteristics of a server:
:Passive ( Slave )
:Waits for requests from clients
:Upon receipt of requests, processes them and then serves replies
:Usually accepts connections from a large number of clients
:Typically does not interact directly with end-users


MULTI-TIERED ARCHITECTURE

Some designs are more sophisticated and consist of three different kinds of nodes: clients, Application Server s which process data for the clients, and Database Server s which store data for the application servers. This configuration is called a Three-tier Architecture , and is the most commonly used type of client-server architecture. Designs that contain more than two tiers are referred to as ''multi-tiered'' or ''n''-tiered.

The advantages of ''n''-tiered architectures is that they are far more Scalable , since they balance and distribute the processing load among multiple, often redundant, specialized server nodes. This in turn improves overall system performance and reliability, since more of the processing load can be accommodated simultaneously.This form of scalability is called ''horizontal scalability''. There is substantial and growing criticism that horizontal scalability is limiting as applications become more complex and interdependent, particularly in the areas of network latency, reliability, and manageability. IBM, in particular, takes this view and promotes both vertical and horizontal scalability. Vertical scalability implements fewer servers able to support multiple application and database tiers, and multiple applications, concurrently. The IBM System Z is the most notable example of a vertically scalable system.

The disadvantages of ''n''-tiered architectures include:
# More load on the network itself, due to a greater amount of network traffic.
# More difficult to program and test than in two-tier architectures because more devices have to communicate in order to complete a client's request.


COMPARISON TO PEER-TO-PEER ARCHITECTURE

Another type of network architecture is known as Peer-to-peer , because each node or instance of the program can simultaneously act as both a client and a server, and because each has equivalent responsibilities and status. Peer-to-peer architectures are often abbreviated using the acronym ''P2P''.

Both client-server and P2P architectures are in wide usage today.


COMPARISON TO CLIENT-QUEUE-CLIENT ARCHITECTURE

While classic Client-Server architecture requires one of communication endpoints to act as a server, which is much harder to implement, Client-Queue-Client allows all endpoints to be simple clients, while the server consists of some external software, which also acts as passive queue (one software instance passes its query to another instance to queue, e.g. database, and then this other instance pulls it from database, makes a response, passes it to database etc.).

Such architecture allows to simplify software implementations many times. Peer-to-Peer architecture was originally based on Client-Queue-Client concept.


ADVANTAGES

  • In most cases, a client-server architecture enables the roles and responsibilities of a computing system to be distributed among several independent computers that are known to each other only through a network. This creates an additional advantage to this architecture: greater ease of maintenance. For example, it is possible to replace, repair, upgrade, or even relocate a server while its clients remain both unaware and unaffected by that change. This independence from change is also referred to as '' Encapsulation ''.

  • All the data are stored on the servers, which generally have far greater security controls than most clients. Servers can better control access and resources, to guarantee that only those clients with the appropriate permissions may access and change data.

  • Since data storage is centralized, updates to those data are far easier to administer than would be possible under a P2P paradigm. Under a P2P architecture, data updates may need to be distributed and applied to each "peer" in the network, which is both time-consuming and error-prone, as there can be thousands or even millions of peers.

  • Many mature client-server technologies are already available which were designed to ensure security, 'friendliness' of the user interface, and ease of use.

  • It functions with multiple different clients of different capabilities.



DISADVANTAGES

  • Traffic congestion on the network has been an issue since the inception of the client-server paradigm. As the number of simultaneous client requests to a given server increases, the server can become severely overloaded. Contrast that to a P2P network, where its bandwidth actually increases as more nodes are added, since the P2P network's overall bandwidth can be roughly computed as the sum of the bandwidths of every node in that network.

  • The client-server paradigm lacks the robustness of a good P2P network. Under client-server, should a critical server fail, clients’ requests cannot be fulfilled. In P2P networks, resources are usually distributed among many nodes. Even if one or more nodes depart and abandon a downloading file, for example, the remaining nodes should still have the data needed to complete the download.



EXAMPLES

Imagine you are visiting an ECommerce web site. In this case, your Computer and Web Browser would be considered the ''client'', while the computers, Database s, and applications that make up the online store would be considered the ''server''. When your web browser requests specific information from the online store, the server finds all of the data in the database needed to satisfy the browser's request, assembles that data into a web page, and transmits that page back to your web browser for you to view.

Specific types of clients include Web Browser s, Email Client s, and online chat clients.

Specific types of servers include Web Server s, Application Server s, Database Server s, Mail Server s, File Server s, Print Server s, and Terminal Server s. Most Web Service s are also types of servers.


NOTES



SEE ALSO