Normally, in the area of technology we hear and talk about DHCP, but after all, what is it?

Well … the DHCP protocol is a service of the TCP / IP, it works in order to assign an IP address, netmask, and optional attributes dns, gateway and others.

It is based on the model of client-server, in which a client requests a message via UDP to DHCP server for DHCP. It will reach the criteria associated with the customer and permissions, and return a package containing at least one IP address, netmask, and optionally gateway and dns servers. There are basically three ways to deliver an address and network mask for a DHCP client.

Manually – There is a table set up by an administrator, to manually associate a MAC address with a default IP address set, it means that IP is reserved for the customer corresponding to the MAC.

Automatically - There is a range of IP available by the administrator in which, when the client requesting the connection, receive one of these IP already allocated and available for use.

Dynamic - Works through the reuse of IP, this means that when a client requests a connection and is within the appropriate criteria, it receives the IP, netmask and attributes / additional settings, so the client terminate the connection, ie, complete the link between this connection and the associated IP, the IP that was used will be available for another client who wants the connection, usually for each connection, a different IP is assigned.

The World Wide Web

The World Wide Web is a network that interconnects thousands of millions of computers around the world, can be considered as a global repository. The World Wide Web is an architectural framework that allows access to linked documents spread across millions of machines on the Internet.

So the Internet is a powerful communication tool and offers a vast and varied amount of information from many different subjects. It is also used for data transfer and can work with file types such as documents, images, audio, video and more.

The Web is seen by the user as a global collection of documents, these documents are typically called pages or Web pages only. Each page can contain links, better known as links to other pages when the user clicks one of these links is taken to the next page, this idea of a page to point to another is known as hypertext, the second concept was created by a professor at MIT (Massachusetts Institute of Technology), Vannevar Bush in 1945, well before the creation of the internet.

The HTTP protocol

HTTP – Hypertext Transfer Protocol is an application layer protocol of the Internet. HTTP is divided into two parts, the client program and dedicated server program, both programs run on different machines talk to each other by means of HTTP messages. HTTP defines the structure and these messages are exchanged between the client and server.

The web pages consist of documents or files of various formats as discussed above, these pages are built with HTML (HyperText Markup Language) which is the standard language for programming web pages, built in the page HTML is interpreted by a browser, which is regarded as HTTP client. The text pages or HTML documents are also considered by the HTTP protocol.

A web page (also called document) is built of objects. An object is simply a file – such as an HTML file, a JPEG, a GIF image, a Java applet, an audio clip and so on – you can access with a single URL. Most web pages are constructed on HTML file base and several referenced objects. For example, if a web page contains an HTML text and five JPEG images, so it will have six objects:

File-based HTML

Web pages are on a web server, with may be several other pages. The customer or user accesses the page through a browser that interprets the HTML code and builds the page that is being viewed by the viewer. A simplified explanation of the operation would be as follows: the client makes a request for a page to the server via HTTP to the client and the server responds with the requested page, as can be seen in figure mentioned below.

This architecture is basically a client that makes requests to another program, the server – it responds. In this architecture the capacity is shared between the clients and servers , but more important are the benefits to organization due to the centralization of the management of information and separation of responsibilities, which facilitates and clarifies the design of system.

The separation between client and server is a separate logical type, where the server does not necessarily run on a single machine and is not necessarily a single program. Specific types of servers include cloud web servers, file , mail servers, etc. While their purposes vary from service to others, the basic architecture remains the same.

A common arrangement is the multilayer system in which the server is broken down into different programs that can be executed by different computers thereby increasing the degree of distribution ofsystem.

Server Features

In the systems C / S the recipient of the request sent by client is known as a server. Its features are:

• At the beginning wait for requests from clients, then play a role passive in the communication device ( slave ).

• Upon receipt of an application, process it and then send the customer response.

• Usually accept connections from a large number of customers (in some cases the maximum number of requests may be limited).

• It is not often that it interact directly with end users.

• Comparison of architecture C / S with other network architectures

• Comparison with networks of peers

The peer networks, also known as network peer-to-peer or peer-to-peer (abbreviated with the acronym P2P ) are another type of architecture network , because every node or element of the system can act at the same time as a client and a server, each node has, therefore, responsibilities and status of both.

Multi-layer architecture

The client / server architecture has two types of generic nodes in the network: clients and servers. Consequently, these generic architectures are sometimes referred to two-tier architectures or two layers .

Some networks have three types of nodes:

• Customers who interact with end users.

• Application servers that process data for customers.

• Servers that store database data for the application servers.

• This configuration is called a three-tier architecture.

Advantages of n-tier architecture:

The key advantage of an architecture n-layers compared to a two-tier architecture (or a three-tier to a two-tier) is that it separates out the process that happens to improve balance and the load on different servers, that is more scalable.

Disadvantages of n-tier architecture:

Puts more load on the network , because of Most of the network traffic.

It is much more difficult to program and test the software in architecture of two levels because more devices have to communicate to complete a transaction user.