Hypertext Transfer Protocol
The request-response role of HTTP in the client-server model of interaction. There is a key difference among an application and a web browser in HTTP. The program running on a PC which hosts a website operates as a server. On the other hand we have a browser which plays the role of a client, and it sends an HTTP request message to this server. The purpose of a server is to store HTML files and different content. The server is always ready to send back a response message in case if the client submits a certain request. The server’s response is able to send any requested content to the client, as well as additional completion status information.
The abovementioned client can be not only a web browser, but also a web crawler. They are often referred to as user agents (UA). Among such agents are the indexing software and voice browsers, but the last group is less widespread at the moment.
The major purpose of the HTTP protocol is to provide improvement of communications between servers and clients with the help of intermediate network elements. The most popular websites need to deal with lots of visitors. They use web cache servers which operate origin servers for improvement of request-response time. The requests and responses executed within the private networks can be accelerated by HTTP proxy servers. Such technology helps the clients to exchange the data within their local network without being connected to the worldwide web.
TCP and UDP
HTTP is a protocol created in the bounds of the Internet Protocol Suite. But what is protocol in fact? It is Transport Layer which provides data transferring from one host to another. The most commonly used protocol for this mission is Transmission Control Protocol (TCP). In some cases HTTP exploits less reliable protocols. For instance the User Datagram Protocol (UDP) is not reliable but it can be beneficial for the Simple Service Discovery Protocol (SSDP).
Different HTTP Resources are situated in different URIs (Uniform Resource Identifiers). Http or https URI schemes are used to identify attachment of a certain HTTP Resource to a corresponding place in the network. Together with HTML (Hypertext Markup Language), URI creates a complex of inter-linked data. This forms hypertext documents which are main component units of the Internet that has been established by Tim Berners-Lee in 1990.