Other attributes
The Internet is a worldwide system of interconnected computer networks built on the use of the IP protocol and the routing of data packets. IP does not guarantee reliable delivery of the packet to the destination - in particular, the packets may arrive in the wrong order in which they were sent, two copies of the same packet may arrive, they may be damaged (usually damaged packets are destroyed) or not arrive at all. The guarantee of error-free delivery of packets is provided by some protocols of a higher level - the transport layer of the OSI network model - for example, TCP, which use IP as a transport.
Computers located in different parts of the globe, as their number increases, acquire means of communication. Computer networks have become the means of communication. Networks are local and global. A local area network is a network that unites computers that are geographically located at a short distance from each other - for example, in the same building. Global networks serve to connect networks and computers that are separated by long distances - hundreds and thousands of kilometers. The Internet belongs to the class of global networks. A protocol is a set of rules that govern the transmission of information over a network.
The main protocols used in the Internet:
TCP/IP; HTTP; FTP; WAIS; Gorpher; POP3; SMTP; IMAP4; WAP; TCP/IP
It is not one protocol, but a whole set of protocols working together. It consists of two levels. The top-level protocol, TCP, is responsible for correctly converting messages into information packets, from which the original message is assembled on the receiving side. The lower layer protocol, IP, is responsible for correctly delivering messages to the specified address. Sometimes packets of the same message can be delivered in different ways.
TCP (Transmission Control Protocol) - is responsible for verifying the correct delivery of data from the client to the server. Data may be lost in the intermediate network. The TCP protocol has added the ability to detect errors or lost data and, as a result,
the ability to request a retransmission until the data is correctly and completely received.
Applications that work with the TCP / IP protocol can perform the functions of the presentation layer and partly the session layer of the OSI model.
Common examples of applications are programs:
Telnet, FTP, HTTP, WWW
Email protocols (SMTP, POP3)
To send data to another application, the application refers to one or another module of the transport module.
The Internet uses two transport protocols - UDP, which provides non-guaranteed delivery of data between programs, and TCP, which provides guaranteed delivery with the establishment of a virtual connection.
The HTTP (Hypertext Transfer Protocol) protocol is a higher layer protocol than TCP/IP, an application layer protocol. HTTP was designed to efficiently transmit Web pages over the Internet. It is thanks to HTTP that it is possible to see the pages of the Web in all its splendor. The HTTP protocol is the backbone of the World Wide Web.
When the HTTP command is used, the browser interface is used, which is an HTTP client. When a link is clicked, the browser queries the Web server for the resource that the link points to, such as the next Web page.
In order for the text that makes up the content of Web pages to be displayed on them in a certain way - in accordance with the intention of the page creator - it is marked up using special text labels - HyperText Markup Language (HTML) tags.
There are three main features that make HTTP a simple yet powerful protocol:
HTTP worked without saving the connection, the flow diagram was as follows:
The HTTP client, the browser, initiates an HTTP request, and after the request is made, the client disconnects from the server and waits for a response. The server processes the request and re-establishes a connection with the client to send a response. In HTTP/0.9 and 1.0 the connection is closed after one request/response pair, this was a very simple implementation. HTTP/1.1 introduced a keep-alive mechanism whereby a connection could be reused for more than one request. These persistent connections reduce request latency because the client does not need to renegotiate a TCP 3-Way-Handshake connection after the first request is sent.
HTTP is independent of the content type:
any type of data can be sent over HTTP, as long as both the client and server know how to process the content of the data. Both client and server require that the content type be specified, which uses the appropriate MIME type.
HTTP is stateless:
HTTP is stateless. This means that no intermediate state is maintained between request-response pairs. The server and client only know each other during the current request. After that, they both forget about each other. Due to this nature of the protocol, neither the client nor the browser can store information between different requests on web pages. However, components that use HTTP can independently store state information related to recent requests and responses (for example, "cookies" on the client side, "sessions" on the server side). The browser that sends the requests can track response delays. The server can store the IP addresses and request headers of recent clients. However, the protocol itself is not aware of previous requests and responses, it does not provide internal state support, it does not have such requirements.
FTP is a file transfer protocol that allows you to view the contents of directories and download files from or to a server. It is possible to transfer files between servers. It is one of the oldest application protocols that appeared long before HTTP <http://ru.wikipedia.org/wiki/HTTP>, in 1971. It is still widely used today for distributing software and accessing remote hosts. The address of an FTP resource on the Internet is as follows: ftp://ftp.netscape.com
Using this protocol, you can connect to a remote computer as a user (if you have the appropriate rights, you know the username and password) and perform actions on files and applications in the same way as if you were working on your computer. It is a terminal emulation protocol. It is operated from the command line.
WAIS stands for Wide-Area Information Servers. This protocol was developed for searching information in databases. The WAIS information system is a distributed database system where individual databases are stored on different servers. Information about their content and location is stored in a special database - the catalog of servers. Viewing information resources is carried out with the help of the WAIS client program.
Information is searched for by keywords specified by the user. These words are entered for a certain database, and the system finds all the corresponding fragments of text on all servers where the data of this database is located. The result is presented as a list of references to documents indicating how often the search word and all search words in the aggregate occur in this document.
The WAIS system can be considered morally obsolete; specialists in many fields, when conducting scientific research, nevertheless, turn to it in search of specific information that they cannot find by traditional means.
The address of the WAIS resource on the Internet looks something like this: wais://google.ru
Gopher is an application layer protocol developed in 1991. Prior to the ubiquity of the hypertext system, the World Wide Web Gopher was used to extract information (mostly text) from a hierarchical file structure. Gopher was the forerunner of the WWW, allowing menus to move from one page to another, gradually narrowing the range of information displayed. Gopher client programs had a text interface. Gopher menu items could point not only to text files, but also, for example, to telnet connections or WAIS databases. Gopher resources can now be viewed with a regular Web browser, as modern browsers support this protocol.
The POP protocol supports simple "download and delete" requirements for accessing remote mailboxes. Most POP clients provide the ability to leave mail on the server after download, using POP clients typically connect, extract all mail, store it on the user's computer as new messages, delete it from the server, and then disconnect.
POP3 is a standard Internet application layer protocol used by email clients to receive mail from a remote server over a TCP connection.
The POP3 server listens on the well-known port 110. Communication encryption for POP3 is requested after starting the protocol using the STLS command (if supported), or POP3S, which connects to the server using TLS or SSL on TCP port 995.
Available client messages are captured when a mailbox is opened by a POP session and are determined by the number of messages for the session or, optionally, by a unique identifier assigned to the message by the POP server. This unique identifier is permanent and unique to the mailbox and allows the client to access the same message in different POP sessions. Mail is retrieved and marked for deletion using the message number. When a client logs out of a session, flagged messages are removed from the mailbox.
