Name of the data transfer protocol. Internet data transfer protocols

Data transmission and conversion in modems are carried out in accordance with accepted protocols.

Data transfer protocol is a set of rules governing the data format and procedures for their transmission in a communication channel. The protocol, in particular, may specify in detail how to present the data, which method of data modulation to choose in order to speed up and secure their transmission, how to connect to the channel, how to overcome the noise in the channel and ensure the reliability of data transmission.

Modem protocols are the language in which communicating modems agree on a specific method of interaction. As a result of the negotiation process, modems select a protocol that is available to both of them, providing the maximum transmission speed in accordance with the conditions set by the users.

When creating modems, certain signal transmission standards are followed. A standard usually includes a set of protocols, or less often one protocol.

The official legislator in the field of data transmission protocols for modems is CCITT - the International Advisory Committee on Telegraphy and Telephony. This Committee has recently been renamed the International Telecommunications Institute (ITU – International Telecommunication Union).

Almost all modem data transmission standards are established by this organization; Some characteristics of the most important of them are given in Table 7.1.

The standards are divided according to the following criteria.

By data transfer rate(V.22, V32, V32bis). Higher speed ones usually implement previous signal transmission standards and, in addition, provide backup modes with lower speeds.

According to error correction protocols- MNP (Microcom Networking Protocol) group protocols MNP1-MNP10. These are hardware protocols that provide automatic error correction and compression of transmitted data. Currently the CCITT V42 standard is used. For compatibility purposes, the V.42 modem includes b MNP functions.

By data compression method– (MNP5, V.42bis). The MNP5 standard, which provides for information compression by only half, is giving way to the CCITT V42bis standard, which provides four times the information compression. The V42bis standard includes the MNP5 standard as a backup data compression method, and the V42 standard as an error correction method.

The quality of a modem is determined by what protocols it supports.

Speed ​​and modulation standards are also called modem communication protocols. They are always implemented in the modem at the hardware level and, in addition to speed, determine the modulation method.

Table 7.1. Protocols for data transmission over telephone communication channels.

Modern high-speed modems should:

comply with protocols no lower than V.34 or V.34 bis;

perform error correction using the V.42 protocol;

be able to work on noisy and cellular communication lines;

support protocols used in older modems.

Based on these requirements, it is necessary that the same modem can use some combination of data transfer and error control protocols to ensure more efficient operation.

For example, when using modems on an asynchronous analog channel between local networks, the following combinations can give good stable results:

V.32bis – transmission;

V42 – error control;

V.42bis – compression.

Asynchronous modems are cheaper than synchronous modems because they do not require circuits or kits to control synchronization.

The main characteristic of a modem is the maximum possible data transfer rate over communication lines, determined by the standard.

Along with the line speed indicators, there is a transmission speed on the port, determined by the speed of information exchange between the PC and the modem.

With the hardware compression method, the port speed should be approximately 4 times the required line speed.

In order to reduce the time and increase the reliability of information transfer during the information exchange process, the following functions can be performed:

information may be compressed during transmission. When received, the information is restored in its original form;

detection and correction of errors that occur during the transmission of information is ensured. For this purpose, all information is transmitted in separate blocks (frames). In addition to their own data, the blocks contain control codes added by the transmitting modem. These codes allow the receiving modem to verify that the block received is correct. If an error is detected, the receiving modem requires the block to be resent.

Data compression and error correction can be implemented in both software and hardware, and the latter is more efficient. To perform compression and correction in software, some switching programs require the installation of a special driver.

The compression method and error correction are usually interrelated. Establishing a connection between two modems begins with automatic agreement in what mode and with what method of compression and error correction the connection will be established.

In order to facilitate such coordination and provide the user with partial control over it, the most common combinations of duplex - compression - correction parameters are numbered and are called protocols MNP1 - MNP10. The higher the standard the modem meets, the more MNP protocols it understands.

MNP1 – uses an asynchronous half-duplex data transfer method with a byte-by-byte organization with an increased degree of error protection. This is achieved at the cost of reduced efficiency.

MNP2 is the same as MNP1, but uses a full-duplex data transmission method, which increases channel throughput.

MNP 3 - does not support start and stop bit technology, but uses a synchronous duplex data transfer method with a byte organization. Having received an asynchronous bit from the computer, the modem removes start, stop and control bits from it. These bytes are then collected into blocks and supplied with a checksum and other service information. Due to this, it is possible to increase the efficiency of data transmission. Efficiency – 108%

MNP4 essentially combined all the best of MNP 2 and MNP 3, like MNP 2 it is able to change the size of the data block and like MNP 3 it can reduce the cost of transferring service information. As a result, the reliability and capacity of the channel increases.

MNP5 features the ability to compress transmitted data by half, which allows for significant increases in throughput in many cases.

MNP10 - designed for use on highly noisy communication lines, which significantly reduces the transmission speed.

In addition to the listed MNP protocols, modems of the V 42 standard have their own, more efficient LAPM protocol, which simultaneously understands the MNP2-4 protocols. The LAPM protocol is enabled if the modem has a standard not lower than V 42. Modems of the V 42bis standard accept an effective compression protocol, which, in addition, recognizes files compressed by the archiver and, unlike the MNP5 protocol, transmits them in a similar form, without increasing the amount of transmitted information. These protocols are implemented not by hardware, but by a communication program and only work when transferring files.

The functions of data transfer protocols include:

splitting data into blocks, calculating checksum

retransmission of erroneously received blocks, flexible change in block sizes depending on the quality of communication.

Many modems, in addition to providing information transfer procedures, also perform a number of other useful functions, such as:

transmit the name, size and creation date of the file;

send multiple files in one package;

remembers in the event of a communication breakdown until what moment the file was transferred and the next time it resumes transfer from the same place.

File transfer has its own protocols, which additionally regulate the procedures for breaking information into blocks, using codes with automatic detection and correction of errors, retransmitting incorrectly received blocks, restoring transmission after a break, etc.

The most common protocols in this group include the Xmodem, Ymodem, Kermit, Zmodem protocols. The first three do not work very efficiently on Russian telephone lines; Zmodem is now perhaps the most common file transfer protocol and can rightfully be recommended for use.

Xmodem uses relatively small blocks (128 bytes) and a simple checksum method. The file name is not transferred, there is no recovery after a break, rather low efficiency.

Kermit transmits all file attributes - name, date, size, is able to send several files in one packet, compressing data, error correction is more reliable than Xmodem.

Ymodem transfers all file attributes and several files in one packet, the block size is 1 K. Due to the fact that the protocol is not able to change this value during transmission, it is characterized by low efficiency.

Zmodem was created in 1986 - the first of the streaming protocols. This means that it sends blocks of data with checksums without stopping in a single stream, and only after the entire block has been transmitted, the receiver transmits the checksum of the blocks, and checksumming them if necessary. Zmodem also transmits file attributes, sends several files in one packet, and recovery after a connection loss is first introduced. It is almost ideal for modems with hardware error correction, because... spends minimal time checking the correctness of the transmission.

Today it is difficult to imagine the existence of human civilization without the World Wide Web. This is about 400 million users, for whom tens of millions of servers, containing a total of more than a million pages, operate around the clock. WWW is the largest repository of publicly available data, the most up-to-date media, electronic stores, interest clubs and much, much more.

No analyst can predict what the network will look like in 10 years. But one thing is clear: if now the WWW, which no one knew about 15 years ago, is studied in school (despite the fact that school education has always been distinguished by conservatism), then soon the ability to use a browser will become as necessary in school education as the ability read and write.

As sad as it is to report this, the Internet has become as much a product of military technology as the computer itself. In the crazy nuclear testing race that marked the fifties of the last century, the United States produced a seemingly not very powerful explosion at an altitude of 20 kilometers. But its consequences were truly terrifying. The electromagnetic pulse generated by the explosion knocked out not only telephone and telegraph lines, but also plunged the entire state of Hawaii, located a thousand miles from the site of the explosion, into darkness for several days. The moral of the story was quite sad for the American military: a high-altitude nuclear explosion of not very high power, carried out in the center of the country, completely deprives it of communication systems, and therefore control. The only solution to the problem was the creation of an ultra-secure communication system capable of transmitting a huge amount of information to all points of the country.

The history of the Internet can be divided into several stages:

One of the important dates in the history of the Internet can be considered 1957, when a separate structure was created within the US Department of Defense - the Advanced Research Projects Agency (DARPA). In the 60s, DARPA's main work was devoted to developing a method for connecting computers to each other.

The first research program dedicated to the global communication system was led by J.C.R. Licklider, who published the work "Galactic Network". In it, he predicted the possibility of a global computer connection in the future between people with instant access to programs and databases from anywhere in the world. His foresight reflects the modern structure of the international Internet. Licklider managed to convince a group of scientists of the reality of his concept, among whom was his future successor, Massachusetts Institute of Technology (MIT) researcher Lawrence G. Roberts. The newly created network had to ensure the management of a huge country in the complete absence of other means of communication, and therefore its capacity was very important.

From this point of view, the theory of packet switching for data transmission, which Leonard Kleinrock developed in 1961 and first published in July 1964, was of great importance. When packet switching occurs, the data required for transmission is broken down into parts and transmitted along different paths through the network. Each part is appended with a header containing complete information about the delivery of the packet to its destination. Packet switching provides greater channel capacity and system reliability. Suffice it to say that the use of packet technology made it possible to increase the proposed transmission speed over the channels of the projected ARPANET network from 2.4 Kbps to 50 Kbps.

In 1966, DARPA invited Larry Roberts to implement the ARPANET computer network project. The goals of the project were to study ways to maintain communications under conditions of a nuclear attack and to develop the concept of decentralized control of military and civilian facilities during wars. Decentralization was fundamentally important because it allowed the network to function even if several nodes were destroyed. To solve the problem, at the first stage it was planned to unite several large research institutions (universities) and conduct experiments in the field of computer communications.

Robert Kahn presented the general architecture of the ARPANET network, Lawrence Roberts developed topology and economic issues, Leonard Kleinrock (Network Measurement Center, UCLA) presented all network measurement and analysis tools.

In 1968, the contract for the project was awarded to Bolt Beranek and Newman (BBN), which completed it by the end of 1969 by connecting four research centers to one computer network: UCLA, SRI, UCSB and the University of Utah.
ARPANET went live in 1969. On October 20, 1969, Professor Klenreuk transmitted a message to his colleague at the University of San Francisco. The message - the word "LOG" (connect) - the professor divided into 3 stages - one letter in each. “We sent one letter and asked if it went through. When we received a positive answer, we sent a second one with the same question. We found out that this message also went through, sent the third letter, but suddenly our computer froze and the connection was interrupted,” recalled Mr. Kleinrock in an interview with the BBC.

October 20, 1969 considered the first day of the Internet.

After the experiment, all Kleinrock's research began to be funded under a special US government program and was considered one of the most promising areas in creating a defense information system. In subsequent years, the number of computers connected to the ARPANET grew rapidly.

The next step, obviously, was to expand the network throughout the country, which would provide senior military and political leaders with a reliable communication channel in case of emergency, which meant, first of all, a nuclear attack from the Soviet Union.

DARPA, inspired by the success of ARPANET, invited Robert Kahn to develop a new program, the “Internetting Project,” to study methods for interconnecting different networks.

In October 1972, Robert Kahn organized a large, highly successful demonstration of ARPANET at the International Conference on Computer Communications. This was the first public demonstration of the new network technology.

Also in 1972, the first "hot" application appeared - email.

In March, Ray Tomlinson, driven by the need to provide ARPANET developers with a simple means of coordination, wrote basic programs for sending and reading electronic messages. In July, Roberts added to these programs the ability to list messages, selectively read, save to a file, forward, and prepare a response. Since then, email has become the largest network application for more than a decade. For its time, e-mail became what the World Wide Web is today - an extremely powerful catalyst for the growth of all types of interpersonal data flows.

Interesting facts

1971: The first e-mail program was written

1972: The @ sign is invented

1973: First international communication by email. mail between England and Norway

1974: The first commercial version of ARPANET was opened - the Telnet network

1976: Robert Metcalfe, an employee of the Xerox research laboratory, creates Ethernet, the first local computer network.

1979: “Smileys” were invented - images of a face turned on its side, to give messages an emotional coloring. For example, like this: :-)

In 1974, the Internet Network Working Group (INWG), created by DARPA and led by Vinton Cerf, developed the Transmission Control Protocol/Internet Protocol (TCP/IP), the heart of the Internet.

In 1980, the INWG, led by Vinton Cerf, declared TCP/IP a standard and presented a plan for unifying existing networks, articulating its basic principles:

The networks communicate with each other using the TCP/IP protocol.

Networks are connected through special “gateways”.

All connected computers use the same addressing methods.

In 1983, DARPA mandated the use of the TCP/IP protocol on all ARPANET computers, on the basis of which the US Department of Defense divided the network into two parts: separately for military purposes - MILNET, and for scientific research - the ARPANET network.

To unite the existing 6 large computer centers and support the global academic and research communities, in 1985 the US National Science Foundation (NSF) began developing a program to build an interregional network NSFNET. Steve Wolf was invited to lead the project in 1986.

1991: The European Physical Laboratory CERN created the well-known WWW protocol - World Wide Web. This development was carried out primarily for the exchange of information among physicists. The first computer viruses spread via the Internet appear.

1993: The first Internet browser, Mosaic, is created by Marc Andreesen at the University of Illinois. The number of Internet hosts has exceeded 2 million. There are 600 sites on the network.

1996: Competition begins between the Netscape browser, created under the direction of Marc Andreesen, and Internet Explorer, developed by Microsoft. There are already 12.8 million hosts and 500 thousand websites in the world.

2002: The Internet connects 689 million people and 172 million hosts.

The Internet is a worldwide computer network that unites into a single whole tens of thousands of heterogeneous local and global computer networks connected by certain agreements (protocols). Its purpose is to provide anyone with constant access to information. Thanks to the Internet, a huge amount of information has become available. Thus, a user in any country can connect with people who share his interests or obtain valuable information from digital libraries, even if they are on the other side of the world. The necessary information will be on his computer in a matter of seconds, having passed through a long chain of intermediate computers, through cables and radios, through mountains and seas, along the bottom of the oceans and through satellites..

The Internet is funded by governments, scientific and educational institutions, businesses and millions of individuals in all parts of the world, but no one in particular owns it. The technical side of the network organization is controlled by the Federal Network Council (FNC), formed from invited volunteers, which on October 24, 1995 adopted a definition of what we mean by the term “Internet”:

The Internet is a global computer system that:

Logically interconnected by the space of global unique addresses (each computer connected to the network has its own unique address);

Able to maintain communications (exchange of information);

Ensures the operation of high-level services (services), for example, WWW, e-mail, teleconferencing, online conversations and others.

The Internet is a peer-to-peer network, i.e. all computers on the network are equal, and any computer can be connected to any other computer. Thus, any computer connected to the network can offer its services to any other.

The nodes of this worldwide connection contain computers that contain the necessary information and offer various information and communication services. These computers are called servers (hosts).

The server computer provides services to other computers requesting information, which are called clients (users, subscribers). Thus, working on the Internet requires the presence of an information transmitter, a receiver, and a communication channel between them. When we “enter” the Internet, our computer acts as a client, it requests the information we need from the server we have chosen.

In order to use road transport, people had to agree on universal rules to which it must obey. In the same way, the Internet cannot exist without uniform rules that determine the order in which computers transmit data on the network, since computers are built on different hardware platforms and are controlled by different operating systems.

The transmitted data is divided into small pieces called packets. Each packet travels through the network independently of other packets. They move from one node to another and are then forwarded to another node located “closer” to the recipient. If the packet is transmitted unsuccessfully, the transmission is repeated. It is theoretically possible that different messages will take different paths, but will still reach the recipient and be collected into a complete document. It is possible that some documents sent from England to Australia will circle the globe from east to west, and others from west to east.

Networks on the Internet all communicate with each other because all computers involved in data transfer use a single communication protocol, TCP/IP (pronounced “TCP/IP”).

TCP/IP is actually two different protocols that define different aspects of data transmission on a network:

TCP (Transmission Control Protocol) is a data transmission control protocol that uses automatic retransmission of packets containing errors; this protocol is responsible for breaking the transmitted information into packets and correctly recovering information from the recipient's packets.

Internet Protocol (IP) is an internetworking protocol responsible for addressing and allowing a packet to pass through multiple networks on its way to its final destination.

The scheme for transmitting information via the TCP / IP protocol is as follows:

The TCP protocol breaks information into packets and numbers all packets;
then, using the IP protocol, all packets are transmitted to the recipient, where, using the TCP protocol, it is checked whether all packets have been received;
After receiving all the packets, the TCP protocol places them in the right order and assembles them into a single whole.

Applications such as e-mail require that information not only be packaged and sent correctly, but that the contents of the packages and how the packages are exchanged must be clearly agreed upon. So, for example, to receive a letter you must provide the password of the owner of the mailbox, and this is a whole sequence of actions. Thus, other protocols are needed.

Hypertext Transfer Protocol

File Transfer Protocol

SMTP

Post Office Protocol 3

Protocol for receiving emails

NNTP

Teleconference protocol

In order for information to be accurately transmitted from one computer to another, it is necessary to have unique addresses that can be used to uniquely determine (identify) the recipient of the information. Just as regular mail delivers postal items to addresses that include a region, city, street, house, apartment, so on the Internet, information packages are delivered to addresses, only the address indicates not houses and streets, but network numbers to to which the recipient computer is connected and the numbers of the computers themselves in these networks.

So, every computer connected to the Internet has a physical address (IP address).

This address is deciphered from left to right. Typically, the first and second bytes are the network address, the third byte defines the subnet address, and the fourth byte is the address of the computer on the subnet.

IP addresses of connected computers.

Thus, an IP address is 4 bytes or 32 bits. If with one byte you can transfer 2 8 = 256 options, then with 4 bytes you can transfer 2 32 = 4 billion options. Thus, a maximum of 4 billion users can be connected to the Internet. Since there is currently a rapid growth in Internet users, and in addition, modern technical advances make it possible to connect not only computers, but also cell phones, televisions, and even refrigerators to the Internet, this address space is becoming very crowded. To expand it, it is planned to transfer the Internet to a 128-bit IP address (maximum users 2,128).

To some extent, a physical address is similar to a regular telephone number, however, it is inconvenient for a person to use it. Therefore, the Internet was introduced Domain Name System (DNS - Domain Name System).

Domain names and IP addresses are allocated by the International Coordination Center for Domain Names and IP Addresses (ICANN), which consists of 5 representatives from each continent.

How is the domain name system built?

The main advantage of this system is clarity. The address is divided into several fields, and neither the number of fields nor their size is limited.

The domain name system has a hierarchical structure: top-level domains - second-level domains - third-level domains. Top-level domains are of two types: geographical (two-letter - each country has a two-letter code) and administrative (three-letter).

Russia owns the geographical domain ru. Long-existing servers may belong to the su (USSR) domain.

Administrative

Type of organization

Geographical

Countries

com

commercial

ca

Canada

edu

educational

de

Domain names are read from right to left. The top level domain is located in the rightmost field. All other address fields are at the discretion of the country to which the top-level domain is assigned. For example, to the left of the country index there may be an abbreviated name of the city: spb - St. Petersburg, e-burg - Yekaterinburg, etc. Then there may be the name of the organization that has a local network. For example, et is an electrical engineering university. Next may be the name of the department: ok - HR department.

Let's consider a specific address: sch458.spb.ru. The top-level domain ru means that the computer with this name is located in the Russian Federation, then comes the second-level domain spb, which means in St. Petersburg, and only the third-level domain - sch458 - a real computer - corresponds to the organization that owns this domain address - this name on the Internet belongs to our school.

All DNS addresses are converted to IP addresses using special DNS servers, which at network nodes retrieve symbolic names from databases and replace them with physical addresses of computers. E-mail addresses and addresses of Internet information resources are also built on the basis of DNS addresses.

An IP address or the corresponding domain name allows you to uniquely identify a computer on the Internet, but the fact is that a computer can contain a lot of different information in different formats, for example, in the form of files, email messages, pages, etc. In order to accurately obtain the necessary information and in the required format, a string of characters is used, which is called the universal resource locator. This string uniquely identifies any resource on the Internet. This is exactly the line that is displayed in the “Address” field of Internet Explorer when we “walk” on the Internet

This example uses the most commonly used protocol, http://, the Hypertext Transfer Protocol.

Note: if the file name is not specified, then the default file name index.htm (index.html) or default.htm (default.html) is used.

The test offered to you contains thirteen questions, each of which has three possible answers. Questions are displayed in a separate window. When answering a question, place the mouse cursor on the selected answer option (it will appear in white) and click on it. Based on the results of the test, the number of correct answers, repeated answer attempts and the score will be displayed.

To start the test, click on the button

A network protocol is a set of rules that allows connection and data exchange between two or more computers connected to a network.

In fact, different protocols often describe only different aspects of the same type of communication; taken together, they form the so-called protocol stack. The names "protocol" and "protocol stack" also indicate the software that implements the protocol.

Who develops and standardizes all these protocols and software?

New protocols for the Internet are approved by the IETF (Internet Engineering Task Force), and other protocols are approved by IEEE (institute of Electrical and Electronics Engineers) or ISO (International Organization for Standardization). standardization). ITU-T (International Telecommunication Union) deals with telecommunication protocols and formats.

The most common classification system for network protocols is the so-called OSI model. In accordance with it, protocols are divided into 7 levels according to their purpose - from physical (generation and recognition of electrical or other signals) to application (API for transferring information by applications):

• Application layer. The upper (7th) level of the model ensures interaction between the network and the user. The layer allows user applications to access network services such as database query processing, file access, and email forwarding. It is also responsible for transmitting service information, providing applications with information about errors, and generating requests to the presentation layer. Example: HTTP, POP3, SMTP.
• Presentation layer. Level 6 is responsible for protocol conversion and data encoding/decoding. It converts application requests received from the application layer into a format for transmission over the network, and converts data received from the network into a format that applications can understand. The presentation layer can perform compression/decompression or encoding/decoding of data, as well as redirecting requests to another network resource if they cannot be processed locally.
• Session layer. Level 5 of the model is responsible for maintaining a communication session, which allows applications to interact with each other for a long time. The session layer manages session creation/termination, information exchange, task synchronization, determination of data transfer rights, and session maintenance during periods of application inactivity. Transmission synchronization is ensured by placing checkpoints in the data stream, from which the process is resumed if interaction is disrupted.
• Transport layer. The 4th level of the model is designed to deliver data without errors, losses and duplication in the sequence in which they were transmitted. It does not matter what data is transmitted, from where and where, that is, it provides the transmission mechanism itself. It divides data blocks into fragments, the size of which depends on the protocol, combines short ones into one, and splits long ones. Protocols at this level are designed for point-to-point communication. Example: TCP, UDP
• Network layer. The 3rd layer of the OSI network model is designed to determine the path for data transmission. Responsible for translating logical addresses and names into physical ones, determining the shortest routes, switching and routing, monitoring problems and congestion in the network. A network device such as a router operates at this level.
• Data Link layer. This level is often called the channel level. This layer is designed to ensure the interaction of networks at the physical layer and control errors that may occur. It packs the data received from the physical layer into frames, checks for integrity, corrects errors if necessary, and sends it to the network layer. The data link layer can communicate with one or more physical layers, monitoring and managing this interaction. The IEEE 802 specification divides this layer into 2 sublayers - MAC (Media Access Control) regulates access to the shared physical medium, LLC (Logical Link Control) provides network layer service. Switches and bridges operate at this level. In programming, this level represents the network card driver; in operating systems there is a software interface for the interaction of the channel and network layers with each other; this is not a new level, but simply an implementation of the model for a specific OS. Examples of such interfaces: ODI, NDIS
• Physical layer. The lowest level of the model is intended directly for transmitting the data stream. Transmits electrical or optical signals into a cable or radio broadcast and, accordingly, receives and converts them into data bits in accordance with digital signal encoding methods. In other words, it provides an interface between the network media and the network device. At this level, signal concentrators (hubs), signal repeaters (repeaters) and media converters operate. Physical layer functions are implemented on all devices connected to the network. On the computer side, the physical layer functions are performed by the network adapter or serial port.

Layers communicate top-down and bottom-up through interfaces and can also communicate with the same layer of another system through protocols.

Data transfer protocols

A protocol is a set of agreements that defines the exchange of data between different programs. Protocols define how messages are transmitted and errors handled in a network, and also allow the development of standards that are not tied to a specific hardware platform.

Network protocols prescribe rules for the operation of computers that are connected to the network. Οʜᴎ are built on a multi-level principle. A protocol at some level defines one of the technical rules of communication. Today, network protocols use the OSI model.

The OSI model is a seven-level logical model of network operation. The OSI model is implemented by a group of protocols and communication rules organized into several layers.

At the physical level, the physical (mechanical, electrical, optical) characteristics of communication lines are determined.

At the data link layer, the rules for using the physical layer by network nodes are determined.

The network layer is responsible for addressing and delivering messages.

The transport layer controls the order in which message components are transmitted.

The task of the session layer is to coordinate communication between two application programs running on different workstations.

The presentation layer is used to convert data from the computer's internal format to a transmission format. The application layer is the boundary between the application program and other levels.

The application layer provides a convenient communication interface for user network programs.

The TCP/IP protocol is two lower-level protocols that are the basis of Internet communications. The TCP (Transmission Control Protocol) protocol breaks the transmitted information into portions and numbers all portions. Using the IP (Internet Protocol) protocol, all parts are transmitted to the recipient. Next, using the TCP protocol, it is checked whether all parts have been received. When all portions are received, TCP places them in the required order and assembles them into a single whole.

Let's look at the most well-known protocols used on the Internet.

HTTP (Hyper Text Transfer Protocol) - hypertext transfer protocol. The HTTP protocol is used to send Web pages from one computer to another.

FTP (File Transfer Protocol) is a protocol for transferring files from a special file server to the user’s computer. FTP allows the subscriber to exchange binary and text files with any computer on the network. Having established a connection with a remote computer, the user can copy a file from the remote computer to his own or copy a file from his computer to the remote one.

POP (Post Office Protocol) is a standard mail connection protocol. POP servers process incoming mail, and the POP protocol is designed to handle mail requests from client mail programs.

The SMTP (Simple Mail Transfer Protocol) standard defines a set of rules for mail transfer. The SMTP server returns either an acknowledgment or an error message, or requests additional information.

UUCP (Unix to Unix Copy Protocol) is a now obsolete but still used data transfer protocol, incl. for email. This protocol involves the use of a packet method of information transfer, in which a client-server connection is first established and a data packet is transmitted, and then it is independently processed, viewed or prepared.

TELNET is a remote access protocol. TELNET allows the subscriber to work on any computer on the Internet as if it were his own, that is, launch programs, change the operating mode, etc. In practice, the capabilities are limited by the access level set by the administrator of the remote machine.

Data transfer protocols - concept and types. Classification and features of the category "Data transmission protocols" 2017, 2018.