Communication protocol: data transmission. Basic Internet protocols

Pre-settingBIOS

The meaning of the settingBIOSconsists in starting the computer from the device that contains the operating system distribution. In our case, we need to make sure that the computer boots fromDVD-drive orUSB-storage. For this we will useBIOS

Theoretical information about networks

Basic data transfer protocols

Basicdata transfer protocols

As you may have already noticed, the number of protocols serving the open systems interaction model is quite large. Some of these protocols, especially the low-level ones, are not particularly interesting in terms of getting to know how they work. But the operating principle and capabilities of other protocols are still worth knowing, especially such as TCP/IP, UDP, POP3, etc.

Protocol stacks

As mentioned above, protocol stacks are often responsible for organizing the work of all layers of the ISO/OSI model. The advantage of using protocol stacks is that all protocols included in the stack are developed by one manufacturer, that is, they are able to work as quickly and efficiently as possible.

During the existence of networks, several different protocol stacks have been developed, among which the most popular are TCP/IP, IPX/SPX, NetBIOS/SMB, Novell NetWare, DECnet, etc.

The stacks contain protocols that operate at different levels of the ISO/OSI model, but usually only three types of protocols are distinguished: transport, network And applied.

The advantage of using protocol stacks is that the protocols operating at the lower levels use long-established and popular network protocols, such as Ethernet, FDDI, etc. Thanks to the hardware implementation of these protocols, it becomes possible to use the same equipment for different types of networks and thereby achieving their compatibility at the hardware level. As for high-level protocols, each of the stacks has its own advantages and disadvantages, and very often it happens that there is no strict binding “one protocol - one level”, that is, one protocol can work at two or three levels at once.

Binding

An important point in the operation of network equipment, in particular a network adapter, is the binding of protocols. In practice, it allows you to use different protocol stacks when servicing one network adapter. For example, you can use the TCP/IP and IPX/SPX stacks at the same time, and if an error occurs when trying to establish communication with the recipient using the first stack, it automatically switches to using the protocol from the next stack. In this case, the binding order is an important point, since it clearly affects the use of one or another protocol from different stacks.

Regardless of how much network adapters installed on a computer, binding can be carried out either “one to several” or “several to one”, that is, one protocol stack can be tied to several adapters at once or several stacks to one adapter.

TCP/IP

TCP/IP protocol stack (Transmission Control Protocol/Internet Protocol ) is the most common and functional today. It works in local networks of any size. In addition, this is the only protocol that allows the global Internet to operate.

The protocol was created in the 70s of the last century by the US Department of Defense. It was with his input that the development of a protocol began, the purpose of which was to connect any two computers, no matter how far they were. Of course, they pursued their goal - to ensure constant communication with the control center, even if everything around was destroyed as a result of hostilities. As a result, the global ARPAnet network was formed, which the ministry actively used for its own purposes.

The impetus for further improvement and widespread distribution of the TCP/IP stack was the fact that its support was implemented in computers with operating UNIX system. As a result, the popularity of the TCP/IP protocol has increased.

The TCP/IP protocol stack includes quite a lot of protocols that run on various levels, but it got its name thanks to two protocols - TCP and IP.

TCP (Transmission Control Protocol) is a transport protocol designed to control data transmission in networks using the TCP/IP protocol stack. IP (Internet Protocol) - protocol network layer, designed to deliver data over a composite network using one of the transport protocols, such as TCP or UDP. The lower level of the TCP/IP stack uses standard data transfer protocols, which makes it possible to use it in networks using any network technology and on computers with any operating system.

Initially TCP protocol/IP was developed for use in global networks, which is why it is as flexible as possible. In particular, thanks to the ability to fragment packets, data, despite the quality of the communication channel, in any case reaches the addressee. In addition, thanks to the presence of the IP protocol, data transfer between dissimilar network segments becomes possible.

The disadvantage of the TCP/IP protocol is the complexity of network administration. Thus, for the normal functioning of the network, additional servers are required, for example DNS, DHCP, etc., maintaining the operation of which takes up most of the system administrator’s time.

IPX/SPX

The IPX/SPX (Internetwork Packet Exchange/Sequenced Packet Exchange) protocol stack is developed and owned by Novell. It was designed for the needs of the operating system Novell NetWare, which until recently occupied one of the leading positions among server operating systems.

The IPX and SPX protocols operate at the network and transport layers of the ISO/OSI model, respectively, and therefore complement each other perfectly. The IPX protocol can transmit data using datagrams using network routing information.

However, in order to transmit data along the found route, a connection must first be established between the sender and the recipient. This is what the SPX protocol or any other transport protocol that works in tandem with IPX does.

Unfortunately, the IPX/SPX protocol stack is initially designed to serve small networks, so large networks its use is ineffective: excessive use of broadcasting on low-speed communication lines is unacceptable.

NetBIOS/SMB

A fairly popular protocol stack developed by IBM and Microsoft, respectively, aimed at use in the products of these companies. Like TCP/IP, standard protocols such as Ethernet, Token Ring and others operate at the physical and data link levels of the NetBIOS/SMB stack, which makes it possible to use it in tandem with any active network equipment. On protocols work at the upper levels NetBIOS (Network Basic Input/Output System) and SMB (Server Message Block).

The NetBIOS protocol was developed in the mid-80s of the last century, but was soon replaced by the more functional NetBEUI (NetBIOS Extended User Interface) protocol, which allows for very efficient information exchange in networks consisting of no more than 200 computers.

For communication between computers to be possible, each of them must have a logical name. To exchange data between computers, logical names are used that are assigned to computers dynamically when they are connected to the network. In this case, the name table is distributed to each computer on the network. It also supports working with group names, which allows you to transfer data to several recipients at once.

The main advantages of the NetBEUI protocol are speed and very low resource requirements. If you need to organize quick exchange data in small network, consisting of one segment, there is no better protocol for this. In addition, to deliver messages established connection is not mandatory requirement: In the case of no connection, the protocol uses the datagram method, where the message is equipped with the address of the recipient and the sender and “goes on the road”, moving from one computer to another.

However, NetBEUI also has a significant drawback: it is completely devoid of the concept of packet routing, so its use in complex composite networks does not make sense.

As for the SMB (Server Message Block) protocol, it is used to organize the operation of the network on the three most high levels- session, presentation and application layers. It is when you use it that access to files, printers and other network resources becomes possible. This protocol has been improved several times (three versions have been released), which makes it possible to use it even in such modern operating systems as Microsoft Vista and Windows 7. The SMB protocol is universal and can work in tandem with almost any transport protocol, such as TCP/IP and SPX.

HTTP

Perhaps the most popular of the protocols, with which tens of millions of Internet users around the world work every day.

The HTTP (HyperText Transfer Protocol) protocol was developed specifically for the Internet: to receive and transmit data over the Internet. It works using client-server technology, which means that there are clients requesting information (for example, viewing the contents of a web page), and a server part that processes these requests and sends a response.

HTTP works at the application level. This means that this protocol must use the services transport protocol, which by default is TCP.

First version HTTP protocol was developed back in the early 90s of the last century and at that time completely satisfied users with its capabilities. But over time, when graphics and dynamic images came to the Internet, the protocol’s capabilities became insufficient and it gradually began to change.

In its work, the protocol uses the concept of URI (Uniform Resource Identifier) ​​- a unique resource identifier, which is usually the address of a web page, file or any other logical object. At the same time, the URI supports working with parameters, which allows you to expand the functionality of the protocol. So, using parameters, you can specify in what format and encoding you want to receive a response from the server.

This in turn allows you to transfer not only text documents, but also any binary data.

The main disadvantage of the HTTP protocol is the excessive volume text information, necessary so that the client can correctly display the response received from the server. If the content of a web page is large, this may create unnecessary high traffic, which impairs the perception of information. In addition, the protocol is completely devoid of any stateful mechanisms, making it impossible to navigate web pages using the HTTP protocol alone. For this reason, third-party protocols are used along with the HTTP protocol, or the user needs to work with a browser that processes HTTP requests.

FTP

FTP protocol ( File Transfer Protocol) is the “brother” of the HTTP protocol, only, unlike the latter, it works not with text or binary data, but with files.

This protocol is one of the oldest: it appeared in the early 70s of the last century. Like HTTP, it operates at the application layer and uses the TCP protocol as its transport protocol. Its main task is to transfer files from/to an FTP server.

The FTP protocol is a set of commands that describe the rules for connecting and exchanging data. In this case, commands and direct data are transmitted using various ports. Ports 21 and 20 are used as standard ports: the first is for data transmission, the second is for command transmission. In addition, ports can be dynamic.

The size of files transferred using the FTP protocol is not limited. There is also a mechanism for resuming the file if the connection is interrupted during the transfer process.

The main disadvantage of the FTP protocol is the lack of data encryption mechanisms, which makes it possible to intercept the initial traffic and use it to determine the user name and password for connecting to the FTP server. To avoid this situation, it is used in parallel SSL protocol, with which the data is encrypted.

POP3 and SMTP

Using email for messaging has long been an alternative to regular mail. E-mail much more efficient and faster. Its use is made possible thanks to the POP3 (Post Office Protocol Version 3) and SMTP (Simple Mail Transfer Protocol) protocols.

The POP3 protocol operates at the application layer and is used to receive electronic messages from mailbox on the mail server. At the same time, it uses one of the ports and the TCP transport protocol.

Communication session with mail server divided into three stages: authorization, transaction And update. User authorization occurs when connecting to the mail server, for which any mail client, supporting POP3 protocol. During the transaction phase, the client requests the server to perform a desired action, such as obtaining information about the number of messages, receiving the messages themselves, or deleting them. The update process is designed to fulfill the client's request. Once the update is complete, the communication session ends until the next connection request arrives.

The POP3 protocol only allows you to receive electronic messages, and to send them you have to use another protocol, which is most often used SMTP, more precisely, its improved version - ESMTP (Extended SMTP).

Like POP3, SMTP operates at the application layer, so it requires the services of a transport protocol, which is the TCP protocol. In this case, sending electronic messages also occurs using one of the ports, for example port 25.

IMAP

IMAP (Interactive Mail Access Protocol) - one more postal protocol, created based on the POP3 protocol. It was developed later than the POP3 protocol. As a result, all the shortcomings were taken into account and added large number new popular functions.

The most useful among them is the ability to partially download messages, analyzing the contents of which you can effectively set up filters that sort messages or filter out spam.

Another important function is a mechanism for optimizing the use of channels through which messages are transmitted. These channels are not always fast and unloaded, so having such a feature makes the user's life much easier. It is also possible to transmit messages in small parts, which is very useful when the message size is large, for example 5-10 MB.

SLIP

The SLIP (Serial Line Internet Protocol) data transfer protocol was created specifically for organizing a permanent connection to the Internet using an existing telephone line and a regular modem. Due to the high cost, few users can afford this type of connection. As a rule, such a connection is created in organizations that have a server on which the organization’s web page and other resources (database, files) are located.

This protocol works together with the TCP/IP protocol and is at a lower level. Before information from the modem is processed by the TCP/IP protocol, it is pre-processed by the SLIP protocol. After completing all the necessary steps, it creates another packet and transmits it to TCP/IP.

RRR

The Point-to-Point Protocol (PPP) does the same job as SLIP described above. However, it performs these functions better, since it has additional features. In addition, unlike SLIP, PPP can interact not only with TCP/IP, but also with IPX/SPX, NetBIOS, DHCP, which are widely used in local networks. The PPP protocol is also more widespread due to its use on Internet servers with an installed operating system Windows family NT (SLIP is used to connect to servers running on the UNIX operating system).

X.25

The X.25 protocol, which was created in 1976 and refined in 1984, operates at the physical, data link and network layers of the ISO/OSI interoperability model. It was developed by a consortium consisting of representatives of many telephone companies, and was created specifically for use on existing telephone lines.

When X.25 was developed, a digital telephone line was rare—mostly analog was used. For this reason, it has an error detection and correction system, which significantly increases the reliability of communication. At the same time, this system slows down the data transfer rate (maximum - 64 Kbps). However, this fact does not prevent it from being used where high reliability is primarily required, for example in the banking system.

Frame Relay

Frame Relay is another protocol designed for transmitting data over a telephone line. In addition to high reliability (like X.25), it has additional useful innovations. Since the transmitted data may be in video, audio or electronic format, it is possible to select the priority of the transmitted content.

Another feature of the Frame Relay protocol is its speed, which reaches 45 Mbit/s.

AppleTalk

The AppleTalk protocol is proprietary to Apple Computer. It was designed to establish communication between Macintosh computers.

Like TCP/IP, AppleTalk is a set of protocols, each of which is responsible for operating a specific layer of the ISO/OSI model.

Unlike the TCP/IP and IPX/SPX protocols, the AppleTalk protocol stack uses its own implementation of the physical and data link layers rather than ISO/OSI model protocols.

Let's look at some protocols in the AppleTalk stack.

· DDP (Datagram Delivery Protocol) - is responsible for the operation of the network layer. Its main purpose is to organize and maintain the data transfer process without pre-installation connections between computers.

· RTMP (Routing Table Maintenance Protocol) - works with routing tables AppleTalk.Any such table contains information about each segment to which messages can be delivered. The table consists of router (port) numbers that can deliver a message to the selected computer, the number of routers, parameters of the selected network segments (speed, congestion, etc.).

· NBP (Name Binding Protocol) - is responsible for addressing, which comes down to binding the logical name of a computer to a physical address on the network. In addition to the process of linking a name, he is responsible for registering, confirming, erasing and searching for this name.

· ZIP (Zone Information Protocol) - works in tandem with the NBP protocol, helping it search for a name in workgroups, or zones. To do this, it uses information from the nearest router, which creates a request throughout the network where computers belonging to a given workgroup may be located.

· ATP (AppleTalk Transaction Protocol) is one of the transport layer protocols that is responsible for transactions. Transaction - this is a set of a request, a response to this request and identification number, which is assigned to this set. An example of a transaction would be a message about the delivery of data from one computer to another. In addition, ATP is able to split large packages into smaller ones and then assemble them after confirmation of acceptance or delivery.

· ADSP (AppleTalk Data Stream Protocol) - protocol similar to ATP. He is responsible for delivering packages. However, in in this case there is not one transaction, but a guaranteed delivery, which may entail several transactions. In addition, the protocol ensures that data will not be lost or duplicated during delivery.

Data transfer protocol- set of interface conventions logic level, which define the exchange of data between different programs. These agreements define a uniform way of transmitting messages and handling errors during the interaction of software of spatially distributed equipment connected by one or another interface.

The signaling protocol is used to control the connection - for example, establishment, forwarding, disconnection. Examples of protocols: RTSP, SIP. Protocols such as RTP are used for data transfer.

Network protocol- a set of rules and actions (sequence of actions) that allows connection and data exchange between two or more devices connected to the network.

Different protocols often describe only different sides one type of connection. The names "protocol" and "protocol stack" also indicate the software that implements the protocol.

The most well-known protocols used on the Internet:

• HTTP (Hyper Text Transfer Protocol) is a transfer protocol

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;

provides detection and correction of errors that occur during the transmission of information. 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-byte organization. Having received an asynchronous bit from the computer, the modem removes the 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, reliability and throughput channel.

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 volume 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 transmits all file attributes and multiple 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 time, 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 transmitting the entire block does the receiver transmit checksum blocks, and if necessary, their control transmission is carried out. Zmodem also transmits file attributes, sends several files in one packet, and first of all, recovery after a connection loss is introduced. It is almost ideal for modems with hardware error correction, because... spends minimal time checking the correctness of the transmission.

First of all, we will define the areas of application of data transmission channels in the electric power industry and the tasks that are solved with their help. Currently, the main areas of application of data transmission systems include relay protection and automation systems (RPA), dispatch and automated technological control of electric power facilities (ATC), as well as automated energy metering systems. Within the framework of these systems, the following tasks are solved:

ASTU systems

1. Transfer data between local devices telemechanics (TM), relay protection and automation devices and a central transceiver station (CPS).
2. Data transfer between the facility and the control center.
3. Data transfer between dispatch centers.

Accounting systems

1. Transferring data from metering devices to data collection and transmission devices (DCD).
2. Transferring data from the USPD to the server.

Regarding relay protection and automation systems, the following can be noted: despite the fact that the collection of data from relay protection and automation devices in automated control systems in digital format began to be implemented from the moment of its appearance digital devices Relay protection and automation, connections between devices are still organized by analog circuits.

In relay protection and automation systems, information transmission systems can perform the following functions:

1. Broadcast discrete signals.
2. Data transfer between relay protection and control devices and control center.

Another important transmission channel, common to both relay protection systems and automated control and metering systems, is the channel through which measurements are transmitted from current and voltage instrument transformers. Until recently, the introduction of digital communication protocols on this level it was not discussed, however, bearing in mind the emergence of a protocol for transmitting instantaneous current and voltage values ​​IEC 61850-9-2, it is also worth dwelling on the problems of this information channel.

We will sequentially consider each of the above information transfer functions and existing approaches to their implementation.

Transfer of measurements from CTs and VTs

Transmission of signals from current (CT) and voltage (VT) instrument transformers is carried out via cables with copper conductors AC and voltage accordingly. This method is characterized by problems that are often mentioned in the literature:

• large branching and length of copper cables, leading to the need to use a large number of auxiliary equipment (test blocks, terminal blocks, etc.) and, as a consequence, to an increase in the cost of systems and the complexity of installation and commissioning;
• exposure of measuring circuits to electromagnetic interference;
• complexity or lack of ability to monitor serviceability measuring channel at the pace of the process, the difficulty of finding the location of damage;
• the influence of the resistance of the measuring circuits on the accuracy of measurements and the need to match the power of the CT/VT with the resistance of the circuits and the load of the receiver.

Transferring discrete signals between devices

The transmission of discrete signals between devices is traditionally carried out by applying operational voltage by closing the output relay of one device to the discrete input of another.

This method of transmitting information has the following disadvantages:

• a large number of control cables are required, laid between cabinets with equipment;
• devices must have a large number of discrete inputs and outputs;
• the number of transmitted signals is limited to a certain number of discrete inputs and outputs;
• there is no ability to control communication between devices;
• Maybe false positive discrete input of the device in case of a ground fault in the signal transmission circuit;
• circuits are susceptible to electromagnetic interference;
• difficulty in expanding relay protection systems.

Data transfer between relay protection and control systems

Data exchange between the relay protection and control systems and the control center at the facility is carried out in digital format. However, due to the need to integrate a large number of various devices this method has the following features:

• the existence of a large number of different data transfer protocols, and the DSP device must support all these protocols for the successful integration of any devices;
• absence unified system names of data, leading to the need to maintain a large amount of descriptive documentation, as well as to difficulties and errors during setup;
• relatively low data transfer rate due to the presence of a large number of serial interfaces.

Data transfer between the facility's central control center and the dispatch center

Data transfer between the facility and the control center is also carried out in digital format. Typically, IEC 60870-101/104 protocols are used for these purposes. Features of the implementation of these communication systems:

• the need to transmit data in supervisory control protocols, which are usually different from the protocols used at the substation;
• transmission of a limited amount of information, which is due to the need to reassign all signals from one protocol to another, and, as a result, the loss of some data, the transmission of which was not considered appropriate at the design stage;
• lack of uniform signal names within the facility and in network control centers (NCC), leading to difficulty in setting up and tracking errors.

Let's turn to Fig. 1, where circuit diagram organization of data transfer. It should be noted that there are a large number of proprietary protocols. Widespread distribution of such protocols requires, firstly, a large number of gateways (converters), and secondly, good qualifications and experience of personnel in working with various protocols. Ultimately, this leads to system complexity and problems during operation and expansion.

Rice. 1. Data transmission organization diagram.

Let us briefly describe the standard protocols shown.

Modbus

Modbus is one of the most common network protocols for the integration of relay protection and automation devices into the automated control system system, built on the “client-server” architecture. The popularity of this protocol is largely due to its openness, which is why most devices support this protocol.

The Modbus protocol can be used to transmit data over serial communication lines RS-485, RS-433, RS-232, as well as the TCP/IP network (Modbus TCP).

The Modbus standard consists of three parts describing the application layer of the protocol, the specification of the channel and physical levels, as well as the ADU specification for transport over the TCP/IP stack.

To the advantages this standard should be attributed to its widespread use and the relative simplicity of implementing systems based on it. The disadvantages are the lack of the possibility of prompt signaling from the end device to the master if necessary. In addition, the standard does not allow end devices to exchange fixed data with each other without the participation of a master. This significantly limits the applicability of MODBUS solutions in real-time control systems.

IEC 60870-5-101/103/104

IEC 60870-5-101 is a telemechanics protocol designed for transmitting TM signals to automatic control systems. It is also built on a client-server architecture and is designed to transmit data via RS-232/485 serial communication lines.

The IEC 60870-5-104 protocol is an extension of the 101 protocol and regulates the use network access via TCP/IP protocol. IEC 60870-5-101/104 standards do not imply the presence of a semantic data model.

The IEC 60870-5-103 protocol is designed to enable the integration of relay protection and automation devices into the control system of a power facility. Unlike IEC 60870-5-101/104 standards, it defines semantics for a fixed set of data generated by relay protection devices. One of the main disadvantages of the IEC 60870-5-103 protocol is the relatively low data transfer rate.

IEC 60870-5-101/103/104 protocols provide fairly high functionality when solving problems of telecontrol, telesignaling and telemetering, and integrating these devices into control systems. Unlike Modbus, they also allow sporadic data transfer from devices.

The protocols, as in the previous case, are based on the exchange of signal tables, and the types of data exchanged are strictly fixed.

In general, protocols are well suited for solving the range of problems described above, but they have a number of disadvantages:

1. Data transfer is carried out in two stages: assignment of indexed communication objects to application objects; assigning application objects to variables in an application database or program. Thus, there is no semantic connection (in whole or in part) between the transmitted data and the data objects of the application functions.
2. The protocols do not provide the ability to transmit real-time signals. In this case, real-time signals mean data that must be transmitted at the pace of the process with the minimum possible time delays, which include, for example, shutdown commands, transmission of instantaneous current and voltage values ​​from instrument transformers. When transmitting such signals, delays in the communication channel are critical. Please note that this item is not related to the ability to synchronize devices with a single time server, but concerns issues of data transfer speed between devices.

DNP3

In Russia, this standard is not widespread, but some automation devices still support it. For a long time The protocol has not been standardized, but is now approved as an IEEE-1815 standard.

DNP3 supports both RS-232/485 serial communications and TCP/IP networks. The protocol describes three layers of the OSI model: application, data link and physical. His distinctive feature is the ability to transfer data both from the master device to the slave device, and between slave devices. DNP3 also supports sporadic data transfer from slave devices.

Data transmission is based, as in the case of IEC-101/104, on the principle of transmitting a table of values. In this case, in order to optimize the use of communication resources, not the entire database is sent, but only its variable part.

An important difference between the DNP3 protocol and those discussed earlier is the attempt to describe the data model objectively and the independence of data objects from the transmitted messages. To describe the data structure in DNP3, an XML description of the information model is used.

A detailed comparison of the protocols is given, but we are in Table. 1 we provide brief excerpts in relation to the protocols discussed above.

Table 1. Data transfer protocols

Conclusions

From the presented brief analysis it is clear that existing communication protocols quite successfully allow the implementation of tasks of supervisory control / data integration into control systems, but do not allow the implementation of real-time functions (such as the transmission of discrete signals between relay protection and automation devices, the transmission of instantaneous values ​​of currents and voltages).

A large number of proprietary protocols complicates the process of integrating devices into a single system:

• The protocols must be supported by the controller and the central processing station, which requires the implementation of support for a large number of protocols in the USO and central processing station at the same time and leads to increased equipment costs.
• Integration of devices using proprietary protocols requires qualification of commissioning personnel in working with each of them.
• Reassigning signals from proprietary protocols to common industry protocols and back often leads to loss of information, including additional information(such as timestamps, quality stamps, etc.).

When transferring data, a large number of serial interfaces are still used, which imposes restrictions on the data transfer speed, the volume of transferred data and the number of devices simultaneously included in the information network.

The transmission of critical control commands (commands for disconnecting circuit breakers from relay protection and automation devices, operational interlocks, etc.) and digitized instantaneous values ​​of currents and voltages is impossible in digital format due to the unsuitability of existing communication protocols for transmitting this kind of information.

It should be noted that existing communication protocols do not impose requirements for a formal description of protocol configurations and transmitted signals, and therefore the design documentation for automated control system systems contains only a description of signals on solid media.

Basic principles when creating the IEC 61850 standard

Work on the IEC 61850 standard began in 1995, and was initially carried out by two independent, parallel groups: one of them, formed by UCA, was developing general object models for substation equipment (GOMFSE); the second, formed within the technical committee 57 of the IEC, was engaged in the creation of a standard for a data transmission protocol for substations.

Later, in 1997, the work of both groups was combined under the auspices of Working Group 10 of IEC TC 57 and became the basis of the IEC 61850 standard.

The standard is based on three provisions:

• It must be technologically independent, that is, regardless of technological progress, the standard must be subject to minimal changes.
• It must be flexible, that is, it must allow different problems to be solved using the same standardized mechanisms.
• It must be extensible.

The development of the first edition of the standard took about 10 years. By meeting these requirements, the standard allows you to meet the changing needs of the power industry and use the latest advances in computer, communication and measurement technologies.

To date, IEC 61850 consists of 25 different documents (including those in development) that cover a wide range of topics and make it much more than just a specification of a number of communication protocols. Let us note the main features of the standard:

• Determines not only how information should be exchanged, but also what information should be exchanged. The standard describes abstract models of an object's equipment and the functions it performs. Information model, which forms the basis of the standard, is represented in the form of classes of data objects, data attributes, abstract services and descriptions of the relationships between them.
• Defines the process of designing and setting up systems.
• Defines the System Configuration Description Language (SCL). This language provides the ability to exchange information about device configurations in a standardized format between software from different manufacturers.
• Describes equipment testing and acceptance procedures.

When working with IEC 61850, it is necessary to understand that the standard:

• does not describe specific implementation methodologies, communication architectures, or requirements for specific products;
• does not standardize the functionality and algorithms of devices,
• focuses on describing the functionality of primary and secondary equipment, protection, control and automation functions, visible from the outside.

Of course, such a large-scale work cannot be ideal. Examples of inaccuracies and shortcomings in the standard include, in particular, the lack of methods for formally checking compliance with the requirements of the standard, a number of technical inaccuracies in the description of parameters and approaches to their processing, and so on. These issues will be discussed in more detail in future publications.

The disadvantages of the standard are often the lack of specificity in the description of requirements and too much freedom in implementation, which, according to the developers, is precisely one of its main advantages.

References

1. Bagleybter O.I. Current transformer in relay protection networks. Countering the saturation of CTs with the aperiodic component of the short-circuit current // Electrical Engineering News. 2008. No. 5(53).
2. Schaub P., Haywood J., Ingram D., Kenwrick A., Dusha G. Test and Evaluation of Non Conventional Instrument Transformers and Sampled Value Process Bus on Powerlink’s Transmission Network. SEAPAC 2011. CIGRE Australia Panel B5.
3. Shevtsov M.V. Transmission of discrete signals between URZA via digital communication channels // Relayman. 2009. No. 1.
4. Schwarz K. Comparison of IEC 60870-5-101/-103/-104, DNP3, and IEC 60870-6-TASE.2 with IEC 61850 (electronic document: http://bit.ly/NOHn8L).
5. Brunner C., Apostolov A. IEC 61850 Brand New World. PAC World Magazine. Summer 2007.
6. IEC 61850-1: Introduction and Overview.

1. protocol - A document that provides objective evidence of work done or results achieved. Construction terminology
2. protocol - -a, m. 1. A document containing a record of everything that happened at a meeting, meeting, trial, etc. Protocol of interrogation. Keep minutes of the meeting. 2. A document certifying something. fact. We drew up an inspection report and recorded the testimony of witnesses. Small academic dictionary
3. protocol - protocol gen. n. -a, already at Kurakin, 1707; see Christiani 30 et seq. Via French protosole or nem. Protokoll (from 1536; see Schultz-Basler 2, 708) from Middle Latin. protosollum from Greek. πρωτόκολλον “a sheet glued to the front on a papyrus scroll”; see Smirnov 247. Etymological Dictionary of Max Vasmer
4. Protocol - An act drawn up by authorized officials to certify certain events. P. are judicial and administrative. Encyclopedic Dictionary of Brockhaus and Efron
5. protocol - noun, number of synonyms: 6 administrative protocol 1 act 21 document 82 internet protocol 1 protocol 1 agreement 41 Dictionary of Russian synonyms
6. protocol - protocol m. 1. A document recording what is happening (at a meeting, session, interrogation, etc.). 2. A document certifying any fact or incident. 3. A written agreement between states (usually on private issues). Explanatory Dictionary by Efremova
7. PROTOCOL - (from the French protocole - first sheet) 1) a document signed by the contracting parties and recording the results of negotiations before concluding an agreement; 2) a record of what happened at the meeting, indicating the participants and decisions made. Economic dictionary of terms
8. protocol - PROTOCOL, a, m. 1. A document recording everything that happens at a meeting, meeting, interrogation. P. meetings. P. interrogation. News item. Enter in item 2. Document, to-Crimea is certified by some. fact. P. medical autopsy. 3. Act on violation of public order. Ozhegov's Explanatory Dictionary
9. protocol - Protocol, protocols, protocol, protocols, protocol, protocols, protocol, protocols, protocol, protocols, protocol, protocols Zaliznyak's Grammar Dictionary
10. PROTOCOL - PROTOCOL (French protocole, from Greek protokollon - the first page of a manuscript) - 1) an official document that records any factual circumstances (the course of a meeting, procedural or investigative actions, a court hearing). Large encyclopedic dictionary
11. protocol - (French protocole, from the gr. protokollon - the first page of a manuscript) 1) an official document in which any factual circumstances are recorded (the course of a meeting, procedural or investigative actions, a court hearing); 2) in international law... Large legal dictionary
12. protocol - orf. protocol, -a Lopatin's spelling dictionary
13. Protocol - (from the Greek protókollon - the first sheet glued to the scroll of a manuscript) 1) in the USSR, an official document that records: the fact of an administrative offense; progress and results of procedural actions during the investigation of a criminal case... Great Soviet Encyclopedia
14. PROTOCOL - PROTOCOL (from the Greek protokollon - first sheet) - English. report/record; German Protokoll. 1. A document containing a description of the actions taken and the facts established. Sociological Dictionary
15. protocol - A document signed by the parties on the results of negotiations before concluding a contract or agreement. Great Accounting Dictionary
16. protocol - Borrowing from French, in which protocole goes back to the Greek protokollon (protos - “first” and kollan - “to glue”). The literal meaning of the word in Greek is "the first sheet of the manuscript that is pasted," which usually included the owner, the time, the name of the copyist, etc. Krylov's etymological dictionary
17. protocol - Protocol, m. [modern Greek. protokollon – the first sheet to which the next one in the scroll is glued] (official). 1. An official document containing a record of everything that was said, done and decided at a meeting, session, interrogation. Protocol of the court session. Large dictionary of foreign words
18. protocol - PROTOCOL -a; m. [from Greek. prōtokollon - the first sheet glued to the scroll of a manuscript] 1. A document containing a brief record of the proceedings of a meeting, session, etc. P. interrogation. Lead the meeting. Entry in the protocol. Make an extract from the protocol. Bring in... Kuznetsov's Explanatory Dictionary
19. protocol - PROTOK'OL, protocol, male. (·Modern Greek protokollon - the first sheet to which the next one in the scroll is glued) (official). 1. An official document containing a record of everything that was said, done and decided at a meeting, session, interrogation. Ushakov's Explanatory Dictionary
20. protocol - PROTOCOL m. a judicial brief, outlining the case, application of the laws and decision; but a protocol is often drawn up instead of a journal, a resolution in general, and even, in the form of a resolution on the issuance of money, etc., on the basis of a journal, doubly so. Dahl's Explanatory Dictionary