Network technology is an agreed set of standard protocols and software and hardware that implements them (for example, network adapters, drivers, cables and connectors), sufficient for building a computer network. The epithet “sufficient” emphasizes the fact that this set is the minimum set of tools with which you can build a workable network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to the Ethernet standard protocols, the use of IP protocol, as well as special communication devices - routers. The improved network will most likely be more reliable and faster, but at the expense of add-ons to the Ethernet technology that formed the basis of the network.
The term "network technology" is most often used in the narrow sense described above, but sometimes its extended interpretation is also used as any set of tools and rules for building a network, for example, "end-to-end routing technology", "technology for creating a secure channel", "IP technology. networks ".
The protocols on the basis of which a network of a certain technology (in the narrow sense) is built were specially developed for collaboration, therefore, no additional effort is required from the network developer to organize their interaction. Sometimes networking technologies are called basic technologies, bearing in mind that on their basis the basis of any network is built. Examples of basic network technologies include, along with Ethernet, such well-known LAN technologies as Token Ring and FDDI, or X.25 and frame relay technologies. To get a workable network, in this case, it is enough to purchase software and hardware related to one basic technology - network adapters with drivers, hubs, switches, cabling, etc. - and connect them in accordance with the requirements of the standard for this technology.
Creation of standard technologies of local networks
In the mid-1980s, the state of affairs in local networks began to change dramatically. The standard technologies for connecting computers into a network - Ethernet, Arcnet, Token Ring - have been approved. Personal computers served as a powerful incentive for their development. These mass-produced products were ideal elements for building networks - on the one hand, they were powerful enough to run network software, and on the other, they clearly needed to combine their computing power to solve complex problems, as well as separate expensive peripherals and disk arrays. Therefore, personal computers began to prevail in local networks, not only as client computers, but also as data storage and processing centers, that is, network servers, displacing mini-computers and mainframes from these familiar roles.
Standard networking technologies have turned the process of building a local area network from an art to a chore. To create a network, it was enough to purchase network adapters of the appropriate standard, for example, Ethernet, a standard cable, connect the adapters to the cable with standard connectors, and install one of the popular network operating systems, for example, NetWare, on the computer. After that, the network began to work and the connection of each new computer did not cause any problems - naturally, if a network adapter of the same technology was installed on it.
LANs, in comparison with wide area networks, have brought a lot of new things to the way users work. Access to shared resources has become much more convenient - the user can simply view the lists of available resources, and not remember their identifiers or names. After connecting to a remote resource, it was possible to work with it using the commands already familiar to the user when working with local resources. The consequence and at the same time the driving force behind this progress was the emergence of a huge number of non-professional users who did not need to learn special (and rather complex) commands for network work at all. And the developers of local networks got the opportunity to realize all these conveniences as a result of the appearance of high-quality cable communication lines, on which even the first-generation network adapters provided data transfer rates up to 10 Mbps.
Of course, the developers of global networks could not even dream of such speeds - they had to use those communication channels that were available, since laying new cable systems for computer networks thousands of kilometers long would require colossal capital investments. And "at hand" were only telephone communication channels, poorly suited for high-speed transmission of discrete data - the speed of 1200 bit / s was a good achievement for them. Therefore, the economical use of the bandwidth of communication channels was often the main criterion for the efficiency of data transmission methods in global networks. Under these conditions, various procedures for transparent access to remote resources, standard for local networks, have long remained an unaffordable luxury for global networks.
Modern tendencies
Today, computer networks continue to evolve, and quite rapidly. The gap between local and global networks is constantly narrowing, largely due to the emergence of high-speed territorial communication channels, which are not inferior in quality to the cable systems of local networks. In global networks, resource access services appear, as convenient and transparent as local network services. The most popular global network, the Internet, demonstrates such examples in large numbers.
Local networks are also changing. Instead of a passive cable connecting computers, a large number of various communication equipment appeared in them - switches, routers, gateways. Thanks to such equipment, it became possible to build large corporate networks with thousands of computers and a complex structure. Interest in large computers has rekindled, mainly because after the euphoria over ease of working with personal computers has subsided, it has become clear that systems with hundreds of servers are more difficult to maintain than a few large computers. Therefore, in a new round of the evolutionary spiral, mainframes began to return to corporate computing systems, but already as full-fledged network nodes that support Ethernet or Token Ring, as well as the TCP / IP protocol stack, which has become the de facto network standard thanks to the Internet.
Another very important trend has emerged, affecting both local and global networks. They began to process information uncharacteristic of computer networks - voice, video images, pictures. This required changes to the way protocols, network operating systems, and communications equipment work. The complexity of transmitting such multimedia information over a network is due to its sensitivity to delays in the transmission of data packets - delays usually lead to distortion of such information at the end nodes of the network. Since traditional computer networking services, such as file transfer or e-mail, generate latency-sensitive traffic and all network elements were designed with this in mind, the emergence of real-time traffic has led to major problems.
Today, these problems are solved in various ways, including with the help of ATM technology specially designed for the transfer of various types of traffic.However, despite significant efforts in this direction, there is still a long way to an acceptable solution to the problem, and much remains to be done in this area. to achieve the cherished goal - the merger of technologies not only local and global networks, but also technologies of any information networks - computing, telephone, television, etc. Although today this idea seems to be a utopia, serious experts believe that the prerequisites for such a synthesis exist, and their opinions differ only in the assessment of the approximate timing of such a merger - the terms from 10 to 25 years are called. Moreover, it is believed that the basis for the merger will be the packet switching technology used today in computer networks, and not the circuit switching technology used in telephony, which, probably, should increase the interest in networks of this type.
Test and course work
on Information Systems in Economics on topic number 69:
"Network technologies Ethernet, Token Ring, FDDI and X.25"
Completed: student gr. 720753 Avdeeva D.M.
Checked by: Associate Professor, Ph.D. Ognyanovich A.V.
Introduction ………………………………………………………………………… ... 3
1. The concept of network technologies …………………………………………… ... 5
2. Ethernet technology ……………………………………………………… ..7
3. Token Ring technology ……………………………………………… ... 12
4. FDDI technology ……………………………………………………… .15
5. Protocol X.25 ………………………………………………………… .19
Conclusion ……………………………………………………………………… .22
List of sources and literature ……………………………………………… 23
Introduction
Computer networks, also called computer networks, or data transmission networks, are the logical result of the evolution of two most important scientific and technical branches of modern civilization - computer and telecommunication technologies. On the one hand, networks are a special case of distributed computing systems in which a group of computers consistently performs a set of interrelated tasks, exchanging data in an automatic mode. On the other hand, computer networks can be considered as a means of transmitting information over long distances, for which they use data coding and multiplexing methods that have been developed in various telecommunication systems.
The main LAN technologies remain Ethernet, Token Ring, FDDI, Fast and Gigabit Ethernet, Token Ring and FDDI - these are functionally much more complex technologies than Ethernet on a shared medium. The developers of these technologies sought to endow the network on a shared medium with many positive qualities: to make the mechanism for separating the medium predictable and manageable, to provide network resiliency, to organize priority service for delay-sensitive traffic, such as voice. In many ways, their efforts paid off, and FDDI networks have been successfully used for quite a long time as backbones for campus-scale networks, especially in cases where high reliability of the backbone was needed.
Token Ring is a prime example of token passing networks. Token-passing networks move a small block of data called a token along the network. Possession of this token guarantees transferability. If the node receiving the token has no information to send, it simply forwards the token to the next end station. Each station can hold the marker for a specified maximum time.
With faster speeds than Ethernet, more deterministic allocation of network bandwidth between nodes, and better performance (fault detection and isolation), Token Ring networks have been the preferred choice for sensitive applications such as banking and systems. enterprise management.
FDDI technology can be considered an improved version of Token Ring, since it, like Token Ring, uses a medium access method based on token transfer, as well as a ring topology of links, but at the same time FDDI operates at a higher speed and has a higher perfect fault tolerance mechanism.
In the FDDI standards, a lot of attention is paid to various procedures that allow you to determine the presence of a network failure, and then make the necessary reconfiguration. FDDI extends Token Ring failure detection mechanisms with redundant links provided by the second ring.
The relevance of this work is due to the importance of studying the technologies of local computer systems.
The aim of the work is to study the characteristics of the Token Ring, Ethernet, FDDI and X.25 networks.
To achieve this goal, the following tasks were set in the work:
Explore the concepts of basic networking technologies;
Reveal the specifics of the use of technologies;
Consider the advantages and disadvantages of Ethernet, Token Ring, FDDI and X.25;
Analyze the types of network technologies.
Network technology concept
In local networks, as a rule, a shared data transmission medium (mono-channel) is used and the main role is assigned to the protocols of the physical and channel levels, since these levels to the greatest extent reflect the specifics of local networks.
Network technology is a consistent set of standard protocols and software and hardware that implement them, sufficient to build a local area network. Networking technologies are referred to as core technologies or LAN networking architectures.
The network technology or architecture defines the topology and method of access to the data transmission medium, cable system or data transmission medium, the format of network frames, the type of signal coding, the transmission rate in the local network. In modern local area networks, technologies or network architectures such as Ethernet, Token Ring, FDDI and X.25 are widely used.
The development of computer networks began with the solution of a simpler problem - access to a computer from terminals located many hundreds or even thousands of kilometers away from it. In this case, terminals were connected to a computer via telephone networks using special modem devices. The next stage in the development of computer networks was modem connections not only "terminal - computer", but also "computer - computer". Computers now have the ability to exchange data automatically, which is the basic mechanism of any computer network. Then, for the first time, there appeared on the network the ability to exchange files, synchronize databases, use email, i.e. those services that are now traditional network services. Such computer networks are called global computer networks.
In essence, a computer network is a collection of computers and network equipment connected by communication channels. Since computers and network equipment can be of different manufacturers, the problem of their compatibility arises. Without the acceptance by all manufacturers of generally accepted rules for building equipment, the creation of a computer network would be impossible.
For an ordinary user, a network is a wire or several wires through which a computer is connected to another computer or modem to access the Internet, but in reality, everything is not so simple. Let's take the most ordinary wire with an RJ-45 connector (these are used almost everywhere in wired networks) and connect two computers, in this connection the Ethernet 802.3 protocol will be used, which allows data transfer at speeds up to 100 Mbps. This standard, like many others, is precisely the standard, that is, one set of instructions is used all over the world and there is no confusion, information is transmitted from the sender to the addressee.
The transmission of information via cable, as some know, is carried out by a stream of bits, which are nothing more than the absence or reception of a signal. Bits, or zeros and ones, are interpreted by special devices in computers in a convenient way and we see a picture or text on the screen, and possibly even a movie. To manually transmit even a small piece of textual information through computer networks, a person would take a very long time, and the calculations would stretch out on huge piles of papers. To prevent this from happening, people came up with all these protocols and means of connecting computers into a single whole.
Ethernet technology
Ethernet is the most widely used standard for local area networks today. The total number of networks using the Ethernet protocol is currently estimated at several million.
When they say Ethernet, they usually mean any of the variants of this technology. More narrowly, Ethernet is a networking standard based on the experimental Ethernet Network that Xerox developed and implemented in 1975.
The access method was tried even earlier: in the second half of the 60s, various options for random access to a common radio environment, collectively known as Aloha, were used in the radio network of the University of Hawaii. In 1980, DEC, Intel, and Xerox jointly developed and published the Ethernet version II standard for a coaxial network. This latest version of the proprietary Ethernet standard is referred to as Ethernet DIX, or Ethernet P.
Based on the Ethernet DIX standard, the IEEE 802.3 standard was developed, which in many respects coincides with its predecessor, but there are still some differences. While the IEEE 802.3 standard separates the protocol functions into MAC and LLC layers, the original Ethernet standard combines them into a single data link layer. Ethernet DIX defines an Ethernet Configuration Test Protocol that IEEE 802.3 does not. The aspect ratio is also slightly different, although the minimum and maximum frame sizes in these standards are the same.
Often, in order to distinguish between the Ethernet standard defined by the IEEE and the proprietary Ethernet DIX standard, the former is called 802.3 technology, and the proprietary standard is left with the name Ethernet without additional designations. Depending on the type of physical medium, the IEEE 802.3 standard has various modifications - 10Base-5, 10Base-2, 10Base-T, 10Base-FL, lOBase-FB. In 1995, the Fast Ethernet standard was adopted, which in many respects is not an independent standard, as evidenced by the fact that its description is simply an additional section to the main 802.3 standard - the 802.3b section. Likewise, the 1998 Gigabit Ethernet standard is described in the 802.3z section of the main document.
For transmission of binary information over cable for all variants of the physical layer of Ethernet technology, providing a throughput of 10 Mbit / s, the Manchester code is used. The faster Ethernet versions use more bandwidth efficient redundant logic codes. All types of Ethernet standards (including Fast Ethernet and Gigabit Ethernet) use the same media separation method - the CSMA / CD method. Consider how the general approaches described above to solving the most important problems of building networks are embodied in the most popular network technology - Ethernet.
Networking technology is a consistent set of standard protocols and software and hardware that implements them (for example, network adapters, drivers, cables, and connectors) sufficient to build a computer network. The epithet “sufficient” underscores the fact that this set is the minimum set of tools with which to build a workable network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to the Ethernet standard protocols, the use of the IP protocol, as well as special communication devices - routers. The improved network is likely to be more reliable and faster, but at the expense of add-ons to the Ethernet technology that forms the basis of the network.
The term "network technology" is most often used in the narrow sense described above, but sometimes its extended interpretation is also used as any set of tools and rules for building a network, for example, "end-to-end routing technology", "technology for creating a secure channel", "IP-networking technology ". The protocols on the basis of which a network of a certain technology (in the narrow sense) is built were specially developed for collaboration, therefore, no additional effort is required from the network developer to organize their interaction. Sometimes network technologies are called basic technologies, meaning that on their basis the basis of any network is built. Examples of basic network technologies include, along with Ethernet, such well-known LAN technologies as Token Ring and FDDI, or X.25 and frame relay technologies. To get a working network, in this case, it is enough to purchase software and hardware related to one basic technology - network adapters with drivers, hubs, switches, cabling, etc. - and connect them in accordance with the requirements of the standard for this technology.
The basic principle behind Ethernet is a random method of accessing shared media. This medium can be thick or thin coaxial cable, twisted pair, optical fiber or radio waves (by the way, the first network built on the principle of random access to a shared medium was the Aloha radio network of the University of Hawaii). The Ethernet standard strictly fixes the topology of electrical connections. Computers are connected to a shared environment according to a typical shared bus structure. Using a time-shared bus, any two computers can exchange data. Access control to the communication line is carried out by special controllers - Ethernet network adapters. Each computer, more precisely, each network adapter, has a unique address. Data transfer occurs at a speed of 10 Mbit / s. This value is the bandwidth of the Ethernet network.
The essence of the random access method is as follows. A computer on an Ethernet network can transmit data over the network only if the network is free, that is, if no other computer is currently exchanging data. Therefore, an important part of Ethernet technology is the procedure for determining media availability. After the computer is convinced that the network is free, it starts transmitting, while "hijacking" the environment.
The time of exclusive use of the shared medium by one node is limited by the transmission time of one frame. A frame is a unit of data that is exchanged between computers on an Ethernet network. The frame has a fixed format and, along with the data field, contains various service information, for example, the recipient's address and the sender's address. The Ethernet network is designed in such a way that when a frame enters the shared data transmission medium, all network adapters simultaneously begin to receive this frame. All of them parse the destination address located in one of the initial fields of the frame, and if this address matches their own address, the frame is placed in the internal buffer of the network adapter.
Thus, the destination computer receives the data intended for it. Sometimes a situation may arise when two or more computers simultaneously decide that the network is free and begin to transmit information. This situation, called a collision, prevents the correct transmission of data over the network. The Ethernet standard provides an algorithm for detecting and correctly handling collisions. The likelihood of a collision depends on the amount of network traffic. After detecting a collision, network adapters that tried to transmit their frames stop transmitting and, after a pause of a random length, try again to access the medium and transmit the frame that caused the collision.
The main advantage of Ethernet networks that has made them so popular is their cost effectiveness. To build a network, it is enough to have one network adapter for each computer plus one physical segment of a coaxial cable of the required length. Other basic technologies, such as Token Ring, require an additional device, a hub, to create even a small network. In addition, in Ethernet networks, fairly simple algorithms for access to the medium, addressing and data transmission are implemented. Simple network logic leads to simplification and, consequently, cheaper network adapters and their drivers. For the same reason, Ethernet adapters are highly reliable.
And finally, another remarkable property of Ethernet networks is their good scalability, that is, the ease of connecting new nodes. Other basic network technologies - Token Ring, FDDI - although they have many individual characteristics, at the same time have many properties in common with Ethernet. First of all, this is the use of regular fixed topologies (hierarchical star and ring), as well as shared data transmission media. Significant differences of one technology from another are related to the peculiarities of the used method of access to the shared environment. Thus, the differences between Ethernet technology and Token Ring technology are largely determined by the specifics of the media separation methods embedded in them - a random algorithm for accessing Ethernet and an access method by transferring a token in Token Ring.
Token Ring technology
Token Ring is a local area network (LAN) technology of a "token access" ring - a local area network protocol that resides on the link layer (DLL) of the OSI model. It uses a special three-byte frame called a marker that moves around the ring. Ownership of a token grants the owner the right to transmit information on a medium. Ring frames with token access move in a loop.
Stations on a Token Ring local area network (LAN) are logically organized in a ring topology with data flowing sequentially from one ring station to another with a control token circulating around the control ring. This token transfer mechanism is shared by ARCNET, the token bus, and FDDI, and has theoretical advantages over stochastic CSMA / CD Ethernet.
The technology was originally developed by IBM in 1984. In 1985, the IEEE 802 committee based on this technology adopted the IEEE 802.5 standard. Recently, even IBM products have been dominated by the Ethernet family of technologies, despite the fact that the company has long used Token Ring as the main technology for building local networks.
This technology offers a solution to the problem of collisions that occurs during the operation of a local network. In Ethernet technology, such collisions occur when information is simultaneously transmitted by several workstations located within the same segment, that is, using a common physical data channel.
If the station that owns the token has information to transmit, it captures the token, changes one bit (as a result of which the token turns into the sequence "start of the data block"), supplements the information that it wants to transmit and sends this information to the next station ring network. When the information block circulates around the ring, there is no token in the network (unless the ring provides an "early token release"), so other stations wishing to transmit information have to wait. Therefore, there can be no collisions on Token Ring networks. If early token release is provided, then a new token may be released after completion of the data block transfer.
The information block circulates around the ring until it reaches the intended destination station, which copies the information for further processing. The information block continues to circulate around the ring; it is permanently removed after reaching the station that sent the block. The sending station can check the returned block to make sure it was viewed and then copied by the destination station.
Unlike CSMA / CD networks (eg Ethernet), token-passing networks are deterministic networks. This means that you can calculate the maximum time that will elapse before any end station can transmit. This characteristic, as well as some reliability characteristics, make the Token Ring network ideal for applications where latency must be predictable and network stability is important. Examples of such applications are automated station environments in factories. It is used as a cheaper technology, has become widespread wherever there are critical applications, for which not so much speed is important as reliable information delivery. Currently Ethernet is as reliable as Token Ring in terms of reliability and significantly higher in performance.
Token Ring networks, like Ethernet networks, use a shared data transmission medium, which consists of lengths of cable connecting all stations on the network in a ring. The ring is considered as a common shared resource, and for access to it, not a random algorithm is used, as in Ethernet networks, but a deterministic one, based on the transfer by stations of the right to use the ring in a certain order. The right to use the ring is conveyed using a special format frame called a token or token.
Token Ring was adopted by the 802.5 committee in 1985. At the same time, IBM adopted the Token Ring standard as its core networking technology. Currently, it is IBM that is the main trendsetter in Token Ring technology, producing about 60% of network adapters for this technology.
Token Ring networks operate at two bit rates - 4 Mb / s and 16 Mb / s. The first speed is defined in the 802.5 standard, and the second is a new de facto standard that appeared as a result of the development of Token Ring technology. Mixing of stations operating at different speeds in one ring is not allowed.
Token Ring networks operating at 16 Mb / s have some improvements in the access algorithm compared to the 4 Mb / s standard.
FDDI technology
Technology Fiber Distributed Data Interface Is the first local area network technology to use fiber optic cable as a data transmission medium.
Attempts to use light as a medium for carrying information have been undertaken for a long time - back in 1880, Alexander Bell patented a device that transmitted speech over a distance of 200 meters using a mirror that vibrated synchronously with sound waves and modulated the reflected light.
In the 1960s, optical fibers emerged that could carry light in cable systems, much like copper wires carry electrical signals in traditional cables. However, the light loss in these fibers was too great to be used as an alternative to copper conductors.
In the 1980s, work also began on the creation of standard technologies and devices for using fiber-optic channels in local networks. The work on the generalization of experience and the development of the first fiber-optic standard for local area networks was concentrated in the American National Institute for Standardization - ANSI, within the framework of the X3T9.5 committee created for this purpose.
Initial versions of the various constituent parts of the FDDI standard were developed by the X3T9.5 committee in 1986-1988, and at the same time the first equipment appeared - network adapters, hubs, bridges and routers that support this standard.
Currently, most networking technologies support fiber optic cables as a physical layer option, but FDDI remains the most mature high-speed technology with standards that have stood the test of time and are well established so that equipment from different manufacturers shows a good degree of compatibility.
FDDI technology is largely based on Token Ring technology, developing and improving its basic ideas. The developers of the FDDI technology set the following goals as the highest priority:
· Increase the bit rate of data transmission up to 100 Mb / s;
· To increase the fault tolerance of the network due to the standard procedures for its recovery after failures of various kinds - cable damage, incorrect operation of a node, a hub, a high level of noise on the line, etc .;
· Make the most of the potential network bandwidth for both asynchronous and synchronous traffic.
The FDDI network is built on the basis of two fiber-optic rings, which form the main and backup data transmission paths between the network nodes.
The use of two rings is the main way to improve resiliency in an FDDI network, and nodes that want to use it must be connected to both rings. In normal network operation, data passes through all nodes and all cable sections of the Primary ring, therefore this mode is called Thru mode - "through" or "transit". The Secondary ring is not used in this mode.
In the event of some type of failure, when part of the primary ring cannot transmit data (for example, a cable break or a node failure), the primary ring is combined with the secondary, forming a single ring again. This mode of operation of the network is called Wrap, that is, "folding" or "folding" rings. The folding operation is performed by the concentrators and / or FDDI network adapters. To simplify this procedure, data on the primary ring is always transmitted counterclockwise, and on the secondary ring, clockwise. Therefore, when a common ring of two rings is formed, the transmitters of the stations still remain connected to the receivers of neighboring stations, which makes it possible to correctly transmit and receive information by neighboring stations.
In the FDDI standards, a lot of attention is paid to various procedures that allow you to determine the presence of a network failure and then make the necessary reconfiguration. FDDI network can fully restore its operability in the event of single failures of its elements. With multiple failures, the network splits into several unconnected networks.
Each station in the network constantly receives frames transmitted to it by its previous neighbor and analyzes their destination address. If the destination address does not match its own, then it broadcasts the frame to its next neighbor. This case is shown in the figure. It should be noted that if a station grabs a token and transmits its own frames, then during this period of time it does not broadcast incoming frames, but removes them from the network.
If the address of the frame coincides with the address of the station, then it copies the frame to its internal buffer, checks its correctness (mainly by the checksum), transfers its data field for subsequent processing to the protocol of the layer above FDDI (for example, IP), and then transmits the original frame over the network to the subsequent station. In the frame transmitted to the network, the destination station notes three signs: recognition of the address, copying of the frame and the absence or presence of errors in it.
After that, the frame continues to travel over the network, broadcast by each node. The station, which is the source of the frame for the network, is responsible for removing the frame from the network after it, having completed a full revolution, reaches it again. In this case, the source station checks the signs of the frame, whether it reached the destination station and whether it was damaged. The process of restoring data frames is not the responsibility of the FDDI protocol; higher layer protocols should do this.
X.25 protocol
X.25 is a family of network layer protocols of the OSI network model. It was intended for organizing WAN based on telephone networks with lines with a sufficiently high error rate, therefore, it contains advanced error correction mechanisms. Focused on working with establishing connections. Historically the predecessor to Frame Relay.
X.25 provides multiple independent virtual circuits (Permanent Virtual Circuits, PVCs and Switched Virtual Circuits, SVCs) on a single link, identified in the X.25 network by connection identifiers (Logical Channel Identifiers (LCI) or Logical Channel Number (LCN).
Due to the reliability of the protocol and its operation over public telephone networks, X.25 has been widely used both in corporate networks and in worldwide specialized networks for providing services such as SWIFT (bank payment system) and SITA (French Société Internationale de Télécommunications Aéronautiques - system information services of air transport), but at present X.25 is being supplanted by other data link layer technologies (Frame Relay, ISDN, ATM) and IP, while remaining, however, quite widespread in countries and territories with undeveloped telecommunications infrastructure.
Developed by Study Group VII of the International Telecommunication Union (ITU), it was adopted in 1976 as a packet data transfer protocol in telephone networks and became the basis of the worldwide PSPDN (Packet-Switched Public Data Networks) system, that is, WAN. Significant additions to the protocol were adopted in 1984, at present the ISO 8208 standard for the X.25 protocol is in force, and the use of X.25 in local networks is also standardized (ISO 8881 standard).
X.25 defines the characteristics of the telephone network for data transmission. To initiate a communication, one computer asks another to request a communication session. The called computer can accept or reject the connection. If the call is accepted, then both systems can start transferring information with full duplication. Any party may terminate communication at any time.
The X.25 specification defines point-to-point communication between terminal equipment (DTE) and information circuit termination equipment (DCE). DTE devices (terminals and hosts in user equipment) connect to DCE devices (modems, packet switches and other ports to the PDN, usually located in the equipment of this network), which are connected to "packet switching exchange" ( PSE or just switches) and other DCEs inside the PSN and finally to another DTE device.
A DTE may be a terminal that does not fully implement all of the X.25 functionality. Such DTEs connect to the DCE through a translator called a packet assembler / disassembler (PAD). The operation of the terminal / PAD interface, the services offered by the PAD, and the interaction between the PAD and the host are defined respectively by CCITT Recommendations X.28, X3 and X.29.
The X.25 specification charts Layers 1-3 of the OSI reference model. X.25 Layer 3 describes packet formats and packet exchange procedures between Layer 3 peers. X.25 Layer 2 is implemented by the Link Access Procedure, Balanced (LAPB). LAPB defines packet framing for DTE / DCE link. X.25 Level 1 defines the electrical and mechanical procedures for activating and deactivating the physical medium connecting DTE and DCE data. It should be noted that Layers 2 and 3 are also referred to as ISO standards - ISO 7776 (LAPB) and ISO 8208 (X.25 packet layer).
End-to-end communication between DTE devices is done through a bi-directional communication called a virtual circuit. Virtual circuits allow communication between various network elements through any number of intermediate nodes without assigning parts of the physical medium, which is typical for physical circuits. Virtual circuits can be either permanent or switched (temporarily). Permanent virtual circuits are commonly referred to as PVCs; switchable virtual circuits - SVC. PVCs are typically used for the most commonly used data transfers, while SVCs are used for sporadic data transfers. Layer 3 X.25 is responsible for end-to-end transmission including both PVC and SVC.
After the virtual circuit is established, the DTE sends the packet to the other end of the link by sending it to the DCE using the appropriate virtual circuit. The DCE looks at the virtual circuit number to determine the route of this packet through the X.25 network. The X.25 Layer 3 protocol is multiplexed between all DTEs served by a DCE device located in the network from the destination side, resulting in the packet being delivered to the destination DTE.
Conclusion
The development of computer technology and information technology has served as an impetus for the development of a society built on the use of various information and called the information society.
Information network technologies are focused mainly on providing information services to users.
All network technologies, such as Ethernet, Token Ring, FDDI or X.25, can be said to be one of the most significant and striking democratic achievements of the technological process. With their appearance, information, and the right to truth and freedom of speech, becomes a potential property and opportunity for most of the world's inhabitants, people can unite and interact regardless of time, distance, state and many other boundaries.
Currently, the whole world is covered by the global Internet. It is the Internet that erases all boundaries and ensures the dissemination of information for an almost unlimited circle of people. Allows people anywhere in the world to easily get involved in the discussion of pressing problems. The main feature and purpose of the Internet is the free flow of information and the establishment of communication between people.
List of sources and literature:
1) Vendrov A.M. Software design of economic information systems: Textbook for economics. universities / A.M. Vendrov. - M .: Finance and statistics, 2000. - 352p .: ill.
2) Gein A.G., Senokosov A.I. Informatics and ICT: textbook. / Recommended by the Ministry of Education and Science of the Russian Federation.- M: Moscow textbooks, 2010.- 336s.
3) Karpenkov, S.Kh. Modern means of information technology: textbook. manual for universities / S.Kh. Karpenkov. - 2nd ed., Rev. and add. - M .: Knorus, 2009 .-- 400 p.
4) Konopleva, I.A. Information technologies [Electronic resource]: electronic textbook / I.А. Konopleva, O.A. Khokhlova, A.V. Denisov. - M .: Prospect, 2009.
5) Korneev, I.K. Information technologies: textbook / I.K. Korneev, G.N. Ksandopulo, V.A. Mashurtsev. - M .: Prospect, 2009 .-- 222 p.
6) Petrov V.N. Information systems / Petrov V.N. - SPb .: Peter, 2008 .-- 688s.: Ill.
7) Information systems and technologies: Textbook. - 3rd ed. / Ed. G.A. Titorenka. - M .: Unity-Dana, 2010 .-- 591 p.
8) Trofimov V.V. Information technologies. Textbook for universities / Trofimov V.V. Publisher: Moscow, YURAYT, 2011. - 624 p.
9) http://nwzone.ru/ - "Modern technologies": news from around the world: hi-tech innovations, gadgets, mobile electronics, the Internet, design, science.
Information systems and technologies: Textbook. - 3rd ed. / Ed. G.A. Titorenka. - M .: Unity-Dana, 2010 .-- p. 176, 177.
Karpenkov, S.Kh. Modern means of information technology: textbook. manual for universities / S.Kh. Karpenkov. - 2nd ed., Rev. and add. - M .: Knorus, 2009 .-- p. 140 s.
Korneev, I.K. Information technologies: textbook / I.K. Korneev, G.N. Ksandopulo, V.A. Mashurtsev. - M .: Prospect, 2009 .-- p. 87.
Gein A.G., Senokosov A.I. Informatics and ICT: textbook. / Recommended by the Ministry of Education and Science of the Russian Federation.- M: Moscow textbooks, 2010.- p.33.
Http://nwzone.ru/ - "Modern technologies": news from all over the world: hi-tech innovations, gadgets.
Petrov V.N. Information systems / Petrov V.N. - SPb .: Peter, 2008 .-- p. 68.
Vendrov A.M. Software design of economic information systems: Textbook for economics. universities / A.M. Vendrov. - M .: Finance and statistics, 2000. - p. 35.
Konopleva, I.A. Information technologies [Electronic resource]: electronic textbook / I.А. Konopleva, O.A. Khokhlova, A.V. Denisov. - M .: Prospect, 2009.
Gein A.G., Senokosov A.I. Informatics and ICT: textbook. / Recommended by the Ministry of Education and Science of the Russian Federation.- M: Moscow textbooks, 2010.- p.95.
Gein A.G., Senokosov A.I. Informatics and ICT: textbook. / Recommended by the Ministry of Education and Science of the Russian Federation.- M: Moscow textbooks, 2010.- p.99.
Information systems and technologies: Textbook. - 3rd ed. / Ed. G.A. Titorenka. - M .: Unity-Dana, 2010 .-- p. 91, 92.
Konopleva, I.A. Information technologies [Electronic resource]: electronic textbook / I.А. Konopleva, O.A. Khokhlova, A.V. Denisov. - M .: Prospect, 2009.
By specialization: specialized and universal
specialized - to solve a small number of special tasks. An example of a specialized technology is the reservation of seats for air flights.
A classic example universal technology is the Academset of the Russian Federation, designed to solve a large variety of information problems.
by way of organization:single-level and two-level
AT single-level In the routing system, all routers are equal in relation to each other.
two-tiertechnologies have, in addition to PCs, with which users directly communicate and which are called workstations, special computers called servers (English to serve). The task of the server is to serve workstations with the provision of their own resources, which are usually significantly higher than the resources of a workstation.
By communication method: wired, wireless.
In wired technologies, the following are used as the physical medium in the channels:
Flat two-core cable;
Twisted pair wires
Coaxial cable
Light guide.
Wireless networking technologiesusing frequency channels of data transmission (the medium is the air), are currently a reasonable alternative to conventional wired networks and are becoming more and more attractive. The biggest advantage of wireless technology is the capabilities it provides to laptop users. However, the data transmission speed achieved in wireless technologies cannot yet be compared with the cable throughput, although it has grown significantly recently.
By the composition of the PC. Homogeneous and heterogeneous
Homogeneous network technologies involve linking in a network of the same type of tools developed by one company. Connection to such a network of means of other manufacturers is possible only if they comply with the standards adopted in a homogeneous architecture.
Another approach is to develop a single universal network technology, regardless of the types of tools used in it. Such technologies are called heterogeneous. The first standard for such networks was the OSI Basic Reference Model (Open Systems Interconnection). This International Standard for the Open Systems Interconnection Reference Model provides a common framework for coordinating the development of standards for systems interconnection. It permits the use of existing standards and defines their future location within the reference model.
The requirements of this standard are mandatory
By Territory Coverage
The use of personal computers (PCs) as part of local area networks (LAN) provides constant and operational interaction between individual users within a commercial or scientific and industrial structure. The LAN got its name because all its components (PCs, communication channels, communication facilities) are physically located in a small area of \u200b\u200bone organization or its separate divisions.
Territorial (regional) refers to a technology (network) whose computers are located at a great distance from each other, usually from tens to hundreds of kilometers. Sometimes the territorial network is called corporate or departmental. Such a network provides data exchange between subscribers who have access to network resources via telephone channels of the general-purpose network, channels of the Telex network, as well as via satellite communication channels. The number of network subscribers is not limited. They are guaranteed a reliable exchange of data in "real time", the transmission of faxes and telephone (telex) messages at a given time, telephone communication via satellite channels. Territorial networks are built according to the ideology of open systems. Their subscribers are individual PCs, LANs, telex installations, facsimile and telephone installations, network elements (communication network nodes).
The main task of the federal network - creation of a backbone data transmission network with packet switching and the provision of real-time data transmission services to a wide range of users, including territorial networks.
Global networks provide the ability to communicate by correspondence and teleconference. The main task of the global network is to provide subscribers not only with access to computer resources, but also with the possibility of interaction between various professional groups dispersed over a large territory.
Topologies
Topology (configuration)Is a way of connecting computers to a network.
The type of topology determines cost, security, performance and
reliability of operation of workstations for which it matters
time to access the file server
There are five main topologies:
- common bus (Bus);
- ring (Ring);
- star (Star);
- tree (Tree);
- cellular (Mesh).
Common bus it is a type of network topology in which workstations are located
laid along one section of the cable called a segment
In this case, the cable is used by all stations in turn,
special measures are taken to ensure that when working with general
with a cable, computers did not interfere with each other to transmit and receive data.
All messages sent by individual computers are received and
listened to by all other computers connected to the network.
Ring – it is a LAN topology in which each station is connected to
two other stations, forming a ring (Figure 4.2). Data is transferred from
from one workstation to the other in one direction (around the ring). Each
The PC works as a repeater, relaying messages to the next PC,
those. data is transferred from one computer to another as if by relay.
If a computer receives data intended for another computer,
xia. The main problem with a ring topology is that
each workstation must actively participate in the transfer of information,
and in case of failure of at least one of them, the entire network is paralyzed. To-
flatness Ringhas a well-predictable response time defined by
the number of workstations.
Star – is a LAN topology in which all workstations
connected to a central site (e.g. a hub) that
establishes, maintains and breaks connections between workstations.
The advantage of this topology is the ability to easily exclude
faulty node... However, if the central node fails, the entire network
fails.
Tree-liketopology - achieved from a star path
cascading hubs. This topology is widely used in
temporary high-speed local computer networks. As
switching nodes are most often high-speed switches.
The most typical representative of networks with a similar structure is
xia network 100VG AnyLan. And in addition, the high-speed version of the master
ethernet LAN - Fast Ethernet also has a tree structure.
Compared to bus and ring networks, tree-like local
networks are more reliable. Disconnect or exit
building one of the lines or a switch, as a rule, does not have a significant
a significant effect on the performance of the rest of the local network.
Honeycombtopology is a topology in which all workers
stationsconnected to all (fully connected topology). Mesh topolo-
gia has found application in the past few years. Her attractiveness is
it consists in relative resistance to overloads and failures. Thanks to
multiple paths from devices connected to the network, traffic can
be directed to bypass failed or busy nodes. Even though
that this approach is notable for its complexity and high cost (protocols
mesh networks can be quite complex in terms of logic,
to provide these characteristics), some users prefer
mesh networks melt to networks of other types due to their high reliability
Wireless technology
Methods of wireless data transmission technology (Radio Waves) are a convenient and sometimes irreplaceable means of communication. Wireless technologies differ in signal types, frequency (higher frequency means faster transmission speed) and transmission distance. Great importance
have interference and cost. There are three main types of wireless technology:
- radio communication;
- communication in the microwave range;
- infrared communication.
routing protocols
Internet is a worldwide collection of computer networks that connects millions of computers. Today the Internet has about 400 million subscribers in more than 150 countries around the world. The size of the network increases by 7-10% every month.
Individual local area networks can be combined into a wide area network (WAN). Devices that are not part of the same local physical LAN establish connections to the wide area network through dedicated communications equipment. The most common method of connecting an "internal" subnet to an "external" subnet is through a gateway computer. The Internet forms the core that connects the various networks belonging to different institutions around the world with one another. The Internet consists of many local and global networks. The Internet can be thought of as a mosaic of small networks of different sizes, which actively interact with one another, sending files, messages, etc.
From the very beginning, backbone and networksconnected to the backbone (autonomous, local). The backbone and each of the autonomous ones had their own administration and
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Today, networks and networking technologies connect people all over the world and provide them with access to the greatest luxury in the world - human communication. People communicate and play without interference with friends who are in other parts of the world.
The events taking place become known in all countries of the world in a matter of seconds. Everyone is able to connect to the Internet and upload their portion of information.
Network information technologies: the roots of their origin
In the second half of the last century, human civilization formed two of its most important scientific and technical industries - computer and For about a quarter of a century, both these industries developed independently, and within their framework, respectively, computer and telecommunication networks were created. However, in the last quarter of the twentieth century, as a result of the evolution and interpenetration of these two branches of human knowledge, what we call the term "network technology", which is a subsection of the more general concept of "information technology", arose.
As a result of their appearance, a new technological revolution took place in the world. Just as a few decades before it, the land surface was covered with a network of high-speed highways, at the end of the last century all countries, cities and villages, enterprises and organizations, as well as individual dwellings, were connected by "information highways." At the same time, they all became elements of various networks for transferring data between computers, in which certain information transfer technologies were implemented.
Network technology: concept and content
Network technology is sufficient for building a certain integral set of rules for the presentation and transmission of information, implemented in the form of so-called "standard protocols", as well as hardware and software, including network adapters with drivers, cables and fiber optic lines, various connectors (connectors).
"Sufficiency" of this complex of means means its minimization while maintaining the possibility of building a workable network. It should have potential for improvement, for example, by creating subnets in it, requiring the use of protocols of various levels, as well as special communicators, usually called "routers". Once improved, the network becomes more reliable and faster, but at the cost of add-ons over the underlying network technology that forms its basis.
The term "network technology" is most often used in the above-described narrow sense, however, it is often interpreted in an extended way as any set of tools and rules for building networks of a certain type, for example, "technology of local computer networks".
Network technology prototype
The first prototype of a computer network, but not yet the network itself, was in the 60s and 80s. last century multi-terminal systems. Being a set of monitor and keyboard located at great distances from large computers and connected to them by means of telephone modems or through dedicated channels, the terminals left the premises of the ITC and were dispersed throughout the building.
At the same time, except for the operator of the computer itself at the ITC, all terminal users had the opportunity to enter their tasks from the keyboard and observe their execution on the monitor, carrying out some task control operations. Such systems, which implement both time-sharing and batch processing algorithms, were called remote job entry systems.
Global networks
Following multi-terminal systems in the late 60s. XX century. the first type of networks was created - global computer networks (GKS). They connected supercomputers, which existed in single copies and stored unique data and software, with mainframes, located from them at distances of many thousands of kilometers, through telephone networks and modems. This networking technology has been previously tested in multi-terminal systems.
The first GKS in 1969 was ARPANET, which worked in the US Department of Defense and combined different types of computers with different operating systems. They were equipped with additional modules for the implementation of communication common to all computers included in the network. It was on it that the foundations of network technologies were developed, which are still used today.
First example of convergence of computer and telecommunication networks
GKS inherited communication lines from older and more global networks - telephone, since it was very expensive to lay new long-distance lines. Therefore, for many years they have used analogue telephone channels to transmit only one conversation at a time. Digital data was transmitted over them at a very low speed (tens of kbit / s), and the possibilities were limited to the transfer of data files and e-mail.
However, having inherited telephone communication lines, the GKS did not take their main technology, based on the principle of channel switching, when each pair of subscribers was allocated a channel with a constant speed for the entire duration of the communication session. The GKS used new computer network technologies based on the principle of packet switching, in which data in the form of small portions of packets at a constant rate are sent to an unswitched network and received by their addressees in the network using address codes embedded in the packet headers.
The predecessors of local networks
Appearance in the late 70s. XX century. LSI has led to the creation of a mini-computer with a low cost and rich functionality. They began to really compete with mainframes.
Minicomputers of the PDP-11 family have gained wide popularity. They began to be installed in all, even very small production units for managing technological processes and individual technological units, as well as in enterprise management departments for performing office tasks.
The concept of computer resources distributed throughout the enterprise emerged, although all minicomputers were still operating autonomously.
The emergence of LAN networks
By the mid 80s. XX century. technologies for combining mini-computers in networks based on data packet switching, as in the GKS, were introduced.
They made building a single enterprise network called a local area network (LAN) an almost trivial task. To create it, you only need to buy network adapters for the selected LAN technology, for example, Ethernet, a standard cabling system, install connectors (connectors) on its cables and connect the adapters to the mini-computer and to each other using these cables. Further, one of the OS was installed on the computer server, intended for organizing a LAN - network. After that, she began to work, and the subsequent connection of each new mini-computer did not cause any problems.
The inevitability of the Internet
If the appearance of mini-computers made it possible to distribute computer resources evenly over the territories of enterprises, then the appearance in the early 90s. The PC caused their gradual appearance, first at every workplace of any knowledge worker, and then in individual human dwellings.
The relative cheapness and high reliability of PCs first gave a powerful impetus to the development of LAN-networks, and then led to the emergence of a global computer network - the Internet, which now swept all countries of the world.
The size of the Internet is growing by 7-10% every month. It is the core that connects various local and global networks of enterprises and institutions around the world with each other.
If at the first stage data files and e-mail messages were mainly transmitted via the Internet, today it provides mainly remote access to distributed information resources and electronic archives, to commercial and non-commercial information services of many countries. Its free access archives contain information on almost all areas of human knowledge and activity - from new directions in science to weather forecasts.
Basic networking technologies of LAN networks
Among them, there are basic technologies on which the basis of any particular network can be built. Examples include such well-known LAN technologies as Ethernet (1980), Token Ring (1985), and FDDI (late 1980s).
In the late 90s. Ethernet technology has emerged as the leader in LAN technology, combining its classic version with up to 10 Mbps, as well as Fast Ethernet (up to 100 Mbps) and Gigabit Ethernet (up to 1000 Mbps). All Ethernet technologies have similar operating principles that simplify their maintenance and interconnection of LAN-networks built on their basis.
In the same period, their developers began to integrate network functions into the kernels of almost all computer operating systems that implement the above network information technologies. There are even specialized communications operating systems like IOS from Cisco Systems.
How GCS technologies evolved
GKS technologies on analog telephone channels, due to the high level of distortion in them, were distinguished by complex algorithms for monitoring and recovering data. An example of them is the X.25 technology developed in the early 70s. XX century. More modern network technologies are frame relay, ISDN, ATM.
ISDN is an abbreviation for Integrated Services Digital Network and allows remote video conferencing. Remote access is provided by installing ISDN adapters in the PC, which work many times faster than any modems. There is also special software that allows popular operating systems and browsers to work with ISDN. But the high cost of equipment and the need to lay special communication lines slow down the development of this technology.
WAN technologies have progressed along with telephone networks. After the advent of digital telephony, the Plesiochronous Digital Hierarchy (PDH) technology was developed, supporting speeds up to 140 Mbps and used by enterprises to create their own networks.
New Synchronous Digital Hierarchy (SDH) technology in the late 1980s. XX century. expanded the bandwidth of digital telephone channels up to 10 Gbps, and Dense Wave Division Multiplexing (DWDM) technology - up to hundreds of Gbps and even up to several Tbps.
Internet technologies
Web sites are based on the use of the hypertext language (or HTML-language) - a special markup language that is an ordered set of attributes (tags) that are previously introduced by the developers of Internet sites into each page. Of course, in this case, we are not talking about text or graphic documents (photographs, pictures) that have already been "downloaded" by the user from the Internet, are in the memory of his PC and viewed through text or We are talking about the so-called web pages viewed through programs -browsers.
Developers of Internet sites create them in HTML (many tools and technologies for this work have now been created, collectively called "layout of sites") in the form of a set of web pages, and site owners place them on Internet servers on lease terms from the owners of their memory servers (so-called "hosting"). They work around the clock on the Internet, serving the requests of its users to view the web pages loaded in them.
Browsers of user PCs, having received access to a specific server through the server of their Internet provider, the address of which is contained in the name of the requested Internet site, gain access to this site. Further, by analyzing the HTML tags of each viewed page, browsers form its image on the monitor screen in the form as it was intended by the site developer - with all headers, font and background colors, various inserts in the form of photos, diagrams, pictures, etc. ...
A computer network is a combination of several computers to jointly solve information and computational problems.
The key concept of network technologies is a network resource, which can be understood as hardware and software components involved in the process of sharing - in the process of network interaction. Access to network resources is provided by network services (network services)
The basic concepts of networking technologies include concepts such as server, client, communication channel, protocol, and many others. However, the concept of a network resource and a network service (service) are fundamental, since the need to organize work based on the joint use of computer resources, and therefore the creation of network resources and corresponding network services, is the primary reason for the creation of computer networks themselves.
Allocate five kinds of network services: file, print, messages, application databases.
File service — implements centralized storage and file sharing. This is one of the most important network services, it assumes the presence of some network file storage (local network file server, ftp server, etc.), as well as the use of various security mechanisms (access control, file version control, information backup).
Print Service - provides opportunities for centralized use of printers and other printing devices. This service accepts print jobs, manages the job queue, and organizes user interaction with network printers. Network printing technology is very convenient in a wide variety of computer networks, as it makes it possible to reduce the number of printers required, which ultimately allows you to reduce costs or use better equipment.
Messaging service - allows you to organize information exchange between users of a computer network. In this case, both text messages (e-mail, messages from network messengers) and media messages of various voice and video communication systems should be considered as messages.
Database service — is intended for the organization of centralized storage, search, processing and protection of data of various information systems. As opposed to simply storing and sharing files, the database service provides and manages, which includes creating, modifying, deleting data, ensuring its integrity and protection.
App Service — provides a way of working in which the application is launched on the user's computer not from a local source, but from a computer network. Such applications can use server resources for data storage and computation. The advantage of using network applications is the ability to use them from any point of connection to a computer network without the need to install the application on a local computer, the ability to collaborate with several users, "transparent" software updates, the ability to use commercial software on a subscription basis.
Application services are the newest and fastest growing type of network service. The office networking applications of the online services Google Drive and Microsoft Office 365 are good examples.
