Network technology terms. Network technologies and standards. Modern computer network technologies: operating principles and protocols
Network technologies
Network technology is a coordinated set of standard protocols and software and hardware that implement them, sufficient for building computer networks.
Protocol- ϶ᴛᴏ a set of rules and agreements that determine how devices exchange data on a network.
Today the following network technologies dominate: Ethernet, Token Ring, FDDI, ATM.
Ethernet technology
Ethernet technology was created by XEROX in 1973. The basic principle underlying Ethernet is a random method of access to a shared data transmission medium (multiple access method).
The logical topology of an Ethernet network is always bus, and therefore data is transmitted to all network nodes. Each node sees each transmission and distinguishes the data intended for it by the address of its network adapter. At any given time, only one node can carry out a successful transmission; therefore, there must be some kind of agreement between the nodes on how they can use the same cable together so as not to interfere with each other. This agreement defines the Ethernet standard.
As network load increases, it becomes increasingly important to transmit data at the same time. When this happens, the two transmissions come into conflict, filling the bus with information garbage. This behavior is known under the term “collision”, that is, the occurrence of a conflict.
Each transmitting system, upon detecting a collision, immediately stops sending data and action is taken to correct the situation.
Although most collisions that occur on a typical Ethernet network are resolved within microseconds and their occurrence is natural and expected, the main disadvantage is essentially that the more traffic on the network, the more collisions, the sharply the network performance drops and a collapse may occur, that is, the network is clogged with traffic.
Traffic– flow of messages in a data network.
Token Ring Technology
Token Ring technology was developed by IBM in 1984. Token Ring technology uses a completely different access method. The Token Ring logical network has a ring topology. A special message known as a Token is a special three-byte packet that constantly circulates around the logical ring in one direction. When a token passes through a node ready to send data to the network, it grabs the token, attaches the data to be sent to it, and then passes the message back to the ring. The message continues its “journey” around the ring until it reaches its destination. Until the message is received, no node will be able to forward data. This access method is known as token passing. It eliminates collisions and random latency periods like Ethernet.
FDDI technology
FDDI (Fiber Distributed Data Interface) technology – fiber optic distributed data interface – is the first local network technology in which the data transmission medium is fiber optic cable. FDDI technology is largely based on Token Ring technology, developing and improving its basic ideas. The FDDI network is built on the basis of two fiber optic rings, which form the main and backup data transmission paths between network nodes. Having two rings is the primary way to increase fault tolerance in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings.
In normal network operation mode, data passes through all nodes and all cable sections of the primary ring only; the secondary ring is not used in this mode. In the event of some type of failure where part of the primary ring cannot transmit data (for example, a broken cable or node failure), the primary ring is combined with the secondary ring, again forming a single ring.
Rings in FDDI networks are considered as a common data transmission medium, and therefore a special access method is defined for it, very close to the access method of Token Ring networks. The difference is essentially that the token retention time in the FDDI network is not a constant value, as in Token Ring. It depends on the ring load - with a light load it increases, and with large congestions it can decrease to zero for asynchronous traffic. It is important to note that for synchronous traffic, the token holding time remains a fixed value.
ATM technology
ATM (Asynchronous Transfer Mode) is the most modern network technology. It is designed to transmit voice, data and video using a high-speed, connection-oriented cell switching protocol.
Unlike other technologies, ATM traffic is divided into 53-byte cells (cells). Using a predefined size data structure makes network traffic more easily quantifiable, predictable, and manageable. ATM is based on transmitting information over a fiber optic cable using a star topology.
Network technologies - concept and types. Classification and features of the category "Network Technologies" 2017, 2018.
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Coursework
on Information systems in economics on topic No. 69:
“Network technologies Ethernet, Token Ring, FDDI and X.25”
Completed by: 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 networks, are the logical result of the evolution of two of the 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 coordinately performs a set of interrelated tasks, exchanging data automatically. On the other hand, computer networks can be considered as a means of transmitting information over long distances, for which they use methods of encoding and multiplexing data, which have been developed in various telecommunication systems.
The main technologies of local networks 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 medium sharing mechanism predictable and manageable, to ensure network fault tolerance, and 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 some time as the backbone of campus-scale networks, especially in cases where it was necessary to ensure high reliability of the backbone.
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 the right to transfer. If the node receiving the token does not have information to send, it simply forwards the token to the next endpoint. Each station can hold a marker for a certain maximum time.
With faster speeds than Ethernet networks, deterministic distribution of network bandwidth between nodes, and better performance characteristics (fault detection and isolation), Token Ring networks have been the preferred choice for performance-sensitive applications such as banking and security 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 the transfer of a token, as well as a ring topology of connections, but at the same time FDDI operates at a higher speed and has more perfect fault tolerance mechanism.
The FDDI standards place a lot of emphasis on various procedures that allow you to determine if there is a fault in the network and then make the necessary reconfiguration. FDDI technology extends the failure detection mechanisms of Token Ring technology through the 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 purpose 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:
Learn the concepts of basic network technologies;
Identify the specifics of technology application;
Consider the advantages and disadvantages of Ethernet, Token Ring, FDDI and X.25;
Analyze the types of network technologies.
Concept of network technologies
In local networks, as a rule, a shared data transmission medium (mono-channel) is used and the main role is played by protocols of the physical and data link layers, since these levels best reflect the specifics of local networks.
Network technology is an agreed set of standard protocols and software and hardware that implement them, sufficient to build a local computer network. Network technologies are called core technologies or network architectures of local area networks.
Network technology or architecture determines the topology and method of access to the data transmission medium, the cable system or data transmission medium, the format of network frames, the type of signal encoding, and the transmission speed of the local network. In modern local area networks, technologies or network architectures such as Ethernet, Token Ring, FDDI and X.25 have become widespread.
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, the terminals were connected to the computer through telephone networks using special modem devices. The next stage in the development of computer networks was connections via modem not only “terminal-to-computer”, but also “computer-to-computer”. Computers have the ability to exchange data automatically, which is the basic mechanism of any computer network. Then, for the first time, the ability to share files, synchronize databases, use email, etc. appeared on the Internet. those services that are currently traditional network services. Such computer networks are called global computer networks.
At its essence, a computer network is a collection of computers and network equipment connected by communication channels. Since computers and network equipment can be from different manufacturers, the problem of their compatibility arises. Without the acceptance by all manufacturers of generally accepted rules for constructing equipment, the creation of a computer network would be impossible.
For the average user, a network is a wire or several wires with which a computer connects to another computer or modem to access the Internet, but in reality everything is not so simple. Let's take the most common wire with an RJ-45 connector (these are used almost everywhere in wired networks) and connect two computers; this connection will use the Ethernet 802.3 protocol, which allows data transfer at speeds of up to 100 Mbit/s. This standard, like many others, is just a standard, that is, one set of instructions is used all over the world and there is no confusion; information is transferred from the sender to the addressee.
The transmission of information via cable, as some know, is carried out by a stream of bits, which is nothing more than the absence or reception of a signal. Bits, or zeroes and ones, are interpreted by special devices in computers into a convenient form and we see a picture or text, and perhaps even a movie, on the screen. To manually transmit even a small piece of text information via computer networks would take a very long time for a person, and the calculations would stretch over huge stacks 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 widespread local network standard today. The total number of networks currently operating using the Ethernet protocol is estimated at several million.
When people say Ethernet, they usually mean any of the variants of this technology. In a narrower sense, Ethernet is a network standard based on the experimental Ethernet Network, which Xerox developed and implemented in 1975.
The access method was tested even earlier: in the second half of the 60s, the University of Hawaii radio network used various options for random access to the general radio environment, collectively called Aloha. In 1980, DEC, Intel, and Xerox jointly developed and published the Ethernet Version II standard for a network built over coaxial cable. This latest version of the proprietary Ethernet standard is called the Ethernet DIX standard, or Ethernet P.
Based on the Ethernet DIX standard, the IEEE 802.3 standard was developed, which largely coincides with its predecessor, but there are still some differences. While the IEEE 802.3 standard separates protocol functions into the MAC and LLC layers, the original Ethernet standard combines them into a single data link layer. Ethernet DIX defines the Ethernet Configuration Test Protocol, which is not found in IEEE 802.3. The frame format is also somewhat different, although the minimum and maximum frame sizes in these standards are the same.
Often, in order to distinguish the IEEE-defined Ethernet standard from 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 ways is not an independent standard, as evidenced by the fact that its description is simply an additional section to the main 802.3 standard - section 802.3b. Similarly, the Gigabit Ethernet standard adopted in 1998 is described in section 802.3z of the main document.
Manchester code is used to transmit binary information over the cable for all variants of the physical layer of Ethernet technology that provide a throughput of 10 Mbit/s. Faster versions of Ethernet use more bandwidth-efficient redundant logic codes. All types of Ethernet standards (including Fast Ethernet and Gigabit Ethernet) use the same method of separating the data transmission medium - the CSMA/CD method. Let's consider how the general approaches to solving the most important problems of networking described above are embodied in the most popular network technology - Ethernet.
Network technology is a coordinated set of standard protocols and software and hardware that implement them (for example, network adapters, drivers, cables and connectors), sufficient to build a computer network. The epithet “sufficient” emphasizes the fact that this set represents the minimum set of tools with which you can build a working network. Perhaps this network can be improved, for example, by allocating subnets in it, which will immediately require, in addition to standard Ethernet protocols, the use of the IP protocol, as well as special communication devices - routers. An improved network will likely be more reliable and faster, but at the cost of building on top of 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 expanded interpretation is also used as any set of tools and rules for building a network, for example, “end-to-end routing technology,” “secure channel technology,” “IP network technology.” " The protocols on which a network of a certain technology is built (in the narrow sense) were specifically developed for joint work, so the network developer does not require additional efforts to organize their interaction. Sometimes network technologies are called basic technologies, meaning that the basis of any network is built on their basis. Examples of basic network technologies include, in addition to Ethernet, such well-known local network technologies as Token Ring and FDDI, or X.25 and frame relay technologies for territorial networks. To obtain a functional network in this case, it is enough to purchase software and hardware related to the same basic technology - network adapters with drivers, hubs, switches, cable system, etc. - and connect them in accordance with the requirements of the standard for this technology.
The basic principle underlying Ethernet is a random method of accessing a shared data transmission medium. Such a 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 defines the topology of electrical connections. Computers are connected to a shared medium in accordance with the typical “common bus” structure. Using a time-shared bus, any two computers can exchange data. Access to the communication line is controlled by special controllers – Ethernet network adapters. Each computer, or 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 idle, that is, if no other computer is currently communicating. Therefore, an important part of Ethernet technology is the procedure for determining the availability of the medium. After the computer is convinced that the network is free, it begins transmission, while “capturing” the medium.
The time of exclusive use of a shared medium by one node is limited by the time of transmission of one frame. A frame is a unit of data exchanged between computers on an Ethernet network. The frame has a fixed format and, along with the data field, contains various service information, such as the recipient's address and the sender's address. The Ethernet network is designed in such a way that when a frame enters a shared data transmission medium, all network adapters simultaneously begin to receive this frame. They all analyze 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 recipient 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 transmitting information. This situation, called a collision, prevents data from being transmitted correctly over the network. The Ethernet standard provides an algorithm for detecting and correctly processing collisions. The probability of a collision depends on the intensity of network traffic. Once a collision is detected, the network adapters that were attempting to transmit their frames stop transmitting and, after a pause of a random duration, attempt to access the medium again and transmit the frame that caused the collision.
The main advantage of Ethernet networks, thanks to which they have become 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 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, Ethernet networks implement fairly simple algorithms for accessing the medium, addressing and transmitting data. The simple logic of network operation leads to simplification and, accordingly, cheaper network adapters and their drivers. For the same reason, Ethernet network adapters are highly reliable.
And finally, another remarkable property of Ethernet networks is their good expandability, that is, the ease of connecting new nodes. Other basic network technologies - Token Ring, FDDI - although they have many individual features, at the same time they have many common properties 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 between one technology and another are associated with the characteristics of the method used to access the shared environment. Thus, the differences between Ethernet technology and Token Ring technology are largely determined by the specifics of the medium separation methods embedded in them - the random access algorithm in Ethernet and the access method by passing a token to Token Ring.
Token Ring Technology
Token Ring is a local area network (LAN) ring technology with “token access” - a local network protocol that is located at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that moves around the ring. Possession of a token gives the owner the right to transmit information on the medium. Token ring frames travel in a loop.
Stations on a Token Ring local area network (LAN) are logically organized in a ring topology, with data transferred sequentially from one ring station to another with a control token circulating around the control access ring. This token passing 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 adopted the IEEE 802.5 standard based on this technology. Recently, even IBM products have been dominated by the Ethernet family of technologies, despite the fact that previously for a long time the company used Token Ring as the main technology for building local networks.
This technology offers a solution to the problem of collisions that arise when operating 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 holding the token has information to transmit, it grabs the token, changes one bit of it (resulting in the token becoming a "beginning of data block" sequence), completes it with the information it wants to transmit, and sends that information to the next station ring network. When a block of information circulates around the ring, there is no token on the network (unless the ring provides early token release), so other stations wishing to transmit information are forced to wait. Therefore, there can be no collisions in Token Ring networks. If early token release is ensured, then a new token can be released after the data block transmission is completed.
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 deleted after reaching the station that sent the block. The sending station can check the returned block to ensure that it was viewed and then copied by the destination station.
Unlike CSMA/CD networks (such as Ethernet), token-passing networks are deterministic networks. This means that it is possible to calculate the maximum time that will pass 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 the environment of automated stations in factories. It is used as a cheaper technology and has become widespread wherever there are critical applications for which it is important not so much speed as reliable information delivery. Currently, Ethernet is not inferior to Token Ring in terms of reliability and is significantly higher in performance.
Token Ring networks, like Ethernet networks, use a shared data transmission medium, which consists of cable segments connecting all network stations into a ring. The ring is considered as a common shared resource, and to access it, not a random algorithm is used, as in Ethernet networks, but a deterministic one, based on the transfer of the right to use the ring by stations in a certain order. The right to use the ring is transferred using a specially formatted frame called a token or token.
The Token Ring standard 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 of 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 emerged as a result of the development of Token Ring technology. Mixing of stations operating at different speeds in the same ring is not allowed.
Token Ring networks, operating at a speed of 16 Mb/s, also have some improvements in the access algorithm compared to the 4 Mb/s standard.
FDDI technology
Technology Fiber Distributed Data Interface- the first local network technology that used fiber optic cable as a data transmission medium.
Attempts to use light as a medium that carries information have been made for a long time - back in 1880, Alexander Bell patented a device that transmitted speech over a distance of up to 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 for them to be used as an alternative to copper cores.
In the 1980s, work also began to create standard technologies and devices for using fiber optic channels in local networks. Work on summarizing experience and developing the first fiber optic standard for local networks was concentrated at the American National Standards Institute - ANSI, within the framework of the X3T9.5 committee created for this purpose.
The initial versions of the various components 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 network technologies support fiber optic cables as a physical layer option, but FDDI remains the most mature high-speed technology, the standards for which have been tested and established over time, 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 FDDI technology set themselves the following goals as their highest priority:
· increase the bit rate of data transfer to 100 Mb/s;
· increase the fault tolerance of the network through standard procedures for restoring it after various types of failures - cable damage, incorrect operation of a node, hub, high levels of interference on the line, etc.;
· use the potential network bandwidth as efficiently as possible 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 network nodes.
Using two rings is the primary way to improve fault tolerance in an FDDI network, and nodes that want to use it must be connected to both rings. In normal network operation mode, data passes through all nodes and all cable sections of the Primary ring, which is why this mode is called Thru mode - “end-to-end” or “transit”. The Secondary ring is not used in this mode.
In the event of some type of failure where part of the primary ring cannot transmit data (for example, a broken cable or node failure), the primary ring is merged with the secondary ring, forming a single ring again. This mode of network operation is called Wrap, that is, “folding” or “folding” of rings. The collapse operation is performed by FDDI hubs and/or network adapters. To simplify this procedure, data is always transmitted counterclockwise on the primary ring, and clockwise on the secondary ring. 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 allows information to be correctly transmitted and received by neighboring stations.
FDDI standards place a lot of emphasis on various procedures that allow you to determine if there is a fault in the network and then make the necessary reconfiguration. The FDDI network can fully restore its functionality in the event of single failures of its elements. When there are 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 subsequent neighbor. This case is shown in the figure. It should be noted that if a station has captured the token and is transmitting 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 matches the address of the station, then it copies the frame to its internal buffer, checks its correctness (mainly by checksum), transfers its data field for subsequent processing to the protocol of a higher 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 this, the frame continues to travel through the network, broadcast by each node. The station that is the source of the frame for the network is responsible for removing the frame from the network after it has completed a full rotation and reaches it again. In this case, the source station checks the characteristics of the frame to see whether it has reached the destination station and whether it has not been damaged. The process of restoring information frames is not the responsibility of the FDDI protocol; this should be handled by higher-level protocols.
X.25 protocol
X.25 is a family of network layer protocols of the OSI network model. It was intended for organizing a WAN based on telephone networks with lines with a fairly high error rate, therefore it contains developed error correction mechanisms. Focused on connection-based work. Historically, it is the predecessor of the Frame Relay protocol.
X.25 provides multiple independent virtual circuits (PVCs and Switched Virtual Circuits (SVCs)) on a single link, identified in an X.25 network by connection connection identifiers (Logical Channel Identifiers (LCIs) 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 in both corporate networks and worldwide specialized service networks such as SWIFT (bank payment system) and SITA (French Société Internationale de Télécommunications Aéronautiques - system information services for air transport), however, currently X.25 is being replaced by other link layer technologies (Frame Relay, ISDN, ATM) and the IP protocol, remaining, however, quite common in countries and territories with undeveloped telecommunications infrastructure.
Developed by Study Group VII of the International Telecommunication Union (ITU), it was adopted as a packet data transfer protocol in telephone networks in 1976 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, currently the ISO 8208 X.25 protocol standard is in force, and the use of X.25 in local networks has also been standardized (ISO 8881 standard).
X.25 defines the characteristics of a telephone network for data transmission. To begin communication, one computer contacts another with a request for a communication session. The called computer can accept or reject the connection. If the call is accepted, then both systems can begin transmitting information with complete duplication. Either party may terminate communication at any time.
The X.25 specification defines point-to-point interaction between terminal equipment (DTE) and data circuit termination equipment (DCE). DTE devices (terminals and host computers in the user equipment) connect to DCE devices (modems, packet switches and other ports to the PDN network, usually located in the equipment of this network), which connect to “packet switching exchanges” ( PSE or simply switches) and other DCEs within the PSN and finally to another DTE device.
The DTE may be a terminal that does not fully implement all X.25 functionality. Such DTEs connect to the DCE through a translation device 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 constitutes Layer 1-3 circuits of the OSI Reference Model. X.25 Layer 3 describes packet formats and procedures for exchanging packets between Layer 3 peer entities. X.25 Layer 2 is implemented by the Link Access Procedure, Balanced (LAPB) Protocol. LAPB defines packet framing for the DTE/DCE link. X.25 Layer 1 defines the electrical and mechanical procedures for activating and deactivating the physical media connecting DTE and DCE data. It should be noted that Levels 2 and 3 are also referred to as ISO standards - ISO 7776 (LAPB) and ISO 8208 (X.25 packet level).
End-to-end transmission between DTE devices is accomplished through a bidirectional link called a virtual circuit. Virtual circuits allow communication between different 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 called PVC; switched virtual circuits – SVC. PVCs are typically used for the most frequently used data transfers, while SVCs are used for sporadic data transfers. X.25 Layer 3 is responsible for end-to-end transmission, including both PVC and SVC.
Once 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 multiplexes between all DTEs served by a DCE located on the destination side of the network, resulting in a packet being delivered to the destination DTE.
Conclusion
The development of computer technology and information technology gave impetus to 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 advent, information and the right to truth and freedom of speech become a potential asset and opportunity for the majority of the planet’s inhabitants; people can unite and interact regardless of time, distance, state and many other borders.
Currently, the whole world is covered by the global Internet. It is the Internet that erases all boundaries and ensures the dissemination of information to an almost unlimited circle of people. Allows people anywhere in the world to easily join in the discussion of pressing problems. The main feature and purpose of the Internet is the free dissemination of information and the establishment of connections between people.
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What is network technology? Why is she needed? What is it used for? Answers to these, as well as a number of other questions, will be given within the framework of this article.
Several important parameters
- Transfer rate. This characteristic determines how much information (measured in most cases in bits) can be transmitted through the network in a certain period of time.
- Frame format. Information that is transmitted through the network is combined into information packets. They are called frames.
- Signal coding type. In this case, it is decided how to encrypt information in electrical impulses.
- Transmission medium. This designation is used for the material, as a rule, it is a cable through which the flow of information passes, which is subsequently displayed on monitor screens.
- Network topology. This is a schematic construction of a structure through which information is transmitted. As a rule, a tire, a star and a ring are used.
- Access method.
The set of all these parameters determines the network technology, what it is, what devices it uses and its characteristics. As you can guess, there are a great many of them.
general information
But what is network technology? After all, the definition of this concept was never given! So, network technology is a coordinated set of standard protocols and software and hardware that implement them in a volume sufficient to build a local computer network. This determines how the data transmission medium will be accessed. Alternatively, you can also find the name “basic technologies”. It is not possible to consider them all within the framework of the article due to the large number, so attention will be paid to the most popular: Ethernet, Token-Ring, ArcNet and FDDI. What are they?
Ethernet
At the moment it is the most popular network technology all over the world. If the cable fails, then the probability that it is the one being used is close to one hundred percent. Ethernet can be safely included in the best network information technologies, due to its low cost, high speed and quality of communication. The most famous type is IEEE802.3/Ethernet. But based on it, two very interesting options were developed. The first (IEEE802.3u/Fast Ethernet) allows for a transmission speed of 100 Mbit/second. This option has three modifications. They differ from each other in the material used for the cable, the length of the active segment and the specific scope of the transmission range. But fluctuations occur in the style of “plus or minus 100 Mbit/second”. Another option is IEEE802.3z/Gigabit Ethernet. Its transmission capacity is 1000 Mbit/s. This variation has four modifications.
Token-Ring
Network information technologies of this type are used to create a shared data transmission medium, which is ultimately formed as the union of all nodes into one ring. This technology is based on a star-ring topology. The first one is the main one, and the second one is the additional one. To gain access to the network, the token method is used. The maximum length of the ring can be 4 thousand meters, and the number of nodes can be 260 pieces. The data transfer rate does not exceed 16 Mbit/second.
ArcNet
This option uses a bus and passive star topology. Moreover, it can be built on unshielded twisted pair and fiber optic cable. ArcNet is a true old-timer in the world of networking technologies. The network length can reach 6000 meters, and the maximum number of subscribers is 255. It should be noted that the main disadvantage of this approach is its low data transfer rate, which is only 2.5 Mbit/second. But this network technology is still widely used. This is due to its high reliability, low cost of adapters and flexibility. Networks and network technologies built on other principles may have higher speeds, but precisely because ArcNet provides high data yield, this allows us not to discount it. An important advantage of this option is that the access method is used through delegation of authority.
FDDI
Network computer technologies of this type are standardized specifications for a high-speed data transmission architecture using fiber optic lines. FDDI has been significantly influenced by ArcNet and Token-Ring. Therefore, this network technology can be considered as an improved data transmission mechanism based on existing developments. The ring of this network can reach a length of one hundred kilometers. Despite the considerable distance, the maximum number of subscribers who can connect to it is only 500 nodes. It should be noted that FDDI is considered highly reliable due to the presence of a primary and backup data path. Adding to its popularity is the ability to quickly transfer data - approximately 100 Mbit/second.
Technical aspect
Having considered what the basics of network technologies are and what they are used, now let’s pay attention to how everything works. Initially, it should be noted that the previously discussed options are exclusively local means of connecting electronic computers. But there are also global networks. There are about two hundred of them in the world. How do modern network technologies work? To do this, let's look at the current construction principle. So, there are computers that are united into one network. Conventionally, they are divided into subscriber (main) and auxiliary. The former are engaged in all information and computing work. What the network resources will be depends on them. Auxiliary ones are engaged in the transformation of information and its transmission through communication channels. Due to the fact that they have to process a significant amount of data, servers boast increased power. But the final recipient of any information is still ordinary host computers, which are most often represented by personal computers. Network information technologies can use the following types of servers:
- Network. Engaged in the transfer of information.
- Terminal. Ensures the functioning of a multi-user system.
- Databases. Involved in processing database queries in multi-user systems.
Circuit Switching Networks
They are created by physically connecting clients for the time that messages will be transmitted. What does this look like in practice? In such cases, a direct connection is created to send and receive information from point A to point B. It includes the channels of one of many (usually) message delivery options. And the created connection for successful transfer must be unchanged throughout the session. But in this case, quite strong disadvantages appear. So, you have to wait a relatively long time for a connection. This is accompanied by high data transmission costs and low channel utilization. Therefore, the use of network technologies of this type is not common.
Message Switching Networks
In this case, all information is transmitted in small portions. A direct connection is not established in such cases. Data transmission is carried out over the first free available channel. And so on until the message is transmitted to its recipient. At the same time, servers are constantly engaged in receiving information, collecting it, checking it and establishing a route. And then the message is passed on. Among the advantages, it is necessary to note the low cost of transmission. But in this case, there are still problems such as low speed and the impossibility of dialogue between computers in real time.
Packet switching networks
This is the most advanced and popular method today. The development of network technologies has led to the fact that information is now exchanged through short information packets of a fixed structure. What are they? Packets are parts of messages that meet a certain standard. Their short length helps prevent network blocking. Thanks to this, the queue at the switching nodes is reduced. Connections are fast, error rates are kept low, and significant gains are made in terms of network reliability and efficiency. It should also be noted that there are different configurations of this approach to construction. So, if a network provides switching of messages, packets and channels, then it is called integral, that is, it can be decomposed. Some of the resources can be used exclusively. Thus, some channels can be used to transmit direct messages. They are created for the duration of data transfer between different networks. When the session for sending information ends, they break up into independent trunk channels. When using packet technology, it is important to configure and coordinate a large number of clients, communication lines, servers and a number of other devices. Establishing rules known as protocols helps with this. They are part of the network operating system used and are implemented at the hardware and software levels.
Material from PIE.Wiki
Modern network technologies have contributed to a new technological revolution. In the United States, the creation of a unified network of computers is given the same importance as the construction of expressways in the sixties. That's why a computer network is called an "information superhighway." Emphasizing the benefits that the network will bring to all users, Microsoft talks about information "at their fingertips."
HIGH SPEED DATA TRANSMISSION CHANNELS
High-speed X.25 and ISDN channels can be used to transmit information. ISDN (Integrated Services Digital Network) allows representatives from different countries to organize video conferences and discuss issues of interest to them without expensive business trips. To implement remote access, digital communication adapters and bridges are inserted into computers, and the slowest adapter for ISDN works many times faster than a modem. Special software has been developed to allow Windows 95 and its Internet browser to work with ISDN. It can be found and obtained for free on the World Wide Web server at http://www.microsoft.com. Currently, Russia is building a nationwide digital network with access abroad, which will be able to provide ISDN communication services and provide end users with remote access to the local networks of their enterprises and interaction with computer networks, including the Internet at speeds of 64 - 128 Kbit/ With. Unfortunately, the implementation of ISDN faces many difficulties, since it requires expensive equipment and requires the installation of special lines.
LOCAL NETWORKS
A computer connected to the network is called a workstation, a computer that provides its resources is called a server, and a computer that has access to shared resources is called a client. Several computers located in the same room or functionally performing the same type of work: accounting or planning, registration of incoming products, etc., are connected to each other and combined into a work group so that they can share various resources: programs, documents , printers, fax, etc. A workgroup is organized so that the computers included in it contain all the resources necessary for normal operation. As a rule, a workgroup that includes more than 10 - 15 computers includes a dedicated server - a fairly powerful computer on which all shared directories and special software for managing access to the entire network or part of it are located. Groups of servers are combined into domains. A domain user can log on to the network at any workstation in that domain and gain access to all of its resources. Typically, in server networks, all shared printers are connected to print servers. From the point of view of organizing the interaction of computers, networks are divided into peer-to-peer (Peer-to-Peer Network) and with a dedicated server (Dedicated Server Network). In a peer-to-peer network, each computer plays an equal role. However, an increase in the number of computers on the network and an increase in the volume of data sent leads to the fact that network bandwidth becomes a bottleneck. Windows 95 is designed primarily to work in peer-to-peer networks, to support the computer as a client of other networks. Windows 95, like Windows for Workgroups, can serve as a server on a network. Compatibility with old network drivers MS-DOS and Windows Z.x is ensured. The new operating system allows you to: share hard drives, printers, fax cards, organize peer-to-peer local area networks (LANs); use remote access and turn your office computer into a callable server; support 16-bit DOS network drivers. The network administrator can set the overall design of the desktop system, determine what operations will be available to network users, and control the configuration of the desktop system. A network located in a relatively small area is called local (LAN - Local Area Network). In recent years, the LAN structure has become more complex due to the creation of heterogeneous networks connecting different computer platforms. The ability to conduct video conferencing and use multimedia increases the requirements for network software. Modern servers can store binary large objects (BLOBs) containing text, graphics, audio, and video files. In particular, if you need to obtain a HR department database over the network, then BLOB technology will allow you to transfer not only personal data: last name, first name, patronymic, year of birth, but also portraits in digital form. Two technologies for using a server There are two technologies for using a server: file server technology and client-server architecture. The first model uses a file server on which most programs and data are stored. At the user's request, the necessary program and data are sent to him. Information processing is performed at the workstation. In systems with a client-server architecture, data exchange is carried out between the client application (front-end) and the server application (back-end). Data is stored and processed on a powerful server, which also controls access to resources and data. The workstation receives only the results of the query. Developers of information processing applications commonly use this technology. The use of large and complex applications has led to the development of a multi-level, primarily three-level architecture with data placed on a separate database server (DB). All calls to the database go through the application server, where they are combined. Reducing the number of database calls reduces license fees for the DBMS. Desktop management interface (DMI) To simplify the installation, security and management of networks using a unified set of APIs and remote management tools, Microsoft, IBM, Novell, DEC, HP, Sun and Synoptics developed the Desktop Management Interface (DMI) standard. direct interaction interface). The standard provides for the possibility of remote updating of programs recorded in ROM, management of groups and individual clients. The implementation of the standard will reduce the cost of operating local networks by reducing staff and increasing the efficiency of its work.
GLOBAL NETWORKS
A local network can be part of a global network that is becoming increasingly recognized throughout the world. The development of media and communications helps to unite people living on different continents according to their interests. Currently, industrialized countries are paying great attention to creating a unified information environment. The creation of an information superhighway will make it easier in the future for people who have common interests but are located in different parts of the world to communicate. The prototype of such a superhighway is the Internet, which provides services to millions of users around the world.
TECHNOLOGIES USED IN INTERNET AND INTRANET
Currently, one of the priority areas of work for companies supplying software is the integration of the local intranet of the enterprise (Intranet), in which the main work of the company takes place, into the global network so that employees of this enterprise can easily create their documents in HTML format ( HyperText Markup Language) and link to other documents. The organization of virtual corporate networks based on the Internet allows you to connect together all branches of suppliers and customers without creating your own network infrastructure. Integration of the corporate Intranet and global network is based on the use of similar methods for storing and presenting information. The computer file system is built on a hierarchical principle, providing a tree-like data storage structure. Internet web servers have a hypertext data presentation scheme, which provides for the creation in documents of links to other documents, which contain explanations of various terms, illustrations, audio files and videos. The standard for constructing such documents is determined by HTML. Software is being developed for text-to-speech technology - translating text into a voice message. In recent years, Microsoft has proposed a number of new technical solutions to provide user experience on the Internet. Together with Intel Corporation, Microsoft is developing a new protocol that improves the way audio and video information is transmitted over the Internet. The protocol, based on ITL) and Internet Engineering Task Force (IETF) specifications, will include the following protocols: T.120 for document conferencing, H.323 for audio and video conferencing, RTP/RTCP and RSVP for Internet teleconferencing management. It should be noted that a number of Bell telephone companies (RBOCs) have filed a complaint with the Federal Telecommunications Commission (FCC) regarding the use of audio technologies on the Internet.
Meaning of the Internet.
It has become commonplace that in the field of information technology the innovation process occurs at an unprecedentedly high pace. “If, since 1971, the automotive industry had developed as rapidly as microprocessor technology, then the car of today would already be racing at a speed of 480 thousand km/hour and would consume 1 liter of fuel per 335 thousand kilometers” - this is how they figuratively compared the pace of scientific and technological progress in two leading US industries by experts from Intel, the world leader in the field of microelectronics. To complete the picture, we can add that this car would have cost only 75 cents! Against this background, the pace with which the transnational Internet network has been formed over the past three years stands out noticeably. Specialized publications have already called it the “Network of Networks,” and the popular business magazine Business Week has defined the near future as the “era of the Internet.” The Internet opens up a new way of human communication, which can be called horizontal. Before its appearance, there was communication and dissemination of information. Basically, vertical: the author writes a book - readers read it. Radio and television transmit something - viewers, and listeners listen and watch it. The newspaper publishes news - subscribers read it. There was almost no feedback, although the need for it was extremely high. This is evidenced by letters to newspapers, requests and responses to radio and television stations, etc. The exchange of information between the readers of a particular book or listeners of a particular program was practically impossible. The Internet provides the dissemination of information to an almost unlimited circle of consumers, and they can easily join in the discussion. The Internet also provides unique opportunities for vertical information communication: between authorities and citizens, for feedback from the latter to the former. There is no organization behind the widespread introduction of the Internet into our lives; the World Wide Web as a phenomenon develops independently, the engine of the Internet is all of humanity. The main idea of the Internet is the free dissemination of information and the establishment of connections between people. This is the most effective way to overcome racial, religious, and ideological barriers between people, countries, and peoples. The Internet is one of the most significant democratic achievements of the technological process. With its advent, information becomes the potential property of the majority of the planet's inhabitants. All global communications associated with telegraph, telephone, radio, television and computer technology are now being integrated into a single whole - the Internet. We are talking about a mechanism for disseminating information, uniting people and their interaction regardless of distance, time, state and many other boundaries.
History of the Internet in Russia
The history of the Russian Internet dates back to the early 80s, when the Kurchatov Institute was the first in our country to gain access to global networks. The Internet in Russia, as well as throughout the world, is increasingly becoming an element of the life of society, of course, becoming more and more similar to this society. Now you can access the Internet from 300-400 thousand computers in Russia and the CIS, and their number is constantly growing. Under favorable conditions, the Russian audience may be much larger than, for example, the German one. Most types of Internet services are already available in Russia. Some (news services, for example) have already been mastered and are almost as good as American ones. The most respected Web servers in Russia can already boast several hundred thousand regular readers. This is not bad compared to, for example, business paper press. And if we compare the qualitative indicators of the Internet audience and the television audience, then in many cases preference may be given to the former. The Russian Internet audience, apart from the number and absolute level of income, is practically no different from the American audience in other respects. Typical users of Web services belong to a socially and economically active segment of the population, are inclined to search for new opportunities for personal and business development, and also generally have a positive attitude towards the reforms being carried out in Russia. In its development, the Russian Internet, in general, repeats the stages of development of the global network. Over the past two years, we have made the leap to almost 2,500 new servers. Go to Yahoo, one of the most popular Internet directories. In the regions (countries) section, opposite each item there is a number - this is the number of links. And you will see what the Russian section looks like. The growth rate is close to the best indicators in the world, although it is limited to some extent by communication problems and the relative high cost of graphics on domestic Internet networks. If we talk about the level of information content of the Russian Internet, then it, of course, could be much higher. The Internet is the country's calling card. The Russian Internet should unite all Russian-speaking users, be the custodian and disseminator of our culture and our language. It is necessary to increase the comfort of the information space in which we live, one of the components of the general standard of human life. The main problems of Russian users include, first of all: a. the lack of a single standard (which, apparently, will never exist until Russia becomes the leading world power in the field of computer technology) for the encoding of Cyrillic characters, which leads to incompatibility of programs. As a result, those who distribute textual information in Russian on the Internet must present it in several encodings, usually three or four, for the main operating systems: MS Windows, UNIX (KOI-8, OS/2, MacOS), which means an increase in labor costs for preparing documents. Otherwise, the user, even having access to the information, will not be able to use it. b. the lack in Russia of developed telecommunication systems and the low quality of telecommunications services. The cost of Internet access via dial-up telephone lines at a speed of 14400-28800 bps in Moscow averages 3-5 dollars per hour. In the USA - $1 per hour or less (with incomparable quality). A high-speed and high-quality connection that allows a Russian user to use the full potential of the Internet will cost tens and sometimes hundreds of times more than its American counterpart.
Application operation on the Internet
Applications running on the Internet are built on Java technology, which includes the Java programming language, the Java virtual machine, and Web browsers that run Java applications. Java is the best language for working with HTML pages. It allows you not to be limited to simply viewing Web pages, but makes it possible to organize the interaction of interactive programs with the user. A technology extension of Java, Java DataBase Connectivity (JDBC), designed for intranets, allows a Java application to access directly a server that may be located on a local network. The concept of Cascade Style Sheets (CSS) has been developed, which defines the styles used in the development of HTML pages, their parts and individual elements. It can be found at http//www.w3org/pub/WWW/TR/WD-style. ActiveX ActiveX technology is the next step in the development of OLE, designed to create interactive applications for the Internet and intranets. It supports Java applications and OLE components. ActiveX is based on COM (Component Object Model) and allows page administrators to use sound and video effects when designing documents. ActiveX controls provide Windows applications with functionality to interact with the Web. The Distributed Component Object (DCOM) model allows developers to create application components that communicate with each other over the Internet. ActiveX with an integrated module (plug-in) is used in Internet Explorer 3.0. Character encoding on the Internet To encode Cyrillic characters on the Internet, mainly four encodings are used: KOI8 (KOI8) - used mainly on computers with UNIX OS, but is not supported by Windows. To solve this problem, it is recommended to install additional KOI fonts and special keyboard drivers such as Cyrwin. CP-1251 - used by Microsoft on Windows, widely used on PC IBM-compatible computers. CP-866 - used mainly on computers running MS-DOS. ISO-8859-5 - applies to UNIX-compatible systems. On most servers, the first two encodings are used. The problem of supporting the Cyrillic alphabet on the Internet is explained by the fact that the codes of Russian letters in the UNIX and Windows operating systems do not match. The difficulties that arise when encoding in KOI8 are discussed in detail on the WWW page at: http://www.nagural.ru/~ache/koi8.html.
Connecting computers into a network has made it possible to organize document flow in a new way both in small firms and in large organizations. There is no longer a need to print documents on paper that a team of users is working on. With the help of appropriate software, a team of users can collaborate to create documents, presentations and databases and send them via e-mail to other project participants, who may work in the same building or in another city, for addition and editing. Alternate mailing allows you to specify the order in which a message is sent between project participants after it has been supplemented and edited. This method of collective work on a document saves a significant part of working time, since there is no need to waste time on personal meetings for collaboration. It is impossible to imagine a modern enterprise without data sharing and developed means of guaranteed information protection. Protocols Used by Email The most popular protocols used on the Internet for receiving email include the Simple Mail Transfer Protocol, SMPT, and the Post Office Protocol, POP. SUPPORT FOR NETWORK OPERATING SYSTEMS Microsoft is committed to making Windows the platform of choice for telecommunications and Internet access. Windows 95 contains a large number of network card drivers and tools designed to manage the network. The single user interface is virtually independent of the type of network supported. To work with various networks, it is necessary that the operating system supports their protocols, i.e. a set of rules (the language of computer communication) used when transmitting information. The network protocol defines routing methods, addressing methods, etc. Windows 95 has built-in support for common network operating systems: Windows NT Advanced Server from Microsoft, Novell NetWare, LAN Manager, LAN Manager for UNIX, LANServer from IBM, 3+Open and 3+Share from 3Com, VINES from Banyan, Pathworks from Digital The operating system allows you to work as part of a heterogeneous network and provides support for a significant part of the 32-bit popular network protocols: TCP/IP, IPX/SPX and NetBEUI and drivers ND1S 2.x, Z.x or ODI. TCP/IP protocol (Transmission Control Protocol/Internet Protocol) is used when working with global networks such as the Internet and Microsoft networks.The IPX protocol makes it possible to connect to NetWare file servers. Windows 95 includes support for various types of network protocols: PPP (Point-to-Point Protocol). Serial Line Internet Protocol, NRN (NetWare Remote Node) and the new Point-to-Point Tunneling Protocol (PPTP), developed by Microsoft together with 3Com. The protocol allows you to create virtual private networks (VPN) over dial-up lines and send secure network packets over the Internet. PPTP is used to organize a “tunnel” when remote users communicate with their corporate networks over the Internet. There is no need for enterprises to share their own global network infrastructure to avoid information leakage. Guaranteed information protection is provided by well-established and proven authentication and encryption tools built into Windows NT Remote Access Service. The disadvantage of Windows 95 is that a dial-up server running this operating system establishes only one connection at a time. To ensure higher performance and flexibility, it is recommended to use Windows NT as a remote access server, which provides up to 256 simultaneous connections and parallel routing.
A computer network is an association of several computers to jointly solve information and computing problems.
The key concept of network technologies is a network resource, which can be understood as hardware and software components participating in the sharing process - in the process of network interaction. Access to network resources is provided by network services (network services)
The basic concepts of network technologies include such concepts 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 sharing of computer resources, and therefore the creation of network resources and corresponding network services, is the root cause of the creation of computer networks themselves.
Allocate five types of network services: file, print, messages, application databases.
File service — implements centralized storage and sharing of files. This is one of the most important network services; it requires 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, network instant messenger messages) and media messages of various voice and video communication systems should be considered as messages.
Database service — is designed to organize centralized storage, search processing and ensure data protection of various information systems. Unlike simply storing and sharing files, a database service also provides management, which includes creating, modifying, deleting data, ensuring its integrity and protecting it.
App Service — provides a method of operation in which the application is launched on the user's computer not from a local source, but from a computer network. Such applications may use server resources for data storage and computation. The advantage of using network applications is the ability to use them from any connection point to a computer network without the need to install the application on a local computer, the ability for multiple users to collaborate, “transparent” software updates, and the ability to use commercial software on a subscription basis.
Application services are the newest and fastest growing type of network service. A good example here is the office network applications of the online services Google Drive and Microsoft Office 365.
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