Network technologies of local networks. Several important parameters

Local networking architectures or technology can be divided into two generations. The first generation includes architectures that provide low and average information transfer rate: Ethernet 10 Mbps), Token Ring (16 Mbps) and Arc Net (2.5 Mbps).

To transfer data, these technologies use cables with copper residential. To the second generation of technologies includes modern high-speed architectures: FDDI (100 Mbit / s), atm (155 Mbps) and upgraded versions of the first generation architectures (Ethernet): Fast Ethernet (100 Mbps) and Gigabit Ethernet (1000 Mbps ). Advanced options for first generation architectures are designed to use cables with copper cores and on fiber-optic data lines. New technologies (FDDI and ATM) are focused on using fiber-optic data transmission lines and can be used to simultaneously transmit information of various types (video images, voices and data). Network technology is a minimum set of standard protocols and implementing their software and hardware, sufficient to build a computing network. Network technologies are called basic technologies. Currently, there are a huge number of networks that have different levels of standardization, such well-known technologies such as Ethernet, token-ring, ArcNet, FDDI received widespread.

Network access methods

Ethernet It is the method of multiple access with listening to carrier and resolution of collisions (conflicts). Before the start of the transfer, each workstation determines whether the channel is free or busy. If the channel is free, the station begins to transmit data. Really conflicts lead to a reduction in network speed only in the case when 80-100 stations are operating. Access method Arcnet. This access method was widespread mainly due to the fact that ArcNet equipment is cheaper than Ethernet or token -ring equipment. Arcnet is used in local networks with a star topology. One of the computers creates a special marker (special message), which is consistently transmitted from one computer to another. If the station must transfer the message, it, having received a marker, generates a package, complemented by the addresses of the sender and destination. When the package comes to the destination station, the message is "uncovered" from the marker and passes the station. Access method Token Ring.. This method is developed by IBM; It is calculated by the network topology network. This method resembles ArcNet, as it also uses a marker transmitted from one station to another. Unlike ArcNet when accessing Token Ring, it is possible to assign different priorities to different workstations.

Basic technology LAN

Ethernet technology is now most popular in the world. The classic Ethernet network uses a standard coaxial cable of two types (thick and thin). However, the Ethernet version of the ethernet is becoming increasingly used as a medium of twisted pairs, since the installation and maintenance of them is much easier. Topologies type "tire" and type "passive star" are used. The standard defines four main types of transmission media.

 10Base5 (thick coaxial cable);

 10Base2 (thin coaxial cable);

 10Base-T (twisted pair);

 10Base-F (fiber optic cable).

Fast Ethernet - high-speed variation of the Ethernet network, providing a transmission rate of 100 Mbps. Fast Ethernet Network Compatible with Networks made according to Ethernet. The main topology of the Fast Ethernet network is a passive star.

The standard defines three types of transmission media for FAST Ethernet:

 100Base-T4 (quad twisted pair);

 100Base-TX (dual twisted pair);

 100Base-FX (fiber optic cable).

Gigabit Ethernet - high-speed variation of the Ethernet network, providing 1000 Mbps transmission speed. The Gigabit Ethernet network standard currently includes the following types of transmission media:

 1000Base-SX is a segment on a multimode fiber optic cable with a light wavelength of 850 nm.

 1000Base-LX is a segment on a multimode and single-mode fiber optic cable with a wavelength of a luminous signal of 1300 nm.

 1000Base-CX is a segment on an electrical cable (shielded twisted pair).

 1000Base-T - segment on the electrical cable (quad-stable unshielded twisted pair).

Due to the fact that the networks are compatible, easily and simply connect the Ethernet segments, Fast Ethernet and Gigabit Ethernet into a single network.

The Taken-Ring network is offered by IBM. Token-Ring was intended to combine all types of computers manufactured by IBM (from personal to large). Taken-Ring network has a star-ring topology. The ArcNet network is one of the oldest networks. As a topology, the ARCNET network uses the "tire" and "passive star". The ArcNet network has enjoyed great popularity. Among the main advantages of the ARCnet network, you can call high reliability, low cost of adapters and flexibility. The main disadvantages of the network is the low speed of information transfer (2.5 Mbps). FDDI (Fiber Distributed Data Interface) -standardized specification for high-speed data network architecture on fiber-optic lines. Transmission rate - 100 Mbps. The main technical characteristics of the FDDI network are as follows:

 The maximum number of network subscribers is 1000.

 Maximum length of the network ring - 20 km

 The maximum distance between network subscribers is 2 km.

 Transmission environment - fiber optic cable

 Mode of access - marker.

 Information transfer rate is 100 Mbps.

Network technology local networks

In local networks, as a rule, a shared data transmission medium (monocanal) is used and the main role is assigned to protocols of the physical and channel levels, since these levels most reflect the specifics of local networks.

Network technology is a coordinated set of standard protocols and implementing their software and hardware, sufficient to build a local computing network. Network technologies are called basic technologies or network architectureslocal networks.

Network technology or architecture determines the topology and access method to the data transfer medium, cable system or data transmission medium, network frame format. Signal coding type, transfer rate on a local network. In modern local computing networks, such technologies or network architectures were widespread as: Ethernet, Token-Ring, ArcNet, FDDI.

2.4.1. Network Technologies of Local Networks IEEE802.3 / Ethernet

Currently, this network technology is most popular in the world. Popularity is provided by simple, reliable and inexpensive technologies. In the classic Ethernet local network, a standard coaxial cable of two types (thick and thin) is used.

However, the Ethernet version of the ethernet is becoming increasingly used as a medium of twisted pairs, since the installation and maintenance of them is much easier. In the local networks of Ethernet, topologies of the type "tire" and type "passive star" are used, and the CSMA / CD access method ( multiple access by listening to carrier and resolution of collisions or conflicts).

The IEEE802.3 standard depending on the type of data transfer medium has modifications:

· 10Base5 (thick coaxial cable) - provides the transfer rate of 10 Mbps and the length of the segment to 500m;

· 10Base2 (thin coaxial cable) - provides the transfer rate of 10 Mbps and the length of the segment to 200m ;;

· 10Base-T (unshielded twisted pair) - allows you to create a network of star topology. The distance from the hub to the end node to 100m. The total number of nodes should not exceed 1024;

· 10Base-F (fiber optic cable) - allows you to create a network of star topology. The distance from the hub to the end node to 2000m.

In the development of Ethernet network technology, high-speed options are created: IEEE802.3U / FAST Ethernet and IEEE802.3Z / Gigabit Ethernet. The main topology that is used in the local networks Fast Ethernet and Gigabit Ethernet, passive star.

Network technology FAST Ethernet provides transmission speed of 100 Mbps and has three modifications:

· 100Base-T4 - unshielded twisted pair (quad twisted pair) is used. Distance from the hub to the end node to 100m;

· 100Base-TX - two twisted pairs (unshielded and shielded) are used. Distance from the hub to the end node to 100m;

· 100Base-FX - Fiber optic cable is used (two fibers in the cable). The distance from the hub to the end node to 2000m;

Network technology of local networks Gigabit Ethernet - provides 1000 Mbps transmission rate. There are the following modifications of the standard:

· 1000Base-SX - A fiber optic cable is used with an 850 nm light wavelength.

· 1000Base-LX - a fiber optic cable with a light signal wavelength of 1300 nm is used.

· 1000Base-CX - used shielded twisted pair.

· 1000Base-T - a quadst unshielded twisted pair is used.

Local Networks Fast Ethernet and Gigabit Ethernet are compatible with local networks made using Ethernet (standard), so easy and easy to connect Ethernet segments, Fast Ethernet and Gigabit Ethernet to a single computing network.

Ethernet, one of the most inexpensive and common technologies is becoming more and more productive, it is endowed with the necessary means of fault tolerance, traffic differentiation and QoS, and therefore is considered as one of the components of the next generation communication networks, especially urban networks (MAN), on the basis of which you can create effective Multiservice solutions.

Network Technologies of Local Networks IEEE802.5 / Token-Ring

The token-Ring network assumes the use of a shared data transfer environment, which is formed by combining all nodes into the ring. Taken-Ring network has a stellar-ring topology (Basic ring and starry additional topology). A marker method is used to access the data transfer medium. (Determined marker method). Standard supports vitua pair (shielded and unshielded) and fiber optic cable. The maximum number of nodes on the ring - 260, the maximum length of the rings is 4000 m. Data transfer rate up to 16 Mbps.

Network Technologies of Local Networks IEEE802.4 / ArcNet

As the topology of the LAN ARCNET network can be used "tire" and "passive star". But in fact, this technology is intended for the organization LAN in the network topology "Star".

The basis of communication equipment is:

• switch (Switch);
• passive / active hub (HUB).

Active hubs are applied with a large removal of the workstation (they restore the signal shape and enhance it). Passive hubs are used with a minor removal of the workstation. The network uses a designated workstation principle of workstations., that is, the right to transfer has a station that received the so-called software marker from the server. I.e implemented determined Network traffic. Supports shielded and unshielded twisted pair and fiber optic cable. The local network Arcnet - this is one of the oldest networks and has enjoyed great popularity.. Among the main advantages of the LAN ARCnet network, you can call high reliability, low cost of adapters and flexibility. The main disadvantages of the network is the low speed of information transfer (2.5 Mbps). Maximum number of subscribers - 255. The maximum network length is 6000 meters.

Network technology is a minimum set of standard protocols and implementing their software and hardware, sufficient to build a computing network. Network technologies are called basic technologies. Currently there are a huge number of networks that have different levels of standardization, such well-known technologies such as Ethernet, token-ring, ArcNet received widespread.

At the moment, Ethernet is the most common technology in local networks. On the basis of this technology, more than 7 million local networks and more than 80 million computers having a network card supporting this technology are operating. There are several Ethernet subtypes depending on the speed and types of the cable used.

One of the founders of this technology is Xerox, which has developed and creating an Ethernet Network test network in 1975. Most of the principles implemented in the mentioned network are used today.

Gradually, the technology was improved, responding to the increasing level of user requests. This led to the fact that the technology expanded the scope of its application to such a data transfer medium as optical fiber or unshielded twisted steam.

The reason for the start of the use of these cable systems has become a fairly rapid increase in the number of local networks in various organizations, as well as the low performance of local networks using a coaxial cable. At the same time, it became necessary in the convenient and cost-effective management and maintenance of these networks, which no longer could provide outdated networks.

Basic principles of Ethernet. All computers included in the network are connected to a shared cable, which is called a common tire. The cable is a transmission medium, and can be used to receive or transmit information any computer of this network.

Ethernet network use packet data method. The sender's computer selects the data you want to send. These data are transformed into short packets (sometimes they are called frames), which contain the addresses of the sender and the recipient. The package is equipped with a preamble information (notes the beginning of the package) - and information about the value of the package checksum, which is necessary to verify the correct transmission of the packet over the network.

Before sending a package, the sender's computer checks the cable controlling in it the absence of a carrier frequency on which the transmission will occur. If this frequency is not observed, it starts the transfer of the package to the network.

The package will be accepted by all network cards of computers that are connected to this network segment. Network cards control the address of the package assignment. If the destination address does not match the address of this computer, the package is deflected without processing. If the addresses are the same, the computer will accept and process the packet, removing all the service data from it and transporting the necessary up information on the levels of the OSI model levels to applied.

After the computer gives the packet, it can withstand a small pause, equal to 9.6 μs, after which again repeats the package transmission algorithm until fully transport the necessary data. Pause is needed so that one computer does not have a physical ability to block the network when transferring a large number of information. While this technological pause lasts, the channel will be able to use any other network computer.

If two computers simultaneously check the channel and attempt to send data packets on a shared cable, then as a result of these actions, a collision occurs, since the contents of both frames face a common cable, which significantly distorts the transmitted data.

After the collision is found, the transmitting computer is obliged to stop the transmission to a small random time interval.

An important condition for the correct operation of the network is the mandatory recognition of the collision by all computers at the same time. If any transmitting computer does not calculate the collision and make a conclusion about the correctness of the package transmission, then this package is simply disappeared due to the fact that it will be very distorted and rejected by the receiving computer (incompatibility of the checksum).

It is likely that lost or distorted information will re-send a top-level protocol that works with establishing a connection and identification of its messages. It should be taken into account that re-transmission will occur after a sufficiently long time interval (tens of seconds), which will lead to a significant reduction in the bandwidth of a particular network. That is why timely recognition of collisions is extremely important for the stability of the network.

All Ethernet parameters are designed so that the collisions are always clearly defined. That is why the minimum length of the data field of the frame is at least 46 bytes (and taking into account the service information - 72 bytes or 576 bits). The length of the cable system is calculated in such a way that during the time the minimum length frame is transported, the signal about the collision has managed to reach the most distant network computer. Based on this, at a rate of 10 Mbps, the maximum distance between arbitrary network elements cannot exceed 2500 m. The higher the data transfer rate, the smaller the maximum length of the network (decreases proportionally). Using the FAST Ethernet standard is limited to the maximum size of 250 m, and in the case of a gigabit Ethernet - 25 m.

Thus, the probability of successful obtaining a common environment directly depends on the workload of the network (the intensity of the emergence of the treatment of personnel.

Permanent increase in the level of network bandwidth requirements was caused by the development of Ethernet technology, the transmission rate in which exceeded 10 Mbps. In 1992, the Fast Ethernet standard was implemented, supporting the transportation of information at 100 Mbps. Most of the principles of Ethernet remained unchanged.

Some changes occurred in the cable system. The coaxial cable was not able to provide the speed of transmission of information in 100 Mbps, so shielded unshielded cables of the type of twisted steam, as well as fiber optic cable come to the Fast Ethernet.

Severe three types of Fast Ethernet:

• - 100Base-TX;
• - 100Base-T4;
• - 100Base-FX.

The 100Base-TX standard uses two cable pairs at once: UTP or STP. One pair is necessary for data transfer, and the second is for receiving. The following requirements correspond to two cable standards: EIA / TIA-568 UTP category 5 and SIT 1 IBM type 1. In 100Base-TX, the possibility of full-duplex mode is available in the process of working with network servers, as well as the use of only two of the four across eight cable - the two remaining pairs will be free and can be used to expand the functionality of this network (for example, based on them is possible telephone network organization).

The standard 100Base-T4 allows you to use category 3 cables and 5. This is due to the fact that in 100Base-T4 four pairs of eight cable are used: one - for transmission, and the other - for reception, the rest can be used as for transmission, And for reception. Accordingly, both reception and data transmission can be carried out immediately for three pairs. If the total bandwidth of 100 Mbps is distributed to three pairs, then 100Base-T4 reduces the frequency of the signal, therefore, for normal operation, there is quite enough less than a high-quality cable. For the organization of 100Base-T4 networks, UTP categories 3 and 5 cables can be used, just like the UTP category 5 and STP type 1.

The standard 100Base-FX uses multimode fiber to transmit data with a 62.5-micron kernel and a 125-micron shell. This standard is intended for highways - connecting Fast Ethernet repeaters within one room. The main advantages of the optical cable were transmitted to the 100Base-FX standard under consideration: immunity to electromagnetic noise, an increased level of information security and increased distances between network devices.

A comparative analysis of local-computing network technologies is presented in Appendix B

For a long time, the FireWire interface (high-speed FireWire serial interface, also known as IEEE1394) was used mainly when processing streaming video. In general, for this it was originally and designed. However, the highest, even today, the bandwidth of this interface (400 Mbps) has made it quite effective for modern peripheral high-speed devices, as well as to organize small high-speed networks.

Thanks to the support of WDM driver, the FireWire interface is supported by operating systems, starting with Windows 98 Second Edition. However, the built-in support for the FireWire interface was first implemented in Windows Millennium, and is now supported in Windows 2000 and Windows XP. All operating systems, except Windows 98SE, also support hot network installation. If the FireWire controller is present in the system, Windows automatically installs the virtual network adapter, with the ability to directly access and modify standard network installations.

By default, the FireWire network supports a TCP / IP protocol, which is enough to solve most of modern network tasks, for example, the Internet Connection Sharing feature, built into the Microsoft operating system.

FireWire provides a significant advantage in speed compared to the standard 100Baset Ethernet network. But this is not the main advantage of the FireWire network. More important is the simplicity of creating such a network, an affordable user not the highest level of preparation. It is also important to note the versatility and low cost.

The main disadvantage of the FireWire network is limited long, cable. According to the specification, for operation at a speed of 400 Mbps, the cable length should not exceed 4.5 meters. To solve this problem, various versions of repeaters are used.

A few years ago, a new Ethernet standard was developed - Gigabit Ethernet. At the moment it is not yet widespread. Gigabit Ethernet technology as optical channels and shielded twisted pair use as an environmental transportation environment. Such a medium is capable of ten times to increase the transfer rate, which is a prerequisite for video conferencing or work of complex programs that operate in large amounts of information.

This technology uses the same principles as earlier Ethernet standards. In addition, the network that is based on a shielded twisted pair can be performed by transitioning to Gigabit Ethernet technology by replacing network cards and network equipment that are used on the network, 1000Base contains three physical interfaces, parameters and characteristics of which are listed below:

• - The interface 1000Base-SX determines the lasers with a permissible radiation length in the range of 770-860 nm, the transmitter radiation power in the range from 10 to 0 dBm, with an existing ON / OFF ratio (there is a signal / no signal) at least 9 dB. The sensitivity of such a receiver is 17 dBm, and its saturation is 0 dBm.
• - The 1000Base-LX interface determines the lasers with a permissible radiation length in the range of 1270-1355 nm, the transmitter radiation power in the range from 13.5 to 3 dBm, with an existing ON / OFF ratio (there is a signal / no signal) at least 9 dB. The sensitivity of such a receiver is 19 dBm, and its saturation is 3 dBm.
• - 1000Base-CX - shielded twisted pair, designed to transport data for short distances. To transport data, all four pairs of copper cable are used, and the transfer rate is in one pair of 250 Mbps. Gigabit Ethernet technology is the fastest of all currently existing local network technologies. Soon most of the networks will be created on the basis of this technology.

Wi-Fi- wireless technology. The name is deciphered as Wireless Fidelity (from English - Wireless Accuracy). Designed to access short distances and, at the same time, at sufficiently high speeds. There are three modifications of this standard - IEEE 802.11a, b and g, their difference from each other in the data rate and the distance to which they can transmit data. Maximum speed of 11/54 / 320 Mbps, respectively, and transmission distance is about 100 meters. The technology is convenient because it does not require great efforts to combine computers to the network, avoids inconveniences of the cable occurring. Currently, services can be used in cafes, airports, parks, etc.

USB network. Designed mainly for users of laptops, because In the absence of a network card in a laptop, it can do quite expensive. The convenience is that the network can be created without the use of network cards and hubs, versatility, the ability to connect any computer.

Data transfer rate 5-7 Mbps Block network via electrical wires. 220V. Electrical networks do not go to any comparison with local and global networks. Electric socket is in each apartment, in each room. Dozens of cable meters, connecting all computers, printers, and other network devices with each other.

But then each computer will become a "workplace" stationary located indoors. To transfer it means shifting the network cable. You can install home wireless IEEE 802.11b network, but problems may occur with the penetration of the signal through the walls and overlaps, besides, this is an extra radiation, which in modern life is enough. And there is a different way to use already existing electrical wires and sockets installed in the walls. The only thing for this will be required - the corresponding adapters. Network connection speed through electrical wires is 14 Mbps. The range of approximately 500 meters.

But it should be borne in mind that the distribution network is three-phase, and to homes are supplied by one phase and zero, evenly loading each of the phases. So, if one user is connected to one phase, and the second to the other, then it will not be possible to use a similar system.

Computer networks are divided into three main classes:

1. Local computer networks (LAN - LocalaReaNetwork) are networks that combine computers that are geographically in one place. The local network combines computers located physically close to each other (in one room or one building).

2. Regional computer networks (MAN - MetropolitanareAnetwork) are networks that combine several local computer networks located within one territory (city, regions or region, for example, the Far East).

3. Global Computing Networks (WAN - WideareAnetwork) are networks that combine many local, regional networks and

computers of individual users located at any distance from each other (Internet, Fido).

The following standards for building local computing networks are currently used:

ArcNet; (IEEE 802.4)

Token Ring; (802.5)

Ethernet. (802.3)

Consider each of them Read more

TechnologyIeee 802.4 ArcNet (or ArcNet, from English. Attached Resource Computer Network) - LAN technology, the purpose of which is similar to the purpose of Ethernet or TKEN Ring. ArcNet was the first technology to create microcomputer networks and became very popular in the 1980s in the automation of the institution. Designed for the organization LAN in the network topology "Star".

The basis of communication equipment is:

switch (Switch)

passive / Active hub

The advantage has switting equipment, as it allows you to form network domains. Active hubs are applied with a large removal of the workstation (they restore the signal shape and enhance it). Passive - with small. The network uses the assignable principle of workstation access, that is, the right to transfer the station that received the so-called software marker from the server. That is, deterministic network traffic is implemented.

Advantages of the approach:

Remarks: Messages transmitted by workstations form a queue on the server. If the queue maintenance time is significantly (more than 2 times) exceeds the maximum package delivery time between the two most remote stations, it is believed that the network bandwidth reached the maximum limit. In this case, further network extension is impossible and the installation of the second server is required.

Limit technical characteristics:

The minimum distance between workstations connected to one cable is 0.9 m.

The maximum length of the network along the longest route is 6 km.

Restrictions are associated with hardware retention of information transfer with a large number of commuting elements.

The maximum distance between the passive concentrator and the workstation is 30 m.

The maximum distance between the active and passive hub is 30 m.

Between active hub and active hub - 600 m.

Advantages:

Low cost of network equipment and the ability to create extended networks.

Disadvantages:

Low data transfer rate. After the distribution of Ethernet as technology to create a LAN, ArcNet has been used in embedded systems.

The support of ArcNet technology (in particular the distribution of specifications) is engaged in the non-profit organization ArcNet Trade Association (ATA).

Technology - ArcNet architecture is represented by two main topologies: tire and star. As a transmission medium, the RG-62 coaxial cable with a 93 ohm wave resistance is used, a plug-based plugs with an appropriate seal diameter (differ from the forks 10Base-2 (thin Ethernet)).

Network equipment consists of network adapters and hubs. Network adapters can be for tire topology, for star and universal. Hubs can be active and passive. Passive hubs are applied to create stellar networks. Active hubs can be for tire, star and mixed topology. The ports for tire topology are physically not compatible with ports for star topology, although they have the same physical connection (BNC socket).

In the case of tire topology, workstations and servers are connected to each other using T connectors (the same as in 10Base-2 (thin "Ethernet)) connected to network adapters and hubs and connected coaxial cable. The extreme points of the segment are terminated with tips with a resistance of 93 ohms. The number of devices on one bus is limited. The minimum distance between the connectors is 0.9 meters and should be more than this magnitude. To facilitate the cutting, labels can be applied to the cable. Separate tires can be combined with tire hubs.

When using star topology, active and passive hubs are applied. Passive hub is a resistive summitor that allows you to connect four cables. All cables in this

the case is connected according to the "point-to-point" principle, without the formation of tires. Between the two active devices, more than two passive hubs should not be connected. The minimum length of any network cable is 0.9 meters and should be a multiple of this magnitude. There is a limitation of the cable length between active and passive ports, between two passive, between two active.

With mixed topology, active hubs are used that support both types of connectivity.

On network adapters of workstation and servers using jumpers or DIP switches, a unique network address is set to the use of the BIOS extension chip, which allows you to remotely boot the workstation (may be disusser), connection type (tire or stellar topology), connecting the built-in terminator ( The last two points is optional). Restriction on the number of workstations - 255 (on the discharge of a network address register). In case two devices have the same network address, both lose their performance, but this conflict does not affect the operation of the network.

With a bus topology, the cable closer or terminator leads to the non-working capacity of the network for all devices connected to the segment, which includes this cable (that is, from the terminator to the terminator). With a starry topology, the breakdown of any cable leads to the failure of the segment, which is turned off by this cable from the server file.

ArcNet logical architecture - ring with marker access. Since such an architecture, in principle, does not allow conflicts, with a relatively large number of hosts (in practice 25-30 workstations was tested) The performance of the ArcNet network was higher than 10Base-2, with four times less in the medium (2.5 versus 10 Mbps ).

TECHNOLOGY 802.5 TOKEN RING - Local computing network technology (LAN) Rings with "marker access" - a local network protocol, which is located on a channel level (DLL) of the OSI model. It uses a special three-seater frame called a marker that moves around the ring. The ownership of the marker provides the right to the owner to transfer information on the carrier. The frames of the ring network with markers are moved to the cycle. In the local computing network (LAN) TOKEN Ring are logically organized into a ring topology with data transmitted sequentially from one ring station to another with a control marker circulating around ring access control. This marker transmission mechanism is shared by ArcNet, a marker tire, and FDDI, and has theoretical advantages over stochastic CSMA / CD Ethernet.

Marker's transfer token Ring and IEEE 802.5 are the main examples of networks with marker. The network with the transmission of the marker is moved along the network a small data block called marker. Owning this marker guarantees the right to transfer. If the node accepting the marker does not have information for sending, it simply rewinds the marker to the next end station. Each station can hold the marker for a certain maximum time (by default - 10 ms).

This technology offers an option to solve the problem of collisions, which occurs when the local network is operating. In Ethernet technology, such conflicts occur while simultaneously transmitting information to several workstations located within one segment, that is, using a common physical data channel.

If the station that owns the marker, there is information for transmission, it captures the marker, it changes in his one bit (as a result of which the marker turns into a "beginning of the data block" sequence), complements the information that he wants to transfer and sends this information to the next station ring network. When the information block circulates over the ring, there is no marker in the network (if only the ring does not provide an "early release of the marker" - Early Token Release), so other stations wishing to transfer information to expect. Consequently, in networks token Ring can not be conflicts. If the earlier release of the marker is provided, the new marker can be released after completing the transmission of the data block.

The information block circulates over the ring until it reaches the intended destination station, which copies the information for further processing. The information block continues to circulate by ring; It is finally removed after reaching the station, which fishes this block. The sending station can check the returned block to make sure it has been viewed and then copied by the destination station.

The scope of application in contrast to CSMA / CD networks (for example, Ethernet) networks with marker transfer are deterministic networks. This means that you can calculate the maximum time, which will pass before any end station can be transmitted. This feature, as well as some reliability characteristics, make the network token Ring ideal for applications where the delay must be predictable and the stability of the network is important. Examples of such applications is the environment of automated stations on the factories.

It is used as a cheaper technology, gained distribution everywhere where there are responsible applications for which not so much speed as reliable delivery of information is important. Currently, Ethernet for reliability is not inferior to token Ring and significantly higher in performance.

Modifications token RingSupply 2 modifications in transmission speeds: 4 Mbps and 16 Mbps. In Token Ring 16 Mbps used

an early liberation technology of the Marker. The essence of this technology is that the station, "capturing" marker, is generated by a free marker at the end of data transfer and launches it to the network. Attempts to implement 100 Mbps did not be crowned with commercial success. Currently, TKen Ring technology is not supported.

802.3 Ethernet technology from English. Ether "Ether") - Package technology of data transmission mainly local computer networks.

Ethernet standards define wired connections and electrical signals at the physical level, frame format and medium access control protocols - on channel level of the OSI model. Ethernet is mainly described by group 802.3. Ethernet has become the most common LAN technology in the mid-90s of the last century, proving such outdated technologies such as ArcNet, FDDI and TKEN Ring.

The following should be taken into account on the creation of a local network:

* Creating a local network and setup equipment for accessing the Internet;

* The choice of equipment should be based on the specifications capable of meeting the requirements for the data transfer rate;

* The equipment must be safe, protected from electric shock;

* Each workstation has a network cable to connect to the network;

* Possible Wi-Fi throughout the Account;

* The location of jobs should satisfy the requirements of standards for placing equipment in educational institutions;

* The cost of creating a local network should be economically justified;

* Local network reliability.

Technologies for building local computing networks are changing fairly quickly, adjusting to the needs of consumers. Now no one wants to wait for hours while the favorite movie is downloaded or a presentation with a lot of photos is passed. Modern networks allow you to increase the quality of connection with computers and other devices so that the loading speed of most materials to the consumer seems the same as from the hard disk.

Basic technology of local networks

Basic technology for building local networks, which are also called architectures, can be divided into two generations. The first generation provides low and medium data transfer speeds, the second is high.

The first generation of technologies includes such that function based on the use of cable with copper residential:

• ARC NET (speed up to 2.5 Mbps);
• Ethernet (up to 10 Mbps);
• Token Ring (up to 16 Mbps).

The second generation of architectures is based mainly on fiber-optic lines, and some options are built on the basis of cable with copper residential high quality. These include:

• FDDI (up to 100 Mbps);
• Atm (up to 155 Mbps);
• Fast Ethernet (up to 100 Mbps);
• Gigabit Ethernet (up to 1000 Mbps).

Local networking technologies

Network technology implies the use of a minimum set of standard protocols and necessary to maintain software and hardware. There are many different protocols, but the most popular are those that develop on the basis of Ethernet, FDDI, TOKEN-Ring, ArcNet.

The most popular is Ethernet technology and its more modern options. For its construction, a thin and thick coaxial cable is used, as well as twisted steam, which is more simple when installing and maintaining.

Local Computer Setup Technology

The most common technology today is the Ethernet architecture, its high-speed Fast Ethernet and Gigabit Ethernet variants are easily combined with each other and with it into a single network, which simplifies scaling tasks. The data transfer rate in such a network depends on the type of cable. Here are variants from a thin coaxial cable to a multimode fiber optic cable with a light signal speed of up to 1300 nm.

• The network of the ArcNet type is outdated and provide low speed (2.5 Mbps). But on a number of enterprises, they can still be found, since they used to be in great demand. This is a very reliable network with low cost adapters and flexibility in setting up. Usually it has a topology in the form of "tires" or "passive star".
• The token-ring ring type itself also goes to the history of the LAN, but it is necessary to know about it, because it has become the basis and prototype of the new generation of the FDDI standard.
• Fiber Distributed Data Interface (Fiber Distributed Data Interface) With a marker method of access, a fiber optic cable is used. This is a high-speed architecture that can support up to 1000 subscribers. At the same time, the maximum length of the ring cannot be more than 20 kilometers, and the distance between the subscribers should be no more than 2 km. These features make it applicable to equip medium and small enterprises with a small number of jobs.

Local Network Technology Developers

Most technologies for building local networks came to Russia from abroad.

• The ArcNet standard was developed by DataPoint under the guidance of John Murphy engineer, he was presented to the public in 1977.
• Ethernet standard in 1975 introduced an American XEROX company, the second generation of the network was developed by DEC, Intel and Xerox, because of which it began to call Ethernet DIX. On its basis, IEEE 802.3 protocol was developed, now used, including to build wireless networks.
• The TOKEN-Ring standard was created by IBM Nerko for the computers produced by it. But since there are many devices of different brands on the market, he did not receive widespread development.
• The FDDI standard appeared in the mid-1980s and became the basis for building second generation networks, although it is based on token-ring technology, within which the information marker is used to transmit it from the computer to the computer. The standard was developed by the ANSI Institute, he immediately supported the transfer rate of 100 Mbps for a double fiber optic cable.

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