New performance requirements networks requirements of modern applications, such as multimedia, distributed computing, and online transaction processing systems, create an urgent need to expand the relevant standards.

The usual ten-megabit Ethernet, which has occupied a dominant position for a long time, at least looking from Russia, is actively being replaced by more modern and significantly more fast technologies data transmission.

On the market high speed(more than 100 Mbit/s) networks, a couple of years ago represented only by FDDI networks, today about a dozen different technologies are offered, both developing existing standards and based on conceptually new ones. Among them, special mention should be made:

· Good old fiber optic FDDI interface, as well as its extended version, FDDI II, specially adapted for working with multimedia information, and CDDI, which implements FDDI on copper cables. All versions FDDI support data transfer speed of 100 Mbit/s.

· 100Base X Ethernet, which is a high-speed Ethernet with multiple access among and collision detection. This technology is an extensive development of the IEEE802.3 standard.

· 100Base VG AnyLAN, new construction technology local networks, supporting data formats Ethernet and Token Ring with a transmission speed of 100 Mbit/s over standard twisted pairs and fiber optics.

· Gigabit Ethernet. Continued development of networks Ethernet and Fast Ethernet.

· ATM, a data transmission technology that works both on existing cable equipment and on special optical communication lines. Supports exchange speeds from 25 to 622 Mbit/s with the prospect of increasing to 2.488 Gbit/s.

· Fiber Channel, a physical switching fiber optic technology designed for applications requiring ultra-high speeds. Landmarks - cluster computing, organization of interaction between supercomputers and high-speed storage arrays, support for connections such as a workstation - a supercomputer. Declared exchange speeds range from 133 Mbit to gigabit per second (and even more).

The outlines of the technology are tempting, but far from clear. FFOL (FDDI Follow on LAN), initiatives ANSI, designed to replace in the future FDDI with a new performance level of 2.4 GB/sec.

ATM

ATM- child of telephone companies. This technology was not developed with computer data networks in mind. ATM radically different from conventional network technologies. The basic unit of transmission in this standard is the cell, as opposed to the usual packet. The cell contains 48 bytes of data and 5 bytes of header. This is partly to ensure very low transmission latency. multimedia data. (In fact, the cell size was a compromise between American telephone companies, which prefer a cell size of 64 bytes, and European telephone companies, which prefer 32 bytes).

Devices ATM establish communication with each other and transmit data via virtual communication channels, which can be temporary or permanent. A permanent communication channel is the path along which information is transmitted. It always remains open regardless of traffic. Temporary channels are created on demand and are closed as soon as data transmission ends.

From the very beginning ATM was designed as a switching system using virtual communication channels that provide a pre-specified level of quality of service (Quality of Service - QoS) and support constant or variable data transfer rates. The QoS model allows applications to request a guaranteed transfer rate between a destination and a source, regardless of the complexity of the path between them. Every ATM- a switch, communicating with another, chooses a path that guarantees the speed required by the application.

If the system cannot satisfy the request, it reports this to the application. True, existing data transfer protocols and applications have no concept of QoS, so this is another great feature that no one uses.

Due to the presence of such beneficial properties ATM No one is surprised by the general desire to continue improving this standard. But so far, existing hardware implementations are rather limited by the original approach, which focused on other, non-computer tasks.

For example, ATM does not have a built-in broadcast notification system (this is typical for ATM, there is an idea, but there is no standard). And although broadcast messages are a constant headache for any administrator, in some cases they are simply necessary. A client looking for a server should be able to send out a message “Where is the server?” and then, upon receiving a response, send its requests directly to the desired address.

Forum ATM specifically developed specifications for network emulation - LAN emulation (LANE). LANE turns point-to-point oriented ATM network into a normal one, where clients and servers see it as a normal broadcast network using IP protocol(and soon IPX). LANE consists of four different protocols: Server Configuration Protocol ( LAN emulation configuration service - LECS), server protocol ( LAN emulation server - LES), general broadcast protocol and unknown server ( Broadcast and Unknown Server - BUS) and client protocol ( LAN emulation client - LEC).

When the client using LANE trying to connect to the network ATM, then initially it uses the protocol LECS. Because the ATM does not support broadcast messages, forum ATM allocated a special address LECS, which no one else uses anymore. By sending a message to this address, the client receives the address corresponding to it LES. Level LES provides the necessary functions ELAN (emulated LAN). With their help, the client can get the address BUS service and send him a message “such and such a client has connected”, so that then BUS the level could, upon receiving messages, forward it to all registered clients.

In order to use ATM protocols must be used L.E.C.. L.E.C. works as a converter, emulating the normal network topology that IP implies. Because the LANE only models Ethernet, then it can eliminate some old technological errors. Every ELAN can use different package sizes. ELAN, which serves stations connected using regular Ethernet, uses 1516 byte packets, while ELAN providing communication between servers can send packets of 9180 bytes. It's all controlled L.E.C..

L.E.C. intercepts broadcast messages and sends them BUS. When BUS receives such a message, it sends a copy of it to each registered L.E.C.. At the same time, before sending copies, it converts the packet back into Ethernet-form, indicating the broadcast address instead of your address.

The cell size of 48 bytes plus a five-byte header means that only 90.5% of the bandwidth is spent on transferring useful information. Thus, the real data transfer speed is only 140 Mbit/s. And this does not take into account the overhead costs of establishing communications and other service interactions between different protocol levels - BUS and LECS.

ATM- complex technology and so far its use is limited LANE. All this greatly hinders the widespread adoption of this standard. True, there is a reasonable hope that it will actually be used when applications appear that can take advantage of ATM directly.

ATM- this abbreviation can denote asynchronous data transfer technology ( Asynchronous Transfer Mode), not only Adobe Type Manager or Automatic Teller Machine, which may seem more familiar to many. This technology for building high-speed computer networks with packet switching is characterized by unique scalability from small local networks with exchange speeds of 25-50 Mbit/sec to transcontinental networks.

The transmission medium is either twisted pair (up to 155 Mbit/s) or optical fiber.

ATMis a development STM (Synchronous Transfer Mode)), technology for transmitting packet data and speech over long distances, traditionally used to build telecommunications highways and telephone networks. Therefore, first of all we will consider STM.

STM model

STMis a connection-switched network mechanism where a connection is established before data transmission begins and is terminated after it has finished. Thus, communicating nodes acquire and hold the channel until they deem it necessary to disconnect, regardless of whether they transmit data or remain silent.

Data in STM transmitted by dividing the entire channel bandwidth into basic transmission elements called time channels or slots. The slots are combined into a cage containing a fixed number of channels, numbered from 1 to N. Each slot is assigned one connection. Each of the clips (there can also be several of them - from 1 to M) defines its own set of connections. The clip provides its slots to establish a connection with period T. It is guaranteed that during this period the required clip will be available. The parameters N, M and T are determined by the relevant standardization committees and differ in America and Europe.

Within the channel STM each connection is associated with a fixed slot number in a specific holder. Once a slot is captured, it remains at the disposal of the connection for the entire lifetime of that connection.

Isn't it a bit like a train station from which a train departs in a certain direction with period T? If among the passengers there is someone for whom this train is suitable, he takes an empty seat. If there is no such passenger, then the seat remains empty and cannot be occupied by anyone else. Naturally, the capacity of such a channel is lost, and it is impossible to carry out all potential connections (M*N) simultaneously.

Transition to ATM

Application studies fiber optic channels on transoceanic and transcontinental scales have revealed a number of features of data transmission of different types. In modern communications, two types of requests can be distinguished:

Transmission of data that is resistant to some losses, but critical to possible delays (for example, high-definition television signals and audio information);

Transfer of data that is not very critical to delays, but does not allow loss of information (this type of transfer, as a rule, refers to computer-to-computer exchanges).

The transmission of heterogeneous data results in periodic occurrence of service requests requiring high bandwidth but low transmission time. A node sometimes requires peak channel performance, but this happens relatively rarely, taking, say, one tenth of the time. For this type of channel, one of ten possible connections is implemented, which, naturally, reduces the efficiency of using the channel. It would be great if it were possible to transfer a temporarily unused slot to another subscriber. Alas, within the framework of the model STM this is impossible.

Model ATM was adopted at the same time AT&T and several European telephone giants. (By the way, this could lead to the emergence of two specification standards at once ATM.)

The main idea was that there is no need for a strict correspondence between the connection and the slot number. It is enough to transmit the connection identifier along with the data to any free slot, while making the packet so small that in case of loss, the loss would be easily replenished. All this looks a lot like packet switching and is even called something similar: “fast switching of short fixed-length packets.” Short packages are very attractive to telephone companies seeking to preserve analog lines STM.

Online ATM two nodes find each other using the “virtual connection identifier” ( Virtual Circuit Identifier - VCI), used instead of slot and clip numbers in the model STM. The fast packet is sent to the same slot as before, but without any indication or identifier.

Statistical multiplexing

Fast packet switching solves the problem of unused slots by statistically multiplexing multiple connections on a single link according to their traffic parameters. In other words, if a large number of compounds are pulsed (the ratio of peak to average activity is 10 or more to 1), it is hoped that the peaks of activity of different compounds will not coincide too often. If there is a match, one of the packets is buffered until free slots become available. This method of organizing connections with correctly selected parameters allows you to efficiently load channels. Statistical multiplexing, not feasible in STM, and is the main advantage ATM.

Types of ATM Network User Interfaces

First of all, this is an interface focused on connecting to local networks that operate data frames (families IEEE 802.x and FDDI). In this case, the interface equipment must translate local network frames to the network transmission element ATM acting as a global backbone connecting two segments of the local network that are significantly distant from each other.

An alternative could be an interface designed to serve end nodes that directly operate data formats ATM. This approach makes it possible to increase the efficiency of networks that require significant amounts of data transmission. To connect end users to such a network, special multiplexers are used.

In order to administer such a network, each device runs a certain “agent” that supports processing administrative messages, managing connections and processing data from the corresponding management protocol.

ATM data format

Plastic bag ATM determined by a special subcommittee ANSI, must contain 53 bytes.

5 bytes are occupied by the header, the remaining 48 are the content of the packet. The header contains 24 bits for the identifier. VCI, 8 bits are control bits, the remaining 8 bits are reserved for the checksum. Of the 48 bytes of the content part, 4 bytes can be allocated for a special adaptation layer ATM, and 44 - actually for the data. Adaptation bytes allow short packets to be combined ATM into larger entities, such as frames Ethernet. The control field contains service information about the packet.

ATM protocol layer

Place ATM in a seven-level model ISO- somewhere around the data transfer level. True, it is impossible to establish an exact correspondence, since ATM itself deals with the interaction of nodes, control of passage and routing, and this is done at the level of preparation and transmission of packets ATM. However, exact correspondence and position ATM in the model ISO not so important.More importantly, understand how to interact with existing networks TCP/IP and in OS Features with applications that require direct interaction with the network.

Applications that have a direct interface ATM, the benefits provided by a homogeneous network environment are available ATM.

The main load is placed on the “Virtual connection management” level ATM", decrypts specific headers ATM, which establishes and breaks connections, performs demultiplexing and performs the actions required of it by the control protocol.

Physical layer

Although the physical layer is not part of the specification ATM, it is taken into account by many standardizing committees. Basically, the physical layer is considered to be a specification SONET (Synchronous Optical Network) is an international standard for high-speed data transmission. Four types of standard exchange rates are defined: 51, 155, 622 and 2400 Mbit/s, corresponding to the international hierarchy of digital synchronous transmission ( Synchronous Digital Hierarchy - SDH). SDH specifies how data is fragmented and transmitted synchronously over fiber optic links without requiring synchronization of the channels and clock rates of all nodes involved in the data transfer and recovery process.

Data flow control

Due to high network performance ATM mechanism traditionally used in networks TSR, unsuitable. If transmission control were assigned to the feedback, then during the time until the feedback signal, having waited for the channel to be allocated and gone through all stages of conversion, reaches the source, it would have time to transfer several megabytes to the channel, not only causing its overload, but possibly completely blocking the source of overload.

Most standards organizations agree on the need for a holistic approach to pass inspection. Its essence is this: control signals are generated as data passes through any part of the chain and are processed at any nearest transmitting node. Having received the corresponding signal, the user interface can choose what to do - reduce the transmission rate or inform the user that an overflow has occurred.

Basically, the idea of ​​traffic control in networks ATM comes down to impacting the local segment without affecting segments that are doing well and achieving maximum throughput where possible.

User interface protocol stack in TCP/IP	Direct ATM interface
Data	Application that analyzes data
	OS application interface
	Managing ATM Virtual Connections
ATM Application Layer
Data level	ATM Interface Driver
Physical layer (SONET)

100VG-AnyLAN

In July 1993, at the initiative of companies AT&T And Hewlett-Packard a new committee was organized IEEE 802.12, designed to standardize new technology 100BaseVG. This technology was a high-speed extension of the standard IEEE 802.3(also known as 100BaseT, or Ethernet on twisted pair).

In September the company IBM proposed to combine support in the new standard Ethernet And Token Ring. The name of the new technology has also changed - 100VG-AnyLAN.

The technology must support both existing network applications and newly created ones. This is achieved by simultaneous support for data frame formats and Ethernet, and Token Ring, which ensures the transparency of networks built using new technology for existing programs.

For some time now, twisted pair cables have been replacing coaxial cables everywhere. Its advantages are greater mobility and reliability, low cost and simpler network administration. The process of replacing coaxial cables is also underway here. Standard 100VG-AnyLAN is focused both on twisted pairs (any existing cable system is suitable for use) and on fiber-optic lines that allow a significant distance between subscribers. However, the use of optical fiber does not affect the exchange speed.

Topology

Because the 100VG designed to replace Ethernet and Token Ring, it supports the topologies used for these networks (logically common bus and token ring, respectively). Physical topology is a star, loops or branches are not allowed.

With cascade connection hubs Only one communication line is allowed between them. The formation of backup lines is possible only if exactly one is active at any time.

The standard provides for up to 1024 nodes in one network segment, but due to reduced network performance, the real maximum is more modest - 250 nodes. Similar considerations determine the maximum distance between the most distant nodes - two and a half kilometers.

Unfortunately, the standard does not allow the combination in one segment of systems that simultaneously use formats Ethernet and Token Ring. For such networks there are special 100VG-AnyLAN bridges Token Ring-Ethernet. But in case of configuration 100VG-Ethernet segment Ethernet with normal transfer speed (10 Mbit/s) can be connected using a simple speed converter.

Equipment

Transmission media . For 100Base-T Ethernet cables containing four unshielded twisted pairs are used. One pair is used to transmit data, one pair is used to resolve conflicts; the two remaining pairs are not used. Obviously, transmitting data on all four pairs will give you a fourfold gain. Replacing the standard "Manchester" code with a more efficient one - 5B6B NRZ- gives the gain almost twice as much (due to the transmission of two data bits in one clock cycle). Thus, with only a slight increase in the carrier frequency (about 20%), the performance of the communication line increases tenfold. When working with shielded cables typical for networks Token Ring, two twisted pairs are used, but at twice the frequency (due to the fact that the cable is shielded). When transmitting over such a cable, each pair is used as a fixed unidirectional channel. One pair carries input data, the other carries output. The standard distance of nodes at which transmission parameters are guaranteed is 100 meters for pairs of the third and fourth categories and 200 meters for the fifth.

Fiber optic pairs may be used. Thanks to this carrier, the covered distance increases to two kilometers. As with shielded cable, a bidirectional connection is used.

Hubs 100VGcan be connected in cascade, which ensures a maximum distance between nodes in one segment on unshielded cables of up to 2.5 kilometers.

Hubs . The main actor in building the network 100VG-AnyLAN is hub(or hub). All network devices, regardless of their purpose, are connected to hubs. There are two types of connections: for uplink and downlink. By “up” connection we mean connection with hub higher level. “Down” is a connection to lower-level end nodes and hubs (one port for each device or hub).

To protect data from unauthorized access, two operating modes for each port are implemented: confidential and public. In confidential mode, each port receives only messages addressed directly to it, in public mode - all messages. Typically, public mode is used to connect bridges and routers, as well as various types of diagnostic equipment.

In order to improve system performance, data addressed to a specific node is transmitted only to it. Data intended for broadcasting is buffered until the end of transmission and then sent to all subscribers.

100VG-AnyLAN and OSI model

In the intended standard IEEE 802.12, 100VG-AnyLAN determined at the data transmission level (2nd level of the seven-level model ISO) and at the physical level (1st level ISO).

The data transfer level is divided into two sublevels: logical connection control ( LLC - Logical Link Control) and media access control ( MAC - Medium Access Control).

Standard OSI The data link layer is responsible for ensuring reliable data transfer between two network nodes. Receiving a packet for transmission from a higher network layer, the data link layer attaches the recipient and source addresses to this packet, forms a set of frames for transmission from it, and provides the redundancy necessary for error detection and correction. The data link layer provides support for frame formats Ethernet and Token Ring.

Upper sublevel - logical connection control - provides data transmission modes both with and without connection establishment.

Lower sublevel - media access control - during transmission, ensures the final formation of the transmission frame in accordance with the protocol implemented in this segment ( IEEE 802.3 or 802.5). If we are talking about receiving a packet, the sublayer determines the correspondence of the address, checks the checksum and determines transmission errors.

Logically MAC-The sublayer can be divided into three main components: the request priority protocol, the connection testing system, and the transmission frame preparation system.

Request Priority Protocol - Demand Priority Protocol (DPP)- interpreted by the standard 100VG-AnyLAN as an integral part MAC sublayer. DPP determines the order in which requests are processed and connections are established.

When an end node is ready to transmit a packet, it sends a normal or high priority request to the hub. If the node has nothing to send, it sends a "free" signal. If the node is not active (for example, the computer is turned off), it naturally does not send anything. In the case of a cascade connection of hubs, when a transmission node requests a request from a lower-level hub, the latter broadcasts the request “up”.

Hubcyclically polls ports to determine their readiness for transmission. If several nodes are ready to transmit at once, the hub analyzes their requests based on two criteria - the priority of the request and the physical number of the port to which the transmitting node is connected.

High priority requests are naturally processed first. Such priorities are used by applications that are critical to response time, such as full-format multimedia systems. The network administrator can associate dedicated ports with high priorities. In order to avoid performance losses, a special mechanism is introduced that prevents all requests originating from one node from being assigned high priority. Multiple high priority requests made at the same time are processed according to the physical port address.

After all high priority requests have been processed, normal priority requests are processed in the order also determined by the physical port address. To ensure guaranteed response time, a normal request that has waited 200-300 milliseconds is given high priority.

When polling a port to which a lower-level hub is connected, polling of its ports is initiated and only after that polling of higher-level ports is resumed. hub. Thus, all end nodes are polled sequentially, regardless of the hub level to which they are connected.

Connection testing system . When testing connections, the station and its hub exchange special test packets. At the same time, all other hubs receive a notification that testing is taking place somewhere in the network. In addition to verifying connections, you can obtain information about the types of devices connected to the network ( hubs, bridges, gateways and end nodes), their modes of operation and addresses.

Connections are tested each time a node is initialized and each time a specified transmission error level is exceeded. Testing connections between hubs is similar to testing end node connections.

Preparing the transmission frame . Before transferring data to the physical layer, it is necessary to supplement it with a service header and ending, including filling out the data field (if necessary), subscriber addresses and control sequences.

100VG-AnyLAN transmission frame

Intended standard IEEE-802.12 supports three types of data frame formats: IEEE 802.3 (Ethernet), IEEE 802.5 (Token Ring) and a special format for connection testing frames IEEE 802.3.

The standard limits the permissible networking by prohibiting the use of different frame formats within the same network segment. Each segment can support only one logical standard, and to build heterogeneous networks, the use of special bridges is prescribed.

Data transfer order for formats Ethernet and Token Ring is the same (the most significant byte is transmitted first, the least significant byte last). The only difference is the order of the bits in the bytes: in the format Ethernet The least significant bits are transmitted first, and Token Ring- seniors.

Frame Ethernet (IEEE 802.3) must contain the following fields:

D.A.- packet recipient address (6 bytes);

S.A.

L- data length indicator (2 bytes);

user data and placeholders;

FCS- control sequence.

Frame Token Ring (IEEE 802.5) contains more fields. Some of them are protocol 100VG-AnyLAN are not used, but are saved only to ensure data compatibility with 4 and 16 Mbit/s segments (when exchanged through the appropriate bridges):

AC- access control field (1 byte, not used);

F.C.- frame control field (1 byte, not used);

D.A.- recipient address (6 bytes);

S.A.- sender address (6 bytes);

R.I.- router information field (0-30 bytes);

information field;

FCS- check sequence (4 bytes).

Physical layer of 100VG-AnyLAN networks

In the model ISO The physical layer is responsible for the direct process of transferring data bits from one node to another. Connectors, cables, signal levels, frequencies and other physical characteristics are described by this level.

As an electrical standard for data transmission, the developers decided to return to the well-known method of direct two-level coding ( NRZ code), where a high signal level corresponds to a logical one, and a low signal level corresponds to a logical zero. Once upon a time, at the dawn of the era of digital data transmission, this method was abandoned. This was mainly due to synchronization difficulties and occurred despite the greater density of information per clock cycle of the carrier frequency - two bits per clock cycle.

Using the encoding 5B6B, which predetermines an equal number of zeros and ones in the transmitted data, allows you to obtain sufficient synchronization. Even the presence of three bits of the same level in a row (and more of them are prohibited by encoding and are interpreted as an error) does not have time to lead to desynchronization of the transmitter and receiver.

Thus, with a code redundancy of 20%, the channel capacity doubles. At a clock frequency of 30 MHz, 25 Mbit/s of original data is transmitted over one pair; the total transmission volume over four pairs of one cable is 100 Mbit/s.

Managing data transmission in networks

Networks built on unshielded twisted pair cables use all four pairs of cable and can operate in both full-duplex (for transmitting control signals) and half-duplex mode, when all four pairs are used to transmit data in one direction.

In shielded pair or fiber optic networks, two unidirectional channels are implemented: one for example, the other for transmission. Reception and transmission data can be carried out simultaneously.

In networks using optical fiber or shielded pairs, data transmission occurs in a similar way. Small differences are determined by the presence of channels constantly operating in both directions. A node, for example, may receive a packet and simultaneously send a service request.

Fast Ethernet

Ethernet, for all its success, has never been elegant. Network cards have only a rudimentary concept of intelligence. They actually send the packet first and then look to see if anyone else was transmitting data at the same time. Someone compared Ethernet with a society in which people can only communicate with each other when everyone shouts at the same time.

Like his predecessor, Fast Ethernet uses data transfer method CSMACD (Carrier Sense Multiple Access with Collision Detection- Multiple media access with carrier sensing and collision detection). Behind this long and confusing acronym lies a very simple technology. When is the fee Ethernet must send a message, it first waits for silence, then sends the packet and at the same time listens to see if anyone has sent a message at the same time. If this happens, then both packets do not reach the destination. If there was no collision, and the board must continue to transmit data, it will still wait a few microseconds.

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L14: High-speed technologiesEthernet

IN 1:FastEthernet

Fast Ethernet was proposed by 3Com to implement a network with a transmission speed of 100 Mbit/s while maintaining all the features of 10 Mbit Ethernet. For this purpose, the frame format and access method were completely preserved. This allows you to completely save the software. One of the requirements was also the use of a twisted-pair cabling system, which by the time of the advent of Fast Ethernet took a dominant position.

Fast Ethernet involves the use of the following cabling systems:

1) Multimode fiber optic link

Network structure: hierarchical tree, built on hubs, since coaxial cable was not intended to be used.

The diameter of the Fast Ethernet network is about 200 meters, which is associated with a reduction in the transmission time of a frame of minimum length. The network can operate in either half-duplex or full-duplex mode.

The standard defines three physical layer specifications:

1) Using two unshielded pairs

2) Use of four unshielded pairs

3) Use of two optical fibers

P1: Specification 100Base- TXand 100Base- FX

These technologies, despite the use of different cables, have much in common in terms of functionality. The difference is that the TX specification provides automatic detection of the baud rate. If the speed cannot be determined, the line is considered to operate at a speed of 10 Mbit.

P2: Specification 100Base- T4

By the time Fast Ethernet appeared, most users used twisted pair cable of category 3. In order to transmit a signal at a speed of 100 Mbit/s through such a cable system, a special logical coding system was used. In this case, it is possible to use only 3 pairs of cable for data transmission, and the 4th pair is used for listening and collision detection. This allows you to increase the exchange speed.

P3:PRules for building multi-segment networksFastEthernet

Fast Ethernet repeaters are divided into 2 classes:

a. Supports all types of logic coding

b. It supports only one type of logical coding, but its cost is much lower.

Therefore, depending on the network configuration, the use of one or two type 2 repeaters is allowed.

AT 2:Specification 100VG- AnyLAN

This is a technology designed to transmit data at a speed of 100 Mbit/s using either Ethernet or Token Ring protocols. For this purpose, a priority access method and a new data encoding scheme, called “quartet encoding,” were used. In this case, data is transmitted at a speed of 25 Mbit/s over 4 twisted pairs, which in total provides 100 Mbit/s.

The essence of the method is as follows: a station that has a frame sends a request to the hub for transmission, requiring low priority for regular data and high priority for delay-critical data, that is, multimedia data. The hub provides permission to transmit the corresponding frame, that is, it operates at the second level of the OSI model (link layer). If the network is busy, the hub queues the request.

The physical topology of such a network is necessarily a star, and branching is not allowed. The hub of such a network has 2 types of ports:

1) Ports for downward communication (to the lower level of the hierarchy)

2) Uplink ports

In addition to hubs, such a network may include switches, routers and network adapters.

Such a network can use Ethernet frames, Token Ring frames, as well as its own connection test frames.

The main advantages of this technology:

1) Ability to use existing 10 Mbit network

2) No losses due to conflicts

3) Possibility of building extended networks without using a switch

AT 3:GigabitEthernet

High-speed Gigabit Ethernet technology provides speeds of up to 1 Gbps, and is described in the 802.3z and 802.3ab recommendations. Features of this technology:

1) All types of frames are saved

2) It is possible to use two media access protocols CSMA/CD and a full-duplex system

The physical transmission medium can be used:

1) Fiber optic cable

3) Coaxial cable.

Compared to previous versions, there are changes both at the physical level and at the MAC level:

1) The minimum frame size has been increased from 64 to 512 bytes. The frame is expanded to 51 bytes with a special extension field ranging in size from 448 to 0 bytes.

2) To reduce overhead, end nodes are allowed to transmit several frames in a row without releasing the transmission medium. This mode is called Burst Mode. In this case, the station can transmit several frames with a total length of 65536 bits.

Gigabit Ethernet can be implemented on Category 5 twisted pair cable, using 4 pairs of conductors. Each pair of conductors provides a transmission speed of 250 Mbit/s

B4: 10 gigabitEthernet

By 2002, a number of companies had developed equipment providing a transmission speed of 10 Gbit/sec. This is primarily Cisco equipment. In this regard, the 802.3ae standard was developed. According to this standard, fiber optic lines were used as data transmission lines. In 2006, the 802.3an standard appeared, which used twisted pair cable of the 6th category. 10 Gigabit Ethernet technology is primarily intended for transmitting data over long distances. It was used to connect local networks. Allows you to build networks with a diameter of several 10 km. The main features of 10 Gigabit Ethernet include:

1) Duplex mode based on switches

2) Availability of 3 groups of physical layer standards

3) Using fiber optic cable as the main data transmission medium

B5: 100 gigabitEthernet

In 2010, a new standard, 802.3ba, was adopted, which provided for transmission speeds of 40 and 100 Gbit/sec. The main purpose of developing this standard was to extend the requirements of the 802.3 protocol to new ultra-high-speed data transmission systems. At the same time, the task was to preserve the infrastructure of local computer networks as much as possible. The need for a new standard is associated with the growth in the volume of data transmitted over networks. Volume requirements significantly exceed existing capabilities. This standard supports full-duplex mode and is aimed at various data transmission media.

The main goals of developing the new standard were:

1) Saving frame format

2) Saving the minimum and maximum frame size

3) Maintaining the error level within the same limits

4) Providing support for a highly reliable environment for transferring heterogeneous data

5) Providing physical layer specifications for transmission over optical fiber

The main users of systems developed based on this standard should be storage networks, server farms, data centers, and telecommunications companies. For these organizations, data communication systems are already proving to be a bottleneck today. The future development of Ethernet networks is associated with 1 Tbit/sec networks. It is expected that technology supporting such speeds will appear by 2015. To do this, it is necessary to overcome a number of difficulties, in particular, to develop higher-frequency lasers with a modulation frequency of at least 15 GHz. These networks also require new optical cables and new modulation systems. The most promising transmission media are considered to be fiber-optic lines with a vacuum core, as well as those made of carbon, and not of silicon like modern lines. Naturally, with such a massive use of fiber-optic lines, it is necessary to pay more attention to optical methods of signal processing.

L15: LANTokenRing

Q1: General information

Token Ring - a token ring is a network technology in which stations can transmit data only when they own a token that continuously circulates through the network. This technology was proposed by IBM and described in the 802.5 standard.

Main technical characteristics of Token Ring:

1) Maximum number of stations in the ring 256

2) Maximum distance between stations 100 m for category 4 twisted pair cable, 3 km for fiber optic multimode cable

3) Using bridges you can combine up to 8 rings.

There are 2 versions of Token Ring technology, providing transfer speeds of 4 and 16 Mbit/sec.

Advantages of the system:

1) No conflicts

2) Guaranteed access time

3) Good performance under heavy load, while Ethernet at 30% load significantly reduces its speeds

4) Large size of transmitted data per frame (up to 18 KB).

5) The actual speed of a 4 megabit Token Ring network turns out to be higher than that of a 10 megabit Ethernet

The disadvantages include:

1) Higher cost of equipment

2) Token Ring network throughput is currently less than in recent versions of Ethernet

B2: Structural and functional organizationTokenRing

The physical topology of Token Ring is star. It is implemented by connecting all computers via network adapters to a multiple access device. It transmits frames from node to node and is a hub. It has 8 ports and 2 connectors for connecting to other hubs. If one of the network adapters fails, this direction is bridged and the integrity of the ring is not compromised. Several hubs can be structurally combined into a cluster. Within this cluster, subscribers are connected in a ring. Each network node receives a frame from a neighboring node, restores the signal level and transmits it to the next one. A frame can contain data or a marker. When a node needs to transmit a frame, the adapter waits for the token to arrive. Once it receives it, it converts the token into a data frame and passes it around the ring. The packet rotates around the entire ring and arrives at the node that generated the packet. Here the correctness of the frame passing through the ring is checked. The number of frames that a node can transmit in 1 session is determined by the token retention time, which is usually = 10 ms. When a node receives a token, it determines whether it has data to transmit and whether its priority exceeds the reserved priority value recorded in the token. If it exceeds, then the node captures the token and forms a data frame. During the transmission of the token and data frame, each node checks the frame for errors. When they are detected, a special error flag is set, and all nodes ignore this frame. As the token passes around the ring, nodes have the opportunity to reserve the priority with which they want to transmit their frame. As it passes through the ring, the frame with the highest priority will be attached to the marker. This guarantees the transmission medium against frame collisions. When transmitting small frames, such as requests to read a file, there is overhead in the delay required for the request to complete its round trip around the ring. To increase performance in a network with a speed of 16 Mbit/s, the early token transfer mode is used. In this case, the node passes the token to the next node immediately after transmitting its frame. Immediately after turning on the network, 1 of the nodes is designated as the active monitor; it performs additional functions:

1) Monitoring the presence of a marker on the network

2) Formation of a new marker when a loss is detected

3) Formation of diagnostic personnel

Q3: Frame formats

The Token Ring network uses 3 types of frames:

1) Data frame

3) Termination sequence

A data frame consists of the following set of bytes:

HP - initial separator. Size 1 byte, indicates the start of the frame. It also notes the type of shot: intermediate, last or single.

UD - access control. In this field, nodes to which data needs to be transmitted can record the need to reserve a channel.

UK - personnel management. 1 byte. Indicates ring management information.

AN - destination node address. Can be 2 or 6 bytes long, depending on settings.

AI - source address. Also 2 or 6 bytes.

Data. This field may contain data intended for network layer protocols. There is no special limitation on the length of the field, however, its length is limited based on the allowable holding time of the token (10 milliseconds). During this time, usually, you can transfer from 5 to 20 kilobytes of information, which is the actual limitation.

KS - checksum, 4 bytes.

KR - end separator. 1 byte.

SC - frame status. May, for example, contain information about an error contained in the frame.

The second type of frame is a marker:

The third frame is the completion sequence:

Used to complete a transfer at any time.

L16: LANFDDI

Q1: General information

FDDI - fiber optic distributed data interface.

This is one of the first high-speed technologies used in fiber optic networks. The FDDI standard is implemented with maximum compliance with the Token Ring standard.

The FDDI standard provides:

1) High reliability

2) Flexible reconfiguration

3) Transfer speed up to 100 Mbit/s

4) Long distances between nodes, up to 100 kilometers

Network advantages:

1) High noise immunity

2) Secrecy of information transfer

3) Excellent galvanic isolation

4) Possibility of combining a large number of users

5) Guaranteed network access time

6) No conflicts even under heavy load

Flaws:

1) High cost of equipment

2) Difficulty of operation

B2: Structural organization of the network

Topology - double ring. Moreover, 2 multidirectional fiber optic cables are used:

During normal operation, the main ring is used for data transmission. The second ring is a backup ring and ensures data transfer in the opposite direction. It is automatically activated in case of cable damage or when the workstation fails

The point-to-point connection between stations simplifies standardization and allows different types of fibers to be used at different sites.

The standard allows the use of 2 types of network adapters:

1) Type A adapter. Connects directly to 2 lines and can provide operating speeds of up to 200 Mbit/s

2) Type B adapter. Connects only to the 1st ring and supports speeds up to 100 Mbit/s

In addition to workstations, the network may include communication hubs. They provide:

1) Network monitoring

2) Fault diagnosis

3) Converting an optical signal into an electrical signal and vice versa if it is necessary to connect a twisted pair

The exchange speed in such networks, in particular, increases due to a special coding method developed specifically for this standard. In it, characters are encoded not using bytes, but using nibbles, which are called nibble.

Q3: Functional network organization

The standard was based on the token access method used in Token Ring. The difference between the FDDI access method and Token Ring is as follows:

1) FDDI uses multiple token transmission, in which a new token is transmitted to another station immediately after the end of the frame transmission, without waiting for its return

2) FDDI does not provide the ability to set priority and redundancy. Each station is considered asynchronous; network access time is not critical for it. There are also synchronous stations, with very strict restrictions on access time and on the interval between data transmissions. For such stations, a complex network access algorithm is installed, but high-speed and priority frame transmission is ensured

Q4: Frame formats

Frame formats are slightly different from the Token Ring network.

Data frame format:

P. The data frame includes a preamble. It serves for initial reception synchronization. The initial length of the preamble is 8 bytes (64 bits). However, over time, during a communication session, the size of the preamble may decrease

NR. Start separator.

UK. Personnel management. 1 byte.

AN and AI. Destination and source address. Size 2 or 6 bytes.

The length of the data field can be arbitrary, but the frame size should not exceed 4500 bytes.

KS. Check sum. 4 bytes

KR. End separator. 0.5 bytes.

SK. Frame status. A field of arbitrary length, no more than 8 bits (1 byte), indicating the results of frame processing. An error was detected\data copied, and so on.

The token frame in this network has the following composition:

L17: Wireless LANs (WLANs)

B1: General principles

There are 2 possible ways to organize such networks:

1) With base station. Through which data is exchanged between workstations

2) Without base station. When the exchange is carried out directly

Advantages of BLWS:

1) Simplicity and low cost of construction

2) User mobility

Flaws:

1) Low noise immunity

2) Uncertain coverage area

3) The “hidden terminal” problem. The "hidden terminal" problem is this: station A transmits a signal to station B. Station C sees station B but does not see station A. Station C believes that B is free and transmits its data to it.

Q2: Data transfer methods

The main methods of data transfer are:

1) Orthogonal frequency division multiplexing (OFDM)

2) Frequency Hopping Spread Spectrum (FHSS)

3) Direct Serial Spread Spectrum (DSSS)

P1: Orthogonal frequency multiplexing

Used to transmit data at speeds up to 54 Mbit/s at a frequency of 5 GHz. The data bit stream is divided into N substreams, each of which is modulated autonomously. Based on the fast Fourier transform, all carriers are folded into a common signal, the spectrum of which is approximately equal to the spectrum of one modulated substream. At the receiving end, the original signal is restored using the inverse Fourier transform.

P2: Spectrum expansion by frequency hopping

The method is based on a constant change in the carrier frequency within a given range. A certain portion of data is transmitted in each time interval. This method provides more reliable data transfer, but is more complex to implement than the first method.

P3: Direct serial spread spectrum

Each one bit in the transmitted data is replaced by a binary sequence. At the same time, the data transmission speed increases, which means the spectrum of transmitted frequencies expands. This method also provides increased noise immunity.

Q3: TechnologyWiFi

This technology is described by the 802.11 protocol stack.

There are several options for building a network in accordance with this stack.

Option	Standard	Range	Encoding method	Transmission speed
		Infrared 850 nm

Q4: TechnologyWiMax (802.16)

High-bandwidth wireless broadband technology. It is represented by the 802.16 standard and is intended for building long-distance regional networks.

It belongs to the point-to-multipoint standard. And it required the transmitter and receiver to be in line of sight.

Option	Standard	Range	Speed	Cell radius
			32 - 134 Mbit\s
			1 - 75 Mbit\s	5 - 8 (up to 50) km
			1 - 75 Mbit\s

The main differences between the WiMax standard and WiFi:

1) Low mobility, only the last option provides user mobility

2) Higher quality equipment requires more money

3) Long data transmission distances require increased attention to information security

4) Large number of users in the cell

5) High throughput

6) High quality serving multimedia traffic

Initially, this network developed as a network of wireless, fixed cable television, but it did not cope with this task very well and is currently being developed to serve mobile users moving at high speed.

Q5: Wireless Personal Area Networks

Such networks are designed for the interaction of devices belonging to the same owner and located at a short distance from each other (several tens of meters).

P1:Bluetooth

This technology, described in the 802.15 standard, ensures the interaction of various devices in the 2.4 MHz frequency range, with an exchange rate of up to 1 Mbit/s.

Bluetooth is based on the concept of a piconet.

Differs in the following properties:

1) Coverage area up to 100 meters

2) Number of devices 255

3) Number of working devices 8

4) One main device, usually a computer

5) Using a bridge, you can combine several piconets

6) Frames are 343 bytes long

P2: TechnologyZigBee

ZegBee is a technology described in the 802.15.4 standard. It is designed for building wireless networks using low-power transmitters. It aims for long battery life and greater security at low data rates.

The main features of this technology are that, with low power consumption, it supports not only wireless technologies and point-to-point communications, but also complex wireless networks with a mesh topology.

The main purpose of such networks:

1) Automation of residential premises and premises under construction

2) Personalized medical diagnostic equipment

3) Industrial monitoring and control systems

The technology is designed to be simpler and cheaper than all other networks.

There are 3 types of devices in ZigBee:

1) Coordinator. Establishing a connection between networks and capable of storing information from devices located on the network

2) Router. To connect

3) End device. Can only transmit data to the coordinator

These devices operate in different frequency ranges, approximately 800 MHz, 900 MHz, 2400 MHz. The combination of different frequencies ensures high noise immunity and reliability of this network. The data transfer rate is several tens of kilobits per second (10 - 40 kbit/s), the distance between stations is 10 - 75 meters.

Q6: Wireless sensor networks

They are a distributed, self-organizing, fault-tolerant network consisting of many sensors that are not discussed and do not require special configuration. Such networks are used in production, transport, life support systems, and security systems. They are used to monitor various parameters (temperature, humidity...), access to objects, failures of actuators, and environmental parameters of the environment.

The network may consist of the following types of devices:

1) Network coordinator. Organizing and setting network parameters

2) Fully functional device. Includes, but is not limited to, ZigBee support

3) A device with a limited set of functions. To connect to the sensor

L18: Principles of organizing global networks

B1: Classification and equipment

A set of different networks located at a considerable distance from each other and united into a single network using telecommunications means constitute a geographically distributed network.

Modern telecommunications combine geographically distributed networks into a global computer network. Since geographically distributed networks and the Internet use the same network formation systems, they are usually combined into a single class WAN (Wide Area Networks).

Unlike local area networks, the main features of global networks are:

1) Unlimited territorial coverage

2) Combining computers of different types

3) Special equipment is used to transmit data over long distances

4) Network topology is arbitrary

5) Particular attention is paid to routing

6) The global network may contain data transmission channels of various types

The advantages include:

1) Providing users with unlimited access to computing and information resources

2) Possibility of accessing the network from almost anywhere in the world

3) The ability to transmit any type of data, including video and audio.

The main types of wide area network devices include:

1) Repeaters and hubs. They are passive means of connecting networks. Operates at the first level of the OSI model

2) Bridges, routers, communicators and gateways. They are active means of building networks. The main function of active tools is signal amplification and traffic control, that is, they operate at the second level of the OSI model

B2: Bridges

This is the simplest network device that unites network segments and regulates the passage of frames between them.

2 segments connected by a bridge turn into a single network. The bridge operates at the second data link layer and is transparent to higher-level protocols.

To transfer frames from one segment to another, the bridge generates a table that contains:

1) List of addresses connected to the station

2) Port to which the stations are connected

3) Time of last record update

Unlike a repeater, which simply transmits frames, a bridge analyzes the integrity of the frames and filters them. To obtain information about the location of a station, bridges read information from the frame passing through it and analyze the response of the station that received this frame.

The advantages of bridges are:

1) Relative simplicity and low cost

2) Local frames are not transmitted to another segment

3) The presence of the bridge is transparent to users

4) Bridges automatically adapt to configuration changes

5) Bridges can connect networks operating using different protocols

Flaws:

1) Delays in bridges

2) Inability to use alternative routes

3) Contribute to bursts of traffic on the network, for example, when searching for stations that are not on the list

There are 4 main types of bridges:

1) Transparent

2) Broadcasting

3) Encapsulating

4) With routing

P1: Transparent bridges

Transparent bridges are designed to connect networks with identical protocols at the physical and data link layers.

The transparent bridge is a self-learning device; for each connected segment it automatically builds station address tables.

The operating algorithm of the bridge is approximately as follows:

1) Reception of the incoming frame into the buffer

2) Analysis of the source address and its search in the address table

3) If the source address is not in the table, then the address and port number from where the frame came is recorded in the table

4) The destination address is analyzed and searched in the address table

5) If the destination address is found and it belongs to the same segment as the source address, that is, the input port number matches the output port number, then the frame is removed from the buffer

6) If the destination address is found in the address table and it belongs to another segment, then the frame is sent to the corresponding port for transmission to the desired segment

7) If the destination address is not in the address table, then the frame is transmitted to all segments except the segment from which it came

P2: Broadcasting bridges

They are designed to combine networks with different protocols at the data link and physical levels.

Broadcasting bridges unite networks by manipulating “envelopes”, that is, when transmitting frames from an Ethernet Token Ring network, the Ethernet frame header and trailer are replaced with the Token Ring header and trailer. A problem that may arise is that the permissible frame size on two networks may be different, so all networks must be configured with the same frame size in advance.

P3: Encapsulating bridges

fiber optic interface network wireless

Encapsulating bridges are designed to connect networks with the same protocols over a high-speed backbone network with a different protocol. For example, the interconnection of Ethernet networks through FDDI interconnection.

Unlike broadcast bridges, in which the header and trailer are replaced, in this case the received frames, along with the header, are placed in another envelope, which is used in the backbone network. The destination bridge retrieves the original frame and sends it to the segment where the destination is located.

The FDDI field is always long enough to accommodate any frame of another protocol.

P4: Bridges with source routing

Such bridges use frame routing information recorded in the frame header by the base station.

In this case, the address table is not needed. This method is most often used in Token Ring to transfer frames between different segments.

Q3: Routers

Routers, like bridges, allow you to effectively combine networks and increase their size. Unlike a bridge, whose operation is transparent to network devices, routers must explicitly indicate the port through which the frame will pass.

Incoming packets are entered into the input clipboard and analyzed using the router's central processor. Based on the analysis results, the output clipboard is selected.

Routers can be divided into the following groups:

1) Peripheral routers. To connect small branches to the central office network

2) Remote access routers. For medium-sized networks

3) Powerful backbone routers

P1: Peripheral routers

To connect to the central office network they have 2 ports with limited capabilities. One to connect to your network, and the other to the central network.

All functions are assigned to the central office, so peripheral routers require no maintenance and are very cheap.

P2: Remote access routers

They usually have a fixed structure and contain 1 local port and several ports for connecting to other networks.

They provide:

1) Providing a communication channel on demand

2) Data compression to increase throughput

3) Automatic switching of traffic to dial-up lines when the main or leased line fails

P3: Backbone routers

They are divided into:

1) With centralized architecture

2) With straightened architecture

Features of routers with distributed architecture:

1) Modular design

2) Availability of up to several dozen ports for connecting to different networks

3) Support for fault tolerance tools

In routers with a centralized architecture, all functions are concentrated in one module. Routers with a distributed architecture provide higher reliability and performance compared to a centralized architecture.

Q4: Routing protocols

All routing methods can be divided into 2 groups:

1) Static or fixed routing methods

2) Dynamic or adaptive routing methods

Static routing involves the use of routes that are set by the system administrator and do not change over a long period of time.

Static routing is used in small networks and has the following advantages:

1) Low router requirements

2) Increased network security

At the same time, it also has significant disadvantages:

1) Very high labor intensity of operation

2) Lack of adaptation to changes in network topology

Dynamic routing allows you to automatically change the route when there are congestions or failures in the network. Routing protocols in this case are implemented programmatically in the router, creating routing tables that display the current states of the network.

Internal routing protocols are based on exchange algorithms:

1) Vector-length tables (DVA)

2) Link state information (LSA)

DVA is an algorithm for exchanging information about available networks and distances to them by sending broadcast packets.

This algorithm is implemented in one of the very first RIP protocols, which has not lost its relevance to this day. They periodically send broadcast packets to update routing tables.

Advantages:

1) Simplicity

Flaws:

1) Slow formation of optimal routes

LSA is an algorithm for exchanging information about the state of channels, it is also called the shortest path preference algorithm.

It is based on building a dynamic network topology map by collecting information about all connected networks. When the state of its network changes, a router immediately sends a message to all other routers.

The advantages include:

1) Guaranteed and fast route optimization

2) Less amount of information transmitted over the network

Along with the development of the merits of the LSA algorithm was the development of the OSPF protocol. This is the most modern and frequently used protocol, it provides the following additional capabilities to the basic LSA algorithm:

1) Faster route optimization

2) Easy to debug

3) Routing packets according to class of service

4) Authentication of routes, that is, the absence of the possibility of packet interception by attackers

5) Create a virtual channel between routers

Q5: Comparison of Routers and Bridges

The advantages of routers compared to bridges include:

1) High data security

2) High reliability of networks due to alternative paths

3) Effective load distribution over communication channels by selecting the best routes for data transmission

4) Greater flexibility by choosing a route according to its metric, i.e. route cost, throughput and so on

5) Possibility of combining with different packet lengths

The disadvantages of routers include:

1) Relatively large delay when transmitting packets

2) Complexity of installation and configuration

3) When moving a computer from one network to another, you must change its network address

4) Higher production cost, as expensive processors, large RAM, and expensive software are required

The following characteristic features of bridges and routers can be distinguished:

1) Bridges work with MAC (that is, physical) addresses, and routers work with network addresses

2) To build a route, bridges use only the addresses of the sender and recipient, while routers use many different sources to select a route

3) Bridges do not have access to the data in the envelope, but routers can open the envelopes and break the packets into shorter ones

4) With the help of bridges, packets are only filtered, and routers forward packets to a specific address

5) Bridges do not take into account frame priority, and routers provide different types of service

6) Bridges provide low latency, although frame loss is possible when overloaded, and routers introduce more latency

7) Bridges do not guarantee frame delivery, but routers do

8) The bridge stops working if the network fails, and the router searches for an alternative route and keeps the network operational

9) Bridges provide a fairly lower level of security than routers

Q6: Switches

In terms of functionality, a switch occupies an intermediate position between a bridge and a router. It operates at the second link layer, that is, it switches data based on MAC addresses.

The performance of switches is significantly higher than that of bridges.

The canonical structure of a switch can be represented as follows:

Unlike a bridge, each port on a switch has its own processor, while a bridge has a common processor. The switch establishes one path for all frames, that is, a so-called burst is formed.

The switch matrix transfers frames from input buffers to output buffers based on the switch matrix.

2 switching methods are used:

1) With full frame buffering, that is, transfer begins after the entire frame is stored in the buffer

2) On the fly, when header analysis begins immediately after entering the input port\buffer and the frame is immediately sent to the desired output buffer

Switches are divided into:

1) Half-duplex, when a network segment is connected to each port

2) Duplex, when only one workstation is connected to the port

Switches are more intelligent network devices than bridges. They allow:

1) Automatically detect communication configuration

2) Translate link layer protocols

3) Filter frames

4) Set traffic priorities

L19: Connection-oriented networks

B1: The principle of packet transmission based on virtual channels

Switching in networks can be based on 2 methods:

1) Datagram method (connectionless)

2) Based on virtual channel (connection-oriented)

There are 2 types of virtual channels:

1) Dial-up (for the duration of the session)

2) Permanent (formed manually and unchangeable for a long time)

When creating a switched channel, routing is carried out once, when the first packet passes through. This channel is assigned a conditional number, through which the transmission of other packets is addressed.

This organization reduces the delay:

1) The decision to forward a packet is made faster due to the short switching table

2) The effective data transfer rate increases

Using permanent channels is more efficient because there is no connection establishment step. However, multiple packets can be transmitted simultaneously over a persistent link, which reduces the effective data transfer rate. Permanent virtual circuits are cheaper than dedicated circuits.

P1: Purpose and structure of the network

Such networks are best suited for transmitting low-intensity traffic.

X.25 networks are also called packet switching networks. For a long time, such networks were the only networks that operated on low-speed, unreliable communication channels.

Such networks consist of switches called packet switching centers located in different geographic locations. The switches are connected to each other by communication lines, which can be either digital or analog. Several low-speed streams from the terminals are combined into a packet transmitted over the network. For this purpose, special devices are used - packet data adapter. It is to this adapter that terminals operating on the network are connected.

The functions of the packet data adapter are:

1) Assembling symbols into packages

2) Parsing packages and outputting data to terminals

3) Management of connection and disconnection procedures over the network

Terminals on the network do not have their own addresses; they are recognized by the port of the packet data adapter to which the terminal is connected.

P2: Protocol stackx.25

The standards are described at 3 protocol levels: physical, channel and network.

At the physical level, a universal interface is defined between data transmission equipment and terminal equipment.

At the link level, a balanced mode of operation is ensured, which means equality of nodes participating in the connection.

The network layer performs the functions of packet routing, connection establishment and termination, and data flow control.

P3: Establishing a virtual connection

To establish a connection, a special Call Request packet is sent. In this packet, in a special field, the number of the virtual channel that will be formed is specified. This packet passes through the nodes, forming a virtual channel. After the packet has passed through and a channel has been created, the number of this channel is entered into the remaining packets and packets with data are transmitted through it.

The x.25 network protocol is designed for low-speed channels with a high level of interference, and does not guarantee throughput, but allows you to set traffic priority.

P1: Features of technology

Such networks are much better suited for transmitting bursty local network traffic if high-quality communication lines are available (for example, fiber optic).

Technology Features:

1) The datagram operating mode provides high throughput, up to 2 Mbit/s, low frame delays, but at the same time there is no guarantee of transmission reliability

2) Support for basic indicators of quality of service, primarily the average data transfer rate

3) Use of 2 types of virtual channels: permanent and switched

4) Frame Relay technology uses a virtual connection technique similar to x.25, however, data is transmitted only at the user and data link levels, while on x.25 it is also transmitted at the network level

5) Frame Relay overhead is less than x.25

6) The link layer protocol has 2 operating modes:

a. Basic. For data transfer

b. Manager. For control

7) Frame Relay technology is focused on high-quality communication channels and does not provide for the detection and correction of distorted frames

P2: Support quality of service

This technology supports the quality of service ordering procedure. These include:

1) Agreed rate at which data will be transferred

2) Agreed volume of ripple, that is, the maximum number of bytes per unit of time

3) Additional ripple volume, that is, the maximum number of bytes that can be transferred in excess of the set value per unit of time

P3: Using networksFrameRelay

Frame Relay technology in territorial networks can be considered as an analogue of Ethernet in local networks.

Both technologies:

1) Provide fast transport services without guarantee of delivery

2) If frames are lost, no attempt is made to restore them, that is, the useful throughput of a given network depends on the quality of the channel

At the same time, it is not advisable to transmit sound, much less video, over such networks, although due to the presence of priorities, speech can be transmitted.

P1: General concepts of ATM

It is an asynchronous mode technology using small packets called cells(cells).

This technology is designed to transmit voice, video and data. Can be used both for building local networks and highways.

Computer network traffic can be divided into:

1) Streaming. Representing a uniform flow of data

2) Pulsating. Uneven, unpredictable flow

Streaming traffic is typical for transmitting multimedia files (video), for which frame latency is the most critical. Bursting traffic is file transfer.

ATM technology is capable of serving all types of traffic due to:

1) Virtual channel techniques

2) Pre-order quality parameters

3) By setting priorities

P2: PrinciplesATM technologies

The approach is to transmit all types of traffic in fixed-length packets - cells 53 bytes long. 48 bytes - data + 5 bytes - header. The cell size was chosen, on the one hand, based on reducing the delay time in nodes, and on the other hand, based on minimizing throughput losses. Moreover, when using virtual channels, the header contains only the virtual channel number, which can hold a maximum of 24 bits (3 bytes).

An ATM network has a classic structure: ATM switches connected by communication lines to which users connect.

P3: ATM protocol stack

The protocol stack corresponds to the lower 3 layers of the OSI model. It includes: adaptation layer, ATM layer and physical layer. However, there is no direct correspondence between the ATM and OSI layers.

The adaptation layer is a set of protocols that convert data from upper layers into cells of the required format.

The ATM protocol deals directly with the transmission of cells through switches. The physical layer determines the coordination of transmission devices with the communication line, and the parameters of the transmission medium.

P4: Ensuring quality of service

Quality is set by the following traffic parameters:

1) Peak cell rate

2) Average speed

3) Minimum speed

4) Maximum ripple value

5) Proportion of lost cells

6) Cell delay

Traffic in accordance with the specified parameters is divided into 5 classes:

Class X is reserved and parameters for it can be set by the user.

L20: Global NetworkInternet

B1: Brief history of creation and organizational structures

The global Internet network is implemented based on a stack of TCP\IP network protocols that ensure data transfer between local and territorial networks, as well as communication systems and devices.

The emergence of the Internet from the TCP\IP protocol stack was preceded by the creation of the ARPANET network in the mid-60s of the last century. This network was created under the auspices of the Office of Scientific Research of the US Department of Defense and its development was entrusted to leading American universities. In 1969, the network was launched and it consisted of 4 nodes. In 1974, the first TCP\IP models were developed and in 1983 the network completely switched to this protocol.

In parallel, in 1970, the development of the inter-university network NSFNet began. And in 1980, these two developments merged, receiving the name Internet.

In 1984, the concept of domain names was developed, and in 1989 it all took shape as the World Wide Web (WWW), which was based on the HTTP text transfer protocol.

The Internet is a public organization in which there are no governing bodies, no owners, but only a coordinating body called IAB.

It includes:

1) Research Subcommittee

2) Legislative Subcommittee. Develops standards that are recommended for use by all Internet participants

3) Subcommittee responsible for the dissemination of technical information

4) Responsible for registering and connecting users

5) Responsible for other administrative tasks

Q2: Protocol stackTCP\IP

Under protocol stack usually refers to a set of standards implementations.

The TCP\IP protocol stack model contains 4 levels; the correspondence of these levels to the OSI model is given in the following table:

At the 1st level of the TCP model, the network interface contains hardware-dependent software; it implements data transfer in a specific environment. The data transmission medium is implemented in various ways, from a point-to-point link to a complex communication structure of an x.25 or Frame Relay network. The TCP\IP protocol network supports all standard physical layer protocols, as well as link layer for Ethernet, Token Ring, FDDI, and so on.

At the 2nd internetworking layer of the TCP model, the routing task is implemented using the IP protocol. The second important task of this protocol is to hide the hardware and software features of the data transmission medium and provide higher levels with a single interface, this ensures multi-platform application applications.

At the 3rd transport layer, the problems of reliable delivery of packets and maintaining their order and integrity are solved.

At the 4th application level there are application tasks that request service from the transport layer.

The main features of the TCP\IP protocol stack are:

1) Independence from the data transmission medium

2) Non-guaranteed package delivery

Information objects used at each level of the TCP\IP model have the following features:

1) A message is a block of data that the application layer operates on. It is passed from the application to the transport layer with the size and semantics appropriate for that application.

2) Segment - a block of data that is formed at the transport level

3) A packet, also called an IP datagram, that the IP protocol operates at the internetwork layer

4) Frame - a hardware-dependent block of data obtained by packaging an IP datagram into a format acceptable for a specific physical data transmission medium

Take a brief look at the protocols used in the TCP\IP stack.

Application layer protocols(you need to know which ones exist, how they differ and what they are)

FTP- file transfer protocol. Designed for transferring files over the network and implements:

1) Connect to FTP servers

2) View directory contents

FTP operates on top of the transport layer of the TCP protocol, uses port 20 for data transfer, port 21 for command transfer.

FTP provides the possibility of authentication (user identification), the ability to transfer files from an interrupted location.

TFTP - simplified data transfer protocol. Designed primarily for initial boot of diskless workstations. Unlike FTP, authentication is not possible, but identification by IP address can be used.

BGP- Border Gateway Protocol. Used for dynamic routing and designed to exchange information about routes.

HTTP- hypertext transfer protocol. Designed to transmit data in the form of text documents based on client-server technology. Currently, this protocol is used to retrieve information from websites.

DHCP- dynamic node configuration protocol. Designed for automatic distribution of IP addresses between computers. The protocol is implemented in a specialized DHCP server using client-server technology: in response to a computer request, it issues an IP address and configuration parameters.

SMNP - Simple Network Management Protocol. Designed to manage and monitor network devices by exchanging control information.

DNS- domain name system. It is a distributed hierarchical system for obtaining information about domains, most often for obtaining an IP address by symbolic name.

SIP- session establishment protocol. Designed to establish and terminate a user session.

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Home > Educational and methodological manual

High-speed network technologies

Classic 10 Mbit Ethernet has suited most users for 15 years. However, at present, its insufficient capacity has begun to be felt. This happens for various reasons:

increasing the performance of client computers; increasing the number of users on the network; the emergence of multimedia applications; increasing the number of services operating in real time.

As a result, many segments of 10 Mbit Ethernet became congested and collision rates increased significantly, further reducing usable throughput.

To increase network throughput, you can use several methods: network segmentation using bridges and routers; network segmentation using switches; a general increase in the capacity of the network itself, i.e. application of high-speed network technologies.

High-speed computer network technologies use types of networks such as FDDI (Fiber-optic Distributed Data Interface), CDDI (Copper Distributed Data Interface), Fast Ethernet (100 Mbit/s), 100GV-AnyLAN, ATM (Asynchronous Transfer Method), Gigabit Ethernet.

FDDI and CDDI networks

FDDI fiber optic networks allow you to solve the following problems:

increase transmission speed to 100 Mbit/s; increase the noise immunity of the network through standard procedures for restoring it after various types of failures; Make the most of network bandwidth for both asynchronous and synchronous traffic.

For this architecture, the American National Standard Institute (ANSI) developed the X3T9.5 standard in the 80s. By 1991, FDDI technology was well established in the networking world.

Although the FDDI standard was originally developed for use with fiber optics, recent research has made it possible to extend this robust, high-speed architecture to unshielded and shielded twisted cables. As a result, Crescendo developed the CDDI interface, which made it possible to implement FDDI technology on copper twisted pairs, which turned out to be 20-30% cheaper than FDDI. CDDI technology was standardized in 1994 when many potential customers realized that FDDI technology was too expensive.

The FDDI protocol (X3T9.5) operates by token transmission in a logical ring on fiber optic cables. It was designed to be as compliant as possible with the IEEE 802.5 (Token Ring) standard - differences exist only where necessary to realize higher data rates and the ability to cover long transmission distances.

While the 802.5 standard specifies a single ring, an FDDI network uses two opposing rings (primary and secondary) in a single cable to connect network nodes. Data can be sent on both rings, but in most networks it is sent only on the primary ring, and the secondary ring is reserved, providing fault tolerance and redundancy to the network. In the event of a failure, when part of the primary ring cannot transmit data, the primary ring closes onto the secondary ring, again forming a closed ring. This mode of network operation is called Wrap, i.e. " by folding" or "folding" rings. The collapse operation is performed using FDDI hubs or network adapters. To simplify this operation, data is always transmitted on the primary ring in one direction, and on the secondary ring in the opposite direction.

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. The FDDI network can fully restore its functionality in the event of single failures of its elements, and in the event of multiple failures, the network breaks up into several operational, but not interconnected networks.

There can be 4 types of nodes in the FDDI network:

· SAS single connection stations (Single Attachment Stations); · DAS (Dual Attachment Stations) stations; · SAC (Single Attachment Concentrators); · Dual Attachment Concentrators (DAC).

SAS and SAC are connected to only one of the logical rings, but DAS and DAC are connected to both logical rings at the same time and can cope with a failure in one of the rings. Typically, hubs have a dual connection and stations have a single connection, although this is not required.

Instead of Manchester code, FDDI uses a 4B/5B encoding scheme that converts every 4 bits of data into 5-bit codewords. The redundant bit allows the use of a self-synchronizing potential code to represent data in the form of electrical or optical signals. In addition, the presence of prohibited combinations makes it possible to reject erroneous characters, which improves the reliability of the network.

Because Of the 32 combinations of the 5B code, only 16 combinations are used to encode the original 4 bits of data, then from the remaining 16 several combinations were selected that are used for service purposes and form a kind of physical layer command language. The most important service characters include the Idle character, which is constantly transmitted between ports during pauses between data frame transmissions. Due to this, stations and hubs have constant information about the state of the physical connections of their ports. If there is no Idle symbol flow, a physical link failure is detected and the internal path of the hub or station is reconfigured, if possible.

FDDI stations use an early token release algorithm, similar to 16 Mbps Token Ring networks. There are two main differences in token handling between the FDDI and IEEE 802.5 Token Ring protocols. First, the access token retention time in an FDDI network depends on the load on the primary ring: with a light load it increases, and with heavy loads it can decrease to zero (for asynchronous traffic). For synchronous traffic, the token holding time remains constant. Second, FDDI does not use priority or reservation areas. Instead, FDDI classifies each station as either asynchronous or synchronous. In this case, synchronous traffic is always served, even when the ring is overloaded.

FDDI uses integrated station management with STM (Station Management) modules. STM is present on every node of the FDDI network in the form of a software or firmware module. SMT is responsible for monitoring data channels and network nodes, in particular for connection and configuration management. Each node in the FDDI network acts as a repeater. SMT operates similarly to the management provided by SNMP, but STM is located at the physical layer and a sublayer of the data link layer.

When using a multimode optical cable (the most common FDDI transmission medium), the distance between stations is up to 2 km, when using a single-mode optical cable - up to 20 km. In the presence of repeaters, the maximum length of the FDDI network can reach 200 km and contain up to 1000 nodes.

FDDI Token Format:

Preamble	Elementary SD separator	Control FC package	Terminal ED separator	Status FS package

FDDI Packet Format:

Preamble

Preamble designed for synchronization. Although its length is initially 64 bits, nodes can dynamically change it to suit their synchronization requirements.

SD start separator. A unique one-byte field designed to identify the beginning of a packet.

FC Packet Control. A one-byte field of the form CLFFTTTT, where the C bit sets the packet class (synchronous or asynchronous exchange), the L bit is an indicator of the length of the packet address (2 or 6 bytes). It is allowed to use addresses of both lengths in one network. The FF (packet format) bits determine whether the packet belongs to the MAC sublayer (ie, for ring control purposes) or the LLC sublayer (for data transmission). If the packet is a MAC sublayer packet, then the TTTT bits determine the type of packet containing the data in the Info field.

Purpose of DA. Specifies the destination node.

Source SA. Identifies the node that sent the packet.

Information. This field contains data. This may be MAC type data or user data. The length of this field is variable, but is limited to a maximum packet length of 4500 bytes.

FCS packet checksum. Contains CRC - amount.

End separator ED. It is half a byte long for a packet and a byte long for a token. Identifies the end of a packet or token.

FS package status. This field is of arbitrary length and contains the bits “Error detected”, “Address recognized”, “Data copied”.

The most obvious reason FDDI is expensive is due to the use of fiber optic cable. Their complexity (giving advantages such as built-in station management and redundancy) also contributed to the high cost of FDDI network cards.

FDDI Network Characteristics

Fast Ethernet and 100GV-AnyLAN

In the process of developing a more productive Ethernet network, experts were divided into two camps, which ultimately led to the emergence of two new local network technologies - Fast Ethernet and 100VG-AnyLAN.

Around 1995, both technologies became IEEE standards. The IEEE 802.3 committee adopted the Fast Ethernet specification as the 802.3u standard, which is not a stand-alone standard, but is an addition to the 802.3 standard in the form of chapters 21 through 30.

The 802.12 committee has adopted 100VG-AnyLAN technology, which uses a new Demand Priority media access method and supports two frame formats - Ethernet and Token Ring.

Fast Ethernet

All the differences between Fast Ethernet technology and standard Ethernet are concentrated on the physical layer. The MAC and LLC layers in Fast Ethernet remain unchanged compared to Ethernet.

The more complex structure of the physical layer of Fast Ethernet technology is due to the fact that it uses three types of cabling systems:

fiber optic multimode cable (two fibers are used); Category 5 twisted pair (two pairs are used); Category 3 twisted pair (four pairs are used).

Fast Ethernet does not use coaxial cable at all. The abandonment of coaxial cable has led to the fact that Fast Ethernet networks always have a hierarchical tree structure built on hubs, like 10Base-T/10Base-F networks. The main difference between Fast Ethernet network configurations is the reduction in network diameter to 200 m, which is associated with a 10-fold reduction in the transmission time of a frame of minimum length due to an increase in transmission speed.

However, this limitation does not really hinder the construction of large Fast Ethernet networks due to the rapid development of switch-based local networks in the 90s. When using switches, Fast Ethernet can operate in full-duplex mode, in which there are no restrictions on the overall network length imposed by the CSMA/CD media access method, but only restrictions on the length of physical segments.

Below we consider the half-duplex version of Fast Ethernet technology, which fully complies with the access method described in the 802.3 standard.

The official 802.3u standard established three different Fast Ethernet specifications and gave them the following names:

100Base-TX for two-pair cable on UTP Category 5 UTP or STP Type 1 shielded twisted pair; 100Base-FX for multimode fiber optic cable with two fibers and 1300 nm laser wavelength; 100Base-T4 for 4-pair UTP Category 3, 4 or 5 UTP cable.

The following general statements are true for all three standards:

Fast Ethernet frame formats are no different from classic 10 Mbit Ethernet frame formats; The IPG interframe interval in Fast Ethernet is 0.96 μs, and the bit interval is 10 ns. All access algorithm timing parameters, measured in bit intervals, remained the same, so no changes were made to the MAC layer sections of the standard; A sign of a free state of the medium is the transmission of the Idle symbol of the corresponding redundant code over it (and not the absence of a signal, as in the Ethernet standard).

The physical layer includes three components:

Reconciliation Sublayer; media independent interfaceMII (Media Independent Interface) between the coordination layer and the physical layer device; physical layer device (PHY).

The negotiation sublayer is needed so that the MAC layer, designed for the AUI interface, can work normally with the physical layer via the MII interface.

The PHY physical layer device provides encoding of data coming from the MAC sublayer for transmission over a certain type of cable, synchronization of data transmitted over the cable, as well as reception and decoding of data in the receiver node. It consists of several sublevels (Fig. 19):

a logical data encoding sublayer that converts bytes arriving from the MAC layer into 4B/5B or 8B/6T code symbols; physical connection sublayers and physical medium dependence sublayers, providing signal generation in accordance with the physical coding method, for example, NRZI or MLT-3; autonegotiation sublayer, which allows all communicating ports to choose the most efficient mode of operation, for example, half-duplex or full-duplex (this sublayer is optional).

Interface MII . MII is a TTL level signal specification and uses a 40-pin connector. There are two options for implementing the MII interface: internal and external.

In the internal version, the chip that implements the MAC and negotiation sublayers is connected via the MII interface to the transceiver chip inside the same structure, for example, a network adapter card or a router module. The transceiver chip implements all the functions of the PHY device. With the external version, the transceiver is separated into a separate device and connected using a MII cable.

The MII interface uses 4-bit chunks of data to transfer them in parallel between the MAC and PHY sublayers. The transmission and reception channels from the MAC to the PHY and vice versa are synchronized by a clock signal generated by the PHY layer. The data transmission channel from MAC to PHY is gated by the “Transmit” signal, and the data reception channel from PHY to MAC is gated by the “Receive” signal.

Port configuration data is stored in two registers: the control register and the status register. The control register is used to set the port operating speed, to indicate whether the port will take part in the process of autonegotiation about the line speed, to set the port operating mode (half- or full-duplex).

The status register contains information about the actual current operating mode of the port, including which mode was selected as a result of auto-negotiations.

Physical Layer Specifications 100 Base - FX / TX . These specifications define the operation of Fast Ethernet over multimode fiber optic cable or UTP Cat.5/STP Type 1 cables in half-duplex and full-duplex modes. As in the FDDI standard, each node here is connected to the network by two multidirectional signal lines coming from the node's receiver and transmitter, respectively.

Fig. 19. Differences between Fast Ethernet technology and Ethernet technology

The 100Base-FX/TX standards use the same 4B/5B logical encoding method at the physical interconnection sublayer, where it has been transferred unchanged from FDDI technology. Illegal combinations of Start Delimiter and End Delimiter are used to separate the start of an Ethernet frame from the Idle characters.

After converting 4-bit code tetrads into 5-bit combinations, the latter must be represented as optical or electrical signals in the cable connecting the network nodes. The 100Base-FX and 100Base-TX specifications use different physical encoding methods for this.

The 100Base-FX specification uses a potential NRZI physical code. The NRZI (Non Return to Zero Invert to ones) code is a modification of the simple potential NRZ code (which uses two potential levels to represent logical 0 and 1).

The NRZI method also uses two signal potential levels. Logical 0 and 1 in the NRZI method are encoded as follows (Fig. 20): at the beginning of each unit bit interval, the potential value on the line is inverted, but if the current bit is 0, then at its beginning the potential on the line does not change.

Fig.20. Comparison of potential NRZ and NRZI codes.

The 100Base - TX specification uses MLT-3 code, borrowed from CDDI technology, to transmit 5-bit codewords over twisted pair cables. Unlike the NRZI code, this code is three-level (Fig. 21) and is a complicated version of the NRZI code. The MLT-3 code uses three potential levels (+V, 0, -V), when transmitting 0, the potential value at the boundary of the bit interval does not change, when transmitting 1 it changes to the adjacent ones in the chain +V, 0, -V, 0, + V, etc.

Fig.21. MLT-3 coding method.

In addition to using the MLT-3 method, the 100Base - TX specification also differs from the 100Base - FX specification in that it uses scrambling. A scrambler is usually an XOR combinational circuit that, before MLT-3 encoding, encrypts a sequence of 5-bit codewords so that the energy of the resulting signal is evenly distributed across the entire frequency spectrum. This improves noise immunity, because Spectral components that are too strong cause unwanted interference to adjacent transmission lines and radiation into the environment. The descrambler in the receiver node performs the inverse descrambling function, i.e. restoration of the original sequence of 5-bit combinations.

Specification 100 Base - T 4 . This specification was designed to allow Fast Ethernet to use existing Category 3 twisted pair wiring. The 100Base-T4 specification uses all four twisted pairs of a cable to increase the overall throughput of a communications link by simultaneously transmitting data streams across all twisted pairs In addition to the two unidirectional pairs used in 100Base - TX, there are two additional pairs that are bidirectional and serve to parallelize data transmission. The frame is transmitted over three lines byte-by-byte and in parallel, which reduces the bandwidth requirement of one line to 33.3 Mbit/s. Each byte transmitted over a particular pair is encoded with six ternary digits according to the 8B/6T encoding method. As a result, at a bit rate of 33.3 Mbit/s, the signal change rate in each line is 33.3 * 6/8 = 25 Mbaud, which fits within the bandwidth (16 MHz) of the UTP cat.3 cable.

The fourth twisted pair is used to listen to the carrier frequency during transmission for collision detection purposes.

In the Fast Ethernet collision domain, which should not exceed 205 m, it is allowed to use no more than one Class I repeater (broadcast repeater supporting different encoding schemes adopted in 100Base-FX/TX/T4 technologies, 140 bt latency) and no more than two repeaters Class II (transparent repeater supporting only one of the encoding schemes, latency 92 bt). Thus, the rule of 4 hubs has turned into a rule of one or two hubs in Fast Ethernet technology, depending on the class of the hub.

A small number of repeaters in Fast Ethernet is not a serious obstacle when building large networks, because the use of switches and routers divides the network into several collision domains, each of which is built on one or two repeaters.

Automatic negotiations on port operating modes . The 100Base-TX/T4 specifications support Autonegotiation, which allows two PHY devices to automatically select the most efficient mode of operation. For this purpose it is provided mode negotiation protocol, by which the port can choose the most efficient mode available to both exchange participants.

A total of 5 operating modes are currently defined that can support PHY TX/T4 devices on twisted pairs:

10Base-T (2 pairs of category 3); 10Base-T full duplex (2 pairs of category 3); 100Base-TX (2 pairs Category 5 or STP Type 1); 100Base-TX full duplex (2 pairs of category 5 or STP Type 1); 100Base-T4 (4 pairs of category 3).

10Base-T mode has the lowest priority in the negotiation process, and 100Base-T4 mode has the highest. The negotiation process occurs when the device's power source is turned on, and can also be initiated at any time by the control device.

The device that has started the auto-negotiation process sends a special burst of FLP pulses to its partner ( Fast Link Pulse burst), which contains an 8-bit word encoding the proposed interaction mode, starting with the highest priority supported by the node.

If the partner node supports the auto-negotiation function and is capable of supporting the proposed mode, then it responds with its FLP pulse burst, in which it confirms this mode and the negotiations end there. If the partner node supports a lower priority mode, then it indicates it in the response and this mode is selected as the working one.

A node that only supports 10Base-T technology sends connectivity test pulses every 16 ms and does not understand the FLP request. A node that receives only line continuity pulses in response to its FLP request understands that its partner can only operate using the 10Base-T standard and sets this operating mode for itself.

Full duplex operation . Nodes that support 100Base FX/TX specifications can also operate in full duplex mode. This mode does not use the CSMA/CD media access method and there is no concept of collisions. Full duplex operation is only possible when connecting a network adapter to a switch, or when connecting switches directly.

100VG-AnyLAN

100VG-AnyLAN technology differs from classic Ethernet in a fundamental way. The main differences between them are as follows:

used media access methodDemand Priority– priority requirement, which provides significantly more fair distribution of network bandwidth compared to the CSMA/CD method for synchronous applications; frames are not transmitted to all network stations, but only to the destination station; the network has a dedicated access arbiter - a central hub, and this significantly distinguishes this technology from others that use a distributed access algorithm; frames of two technologies are supported - Ethernet and Token Ring (hence the name AnyLAN). The abbreviation VG stands for Voice-Grade TP - twisted pair for voice telephony; data is transmitted in one direction simultaneously over 4 UTP category 3 twisted pairs; full duplex is not possible.

Data encoding uses 5B/6B logic code, which provides signal spectrum in the range of up to 16 MHz (UTP category 3 bandwidth) at a bit rate of 30 Mbit/s in each line. The NRZ code was chosen as the physical encoding method.

A 100VG-AnyLAN network consists of a central hub, called the root, and end nodes and other hubs connected to it. Three levels of cascading are allowed. Each hub or network adapter on this network can be configured to operate either Ethernet frames or Token Ring frames.

Each hub cyclically polls the status of its ports. A station wishing to transmit a packet sends a special signal to the hub, requesting transmission of the frame and indicating its priority. The 100VG-AnyLAN network uses two priority levels - low and high. Low priority corresponds to normal data (file service, print service, etc.), and high priority corresponds to time-sensitive data (such as multimedia).

Request priorities have static and dynamic components, i.e. a station with a low priority level that does not have access to the network for a long time receives high priority due to the dynamic component.

If the network is free, then the hub allows the node to transmit the packet, and sends a warning signal to all other nodes about the arrival of the frame, upon which the nodes must switch to the frame reception mode (stop sending status signals). After analyzing the destination address in the received packet, the hub sends the packet to the destination station. At the end of frame transmission, the hub sends the Idle signal, and the nodes again begin transmitting information about their state. If the network is busy, the hub puts the received request in a queue, which is processed in accordance with the order in which requests were received and taking into account their priorities. If another hub is connected to the port, polling is suspended until the downstream hub completes polling. The decision to grant access to the network is made by the root concentrator after polling the ports by all concentrators on the network.

Despite the simplicity of this technology, one question remains unclear: how does the hub know which port the destination station is connected to? In all other technologies this issue did not arise, because the frame was simply transmitted to all stations on the network, and the destination station, having recognized its address, copied the received frame to a buffer.

In the 100VG-AnyLAN technology, this problem is solved in the following way - the hub finds out the MAC address of the station at the moment it is physically connected to the network by cable. If in other technologies the physical connection procedure determines the cable connectivity (link test in 10Base-T technology), port type (FDDI technology), port speed (auto-negotiation in Fast Ethernet), then in 100VG-AnyLAN technology, when establishing a physical connection, the hub finds out the MAC -address of the connected station and stores it in its MAC address table, similar to the bridge/switch table. The difference between a 100VG-AnyLAN hub and a bridge or switch is that it does not have an internal frame buffer. Therefore, it receives only one frame from network stations and sends it to the destination port. Until the current frame is received by the recipient, the hub does not accept new frames, so the effect of the shared medium remains. Only network security improves, because... now frames do not reach foreign ports, and they are more difficult to intercept.

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Currently, the Russian tourism market is developing extremely unevenly. The volume of outbound tourism prevails over the volume of inbound and domestic tourism.

Program on pedagogical practice (German and English): Educational and methodological manual for students of the IV and V courses of the Faculty of Philology / Comp. Arinicheva L. A., Davydova I. V. Tobolsk: TGSPA im. D. I. Mendeleeva, 2011. 60 p.

Program

Lecture notes on the discipline: “network economics” Number of sections

Abstract

The emergence of Internet technologies that make it possible to build business relationships in the Internet environment makes it possible to talk about the emergence of a new image of the economy, which can be called the “network” or “Internet economy.”

Attention is paid to the increasingly popular technology software-defined networks.<...>Of course, it is necessary to provide requirements for other indicators that define the concept QoS(quality of services).<...>Here is a description of technologies such as ATM, SDH, MPLS-TP,PBB-TE.<...>The appendix to the manual provides a brief summary of the principles of construction software-defined networks that have recently gained more and more popularity.<...>A description of the technology for virtualizing network functions is given. NFV(Network Function Virtualization), comparison is given SDN And NFV. <...>Physical Wednesday transfers data General characteristics of physical environment. <...>Physical Wednesday transfers data (medium) can represent a cable, the earth's atmosphere or outer space.<...> Cables higher categories have more turns per unit length.<...> Cables categories 1 are used where transmission speed requirements are minimal.<...> Cables categories 2 cables were first used by IBM when building its own cable system.<...> Cables categories 4 are a slightly improved version cables categories 3. <...> High speed broadcast Wireless-based data is discussed in Chapter 7.<...>The choice of network topology is the most important task solved during its construction, and is determined by the requirements for efficiency and structural reliability. <...>Work on standardizing open systems began in 1977. In 1983, a reference standard was proposed model VOS- the most general description of the structure of standards development.<...> Model VOS, which defines the principles of the relationship between individual standards, is the basis for the parallel development of multiple standards and ensures a gradual transition from existing implementations to new standards.<...>Reference model VOS does not define protocols and interaction interfaces, structure and characteristics of physical means of connection.<...>Third, network level, performs routing<...>

Network_technologies_for_high-speed_data_transmission._Tutorial_manual_for_universities._-_2016_(1).pdf

UDC 621.396.2 BBK 32.884 B90 REVIEWERS: Doctor of Engineering. Sciences, Professor of Engineering. sciences, professor; Doctor Budyldina N.V., Shuvalov V.P. B90 Network technologies for high-speed data transmission. Textbook for universities / Ed. Professor V.P. Shuvalov. – M.: Hotline – Telecom, 2016. – 342 p.: ill. ISBN 978-5-9912-0536-8. The issues of building infocommunication networks that provide high-speed data transmission are presented in a compact form. Sections are presented that are necessary to understand how to ensure transmission not only at high speed, but also with other indicators characterizing the quality of the service provided. A description of the protocols of various levels of the reference model of interaction of open systems and transport network technologies is given. The issues of data transmission in wireless communication networks and modern approaches that ensure the transfer of large amounts of information in acceptable periods of time are considered. Attention is paid to the increasingly popular technology of software-defined networks. For students studying in the field of training “Infocommunication technologies and communication systems” with qualifications (degrees) of “bachelor” and “master”. The book can be used to improve the skills of telecommunication workers. BBK 32.884 Budyldina Nadezhda Veniaminovna, Shuvalov Vyacheslav Petrovich Network technologies for high-speed data transmission Textbook for universities All rights reserved. Any part of this publication may not be reproduced in any form or by any means without the written permission of the copyright holder © Scientific and Technical Publishing House "Hot Line - Telecom" LLC www.techbook.ru © N.V. Budyldina, V.P. Shuvalov L. D. G. Nevolin G. Dorosinsky Address of the publisher on the Internet www.tech b o o k .ru

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Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 References for the introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Chapter 1. Basic concepts and definitions. . . . . . . . . . . . . . . . . . . 6 1.1. Information, message, signal. . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Information transfer speed. . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3. Physical data transmission medium. . . . . . . . . . . . . . . . . . . . . . . 14 1.4. Signal conversion methods. . . . . . . . . . . . . . . . . . . . . . . . . 22 1.5. Methods of multiple access to the environment. . . . . . . . . . . . . . . . . 31 1.6. Telecommunication networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1.7. Organization of work on standardization in the field of data transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 1.8. Reference model for open systems interaction. . . . . . . 47 1.9. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.10. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Chapter 2. Ensuring service quality indicators. . 58 2.1. Quality of service. General provisions. . . . . . . . . . . . . . . 58 2.2. Ensuring the accuracy of data transmission. . . . . . . . . . . . . . . . . . 64 2.3. Providing indicators of structural reliability. . . . . . . . 78 2.4. QoS routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 2.5. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 2.6. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Chapter 3. Local networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 3.1. LAN protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 3.1.1. Ethernet technology (IEEE 802.3). . . . . . . . . . . . . . . . . . 92 3.1.2. Token Ring Technology (IEEE 802.5). . . . . . . . . . . . . . . 93 3.1.3. FDDI technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 3.1.4. Fast Ethernet (IEEE 802.3u). . . . . . . . . . . . . . . . . . . . . . . . 96 3.1.5. 100VG-AnyLAN technology. . . . . . . . . . . . . . . . . . . . . . . 101 3.1.6. High-speed Gigabit Ethernet technology. . . . . 102 3.2. Technical means ensuring the functioning of high-speed data networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 3.2.1. Hubs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 3.2.2. Bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 3.2.3. Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 3.2.4. STP protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 3.2.5. Routers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 3.2.6. Gateways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 3.2.7. Virtual local area network (VLAN). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

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342 Contents 3.3. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 3.4. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Chapter 4. Link layer protocols. . . . . . . . . . . . . . . . . . . . . . . 138 4.1. Main tasks of the link layer, protocol functions 138 4.2. Byte-oriented protocols. . . . . . . . . . . . . . . . . . . . . . . . 142 4.3. Bit-oriented protocols. . . . . . . . . . . . . . . . . . . . . . . . . . 145 4.3.1. HDLC (High-Level Data Link Control) protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 4.3.2. Frame protocol SLIP (Serial Line Internet Protocol). 152 4.3.3. PPP (Point-to-Point Protocol) protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 4.4. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 4.5. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Chapter 5. Network and transport layer protocols. . . . . . . . 161 5.1. IP protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 5.2. IPv6 protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 5.3. Routing Protocol RIP. . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 5.4. OSPF Internal Routing Protocol. . . . . . . . . . . . . . 187 5.5. BGP-4 protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 5.6. The resource reservation protocol is RSVP. . . . . . . . . . . . . . 203 5.7. Transfer protocol RTP (Real-Time Transport Protocol). . . . 206 5.8. DHCP (Dynamic Host Configuration Protocol) protocol. . . 211 5.9. LDAP protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 5.10. Protocols ARP, RARP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 5.11. TCP (Transmission Control Protocol) protocol. . . . . . . . . . . . 220 5.12. UDP (User Datagram Protocol) protocol. . . . . . . . . . . . . . . . . 229 5.13. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 5.14. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Chapter 6. Transport IP networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 6.1. ATM technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 6.2. Synchronous Digital Hierarchy (SDH). . . . . . . . . . . . . . . . . . . 241 6.3. Multiprotocol label switching. . . . . . . . . . . . . . . 245 6.4. Optical transport hierarchy. . . . . . . . . . . . . . . . . . . . . . . 251 6.5. Ethernet model and hierarchy for transport networks. . . . . . 256 6.6. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 6.7. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Chapter 7. Wireless technologies for high-speed data transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 7.1. Wi-Fi technology (Wireless Fidelity). . . . . . . . . . . . . . . . . . . . . . 262 7.2. WiMAX (Worldwide Interoperability for Microwave Access) technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

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343 7.3. Transition from WiMAX to LTE technology (LongTermEvolution). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 7.4. State and prospects of high-speed wireless networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 7.5. Control questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 7.6. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Chapter 8. Instead of a conclusion: some thoughts on the topic “what needs to be done to ensure high-speed data transmission in IP networks.” 279 8.1. Traditional data transmission with guaranteed delivery. Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 8.2. Alternative data transfer protocols with guaranteed delivery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 8.3. Congestion control algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . 285 8.4. Conditions for ensuring high-speed data transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 8.5. Implicit problems in ensuring high-speed data transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 8.6. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 Appendix 1. Software-defined networks. . . . . . . . . . 302 P.1. General provisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 P.2. OpenFlow protocol and OpenFlow switch. . . . . . . . . . . . . . 306 P.3. NFV Network Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 P.4. Standardization of PKS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 P.5. SDN in Russia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 P.6. Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 Terms and definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

• Preface
• Chapter 1.
  Historical background for the development of high-speed data networks
• Chapter 2.
  Reference model for interaction of open systems EMVOS (Open System Interconnection - OSI model)
• Chapter 3.
  International standard organizations
• Chapter 4.
  Physical and logical data encoding
• Chapter 5.
  Narrowband and broadband systems. Data multiplexing
• Chapter 6.
  Data transmission modes. Transmission media
• Chapter 7.
  Structured Cabling Systems
• Chapter 8.
  Data transmission system topologies
• Chapter 9
  Channel access methods
• Chapter 10.
  Switching Technologies
• Chapter 11.
  Communication of network segments
• Literature

Chapter 5. Narrowband and broadband systems. Data multiplexing

A narrowband system (baseband) uses a digital signal transmission method. Although a digital signal has a wide spectrum and theoretically occupies an infinite frequency band, in practice the width of the spectrum of the transmitted signal is determined by the frequencies of its fundamental harmonics. They make the main energy contribution to signal formation. In a narrowband system, transmission is carried out in the original frequency band; there is no transfer of the signal spectrum to other frequency regions. It is in this sense that the system is called narrowband. The signal occupies almost the entire bandwidth of the line. To regenerate the signal and amplify it in data transmission networks, special devices are used - repeaters.

An example of narrowband transmission implementation is local area networks and related IEEE specifications (for example, 802.3 or 802.5).

Previously, narrowband transmission, due to signal attenuation, was used at distances of about 1-2 km via coaxial cables, but in modern systems, thanks to various types of coding and multiplexing of signals and types of cable systems, the restrictions have been pushed back to 40 kilometers or more.

The term broadband transmission was originally used in telephone communication systems, where it designated an analog channel with a frequency range (bandwidth) of more than 4 KHz. In order to save resources when transmitting a large number of telephone signals with a frequency band of 0.3-3.4 KHz, various schemes for compressing (multiplexing) these signals have been developed, ensuring their transmission over one cable.

In high-speed network applications, broadband transmission means that an analog carrier rather than a pulse carrier is used to transmit data. By analogy, the term “broadband Internet” means that you are using a channel with a bandwidth of more than 128 Kbps (in Europe) or 200 Kbps (in the USA). The broadband system has high throughput and provides high-speed transmission of data and multimedia information (voice, video, data). Examples are ATM networks, B-ISDN, Frame Relay, CATV cable broadcast networks.

The term "multiplexing" is used in computer technology in many ways. By this we mean the combination of several communication channels in one data transmission channel.

Let's list the main multiplexing techniques: frequency division multiplexing (FDM), time multiplexing - Time Division Multiplexing (TDM) and spectral or wavelength division multiplexing (WDM).

WDM is only used in fiber optic systems. Cable TV, for example, uses FDM.

FDM

With frequency multiplexing, each channel is allocated its own analog carrier. In this case, any type of modulation or a combination of them can be used in FDM. For example, in cable television, a coaxial cable with a bandwidth of 500 MHz provides transmission of 80 channels of 6 MHz each. Each of these channels in turn is obtained by multiplexing subchannels for transmitting audio and video.

TDM

With this type of multiplexing, low-speed channels are combined (merged) into one high-speed one, through which a mixed data stream is transmitted, formed as a result of aggregation of the original streams. Each low-speed channel is assigned its own time slot (time period) within a cycle of a certain duration. Data is represented as bits, bytes, or blocks of bits or bytes. For example, channel A is allocated the first 10 bits within a time interval of a given duration (frame, frame), channel B is allocated the next 10 bits, etc. In addition to data bits, the frame includes service bits for transmission synchronization and other purposes. The frame has a strictly defined length, which is usually expressed in bits (for example, 193 bits) and structure.

Network devices that multiplex data streams of low-speed channels (tributary, component streams) into a common aggregate stream (aggregate) for transmission over one physical channel are called multiplexers (multiplexer, mux, mux). Devices that divide an aggregated stream into component streams are called demultiplexers.

Synchronous multiplexers use a fixed division into time slots. Data belonging to a particular component stream has the same length and is transmitted in the same time slot in each multiplexed channel frame. If information is not transmitted from a certain device, then its time slot remains empty. Statistical multiplexers (stat muxes) solve this problem by dynamically assigning a free time slot to the active device.

WDM

WDM uses different wavelengths of light to organize each channel. In fact, it is a special type of frequency division multiplexing at very high frequencies. With this type of multiplexing, transmitting devices operate at different wavelengths (for example, 820nm and 1300nm). The beams are then combined and transmitted over a single fiber optic cable. The receiving device separates the transmission by wavelength and directs the beams to different receivers. To merge/separate channels by wavelength, special devices are used - couplers. Below is an example of such multiplexing.

Fig.5.1. WDM multiplexing

Among the main coupler designs, a distinction is made between reflective couplers and centrally symmetrical reflective couplers (SCR). Reflective couplers are tiny pieces of glass “twisted” in the center in the shape of a star. The number of output beams corresponds to the number of coupler ports. And the number of ports determines the number of devices transmitting at different wavelengths. Two types of reflective couplers are shown below.

Fig.5.2. Transmitting star

Fig.5.3. reflecting star

A centrally symmetric reflective coupler uses light reflected from a spherical mirror. In this case, the incoming beam is divided into two beams symmetrically to the center of the bend of the mirror sphere. When the mirror is rotated, the position of the sphere's bend changes and, accordingly, the path of the reflected beam. You can add a third fiber optic cable and redirect the reflected beam to another port. The implementation of WDM multiplexers and fiber optic switches is based on this idea.

Fig.5.4. Centrally symmetrical reflective coupler

Optical multiplexers can be implemented not only using CSR couplers, but also using reflective filters and diffraction gratings. They are not covered in this tutorial.

The main factors that determine the capabilities of various implementations are interference and channel separation. The amount of crosstalk determines how well the channels are separated and, for example, shows how much of the 820nm beam's power ended up at the 1300nm port. A pickup of 20 dB means that 1% of the signal appeared on the unintended port. To ensure reliable signal separation, the wavelengths must be spaced “widely”. It is difficult to recognize close wavelengths, such as 1290 and 1310 nm. Typically, 4 multiplexing schemes are used: 850/1300, 1300/1550, 1480/1550 and 985/1550 nm. The best characteristics so far have been found in CSR couplers with a system of mirrors, for example, two (Fig. 5.5).

Fig.5.5. SCR coupler with two mirrors

WDM technology, which is one of three types of wavelength division multiplexing, occupies a middle position in terms of spectrum efficiency. WDM systems combine spectral channels whose wavelengths differ from each other by 10 nm. The most productive technology is DWDM (Dense WDM). It involves combining channels spaced across the spectrum by no more than 1 nm, and in some systems even by 0.1 nm. Due to this dense distribution of signals across the spectrum, the cost of DWDM equipment is typically very high. Spectral resources are used least efficiently in new systems based on CWDM technology (Coarse WDM, sparse WDM systems). Here the spectral channels are separated by at least 20 nm (in some cases this value reaches 35 nm). CWDM systems are typically used in metro networks and LANs, where low equipment cost is an important factor and 8-16 WDM channels are required. CWDM equipment is not limited to one part of the spectrum and can operate in the range from 1300 to 1600 nm, while DWDM equipment is tied to a narrower range of 1530 to 1565 nm.

conclusions

A narrowband system is a transmission system in the original frequency band using digital signals. To transmit several narrowband channels in one broadband channel, modern transmission systems over copper cables use TDM time multiplexing. Fiber optic systems use WDM wavelength multiplexing.

Additional Information

Control questions

• A device in which all incoming information flows are combined into one output interface performs the following functions:
  • switch
  • repeater
  • multiplexer
  • demultiplexer
• Ten signals, each requiring 4000 Hz bandwidth, are multiplexed into one channel using FDM. What should be the minimum bandwidth of a multiplexed channel with a guard interval width of 400 Hz?
  • 40800 Hz
  • 44000 Hz
  • 4800 Hz
  • 43600 Hz