Modem protocols of physical education. Modem protocols of the physical level

Local counting measures were based on various types of protocols of physical level, which are determined by the type of transmission medium, frequency range of signals, levels of signals, encoding methods.

The first technologies inspired scrap, they took away commercial recognition, patented solutions ARCNET (Attached resource Computer NETwork) that token ring(Markerne kіltse), prote on the cob of the 90s of the last century, the stench of the stench was practically everywhere woven with strings on the basis of a family of protocols ethernet.

This protocol was expanded by the Palo Alto Post Office Center (PARC) of the Xerox Corporation in 1973. In 1980, Digital Equipment Corporation, Intel Corporation and Xerox Corporation jointly expanded and adopted the Ethernet specification (Version 2.0). Similarly, at the IEEE Institute (Institute of Electrical and Electronics Engineers), the committee 802 of the organization of standardization of local measures, as a result of the work, a family of standards IEEE 802.x was adopted, as a result of recommendations for the design of lower levels of local measures. This family includes a few groups of standards:

802.1 – joint measure.

802.2 - Logic call control.

802.3 - LAN with multiple access, carrier control and collision detection (Ethernet).

802.4 - LOM bus topology with token passing.

802.5 - LAN topology "ring" with token passing.

802.6 - a measure to the scale of the city (Metropolitan Area Network, MAN).

802.7 - Broadcast Technical Advisory Group.

802.8 - Fiber-Optic Technical Advisory Group.

802.9 - Integrated Voice/Data Networks.

802.10 - Bezpeka merezh.

802.11 - Bezdrotov hemstitch.

802.12 - LAN with priority access (Demand Priority Access LAN,

lOObaseVG-AnyLan).

802.13 is not a vikolist number!

802.14 - Data transmission through cable TV networks (not active since 2000)

802.15 - Wireless personal networks (WPAN), e.g. Bluetooth, ZigBee, 6loWPAN

802.16 - WiMAX wireless networks ( World-wide Iinteroperability for Mmicrowave Access, read in Russian wymax)

802.17 is called RPR (Resilient Packet Ring - adaptive packet ring). It has been expanding since 2000 as a modern main line on a Russian scale.

According to the skin group, there is a committee of judges, which is responsible for accepting updates. The standards of the IEEE 802 series describe two equal OSI models, but for the time being we only refer to those of them and in that part, as they describe the physical equal.

ethernet (802 .3) - LOM with multiple access, control of the carrier and the manifestation of collisions.

Today, Ethernet is the most widely used local counting protocols. Moreover, the IEEE 802.3 specification for today describes a few options for the physical implementation of LOM with different transmission mediums and data transmission speeds.

The basic power that combines all of these specifications access method to the middle of the transmission. For Ethernet multiple access with carrier control and detection of collisions(CSMA/CD, Carrier Sense Multiple Access with Collision Detection). In the Ethernet network, all universities are equal, there is no centralized management of their activity and differentiation (like, for example, Token ring). The skin node is constantly eavesdropping on the middle of the transmission, and it analyzes all data packets, as if the package of assignments is not given to the node, it is not heard from it and is not transmitted to the upper levels. Problems are blamed on the hour of transmission, but no one can guarantee that two nodes will not try to transmit at the same time (as a result, in the cable, the winkne superposition, which is not received, two signals). For the sake of such situations ( kolіzіy) leather vuzol first lower start the transmission is reconverted at the presence in the signal cable from other framing outbuildings ( carrier control). Alecia is not enough to zapobіgannya kolіzіy through obmezhenіst shvidkostі broadening the signal of the middle transmission. There is a possible situation, that some other voice has already opened the transmission, just a signal that has not yet reached the building we have looked at. So in an Ethernet network, it is possible and standard situations, if two or more nodes are simultaneously trying to transmit data to one another. The procedure for solving such a collision is due to the fact that, having revealed in the process of transmission the presence of an alien signal in the cable, all the universities that have been in such a situation, attach the transmission and try to restore it through different hour intervals.

Nedolіk іmovіrіnіsnogo access method - nevyznachenny hour passing frame, scho sharply increases zbіlshennyam vantazhennya on the fence, scho yogo zastosuvannya in real time systems.

Let's take a look at the procedure for revealing the number and interdependence of admissible transfers of data and data packets that are transmitted through the border. Vmіst and vmіshnіy pristrіy kadіv ethernet rozbiratimeme on the channel level. For the time being, we’ll just be safe that, with a speedy signal width in the conductor, it’s close to 200,000,000 m / s with an IEEE 802.3 thier Ethernet adapter with a data transmission speed of 10 Mbps per byte correction of a 0.8 µs ide packet close to 150 m-code.

Now let's turn to the little one again. In order for the working station “A” to recognize that in the process of transmission there was a small amount of collision, a superposition of signals that “zistovkhnulis”, is guilty of reaching before the transfer is completed. This imposes an exchange on the possibility of a minimum allowance for packages that are managed. In fact, it’s possible to win packets short for a long cable between working stations “A” and “B”, a situation is possible if the packet is redirected to the first station (it’s already wrong that the transmission was successful), but it’s not possible to go to the other one, and won't have the right to start transferring your data, be it at the right time. It doesn’t matter if you get lost in such incomprehensible ways, you can only use vicorist packets of such a long time that for their transmissions the signal reaches the very distant station and turn back.

With a speed of transmission of 10 Mb/s, this problem played an important role and the minimum length of the frame was surrounded by a size of 64 bytes. For an hour of transmission, the first bits reach about 10 km, and for the distance with a maximum segment length of 500 m.

When moving up to 100 Mb/s, the minimum frame rate will be reduced by 10 times. It is important to increase the parameters of the work and the maximum distance between the stations was shortened to 100 m.

With a speed of 1000 Mb/s, 64 bytes are transmitted in total for 0.512 microseconds, and in gigabit volumes it was possible to increase the minimum frame length by 8 times to 512 bytes. Although there are no data for filling the frame, the adapter simply adds a special sequence of characters to the previous one. This technique is called "extended nose".

Virishyuchi the problem of the manifestation of collisions, expanding the nose of the smartly stained smog of the transmission channel of the transmission channel for the hour of transmission of small packets. In order to change the injection factor in a gigabit Ethernet adapter, it is allowed for the presence of a few short frames ready for transmission to form one full frame of a “normal” length up to 1518 bytes.

Moreover, it was suggested to allow the replacement of more advanced, lower than Ethernet standards. This proposition was implemented in such a way as the titles "jumbo" - shots of the start up to 9018 or more bytes.

IEEE 802.3 defines a number of different standards of physical equality. Skin from the standards to the protocol of the physical level IEEE 802.3 may be named.

It can be seen from the table that the topology of the hot bus (thin Ethernet, thin Ethernet) is easily replaced by the bus.

Token Ring (IEEE 802.5)

The Token Ring measure was introduced by IBM in 1984, as part of the way it propagated to combine the entire range of computers and computer systems that are available. In 1985, the Rotis Committee of IEEE 802 adopted the IEEE 802.5 standard on the basis of this technology. Fundamental authority in Ethernet - determinations meth od access to the middle of the assigned order. Implemented access with the transfer of the token (also zastosovuetsya for ARCnet and FDDI).

Kiltseva topology means ordered transmission of information from one station to another in one straight line, strictly in order of inclusion. Kіltseva logical topology is implemented on the basis of a physical world, in the center of which there is a rich station access unit (MSAU - Multi-Station Access Unit).

At any hour, data transmission can only be carried out by one station, which marker beforemortar(Token). When transferring data, a note about employment appears at the marker heading, and the marker turns into a frame frame on the cob. Other stations bit by bit broadcast the frame from the forward (upstream) station to the next (downstream). The station, which is addressing a streaming frame, takes a copy from its buffer for further processing and broadcasts it further around the country, having made a sign of removal. In such a rank, the frame is within the reach of the transmission station, as if you could see it from the ring (not broadcast far). If the station finishes the transmission, it will indicate the marker as a valid one and transmit further along the ring. The hour by which the station has the right to use a marker is regulated. The hoarding of the marker is the basis of the priorities that are assigned to the stations.

With the increase in the activity of nodes, a smug of transmission, which is distant to the skin node, sounds, but there is no landslide degradation of productivity (like with Ethernet). In addition, the mechanism of priorities and exchange for an hour with a marker allow the privileged nodes to see a guaranteed amount of traffic independently from the flooded network. The number of nodes per node can be 260 (an Ethernet segment theoretically allows 1024 nodes). Transmission speed 16 Mb/s, frame size can reach 18.2 Kb.

Packet transfer time limit token ring 10 ms. For the maximum number of subscribers 260, the last cycle of the warehouse operation is 260 x 10 ms = 2.6 s. In one hour, 260 subscribers will be able to transfer their packets (so, obviously, they can transfer). For tsey hour vіlny marker obov'yazkovo didde to the skin subscriber. The same interval is the upper time limit for access token ring

Qi chotiri bet UTP cable category 5 establish a channel, which means 1000 Mbit per second data can be transmitted in both directions. The maximum allowable speed of data transmission on a UTP category 5 cable should not exceed 125 MHz, the 1000 Base T channel is responsible for the transmission of 8 bits of data in the skin signal change period (8 ns).

4) Merezhny equal protocol (eng. network layer) - protocol of the 3rd level of the OSI mesh model, assigned to the data transfer path. Vіdpovіdaє for translation of logical addresses and names in physical, designation of the shortest routes, commutation and routing, troubleshooting and congestion in the merezhі. On the other side of the river, such a merezhny attachment is used, like a router.

Within the boundaries of the semantics of the hierarchical representation of the OSI model, the Merezhevy riven vіdpovіdє on the request for service in the Transport rіvnya and the power to request the service on the Canal rіvіn.

The protocols of the intermediary level route the data from the dzherel to the owner and can be divided into two classes: the protocols from the established data and without it.

· Protocols with the setting of the date to start the transfer of data from the call or setting the route for passing packets from the dzherel to the controller. After what to start the last transfer of data and after the end of the transfer, open the call.

· Protocols without insertion of data are enforced to cover the address information in the skin package. The leather package should be sent to the address of the owner of that oberzhuvach. They gave the skin of the intermediary fences to read the address information and make a decision about the routing of data. The sheet or package of data is transferred from one intermediate building to the next, the docks will not be delivered to the owner. Protocols without the establishment of an order do not guarantee that the correct information will be kept in order, for which it was corrected, because Different packets can go through different routes. For the renewal of the order of data and the hour of the change of the merging protocols without the establishment of the order, transport protocols are required.

Functions of the Merezhevoy river:

· models of the order: with the installation of the order and without the installation of the order

Merezhevy riven of the OSI model can be both from the installed system, and without it. For povnyannya - inter-merezhevy rіven (eng. internet) the protocol stack in the DoD Model (TCP/IP Model) supports only the IP protocol, which is a protocol without the establishment of a connection; the protocols from the established records are on the next level of the model.

addresses assigned to a merezhny node

The skin of the host at the merezhі is to blame for the mother's unique address, how to designate, de vin to be known. Tsya addresses sound assigned from the hierarchy system. On the Internet, addresses are known as IP addresses.

· Passing data

The shards of a large number of divisions on the subdivisions are connected with other networks with wide channels, the networks are called special hosts, which are called gateways or routers (routers) for the delivery of packets between the borders. This is also victorious in the interests of mobile programs, if the coristuvach collapses in one program to another, in this case, the packages (instruction) are to follow him. The IPv4 protocol has such an idea, but in practice it does not stop. IPv6 revenge rational solution.

ICMP (English) Internet Control Message Protocol- protocol of intermarriage support) - intermediary protocol, which is included in the protocol stack of TCP/IP. In general, ICMP is used to send notifications about pardons and other faulty situations that are blamed when transmitting data, for example, the service is unavailable, either the host or the router does not acknowledge. Also, ICMP is supported by some service functions.

ICMP alerts (type 12) are generated when pardons are significant at the IP packet header (because of the fault of the ICMP packets themselves, so as not to cause an ICMP alert about an ICMP alert to an infinitely growing flow).

ICMP notifications (type 3) are generated by the router for the number of days on the route to the destination.

The Ping utility, which is used to check whether IP packets can be delivered, beats ICMP notifications with type 8 (verify) and 0 (verify).

The Traceroute utility, which displays the path of IP packets, ICMP notification with type 11.

Type 5 ICMP notifications are retrieved by routers to update entries in the router's routing table.

Type 4 ICMP alerts are handled by the master (or the router) to handle the security alert by the router.

5) Transport riven (engl. transport layer) - 4th line of the OSI merging model, destinations for data delivery. It doesn’t matter if the data is transmitted, the stars and the cudi, so that the transmission mechanism itself is given. Blocks of these wines are subdivided into fragments, rozmіr of them to be deposited according to the protocol, short one at a time, and breaking them for a long time. The protocols of this level are recognized as intermodal type point-to-point. Butt: TCP, UDP, SCTP.

Існує безліч класів протоколів транспортного рівня, починаючи від протоколів, що надають лише основні транспортні функції, наприклад, функції передачі даних без підтвердження прийому, і закінчуючи протоколами, які гарантують доставку до пункту призначення декількох пакетів даних у належній послідовності, мультиплексують кілька потоків даних, забезпечують the mechanism of data flow management and guarantees the reliability of received data.

Actual protocols of the transport level, which are called protocols without the establishment of a date, do not guarantee that data will be delivered for recognition in the order in which the stench was sent by the annex-dzherel. Deyakі transport rіvnі cope with cim, collecting data in the required sequence before their transfer to the session rіvnі. Multiplexing (multiplexing) of data means that the building's transport system can simultaneously process a small amount of data flows (flows can be found in various supplements) between two systems. The data flow control mechanism is a mechanism that allows you to regulate the amount of data that is transmitted from one system to another. Transport layer protocols often interfere with the data delivery control function, silencing the system that data is being received, and correcting the transmitting party's confirmation that data has been received.

UDP (English) User Datagram Protocol- datagram koristuvach protocol) - one of the key elements of the Transmission Control Protocol/Internet Protocol, a set of networking protocols for the Internet. UDP computer programs can alert (in this type of datagram rank) to other hosts by IP-merezhі without the need for forward notification to install special transmission channels or data channels. Minutes of decommissioning by David P. Reed in 1980 rotation and official designation by RFC 768.

UDP is a simple transmission model, without implicit "hands-on" for ensuring the reliability, ordering the integrity of data. In this way, UDP sends an undesirable service and datagrams can arrive out of order, duplicating or calling without a trace. UDP may be on the verge of re-verification of pardons and rectification, or it is not necessary, or it is due to pay as an addendum. Sensitive up to an hour, programs often use UDP, so it’s easier to drop packets, lower check packets, which have been trimmed, which may not be possible in real-time systems. If it is necessary to fix the pardons on the network interface, the program can fix TCP or SCTP, seperate for the purpose.

The nature of UDP as a protocol without savings will also become familiar for servers that operate on small networks with a large number of clients, for example DNS and streaming multimedia programs such as IPTV, Voice over IP, IP tunneling protocols and a lot of online games.

Past stats have recognized us, . Let's talk about fencing protocols.
Transmission protocols are those that allow the transfer of information according to the rules of the interoperability model between different systems. Skin from the seven equals described in the last statistical model of the interaction between different systems is served by its own set of protocols, otherwise, as it seems, protocol stack .

There are few stacks of protocols. For example, in Ethernet networks, there are TCP/IP stack(Transmission Control Protocol/Internet Protocol - Transmission Control Protocol/Internet Protocol).

By analogy with the OSI model, the protocols are also subdivided into low-income і high-yellow : low roots work on two or three lower levels, high roots - on the highest ones. For some low-level protocols, sound, may be hardware implementation, and high-level ones are implemented by software way.

At the discretion of the protocols of the lower river, the protocols of the higher rivers are constantly modernized or new ones are added to them. Tse allow vykoristovuvaty new methods of data processing and encryption of data, which allow the current state of the world to ensure the safe transmission of information.

We have changed the most extensive protocols for skin care in the OSI model:

Protocols of physical equality

Physically, there are no such protocols, for a little bit of a modem. Vikoristovuєtsya іnshe understand - standard. From the most popular standards it is possible to determine X.24, RS-232, EIA-422, RS-485. Butts modem є protocols V.21, ZyX, PEP.

Link protocols

Channel number of presentations of anonymous protocols, zokrema ARP, Ethernet, Token Ring, FDDI, X.25, SMT, SNAP, Frame relay, PPP.

Merezhnye protocols

Representatives of the protocols of the merezhny equal are the same protocols, like IPX, IP, DDP, RTMP, CLNP, RARP that in.

Transportation protocols

Transport rіven as a representative of the greater intellectual rіvnіv vengeance at your warehouse without any other protocols, as representatives of such protocols NetBIOS, UDP, TCP, ATP, SPX, SKIP.

Session protocols

Representatives of the session protocols are such protocols as RPC, SSL, WSP. Really stinks with an interface - a happy lanka between the protocols of the higher and lower levels.

Protocols equal to vistavi

At the same time, such protocols are practiced, like LDAP, XDR that in. Dії tsikh protocolіv practically repeat one of one. Їhnє zavdannya - organization of the process of re-creating data in that kind, which is wise as a dzherel, so it is to the right-hand man.

Application protocols

Applied rіven is characterized by the largest number of different protocols, their most prominent representatives HTTP(transmission protocol to hypertext), FTP(file transfer protocol), SMTP(transmission protocol by mail), X.400, Telnet, SNMP, POP3, IMAP4 that in.

MODEM PHYSICAL PROTOCOLS

Telecommunications are the eye of the world, which develops most dynamically. It is important to reevaluate the relevance of the galuzia itself for our country through її expansion and traditional problems of durability and keratinization. From the other side, inseparability, unfortunately, of today's communication channels does not allow the world to speed up with light achievements in the sphere of high digital transmission systems. Therefore, modems for switching telephone channels are deprived of communication and, I think, they will again be deprived of the widest range of information communications. Before that, judging by the enthusiasm, with some foreign providers of telecommunications companies, they took up the development and selection of modems for the new V.34 standard, the interest in modem topics did not die out soon and in the infrastructures that were successful in the communications infrastructure.

At this article, try to give an overview of the protocols of the physical level and of their parameters for modems that work on switching and video channels to communicate the tone frequency (telephone channels). First, let’s take a closer look, arbitrarily sprout a piece of respect for the slanderous character of the commonly accepted terminology and the principles of robotic modems. Tse allow znyat mozhlivі nepozumіnnya, po'yazanі z vagueness stating the general public about the difference between the understanding of the body and bit / with the vodpovidno between the modulation swidkіstyu and information. In addition, information about the possible types of modulation that can be installed in modems, as well as about duplex communication and methods of security, will be indispensable.

Shvidkist

Analog tone frequency channels are characterized by the fact that the spectrum of the signal that is transmitted through them is surrounded by a range of 300 Hz to 3400 Hz. Causes, for some reason, there may be a place, don’t let yourself be left behind the framework of these statutes. Let's take it as a given. The very same spectrum exchange is the main bridging at the alternative telephone channels for high-speed transmission of digital information. Lyudina, who is familiar with the Nyquist procedures, will tell us without any doubt that the speed of transmission from a channel with an interleaved spectrum is impossible to exceed the width of the spectrum, i.e. 3100 baud at a time. How about using modems that transmit information with speeds of 4800, 9600, 14400 bit/s and navigate more? You should ask yourself: in the analog technology of transferring data baud and bit / s, there is no one and the same. To clarify the values ​​of these warto, look at the more important physical level of the robot modem.

The electric signal, which is expanded by the channel, is characterized by three parameters - amplitude, frequency and phase. The very change of one of these parameters, or to induce a wholesomeness of their totality, depends on the value of the information bits and becomes the physical reality of the modulation process. The skin information element needs to be fixed for an hour, on which electric signal the maximum value of the parameters, which characterize the value of the information element. This hour is called a bodov interval. If the element that is encoded sends one bit of information, which can take the value 0 or 1, then on the baud interval of the signal parameters, it is likely that one of the two zooms of the amplitude, frequency and phase values ​​can be received. In this way, modulation speed (also called linear or baud) is more informational, so 1 baud = 1 bit / s. Ale element, which is encoded, may represent not one, but, for example, two bits of information. In this mode, the information frequency of the baud interval is overridden by the baud interval, and the signal parameters on the baud interval can take one of four aggregations, which means 00, 01, 10 or 11.

In a vipadku, as if n bits are encoded on the baud interval, then the information speed is reversed to baud interval n times. Ale kіlkіst kіlkіst stanіv signal in trivіlіrіmі (in zagalnomu vipadku) expanses - amplitude, frequency, phase - more 2 ** n. Tse means that the demodulator to the modem, having received a signal on the baud interval, will be responsible for pairing with 2 ** n reference signals and selecting one of them to decode n bits. In this way, with the increase in the number of coding and the growth of informational speed, it is worthwhile to stand near the signal space between two suicidal points, to stagnate at the steady progression. And tse, in his line, impose daedals and zhorstkishi vimogi to "purity" to the transmission channel. Theoretically, the speed of a real channel is determined by Shannon's home formula:

V = Flog(1+S/N),

where F is the bandwidth of the channel, S/N is the signal/noise difference.

Another one is changing and assigning the possibility to the channel from the point of view of the noise level due to the reliable transmission of the signal, which encodes more than one bit of information in the baud interval. So, for example, if the signal / noise ratio is equal to 20 dB, then the intensity of the signal, which reaches the remote modem, is 100 times greater than the intensity of the noise, and the tone frequency channel (3100 Hz) is victorious, the maximum distance between Shannon is 2060 b/s .

Modulation

Speaking about the type of modulation, let's talk about the few that really vikoristovuyutsya in modems. And there are really only three of them: frequency, phase-difference, and rich-positional amplitude-phase modulation. Reshta - no more, lower variations of these three.

With frequency modulation (FSK, Frequency Shift Keying), the values ​​of 0 and 1 of the information bit correspond to the frequency of the physical signal with a constant amplitude. Frequency modulation is more than a pereskodostіyka, oskіlki spovorennia at pereskodіtsya in the main amplitude of the signal, and not the frequency. At the same time, the reliability of demodulation, and therefore the stability before the transition, is greater, the more periods the signal is consumed in the baud interval. Ale zbіlshennya baud interval zі zrozumіlih reasons reduce the speed of transmission. On the other hand, the width of the signal spectrum required for this type of modulation can be significant for any channel. Zvіdsi vitikaє sphere zastosuvannya FSK - nizkoshvidkіsnі, ale vysokonadіynі standards, scho allow zdіysnyuvat sv'yazok on channels with great frequency response, or to wind with a narrowed range of transmission.

With phase-difference modulation (DPSK, Differential Phase Shift Keying), it is necessary to change the value of the information element by the parameter - the phase of the signal at constant frequency amplitudes. In case of any skin information element, it is not the absolute value of the phase that should be set, but rather the change of the forward value. If the information element is dibit, then depending on the value (00, 01, 10 or 11), the phase of the signal can change by 90, 180, 270 degrees, or not change. From the theory of information, it seems that phase modulation is the most informative, however, the increase in the number of bits that are encoded, more than three (8 positions of phase rotation) lead to a sharp decrease in zavadnost. Therefore, at high speeds, combinations of amplitude-phase modulation methods are used.

Bagatoposition amplitude-phase modulation is also called quadrature amplitude modulation (QAM, Quadrature Amplitude Modulation). Here, you can change the phase of the signal by changing the amplitude of the signal, which allows you to increase the number of bits that are encoded. In this hour, there are modulations, in which the number of encodings on one baud interval of information bits can be 8, and, apparently, the number of signal positions in the signal space is up to 256. with insufficient zeal of coding. Therefore, in all current high-level protocols, there are various types of modulation, i.e. modulation with lattice coding or trellis-coded modulation (TCM, Trellis Coded Modulation), which allows you to increase the transmission security of the transmission of information - reduce the noise to the signal-to-noise ratio in the channel by a value of 3 to 6 dB. The essence of this coding is based on the introduction of supermundane. The expanse of signals expands in two ways, adding to the informational bits of one more, which settles for the help of a short coding over a part of the informational bits and the introduction of the elements of the delay. Expanded by such a rank, the group is given the same rich positional amplitude-phase modulation. In the process of demodulation of the received signal, the first decoding is carried out for the more subtle algorithm of Vitterbi, which allows for the introduced supermundaneity and knowledge of the prehistory to be selected for the criterion of maximum plausibility of the signal space, the most significant point of significance, in particular, the shape

Under the duplex mode, the robot is able to transmit information to the offending parties at once. Typical telephone channel - a typical example of a duplex channel. Win permits you to speak to your counselor at the same hour, if that one at his hand is trying to help you. For more food, you will understand one another, but still your problems. Analogy can be seen all over the world and modem connection. The problem for the modem is not the capacity of the channel to transmit duplex information, but the ability of the modem demodulator to recognize the input signal and the nature of the input signal of the PBX equipment of the wet output signal, which practically becomes noise for the modem. In this case, the tightness can be not only equal, but in more cases it is significant to change the tightness of the core signal that is received. The one who can transmit information by modems at the same time on the offending side is recognized by the capabilities of the protocol of the physical level.

How to secure a duplex? The most obvious way, which does not affect the retailers of modems and especially fantasies, but it does not affect the telephone connection, up to a chotiriprovidny termination, vyplyvaet zgadana posibility. If such a possibility is, then in every case the skin pair is victorious for the transmission of information only in one direct way.

If it is necessary to secure a duplex for an hour of work from a two-wire line, then it must be done in other ways. One of them is the frequency subdivision of channels. The whole smuga channel is divided into two frequency subchannels, the skin channel is transmitted in one straight line. The selection of the transmission subchannel contains the installation steps of the call and, sound, unequivocally prompted the modem to roll in the call session: what is called, what is the sound. It is obvious that this method does not allow the possibility of victoring the channel in full communication through the value of the sound of the smog of transmission. Tim more, to turn off the penetration of the terrestrial harmonics in the land subchannel, the separation of them should be brought with a significant "gap", after which the frequency subchannels occupy not half of the total spectrum. Vіdpovіdno (div. Shannon's formula), a Danish way to secure a duplex connection between transmission speeds. Known physical level protocols, which victorious channel sub-channels, ensure symmetrical duplex calls with speed, which do not exceed 2400 bit/s.

The warning about the symmetrical duplex is not vipadkove. On the right, in the fact that a number of protocols secure and a larger swedish connection, but in one straight, even as a return channel, it is significantly more important. The sub-frequency subdivision is different for different widths of the subchannel bandwidth. This kind of duplex connection is called asymmetric.

Another method for securing symmetrical duplex, which is used in all high-level protocols, is the technology of echo-adjustment (exo-compensation). The essence of it is that modems, volodiyuch іnformatsiєyu about the power of the outgoing signal, can extract the knowledge for filtering the "man-made" noise of the received signal. At the input stage, a skin modem is connected to the comms, which, by means of a probing signal, sets the parameters of the echo: the hour of delay and the intensity of the received signal. And during the communication session, the echo-compensator to the modem "sees" from the input signal, which is received, its own output signal, it is adjusted to remove the parameters of the echo-display. This technology allows to use for duplex transmission the entire bandwidth of the channel bandwidth, but it helps in the implementation of even serious costing resources for the signal processing.

Please, varto designate that there are a lot of protocols and do not try to secure duplex calls. These are the so-called napіvduplex protocols. Zokrema, all protocols accepted for facsimile communication are duplex. And here at the skin moment the information is transmitted to one side only. After the completion of receiving/transferring the current portion of information, the modem (fax) will synchronously switch over to the direct data transmission (ping-pong). Due to the variety of problems due to the mutual penetration of the transmission channel, as well as to the echo-voices, the duplex protocols in general are characterized by a greater degree of confidence and the possibility of varying the width of the bandwidth of the channel. The efficiency of the data transmission channel is compared with the duplex protocols below. It is related to the fact that all transfer protocols, like channel level (MNP, V.42), and file transfer level (X, Y, Zmodem, and about protocols like BiDirectional), require two-way exchange, accepting confirmation received information. And if it’s a direct transfer, it’s impossibility at the moment to transfer a hell of a portion of information, using additional overhead vitrates hour by hour for mutual resynchronization of the receiving and transmitting sides.

Global modem protocols ITU-T

Duplex protocol with frequency subdivision of channels and frequency modulation FSK. On the lower channel (sound the victor transmission and the modem beeps), "1" is transmitted at a frequency of 980 Hz, and "0" - 1180 Hz. On the upper channel (transmitted in the upper channel) "1" is transmitted at a frequency of 1650 Hz, and "0" - 1850 Hz. Modulation and information speed - 300 baud, 300 bit/s. Regardless of the low speed, we know the protocol to be known as an "emergency" one, if it is impossible to change the protocol of the physical level after a high level. In addition, due to their lack of vibrancy and zavadostіykіst, they are victorious in special high-quality additions, which imply a high superbness of the transmission. For example, when connecting between modems according to the new Recommendation V.8, or when transmitting certain commands during a facsimile call (upper channel).

Duplex protocol with frequency subdivision of channels and DPSK modulation. Nesucket frequency of the lower channel (transmitted Viklika Hz, Upper (transfer Vidpovіdov -Hz. Modulesyin Shvidkіst - 600 invigorates. buti 600 or 1200 bits / s.

Duplex protocol with frequency subdivision of channels and QAM modulation. Nesucket frequency of the lower channel (transmitted by the Zhvaliy, Upper - 2400 Hz. Modulatsin Shvidkіst - 600 invigorates. May of Chotirositsyno (codes dibat) і іrtnadtsyatiyno (codes) regardless of the other type of modulation On the right, in that the first two bits in the 16-QAM mode (quad) indicate the change in the phase quadrant of the forward signal element and the amplitude is not considered, and the remaining two bits indicate the position of the signal element in the middle of the quadrant of the amplitude variant. In this way, DPSK can be considered as the only QAM drop, where the two remaining bits do not change their value, including the same amplitude.The V.22bis protocol is the de facto standard for all midrange modems.

The whole duplex protocol with echo-smothering and quadrature amplitude modulation or modulation with short-part coding. The frequency of the carrier signal is 1800 Hz, the modulation speed is 2400 baud. In this rank, the spectrum of the top line is victorious in the range of 600 to 3000 Hz. May have two-position (bit), four-position (dibit) and sixteen-position (quadrobit) QAM modes. Vidpovidno, information speed can be 2400, 4800 and 9600 bit/s. In addition, for the speed of 9600 b/s, there may be an alternative modulation - 32-position TCM.

Tse duplex protocol with echo-smothering and TCM modulation. The frequency of the carrier signal is 1800 Hz, and the modulation speed is 2400 baud. Available modes are 16-TCM, 32-TCM, 64-TCM and 128-TCM. Vidpovidno, information speed can be 7200, 9600, 12000 and 14400 bit/s. 32-TCM mode is more complex than V.32 mode. The V.32bis protocol is the de facto standard for all Swedish modems.

Exotic modem protocols ITU-T

The full duplex protocol is based on FSK frequency modulation. New has two swedish modes: 600 bit/s and 1200 bit/s. Modulation and information speed equals: 600 and 1200 baud. In both modes "1" is transmitted at a frequency of 1300 Hz. In the 600 bit/s mode, "0" is transmitted at a frequency of 1700 Hz, and in the 1200 bit/s mode, at a frequency of 2100 Hz. The implementation of the protocol can optionally include a return channel, which works on a speed of 75 bits / s, which converts the protocol to duplex asymmetric. Transmission frequency "1" at the return channel - 390 Hz, "0" - 450 Hz. This protocol is practically new from the standpoint of a standard intermodem communication protocol, and not every standard modem has equipment. However, vin serving and dosі zalishaєsya basic for the implementation of non-standard modemіv, nabula wide width in our country (like LEXAND). Mabut, zavdyaki simplicity, high stability to the transition and decent (in the case of V.21) firmness. In addition, in the lower European countries, the protocol is stored in the Videotex information system.

V.26, V.26bis, V.26ter

There are three protocols for each type of modulation - DPSK, carrier frequency - 1800 Hz and modulation speed - 1200 baud. The difference between them is based on the possibility and methods of providing duplex communication and in information security. V.26 provides only duplex security over a second line of sight lines, V.26bis provides a full duplex protocol for assignments over a two-wire switched line, and V.26ter provides full duplex security over an additional echo-smothering technology. In addition, the first two protocols can be asymmetric duplex, optionally including a return channel, which works on a speed of 75 bit/s and is valid up to V.23. All three protocols ensure the speed of information transmission at 2400 bit/s for an additional 4-position (dbit) DPSK. V.26bis and V.26ter also support DPSK bi-directional (bit) mode, providing 1200 bit/s speed.

In this protocol, there is a modulation with the shortest part of the TCM coding. Vіn appointments for secure duplex communication on chotiriprovіdny vidilenіh channels. The frequency of the carrier signal is 1800 Hz and the modulation speed is 2400 baud. Works in 64-TCM and 128-TCM modes. Vidpovidno, informational speed can be 12000 and 14400 bit/s. This protocol is already guessing V.32bis without moon. Moreover, if a modem with V.33 protocol is installed on a remote wire terminated to a PBX differential system, it will be possible to communicate with a remote V.32bis modem installed on a two-wire line.

Overloading ITU-T fax protocols

In this protocol, phase-differential modulation with a carrier signal frequency of 1800 Hz is required. There are two modes with different information speeds: 2400 and 4800 bit/s. Informational speed of 2400 bit/s is available with modulation speed of 1200 baud and coding bit (4-position DPSK), and 4800 bit/s - with 1600 baud and coding bit (8-position DPSK). It is important that the modem protocols of this family are based on V.27 and V.27bis, which are considered to be V.27ter, the main rank of channel type (visions of chotiripprovidny), for which the stench is recognized.

Which protocol has quadrature amplitude modulation. The frequency of the carrier signal is 1700 Hz, the modulation speed is 2400 baud. May have 8-position (tribit) and 16-position (quad) QAM modes. Vidpovidno, information speed can be 7200 and 9600 bit/s.

This protocol is guessing V.32bis for its parameters. There is a new twist on modulation with short coding. The frequency of the carrier signal is 1800 Hz, and the modulation speed is 2400 baud. Available modes are 16-TCM, 32-TCM, 64-TCM and 128-TCM. Vidpovidno, information speed can be 7200, 9600, 12000 and 14400 bit/s.

Non-standard modem protocols

This protocol, razrobleniya firm AT&T, є vіdkritim realіzatsiї ї rozrobnik modemіv. Zokrema, AT&T's CRM BIS, the implementation protocol for some U.S. Robotics modems. The protocol is actually a mechanical development of V.32bis technology: duplex with echo-choking, modulation with lattice coding, modulation speed - 2400 baud, carrying capacity - 1800 Hz, extension of information speed with values ​​of 16800 or 19200 bits TCM. As a result of such an approach, it is even more difficult, as it is presented by this protocol to the line. So, for example, for a stable operation on a speed of 19200 b/s, the signal/noise ratio can be no less than 30 dB.

The protocol of expansions by ZyXEL Communications Corporation and implementations in power modems. This protocol is the same as V.32terbo, extending V.32bis with data rates of 16800 and 19200 b/s using the saving technology of echo-choking, modulation with trill coding and carrier 1800 Hz. The modulation rate of 2400 baud is saved at 16800 bit/s. The speed of 19200 bits/s is supported by the modulation speed up to 2743 baud for saving the modulation mode 256-TCM for both speeds. This solution allows you to reduce the signal/noise on the line by 2.4 dB, however, the expansion of the bandwidth can be negatively signified with large changes in the amplitude-frequency characteristic of the channel.

The HST (High Speed ​​Technology) protocol was developed by U. S. Robotics and implemented in Courier series modems. Tse asymmetric duplex protocol with frequency subdivision of channels. The Zvorotny channel has 300 and 450 bit/s modes. The main channel is 4800, 7200, 9600, 12000, 14400 and 16800 b/s. Zastosovuetsya modulation with ґratchast coding and modulation speed 2400 baud. It is characterized by relative simplicity and high arrogance due to the presence of the need for echo-compensation and the interdependence of the channels.

The duplex protocols of the PEP (Packetized Ensemble Protocol) family are developed by Telebit and implemented in the TrailBlazer (PEP) and WorldBlazer (TurboPEP) series modems. In these protocols, in principle, the whole range of transmission to the tone frequency channel for high-speed transmission is victorious. The entire channel is divided into anonymous high frequency subchannels, which transmit their own portion of bits from the wild flow of information through the skin. Such protocols are called rich-channel, or parallel, or protocols without any carriers (multicarrier). In the PEP protocol, the channel is divided into 511 subchannels. At the skin subchannel with a width of about 6 Hz with a modulation sweep of 2 to 6 baud, an additional amplitude quadrature modulation is encoded from 2 to 6 bits per baud. Є kіlka stаіnіv svobodіv dо bezpechennya maximії throughput ї smozhї ї smoїї ї sromozhnostі dermal specific channel, scho є є є ї є ї ї ї є є є є ї ї ї ї ї ї ї ї ї ї ї ї ї є spotvorenі і zavodovoї situatsii. During the installation process of the skin frequency subchannel, it is independently tested and the possibility of the second choice is determined, as well as the parameters: modulation speed of the subchannel and the number of modulation positions. The maximum transmission speed for the PEP protocol can reach 19200 b/s. In the process of a session, in case of an impaired change, the parameters of the subchannel can be changed, and the deacons of the subchannel can be turned off. For whom, the decrement of the decrease in speed is selected at 100 bits / s. The TurboPEP protocol for increasing the number of baud channels, as well as the number of bits that are encoded on one baud interval, can reach a speed of 23,000 bits / s. In addition, the TurboPEP protocol zastosovuetsya modulation with trill-encoding, which makes the protocol more resilient.

The main advantages of these protocols are weak sensitivity to the amplitude-frequency characteristics of the channel and significantly less sensitivity to impulse shifts in similar to traditional protocols. If you don’t call for food first, then you need impulsive changes in comments. On the right, in the fact that if you want a “b'є” pulse jump over the entire spectrum width, then over all subchannels, but in a connection with a significantly greater signal trivality in pairing with traditional protocols (6 baud versus 2400), it is caused by a jump in a part of the signal much less, which allows a number of vipadkіv normal demodulation. And the rest, which varto is significant, are those that in a number of countries are protocols of the same type of fence for vikoristannya on telephone channels, which are commuted. It is possible that the rich channel protocols allow successful operation on the lines, on which responsive channels are installed notch filters (in order, perhaps, to save customers, as if they were blamed, the ability to win over telephone channels for the transmission of data) to standard modem channels for data transmission.

І to stop

Practically, there is a lot of mystery about the remaining reach in the field of superficial data transmission over telephone channels - the projects of V. fast from various companies, V. FC from Rockwell International and, now, Recommendation V.34 ITU-T - in an overview of modem protocols in the physical world, we can see . However, just to lightly bump into those V.34, it turns out that it's not just a hell of a rock on the way to increase the speed of the modem connection, but a majestic revolutionary breakthrough in the practical selection of all the reserves for the tone frequency channel. Having broken through, in a singing rank, at the light-gazer, which demonstrates a deep-systemic approach to the problem, which is based on a sharp technological cut in instrumental systems, which allows you to get as close as possible to Shannon's theoretical boundary. For this reason, the theme of Varta is okremoї statti...

Oleksandr Paskovaty, "Analytic-TelecomSystems"

Physical riven:

• transmission of battles by physical channels ;
• shaping electrical signals ;
• coding information;
• synchronization;
• modulation.

Implemented in hardware.

Functions physical equal are implemented at all outbuildings connected to the yard. From the side of the computer functions physical equal consign thread adapter or last port.

butt protocol physical equal the specification of 10Base-T Ethernet technology can serve, as it indicates how the twisted cable is an unshielded twisted pair of category 3 with a cable support 100 Ohm, RJ-45 sockets, the maximum length of the physical segment is 100 meters, Manchester code for the presentation of data on the cable, as well as other characteristics of the medium electrical signals.

Channel riven

On the physical equal the beats are simply overwhelmed. You don’t have to worry about it, but at the lines, at some lines, the connection is vicorous (subdivided) alternately by pairs of mutually compatible computers, the physical medium of transmission is possibly occupied. To that one of the zavdan canal level(Data Link layer) availability of transmission medium. More appointment canal level- implementation of mechanisms revealed and corrected pardons. For whom canal equal- bits are grouped into sets, how to name personnel ( frames). Channel riven ensure the correctness of the transfer of the skin frame using a special sequence of bits on the cob and the end of the skin frame, for visualization, as well as calculating checksum, processing all bytes of the frame in a singing way, and adding checksum up to the frame. If the frame arrives through the mesh, the holder is again calculated checksum take away the data and correct the result checksum out of frame. As the stinks run away, the frame is considered correct and accepted. Yakshcho control sums if they don’t run away, then a pardon is fixed. Channel riven maybe not only show pardons, but also correct them for the re-transmission of poor frames. It is necessary to indicate that the function of pardons has been corrected for canal level not obov'yazkovoy, to that in deakieh protocols tsgogo eve vіdsutnya, for example Ethernet and frame relay.

Channel level functions

Na_yna shipping package:

1. Between two land stations near the border with a sufficient topology.
2. Mіzh be-yakimi stantsіyami in mezhі z typical topology:
   • accessibility review rozpodіlenogo middle;
   • seeing shots from the flow of data that come as needed; shaping frames with overstretching data;
   • pіdrakhunok that perevіrka checksum.

Implemented in software and hardware.

At protocols canal level, which vykoristovuyutsya in local merezhah, laid down a single structure zv'yazkіv mіzh computers and ways of addressing. hocha channel riven and ensure the delivery of the frame between the two nodes of the local border, we need to work only in the border topology of calls, the very same topology, on the basis of the best of the divisions. To such typical topologies, which are supported by protocols canal level local lines can be seen as "solid tire", "kіltse" and "zirka", as well as structures removed from them behind auxiliary bridges and commutators. Butt protocols canal levelє Ethernet, Token Ring, FDDI, 100VG-AnyLAN protocols.

Local networks have protocols canal level beaten by computers, bridges, switches and routers. Functions of computers canal level implemented by joint efforts lace adapters and their drivers.

In global meshes, it is rare to have a regular topology, channel riven often safe exchange of notifications only between two landline computers connected to an individual line of communication. Point-to-point protocols (as such protocols are often called) can be extended to PPP and LAP-B protocols. In times for delivery, we need to create a border line through the border of the vicorist. This is how the measures are organized X.25. Other functions in global links canal level in a clean look, it is important to see that in the same protocol the stench is combined with the functions of the lace line. The protocols of ATM and frame relay technologies can serve as examples of such an approach.

In general channel riven is already a tight set of functions overstrength support between the knots of the merezh. Do some vipadkah protocols canal level vyyavlyayutsya by self-sufficient transport facilities, and even on top of them can be processed without intermediary protocols of application level or programs, without obtaining the costs of transport and transport lines. For example, basic implementation management protocol SNMP network directly over Ethernet, if you want to standardly run this protocol over twill protocol IP and UDP transport protocol. Naturally, if such an implementation will be interchanged, it will not be suitable for warehouse storage of different technologies, for example, Ethernet і X.25, and navit for such a measure, in all segments, Ethernet will be stagnant, and between segments, use loops. And the axis of a two-segment Ethernet network, connected by a bridge, the implementation of SNMP over canal level be a whole lot of practice.

Tim is not less, for the safety of yakіsnoy transportation podomlen at merezhakh whether any topology and technology functions canal level appears to be insufficient, to that in the OSI model the top of the task is based on two steps - the rail and the transport.