Packet switching node. Scheme of organizing communication on the station

Chapter 7. Principles of building switching systems.

§ Structure and classification of switching nodes

Under switching refers to making, opening and switching electrical circuits. Switching is carried out at switching nodes. On telecommunication networks, through switching, subscriber devices are connected to each other to transmit (receive) information. Switching is carried out at switching nodes (CU), which are components of the telecommunication network.

Subscriber devices of the network are connected to the KU by subscriber lines. CUs located on the territory of one locality are connected by connecting lines. If CUs are located in different cities, then the communication lines connecting them are called intercity or intrazonal.

The switching node into which subscriber lines are connected is called switching station or simply station. In some cases, subscriber lines are included in substations. A person who uses a subscriber device to transmit and receive information is called subscriber. To transfer information from one network subscriber device to another, it is necessary to establish a connection between these devices through the appropriate nodes and communication lines. To make the connection, switching equipment is installed at the switching nodes.

The set of line and station facilities designed to connect terminal subscriber devices is called connecting path. The number of switching nodes between connected subscriber devices depends on the network structure and direction of connection.

To implement the required connection, the switching node and the subscriber device exchange control signals.

At the switching node, the connection can be established for the time necessary to transmit one message (for example, one telephone conversation), or at long time, exceeding the transmission time of one message. The first type of commutation is called operational, and the second - cross (long-term).

Switching node (CU) is a set of equipment designed to receive, process and distribute incoming information. The most typical example of a control system is a switching station, which includes subscriber and trunk lines. A simplified block diagram of the switching node is shown in Fig.

Rice. Switch node structure

To perform its functions, the CU must include the following: main blocks:

Commutation field (KP) - represents a collection switching devices, with the help of which the connection of the subscriber and trunk lines included in the station is ensured.

Control device (CU) - designed to control the process of establishing connections. It includes equipment for receiving, generating and transmitting control information. Based on the information about the number of the called subscriber or the direction of communication received from the call source, the CU includes the corresponding elements of the switching field, resulting in a connection between the corresponding input and output.

Trunk blocks (BSL), through sets of trunk lines (CLS) of which communication lines from (to) other CUs are connected via analog or digital trunk lines (CL). When using unidirectional trunk lines, incoming and outgoing trunk lines are separated.

Subscriber line blocks (BAL), through subscriber kits (SK) of which subscriber lines are connected to the station.

The CU equipment also includes additional blocks :

Cross - line input and output device.

Cord kits (ShK), which in coordinate-type automatic telephone exchanges serve to power telephone sets, as well as receive and send service signals during the process of establishing a connection.

Power supplies.

Equipment operation monitoring devices.

Load parameters metering devices.

The following types of connections can be established at switching nodes:

intra-station - the connection is made between subscribers of this telephone exchange;

outgoing - a connection is established at the initiative of a subscriber of a given station with a subscriber of another station through a connecting line;

incoming - a connection is established with a subscriber of a given station by a call received via a trunk line from another station;

transit - at this station two connecting lines are switched in order to connect subscribers of other stations.

Switching nodes of communication networks are classified according to a number of criteria:

by appearance transmitted information (telephone, telegraph, broadcasting, data transmission, etc.);

by connection servicing method (manual, automatic);

by place occupied in the telecommunication network (district, central, hub, terminal, transit stations, nodes of incoming and outgoing traffic);

by type of communication network (urban, rural, institutional, intercity);

by type of switching and control equipment (ten-step, coordinate, quasi-electronic, electronic);

by capacity ,T. i.e. by the number of incoming and outgoing lines or channels (small, medium, large capacity);

by switching type (operational, cross-country);

by channel separation method (spatial, space-time);

by switching method (circuit switching, message switching, packet switching).

To carry out switching (connection) of lines (or channels) and control the connection establishment processes on the PBX, switching devices are used.

Switching device (KPR) is a device that provides an abrupt change in the conductivity of electrical circuits for a certain period of time. There are switching devices contact And contactless.

In contact devices, conductivity changes by closing and opening contacts included in the electrical circuit. In non-contact devices, a change in conductivity is achieved by changing any parameter (resistance, inductance or capacitance) of one of the elements of the electrical circuit. The conductivity of electrical circuits in the switching device is changed switching element (CE).

Lines with different conductivity (two-, three-wire, etc.) can be connected to the switching device, so their switching is carried out by several CE, which are combined into switch group. In this case, the switching elements switch simultaneously under the influence of the control signal.

According to the control methods, KPR can be divided into manual and automatic switching devices. Devices manual switching controlled by human mechanical action (keys, push-button switches, telephone jacks and plugs). Devices automatic switching controlled by electrical signals.

Depending on the number of input and output lines, a different number of switching groups can be installed in a switching device. A set of switching groups that provides switching of inputs and outputs is called switching field of the device.

The location of a switching group in the switching field of a device (or in a switching block built from several devices) is called commutation point.

To switch electrical circuits, devices are used that provide two stable states of their switching elements (or groups). In this case, the electrical circuit passing through the CE is open in one state (i.e. closed state), and in the other it is closed (open state).

Switching devices differ from each other in structural and electrical parameters.

TO structural parameters include: number of inputs n, number of outputs m, accessibility of entrances D in relation to outputs, the number of simultaneously switched electrical circuits (conductivity), memory property. The derivatives of these parameters are the total number of switching points T,the number of switching groups and the number of switching elements, as well as the maximum number of simultaneous connections.

TO electrical parameters switching devices include: the resistance of the switching element in the closed (open) state and the open (closed) state, the ratio of which is called commutation factor ; time of switching CE from one state to another; insertion attenuation into the conversation path; noise level; supply voltage; the amount of current required to switch the CE; power consumption.

Some switching devices have property of memory ,those. the ability to maintain operating condition after the control input is stopped. This allows you to reduce energy consumption to maintain the operating condition of the device. To return the device to its original state, a new control action is required.

The switching devices currently used can be divided into four types according to their structural parameters:

1. Switching devices such as relays (1 x 1) have one input and one output.

2. Finder type switching devices (1 x m)have one entrance n= 1 and m exits.

3. Switching devices of multiple type connector n(1 x m) have n entrances and nm exits.

4. Connector type switching devices (n x m)have n entrances and m exits.

By means of switching devices, switching blocks, search stages and the switching field of automatic telephone (telegraph, etc.) stations and nodes, control devices, linear and service sets are built.

Classification. Switching nodes, depending on their position in the data network, can perform quite various functions. First of all, it is necessary to distinguish switching nodes, to which only connecting lines leading to other nodes are connected (i.e., transit nodes), from nodes, to which, in addition, subscriber lines from terminal installations are connected. In the latter case, control functions can be more diverse, since the signaling methods used in subscriber and trunk lines, generally speaking, do not coincide. The difference in management functions is also related to the special services provided to subscribers (see Section 3.2). Finally, we should not forget about various characteristics loads. Management functions are especially extensive in such transit switching nodes, to which trunk lines from different data networks are connected.

However, another difference plays a practically more important role - the difference between hubs and other switching devices. Hubs are designed to combine the load from multiple peripheral endpoints so that it is transferred to a higher switching node or (in private data networks) to a central endpoint, such as data processing equipment (i.e., a central computer), via fewer connecting lines (Fig. 2.1).

Rice. 2.1. Data switching equipment installed in switched network nodes: a) hub and switching node; b) concentrator: OUPD - data transmission terminal; AL - subscriber line; K - concentrator; SL - connecting line; KU - switching unit; CC - central installation, for example computer

Hubs also allow load transfer in the opposite direction to end units. The connecting paths between terminal units connected to the same hub generally pass through a higher-level switching node. (Such hubs are called linear, in contrast to similar devices that are used to connect a large number of lines with a small number of control devices, for example registers for receiving dialing characters

numbers, and are known as register hubs.)

First of all, the principle of construction of switching equipment is determined by the switching method used (see Volume 1, Section 6.1.2), which depends on whether an end-to-end (direct) connection between the terminal units should be established or not. In the first case, there is no need for intermediate storage of data in switching nodes (channel switching). If, however, as far as possible, only one particular section of the connecting path is occupied, then intermediate storage of data in memory (message switching) is required. In this case, whole messages can be stored in memory (switching with message storage) or only parts of them (packet switching).

To implement both channel switching and message switching during data transmission, it has been developed big number various devices. One or another switching method can be implemented different ways: it is possible, for example, to switch channels with spatial and temporal separation, as well as time switching meaningful moments or groups of bits (bytes). For intermediate storage of data, you can use punched tape or magnetic media. The type of management is also of great importance: decentralized or centralized, rigid (with constant functional connections) or programmatic.

Structure and methods of service. The variety of possibilities for implementing switching functions leads to the fact that there is no general structure of switching equipment suitable in all cases, in other words, a single generalized circuit of some basic elements that, regardless of their specific implementation, could be identified in any switching equipment. Apparently, with the same switching methods and node location in the network, the same functions should be performed, but it is hardly possible to indicate an unambiguous and always fair rule by which certain elements would be assigned to them. Therefore, the following presentation is largely based on examples of specific technically implemented devices.

As already noted, devices with the same or similar purpose may have different names. In what follows, we mainly use the names that are used in the relevant literature on the switching systems described, as far as this is permissible with a natural desire for unity of presentation.

Service modes are the ways in which demands for an occupation are processed. certain devices. In this case, control devices should

distinguished from devices intended directly for switching or intermediate storage of data. The waiting service system is typical for centralized control devices: the occupation of these devices is associated with the need to wait for their release in the order of a certain queue - generally speaking, with limited number waiting areas and sorted by priority. An example would be queues that are processed in a switching node by a computing device using given program, stored in memory. In contrast, there is often no provision for waiting for the release of decentralized control devices, such as memory zones for intermediate storage of data required during the connection establishment process; in this case we talk about a system with losses. Often there is no possibility of waiting when devices directly used for switching data and commas are occupied for the entire time for which the connection is established. These are, for example, the intermediate lines of a spatial circuit switching system. The situation is different in the case of processes occurring during time division switching: here we can already talk about a system with waiting.

Criteria for evaluation. Before considering specific types of switching systems, let us name some criteria for their evaluation. First of all, the scope of application should be characterized, i.e., its characteristics in various functional aspects should be indicated (for example, the first aspect may concern the transfer speed, the second - the data transfer procedure). An important indicator is also the flexibility of the system. The trends in the development of data networks in the coming years are such that for switching equipment it is becoming increasingly important not only to increase the number of connected lines and the volume of load it serves, but also to the possibility of transitioning to networks with different characteristics or introducing new types of services for subscribers.

The performance of switching equipment can be roughly characterized by the permissible number of connected lines, the maximum possible load, as well as indicators regarding the transmitted data - primarily the transmission speed. Equipment intended for circuit switching is characterized by the performance of switches, and equipment for message switching is characterized by the possible performance of receiving and transmitting messages and, if the length of messages is known, by the capacity of the storage device. Along with this, it is necessary to have information about the performance of control devices, i.e., the number of connections that can be established and disconnected within certain time, or the number of messages or packets that can be processed in

unit of time. However, these indicators can be compared only if the type of connection being established or the message being transmitted, the distribution of intervals between calls, the duration of connections and other similar parameters are additionally taken into account.

Finally, great importance, especially when centralized management, has the reliability of the switching system as a whole. Reliability is characterized by the average time between two complete system failures or other similar indicators. To ensure high reliability, they resort to duplication or even multiple redundancy of switching equipment (usually its central parts). In this regard, it is of interest how many connected lines are affected by the failure of one duplicated piece of switching equipment; this number is called the failure volume. In large switching systems, a failure of up to ten lines is often considered acceptable.

Switching node- is a set of equipment designed to receive, process and distribute incoming information. The most typical example of a control system is a switching station, which includes subscriber and trunk lines. To perform its functions, the CU must include the following main blocks:

Commutation field- a set of switching devices with the help of which the connection of subscriber and trunk lines included in the station is ensured.

Control device (CU) - designed to manage the connection establishment process. It includes equipment for receiving, generating and transmitting control information. Based on information about the number of the called subscriber or the direction of communication received from the call source, the control unit includes the corresponding CP elements, resulting in a connection between the corresponding input and output.

Switching block- part of the search stage, which is a set of switching points serving a specific group of inputs

Trunk line blocks (BLB), through sets of connecting lines which connect communication lines from other control units.

Subscriber line blocks (BAL), through subscriber kits of which subscriber lines are connected to the station.

Switching element- element that performs switching in the communication network

Crosspoint- a group of switching elements that perform switching simultaneously when one control signal is applied

The CU equipment also includes additional units:

Cross-device for input and output of lines.

Power supplies.

Instruments for monitoring equipment operation.

Load parameters metering devices.

The following types of connections can be established at switching nodes:

Intra-station connection is carried out between subscribers of a given telephone exchange;

Outgoing connection established at the initiative of a subscriber of a given station with a subscriber of another station through a connecting line;

An incoming connection is established with a subscriber of a given station based on a call received via a trunk line from another station;

Transit - at this station two connecting lines are switched in order to connect subscribers of other stations.

The interaction of CSK blocks can be considered using the example of an intra-station connection. To describe the entire process of servicing a call in a simplified form, we will divide it into five main stages. To illustrate the interaction of blocks during an intra-station connection, Fig. 2.1 shows a simplified structure of the DSS.

Stage 1. Subscriber A picks up the handset of the telephone and the station transmits the “station answer” signal.

After withdrawal by the subscriber A The SU handset determines the fact that the subscriber line is occupied by scanning the MAL subscriber line modules (in the AK subscriber kit). Then the control system issues a command to connect the acoustic signal module (MAC) through the digital switching field (the digital path in the control panel is switched). From the acoustic signal module to the subscriber A a “station answer” signal is given at a frequency f = 425 Hz.

Figure 2.1 . Simplified structure of the CSK for intra-station connection.

Stage 2. The subscriber dials the number.

When dialing a number, the scanning point is in the subscriber's subscriber kit A changes its state. These changes are detected by peripheral scanning devices and transmitted to the control system. After receiving the first dialing pulse, the control system gives a command to turn off the “answer” signal from the MAC, i.e. the transmission of acoustic signals through the CP stops. The number is transmitted to the SU.

Stage 3. The PBX analyzes the number and transmits PV and CP signals.

After reception and analysis subscriber number, The control system determines, from the data stored in its memory, the direction of communication as intra-station and gives a command to turn on the call signal (CR) from the subscriber line module (SAL) with a frequency of f = 25 Hz to the subscriber IN. Synchronously with the PV signal to subscriber A from the acoustic signal module (MAC), a ringback control signal is transmitted at KPV frequency f=425Hz,. MAC connects through the control panel upon command from the control system.

Stage 4. Subscriber IN responds and the conversational connection is switched.

When the subscriber answers IN the state of the scanning point in his subscriber set changes. This information enters the control system, which turns off the PV and KPV signals and the transmission of acoustic signals through the CP stops. Then the control system switches the conversation path to the CP and the subscribers talk.

Stage 5. Hang up and disconnect.

If we assume that subscriber B hung up first, then hang up is determined by the change in the state of the scanning point in his subscriber set. This information enters the control system, which gives the command to MAC connection through CP, i.e. switches the connection of acoustic signals in the control panel. From MAC to subscriber A a busy signal is given, and the control system issues a command to disconnect the conversational connection in the control panel. Subscriber A hangs up. When both subscribers hang up, the control system gives a command to destroy the connection of the acoustic signals of the control panel, i.e. disables MAC.

End of work -

This topic belongs to the section:

Methods for building communication networks

Section Types and construction of communication networks.. Methods of constructing communication networks.. Structural topological construction of communication networks..

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Switching node is a device designed to receive, process and distribute incoming information. To perform its functions, the switching node must have: a switching field CP, designed to connect incoming and outgoing lines (channels) during the transmission of information; control device A control unit that ensures the establishment of connections between incoming and outgoing lines through a switching field, as well as the reception and transmission of control information.

Equipment for receiving and transmitting control information includes Reg registers, or gearbox number receiving kits, code transceivers and converting devices; linear sets of incoming and outgoing lines (channels) LC, designed for receiving and transmitting linear signals (interaction signals) along incoming and outgoing lines or channels to allocate channels in transmission systems, as well as for receiving and transmitting interaction signals with node control devices; ShK cord sets are designed to power telephone microphones, receive and send service signals during the connection establishment process; line input and output devices (cross). In addition, the node has power supplies, alarm devices and load parameters accounting devices (number of messages, losses, duration of activity, etc.).

In some cases, a switching node may have devices for receiving and storing information, if it is not transmitted directly to the information consumer, but is previously accumulated at the node. Such nodes are used in message switching systems.

Switching nodes of communication networks are classified according to a number of criteria:

• by type of information transmitted (telephone, telegraph, broadcasting, telecontrol, data transmission, etc.);
• by the method of servicing connections (manual, semi-automatic, automatic);
• by location occupied in the telecommunication network (district, central, hub, terminal, transit stations, nodes of incoming and outgoing messages);
• by type of communication network (urban, rural, institutional, long-distance);
• by type of switching and control equipment (electromechanical, mechanoelectronic, quasi-electronic, electronic);
• according to the systems of switching equipment used (decadal-step, coordinate, machine, quasi-electronic, electronic);
• by capacity, i.e. by the number of incoming and outgoing lines or channels (small, medium, large capacity);
• by type of switching (operational, cross, mixed);
• by the method of channel separation (spatial, spatial-temporal, spatial-frequency);
• by the method of transmitting information from the transmitter to the receiver (channel switching nodes, providing channel switching for direct transmission of information in real time from the transmitter to the receiver after establishing a connecting path: message switching nodes and packet switching nodes, ensuring the reception and accumulation of information at the nodes with subsequent its transmission to the next node or to the receiver).

Stages of quest Each subscriber line on the PBX is included in a subscriber set (SK), containing two relays that receive the station calling signal and mark the state of the AL. To create a conversational communication path between two AK subscribers caller(hereinafter we will call him subscriber A) must connect to the called subscriber’s telephone number (subscriber B) through one of the collective devices available at the station, called cord sets (CS). The cord kit contains about a dozen relays, provides the supply direct current supplies power to the AL of talking subscribers, sends information (acoustic) signals to the AL, receives hang-up signals after the end of the conversation and performs a number of other functions. In high-capacity PBX systems, two CBs are involved in the conversational path - an outgoing cord set (IKhK) interacting with subscriber A, and an incoming cord set (IKhK) that controls the line of subscriber B. The total number of IKhK (or VShK) on the PBX is significant (approximately 10-12 times) less than the number of ACs, which is equal to the station capacity. This is explained by the fact that in every this moment time need for telephone communication occurs only in a small part of PBX subscribers. The difference in the number of AC and ShK leads to the need to include a switching stage of preliminary search (PI) or preselection between these devices. The preselection stage is characterized by the following parameters

• load group capacity Nн.г, equal to the number of ACs included in one switching unit (cabinet) of the pre-stage; capacity of the subscriber group Na.g, equal to the total capacity of all load groups served by one set (bundle) of ShK or IShK; number of devices (sets) VISHK in a bundle of ShK or IShK, serving one subscriber group;
• availability D, equal to the number of ShK or IShK to which any calling AK can connect. If D< VИШК, то пучок ИШК является неполнодоступным, при D=VИШК пучок полнодоступный. Как видно приборы ступени предыскания в various systems PBXs are called differently: call finders (CT) - in machine PBXs; preselectors (PI) - in decade-step automatic telephone exchanges; subscriber search devices (AI) - in coordinated telephone exchanges. If there are no free CHIs available to the calling AK, call loss occurs. In ten-step PBXs, subscriber A receives an acoustic “Busy” signal and must hang up. In machine and point-by-point telephone exchanges, losses are expressed in the fact that subscriber A*, without receiving any signal, waits for the release of any IBK (if the wait is long, the subscriber may hang up).

After the operation of the switching devices at the pre-discovery stage is completed and the ISHK is connected to the subscriber A, the latter receives an acoustic signal “Station Reply” and dials the digits of the subscriber B number one after another. Based on this address information coming from the AL of subscriber A, the ATS devices must connect the switching device , occupied by subscriber A, with the AC of subscriber B, thereby creating a conversational communication path for subscribers A and B. On a small-capacity PBX, to solve this problem, one linear search (LS) stage is sufficient, the outputs of which include all AC of a given station

The parameters of the LI stage are:

• the capacity of the linear search block MLI, equal to the number of ACs included in the outputs of the block;
• the number of inputs of the NLI block is equal to the number included in this block VShK (or ShK).

a - direct control and direct establishment of connections; b - register control In coordinate automatic telephone exchanges, the preliminary and linear search stages are combined into the subscriber AI search stage. In example 1, all CCs are connected to the inputs of the LI stage. Under the image of the LI stage, the circles indicate the numbers of the subscriber number, on the basis of which the operation of the LI switching devices was carried out. From what was discussed above, it is clear that in the process of establishing a connection on the PBX, two types of searches are performed: free, which does not require the use of address information, and forced, for which such information is necessary. It is clear that the pre-search stage operates in the free search mode, and at the LI stage a forced search is performed. After connecting the ShK (or VShK) to subscriber B's AC, the called AL is tested. If this AL is busy, i.e. participates in another, previously established conversational connection, then an acoustic “Busy” signal is sent to subscriber A from the BSC (VShK). In some systems, such a signal is sent from subscriber A’s AC after the SBK and ATS devices are released at the search stages. If the AL of subscriber B is free, then a “Call Signal” is sent to this AL for the telephone to ring, and an acoustic signal “Call Ringback Control” (CRV) is sent to the AL of subscriber A. After subscriber B answers, the sending of signals stops, and a conversational current transmission circuit is formed.

When a hang-up signal is received from the AL by talking subscribers (long-term disconnection of the AL loop), the established conversational connection is disrupted and the PBX devices participating in it are released. Parameters of information signals sent to the AL Along with the preliminary and linear search stages, group search (GS) stages are used in city telephone exchanges. This is due to the fact that the total number of AC stations is much greater than the capacity of the LI switching block (N>M LI), and, therefore, it is impossible to include all ACs in one LI block. Therefore, the LI stage is divided into subscriber groups (with a capacity of Mnl each), and to select these groups, one or more GI stages are used. The GI stage is characterized by the following parameters:

• the maximum possible number of directions (subscriber groups) H, which can be selected using the GI stage;
• availability D equal to the number of outputs of one direction to which the input of the switching block GI can be connected during the search process;
• number of inputs Nin of one GI block.

If switching blocks with H = 10 are used at the GI stage, then one GI stage will not be enough to select all 30 LI blocks. Therefore in in this case two stages of the GI are required: one stage (IGI) is used to select the direction to one of the three thousandth groups, and the other stage (IIGI) ensures the selection of the hundredth LI block within a given thousandth group. In the general case, the required number of GI stages s, the total capacity of the GTS N and the parameters H and MLI are related by the relation Let us determine, for example, the number s of GI stages for the GATS, under the assumption that it is a decade-step one. Total network capacity N = NGATS + Nps + NAUPATS = 4000 + 1000 + 500 = 5500; from table 1.2 we define H=10, MLI = 100, so the condition takes the form 10s-100>5500, i.e. 10s > 55, which is fulfilled at s = 2. At any stage of the GI, two types of search are always performed: forced - to select the required direction and free - to select a free exit in a given direction (i.e., exit to the next search stage). In Fig. 6.3.2 indicates "which digits of the number dialed by the subscriber are used in in this example for forced search at stages IGI and III. To simplify, cord sets and a pre-emphasis stage. The principles of connection establishment discussed above apply to automatic telephone exchanges with direct control, in which address information is sent directly to the control sets (CM) of the switching units of the search stages. In contrast, on an automatic telephone exchange with register control, address information is received and accumulated first in a special device - a register, from where it is then, as necessary, transmitted in a high-speed manner to control devices at the search stages. To receive information, the register must be connected to the bar code. During a conversation, the register is not occupied, so the total number of registers is significantly (5-10 times) less than the number of bar codes. The difference in the number of CCs and registers makes a register search (RS) stage necessary. The RI stage always operates in the free search mode, ensuring the connection of any free register to the occupied SC.

PBX systems also differ in the method of establishing a connection at the search stages. Shown is a PBX with direct connection establishment, in which the MCs of the LI switching unit are individual, i.e. assigned to individual block inputs. Such CCs are actually connected with conversational paths and are structurally combined with the CC. In PBXs with bypass connection establishment, switching units are served by collective management units, which are called markers in coordinate PBXs. The marker serves one by one all calls arriving at the inputs of the switching unit; it is not connected with conversation paths.

Switching– the process of closing, opening and switching electrical circuits.

Switching unit (CU) - component telecommunication network on which switching is carried out. The CU is connected to each other by trunk lines (local or long-distance).

Switching station (station)- KU, which includes subscriber lines. Subscriber– a person using a subscriber device to transmit and receive information.

Channel (line)– a set of technical means (line and station, providing connection and transmission of information between two adjacent CUs, as well as between the subscriber device (stationary telephone, teletype, computer, etc.) and the station.

KU– a device designed to receive, process and distribute incoming information.

To perform its functions, the CU must have:

1. Switching field (CF), which is intended for switching incoming and outgoing lines (channels) for t transmission of information.
2. The control device (CD), which ensures the establishment of a connection between the incoming and outgoing lines in the control panel, as well as the reception and transmission of control information to the equipment for receiving and transmitting control information, includes: registers (PN sets), checkpoints, and converters.
3. Linear LC sets (these are AK and KSL), which receive and transmit linear signals (interaction signals)
4. Cord sets (CS) are designed to power SLT microphones and issue service signals
5. Cross – device for input and output of lines.
6. Power supplies.
7. Alarm devices US
8. Devices for recording load parameters (number of messages, losses, duration of exercise, etc.)

The control system of communication networks is classified according to a number of characteristics:

1. By type of information transmitted: telephone, telegraph, broadcasting, telecontrol, data transmission, etc.
2. According to the method of servicing connections: manual, semi-automatic, automatic.
3. According to the place occupied in the telecommunication network: regional, central, hub, terminal, transit stations, UVS, UIS.
4. By type of communication network: long-distance, urban, rural, institutional.
5. By type of switching and control equipment: electromechanical, mechanoelectronic, quasi-electronic, electronic.
6. According to the systems of switching equipment used: DS, coordinate, machine, quasi-electronic, electronic.
7. By capacity, i.e. by the number of incoming and outgoing lines, connected subscribers: small, medium, large capacity.
8. By type of switching: operational, cross, mixed.
9. According to the method of channel separation: spatial, spatial-temporal, spatial-frequency.
10. According to the method of transmitting information from the transmitter to the receiver: circuit switching nodes, message switching nodes, packet switching nodes.

There will be no decoding of the information received, since this is precisely the task and object of our study in the future.

4.2. Construction of single-link switching blocks

Single-link switching is called one in which the input and output of the CS (switching system) are connected through one switching point.

KB– a set of switching devices having all or part of common outputs and combined general parameters(this concept is practically not used in DS ATS)

Load Sources– lines through which the TF load is supplied to the input of the switching system.

Bunch of lines– a set of lines connected to the output of the CS and available to a certain group of load sources.

Load group– a set of load sources that have access to a specific bundle of lines, for example, connected in a given direction of the search stage (to all inputs of a given KB).

Search stage– part of the CP of a given CU, consisting of interconnected KBs of the same type. KB has certain structural parameters. They can be obtained by combining the inputs and outputs of switching devices in a certain way.

The KB is characterized by the following structural parameters: the number of inputs and outputs, the number of PLs, D-availability of inputs in relation to outputs, the number of links (switching points), the total number of switching points for building a block, the conductivity of lines switched in the block, the number of simultaneous connections in the block .

When building a KB, you can perform the following operations: combining inputs, combining outputs, serial connection of switching devices (organization of ladder circuits). Operations can be combined.

In a CS, the inclusion of outputs in relation to inputs can be fully accessible or NAP.

PD switching on- this is when any input of the CS can be connected to any free output

NAP inclusion– this is when the input can be connected only to a part of certain outputs of the block.

D availability– the number of CS outputs with which the CS input can receive a connection (the number of CS outputs in a given direction - for the GI stage)

Direction- this is a bundle of lines, along any of which you can arrive at the required commutation point.

Merging inputs:

Switching parameters n x m
n - input
m – output

Design bureaus can be built on the basis of any switching devices Shi, DSHI, MKS, MSF, etc.

The result is a KB with parameters 1x2m, each input has access to 2m outputs, therefore D = 2m

Symbols of the ISS on the diagram:

Parameters n x 2m

Increasing the number of outputs and D by combining inputs requires an increase in the volume of equipment, i.e. increasing the number of switching devices.

Output merging

to m
D = m

The inputs of all switching devices have access to the same group of outputs. The maximum number of simultaneous connections in such a KB is determined by the number m, if k > m, or the number of inputs k, if k< m .

In addition to the line switching function, KB can perform other functions, for example:

What was discussed above is practically switches.

Switch- this is the simplest single-link fully accessible KB, in which any input has access to any output.

The disadvantage of single-link CBs is that to create a CS with parameters n x m, n × m switching devices will be required - a lot: for example, 100x100, MKS type 10x10 - you need 100 such MKS (unthinkable)

4.3. Single-link search stages

Search stage– part of the control panel for the entire set of inputs of which there is access to the same directions that combine the outputs.

The CP is built from individual KBs, which are then combined into search stages.

There are several types of search stages: preliminary, group, linear and register search stages. In accordance with this, SI can operate in free, group and linear (forced) search modes.

4.3.1. Search modes

1. Free search mode – when there is no reception of address information (dialing information) and the incoming line is provided with any free channel (output) from among the available ones.

   In this case, the number of directions H = 1, and D = M

   The PI and RI stages operate in this mode.

2. Forced search mode (linear search) - when the search is performed under the influence of received address information and incoming channel a specific outgoing channel is represented, therefore H = M, and D = 1

   The LI stage operates in this mode.

3. Group search mode - when the search for a certain direction is carried out under the influence of address information, i.e. in the forced search mode, and the output in a given direction is in the free search mode. That. an incoming channel is given any free outgoing channel in a certain direction, therefore

   1 < Н < М, а Д > 1

   The GI stage operates in this mode.

4. Some systems have combined search stages. For example, in ATSC, the AI ​​stage combines the PI and LI stages, but only one connection can be established at a time, so for of this connection either free or linear search mode is performed.

4.3.2. Stage LI

A single-link LI stage can be built using DSHI-100. The maximum capacity of a station built in this way can be equal to 100 (no more)

In this case, each AL has its own individual DSHI. The AL is connected to the brushes of its finder and is also connected to the corresponding contacts of all 100 finders of this automatic telephone exchange. Pamels of the same name in decades of the same name. are parallelized and connected to the corresponding AL. AK is used to receive a call signal from a subscriber and coordinate 2-wire subscriber lines with multi-wire lines of station devices. To establish a connection, the subscriber must dial a 2-digit number. According to the first digit, the brushes rise to the required decade (selection of ten), and according to the second in this decade, they select the desired pamel (selection of one). Consequently, both the lifting and rotation of the brushes will be forced, and the search mode at the LI stage is called linear. This method of construction is uneconomical, since it requires a large number of expensive searchers (for each subscriber).

4.3.3. Stage PI

During operation, it was found that 10-15% of connections from the total number of subscribers on a PBX may be required at the same time (on a PBX for 100 subscribers, the maximum number of simultaneous connections is 50, but in reality it is even less - 10-15). Therefore, it is enough to have 10 - 15 DSHI at the LI level, but all 100 subscribers should be able to use them.

Then each subscriber can be assigned an individual LI, which is called a predictor, and outputs to the LI can be included in its contact field.

This is a direct pre-search mode (there is also a reverse pre-search mode) and line finders become group devices. Their number depends on the load.

a) The process of establishing a connection with direct pre-search goes like this: when the subscriber picks up the handset TA (calling the station), the PI brushes begin to move, searching in their field for an exit to the currently free LI (free search mode). After seizing the LI from the station, the subscriber receives a “station response” and begins dialing a 2-digit number. The first digit causes forced lifting of the brushes, the second – forced rotation and then access to the called subscriber’s telephone station.

Simplified diagram

That. The PI stage allows you to create a more economical automatic telephone exchange scheme, because at a cost of 100 SHI + 10-15 DSHI cheaper than 100 DSHI.

Through the PI stage, the AL is connected to the station devices (LI).

b) With reverse pre-search, a cord pair is formed - IV - IL, the number of which = 10-15 per hundredth group.

IV - call seeker

AL is repeatedly included in the field of all IV and LI. When the subscriber picks up the handset, the “busy” signal arrives at the call center and is marked with the corresponding potential in the IV field. Starting device The PU activates a free IP, which searches for the calling subscriber’s line in its field, and from the “hard” connected IP, the subscriber receives a “station response” and begins to dial a 2-digit number. In the forced search mode, the LI brushes find an exit to the called subscriber's telephone station.

IV operates in a free search mode, which is called pre-search (pre-search)

The maximum capacity of an automatic telephone exchange with the PI and LI stages can be = 100 numbers, which is due to the capacity of the LI field.

4.3.4. GI level

Since increasing the capacity of the automatic telephone exchange by increasing the contact field of the seeker is impossible, the principle of group search is introduced, which is implemented with the introduction of the GI stage.

One GI stage increases the capacity of the telephone exchange by 10 times (by an order of magnitude), since at the stage we have 10 directions (10 decades), each of which connects 10 lines to the 100th capacity LI group, hence 100x10 = 1000 numbers.

If there are 2 levels of GI, then the capacity = 100x10x10 = 10000 numbers

The search mode at the GI stage is group, i.e. lifting of brushes is forced, rotation is free.

To implement the GI, 1 digit of the subscriber number is used.

Example: What is the capacity of an automatic telephone exchange with 2 stages of GI?
100x10x10=10000 numbers

What is the significance of the number dialed by the subscriber?
2(LI) + 1(IGI) + 1(IIGI) = 4

DSHI is used as switching devices at the GI stage of the automatic telephone exchange.

So, single-link search stages are used on automatic telephone exchanges of the DS type (mostly), because RI on ATSC too.