The composition of the switch and its working principle

The composition of the switch and its working principle

Basic composition of a switch:

1. Switching network

The basic function of the switching network is to establish a connection command through the control part according to the user’s call requirements

The connection path between the calling and called users.

In the crossbar switch, it uses various electromechanical connectors (such as vertical

Horizontal connectors, coding connectors, flute spring connectors, etc.), currently mainly used in program-controlled switches by electronic switches

A space-division switching network composed of arrays, and a time-division connection network composed of circuits such as memory.

2. User circuit

The function of the subscriber circuit is to realize the connection between various subscriber lines and switches, usually also called subscriber line interface

Circuit (sLic, subscriber Line interface circuit).

Depending on the switch format and application environment

Different, there are also many types of user circuits. For program-controlled digital switches, there are mainly analog telephones

The connected analog subscriber line circuit (aLc) and the digital subscriber line circuit (dLc) connected with the digital telephone, data terminal (or terminal adapter).

The analog subscriber line circuit is an interface configured to adapt to the simulated user environment, and its basic functions include;

Battery feed: The switch feeds DC power to the common telephone through the subscriber line;

Overvoltage Protection: Prevents the switch from being damaged by voltage surge or overvoltage on the subscriber line.

Ringing: Feed the ring current to the called party’s phone.

Supervision: Monitor the on-off state of the subscriber line with the help of scanning points to detect the off-hook of the phone,

Subscriber line signals such as on-hook, dial pulse, etc. are forwarded to the control device to indicate the user’s busy and idle status and connection requirements

Please.

Codec (codec): use the encoder and decoder (codec), filter, complete the modulus of the voice signal

Exchange with digital-to-analog to interface with the digital switching network of the digital switch.

Hybrid: 2/4 line conversion of the subscriber line to meet the four-line transmission of codec and digital switching

requests.

Test (test): Provide a test port to test the user circuit.

These seven functions are often represented by an acronym (boRscht) consisting of the first letter.

For analog program-controlled switches, no codec function is required; while in digital program-controlled switches, most of them use Pcm codecs, except for some small switches for specific applications that use delta modulation.

The digital subscriber line circuit is adapted to the digital subscriber line

The interface set by the user environment, it is mainly used to pass the line adapter (Lam) or digital telephone

(soPho-set) is connected with various data terminal equipment (dte) such as computer, printer, Vdu, telex.

In and Out Repeater

The incoming and outgoing repeater is the interface circuit between the trunk line and the switching network, which is used for the connection of the switch trunk line.

Its function and circuit are closely related to the standard of the switching system used and the signal mode of the inter-office trunk line.

For the analog trunk interface unit (atu), its function is to realize the interface between the analog trunk line and the switching network. The basic functions are generally as follows:

Send and receive line signals indicating trunk status (eg idle, occupied, answer, release, etc.).

Forward and receive the register signal representing the called number.

Supplies call power and signal tone.

Provides the received line signal to the control device.

For the simplest case, a repeater from one switch is connected to another switch via a solid-line trunk,

And adopt user loop signaling, the function and function of the analog repeater is equivalent to a “telephone”.

If other more complex signaling methods are used, the repeater should realize the corresponding voice, signaling transmission and control functions.

The function of the digital trunk interface unit (dtu) is to realize the interface between the digital trunk and the digital switching network. It transmits the trunk signaling through the relevant time slots of the Pcm, and completes the basic functions similar to the analog repeater.

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Can.

But because the digital trunk transmits the Pcm group digital signal, it has some characteristics of digital communication

Special problems, such as frame synchronization, clock recovery, code pattern exchange, signaling insertion and extraction, etc., are to solve the connection problems of signal transmission, synchronization and signaling coordination.

The basic functions of the digital trunk interface unit include frame and multi-frame synchronization code generation, frame adjustment, even zero suppression,

Pattern conversion, alarm processing, clock recovery, frame synchronization search and inter-office signaling insertion and extraction, etc., just like analog

The boRscht of the user circuit can also summarize the above-mentioned 8 functions of the digital relay unit as gazPacho.

4. Control equipment

The control part is the core of the program-controlled switch, and its main task is to manage according to external users and internal maintenance

Required, execute stored programs and various commands to control the corresponding hardware to achieve switching and management functions.

The main body of the control device of the program-controlled switch is the microprocessor, usually according to its configuration and control work mode,

It can be divided into two types: centralized control and decentralized control.

In order to better meet the requirements of software and hardware modularization, improve processing

The ability to enhance the flexibility and reliability of the system, the degree of decentralized control of the current program-controlled switching system is increasing day by day,

Partially or fully distributed control is widely used.

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