SWITCHING ELEMENT FOR PCM SIGNALS

Abstract: Switching element for PCM signals, particularly fit to be used inperipheral units in a private automatic branch exchange (PABX). The element is so shaped as to be easily integrated in a semicustom technology and it therefore comprises: a plurality of switching cells (CC) suitable to cause a time switching of the PCM channels; a multiplexer (MX1) suitable to cause a space switching of the PCM channels; control means (CN).

Description: DESCRIPTION The present invention refers to a switching element of the PCM signals, so shaped as to be easily integrated in a semicustom technology. More in particular it regards an element suitable to carry out switching operations, in particular in peripheral units in a private branch exchange. The Italian patent application No. 22459 A/86 describes a private branch exchange (PABX = Private Automatic Branch Exchange) which comprises a plurality of centralized units and a plurality of peripheral units. The switching operations of the audio signals are performed in the centralized units, while the signal switching (for example, tone sending, ultifrequency signals reception, etc.) are performed in the peripheral units, that are referred to as "line units" because they represent functional units to which a predetermined number of users' lines are joined. The switching elements for PCM signals are well-known - they are executed according to a "custom" technology - and are suitable to switch - without any bloc - 256 incoming PCM channels out of 256 outgoing PCM channels. Said elements have a high switching capacity and they are therefore particularly expensive, being their use justified only in the centralized means of the autoswitcher, as their capacity is there fully exploited. The use of said elements in the peripheral means of the autoswitch (line unit) is not justified from an economical point of view because of the reduced number of switching operations that are required. According to a preferential embodiment of the invention, 16 user lines are joined to said line units and the number of the switching operations to be performed by the peripheral means (16 operations) is therefore by far inferior to the switching capacity of said known elements (256 operations). • Within a private branch exchange of the present type, the above peripheral elements present a high degree of repetitiveness and in order to limit costs and dimensions of the switching element it is necessary to integrate it in a single chip, of a semicustom technology for example. As known, said technology provides the integration on a single silicon substrate of a predetermined number of transistors which corresponds to a predetermined and corresponding number of gate-equivalent (for example 12.000 transistors correspond to 3000 gate-equivalent). Any functional unit executed according to said technology requires connections among said gate-equivalent in order to implement the electric functions that are there arranged. It is herein underlined that the switching elements of known type are not suitable to be implemented according to a semicustom technology, due to the fact in particular that the switching operations - both time and space ones - of the PCM signals are performed through a writing/reading operation of said signals in a memory unit having a high capacity. As known, the implementation of memory cells according to a semicustom technology requires a large number of gate-equivalent and - even if an undersea!ing of said memory unit is effected in order to allow the •■ performance of a reduced number of switching operations - it is impossible to use the semicustom technology in order to execute an operating switching element according to those principles on the basis of which said known elements operate. Purpose of the present invention is a switching unit of the PCM signal, so shaped as to comprise the electrical functions which require a reduced number of gate-equivalent according to a semicustom technology. To this end, the switching operations of the PCM signals in the unit object of the present invention are effected through a plurality of switching elements suitable to cause a time switching as well as through a multiplexer unit suitable to cause a space switching. As said switching cells fundamentally arrange the presence of multiplexer and registers which can be implemented through a limited number of gate-equivalent, the unit fully meets the requirements of the present invention. Object of the present invention is therefore a switching element of the PCM signals, suitable to receive at its input a plurality of PCM groups and to switch in the same mesh a predetermined number of byte allocated in the time channels of said PCM input groups and in the time channels of the PCM output groups. The switching element comprises: X switching cells, where X represents the maximum number of switching operations that can be performed in the same mesh, suitable to receive said PCM input groups, further suitable to select the PCM group and channel which is interested by a switching operation and suitable further to cause a time switching of the byte allocated in the selected channel; a first multiplexer suitable to receive at its input the outputs of the X switching cells and further suitable to transfer to the output the byte which is keyed by the switching cell corresponding to a digital word applied to its own control input; - control means, suitable to send to each switching cell a first digital word which expresses the PCM group and channel interested by a switching operation as well as a second digital word expressing the time channel interested by a scanning operation at the considered time, and further suitable to send a third digital word to the control input of said multiplexer. Further characteristics of the unit can be taken from the following description which refers to a non-limiting example shown in the following drawings, whereas: Figure 1 shows the block diagram of the switching element according to the invention; Figure 2 shows in details a switching cell CC of Fig. 1. In the switching element of Fig. 1, the K PCM input groups are joined to a plurality of switching cells CC,, CC χ in a number which corresponds to the maximum possibile switching operations in a mesh of the PCM signal. Each switching cell is therefore suitable to select a PCM group and channel interested by a switching operation as well as to perform a time switching of the byte allocated in the selected channel. The X outputs of said cells reach the input of a multiplexer MX, fit to determine a space switching of the PCM' channels by drawing each time the byte corresponding to the digital word applied to its control input and by allocating it in the outgoing PCM group. The selection operations performed by the single switching cells CC as well as those ones carried out by the unit MX, are monitored by control means CN which are suitable to arrange: at an output a_ a first digital word which expresses the PCM channel and group interested by a switching operation; at an output _b a second digital word which expresses the time channel at the considered time; at a.n output a third digital word adapted to monitor the switching operations of the multiplexer unit MX,. The operation of the circuit arrangement as herein described and shown in Figure 1 is clearer from the examination of a switching cell CC shown in Figure 2, where the K PCM groups which come to each switching cell are joined to the input of a multiplexer MX 2 . According to a preferential embodiment, the number K is equal to four and the unit MX 2 can therefore receive a word of n = 2 Bit/s at its control input. The control circuit CN makes in fact available a release signal abi at this first output _a as well as a digital word corresponding to n + N = seven Bit/s that is memorized in a register RG when the signal abi is activated. The two most significant Bit/s of said word form the address Bit/s of the unit MX , to the output of which the PCM group, where the channel interested by a switching operation is allocated, corresponds. The PCM group which is selected as above specified comes to an additional multiplexer MX,, which is in turn addressed by the bit corresponding to the output of a comparison circuit CC. This latter receives the less significant Bit/s of the digital word memorized in the register RG at an input and the digital word, available at the output _b_ of the control circuit CN, at the other input. As the binary configurations suitable to the scanning of 32 channels of the PCM group are available at the output b_, when the coincidence among the digital words applied to the inputs of the unit CC occurs, this latter operates its own output and enables the multiplexer MX., to transfer to its own output the content of the time channel which is destinated to be switched by the switching cell and which corresponds to the digital word memorized in the register RG. The byte so selected is transferred into a slide register SR and through the multiplexer MX 3 it is recirculated in the unit SR as long as it necessary in order to determine the time switching which is provided in the referenced connection. Assuming that the byte is positioned in the time channel 3 of the group selected through MX„ and that it should be allocated in the time channel 18 of the PCM group which corresponds to the output of MX,, said byte is recirculated in the register SR for an interval of time equal to 15 time channels. When said interval has elapsed, a digital word will correspond to the output of the control means CN, suitable to cause the transfer to the output of MX, of the byte contained in the register SR of the switching cell CC, which has been considered. On the basis of what above stated it is evident that the switching unit according to the present invention can perform the switching operations without using the memory cells that are at the base of said known elements. The switching cells arrange the time switching, while the multiplexer MX, provides the space switching. Multiplexer and registers implemented according to the semicustom technology requires a limited number of gate-equivalent and execute the switching unit according to the invention.

Claims: CLAIMS 1. Switching unit of the PCM signals, suitable to receive at the input a plurality of PCM groups as well as to switch in the same group a predetermined number of bits allocated in the time channels of said PCM input groups to the time channels of the PCM output groups, characterized in that it provides the presence of the following elements so arranged: - X switching cells (CC,,..., CC χ ), where X represents the maximum possible of switching operations performed in the same mesh, which are suitable to receive said PCM input groups, further adapted to select the group and the time channel interested by a time switching operation of the byte allocated in the selected time channel; a first multiplexer (MX,) suitable to receive at its input the outputs of the X switching cells (CC) and further suitable to transfer to the output the byte so keyed by the switching cell corresponding to the digital word applied to its control input; control means (CN), suitable to forward to each switching cell (CC) a first digital . word (output a) expressing the PCM channel and group interested by a switching operation as well as a second digital word (output _b_) expressing the time channel interested by a scanning operation at the time which has been considered and further suitable to forward a third digital word (output £) to the control input of the first multiplexer. 2. Switching element as claimed under claim 1, characterized in that each switching cell (CC) provides the presence of the following elements so arranged: a second multiplexer (MX 2 ) suitable to receive said PCM input groups; 5 - a register (RG) suitable to receive said first digital word coming from the control means when the release signal (abi) is activated and further suitable to forward the most significant bits of said word to 10 the control input of the second multiplexer (MX 2 ); a comparison circuit (CC) suitable to activate its own output once detected the identity among the less significant bits of 15 the digital word memorized in said register (RG) and the bits of the second digital word supplied by the control means (CN); a third multiplexer (MX,) having the control input connected to the output of the 20 comparison circuit (CC) and further having the first input connected to the output of the second multiplexer (MX 2 ); a slide register (SR) having its input connected to the output of the third 25 multiplexer (MX,) and further having the output connected to the output of the switching cell as well as to the second input of the third multiplexer (MX-). 30

Inventors: DANNA ROBERTO, DI GIULIANO SABATINO, DANNA, ROBERTO, DI GIULIANO, SABATINO
Applicants: ITALTEL TELEMATICA, ITALTEL TELEMATICA S.P.A.
Application year: 1988
Main classification: H04Q11
IPC codes: H04Q11