AN ARRANGEMENT FOR THE CONTROL OF AN ECHO CANCELLER

Abstract: The invention relates to an arrangement for the control of an echo canceller. In the arrangement according to the invention the operation of the echo canceller (4A to 4D) is controlled by a call control (2) of a telephone exchange over an internal control bus (3, 5) of the telephone exchange. The exchange then attends to the necessary signalling and the echo canceller does not need to know how the associated signalling is routed in the telephone network.

Description: An arrangement for the control of an echo canceller *, Field of the Invention The invention relates to an arrangement for the * 5 control of an echo canceller. Background of the Invention End-to-end connections of a data transmission system, such as a telephone network, often show long 10 transit time delays, in consequence of which echo is observed for instance in the case of normal speech, when a signal is reflected from the far end of a con¬ nection back to the talker. An echo canceller is an analog or digital device for processing a signal, 15 such as a speech signal, which device is used for reducing echo by subtracting estimated echo from the echo (signal) occurring in a connection. However, echo cancellation cannot be used in all cases, as for instance: 20 1) in connection with establishing a speech connection during multifrequency signalling (DTMF) in a telephone channel. Simultaneously transmitted sig¬ nals produce a double talk situation and operation of an echo canceller would cause undesired changes in 25 the signalling. 2) during a data transmission effected as a continuous bit flow in a telephone channel, because the bit flow shall get through unchanged at original transfer rate. 30 3) during a data transmission effected by means of a baseband modem in a telephone channel. 4) during automatic testings and measurings of i a speech connection. For accurate results, the echo cancellation shall be switched off. 35 5) If there are several echo cancelling devices in a speech connection, only the echo cancellers at the ends of the connection are used and the operation of the intermediate echo " cancellers is disabled. In order that echo cancellers along a connec- tion can be switched on and off in appropriate situa¬ tions, they shall be capable of monitoring channel- associated or common channel signalling to observe the commands relating to the echo cancelling. In the case of channel-associated signalling, polarities of bits a and c of line signalling (T16) can be used to control the echo canceller. Also in common channel signalling, particular signals have been reserved for the control of the echo canceller, but for the iden¬ tification of the signals, the echo canceller shall be provided with a common channel signalling ter¬ minal. It will be especially difficult to control the echo canceller, if a common channel signalling time slot is routed along a path different from that of the speech itself. Disclosure of the Invention The object of the invention is to provide a new arrangement for the control of an echo canceller. An arrangement for the control of an echo can- celler according to the invention is characterized in that the echo canceller is under direct control of a call control of a telephone exchange over an internal control connection of the telephone exchange. The basic idea of the invention is to integrate the echo canceller into the telephone exchange in such a way that the echo canceller can be controlled internally within the telephone exchange under the call control. Then the exchange attends to the neces¬ sary signalling and controls the echo canceller by internal control. Thanks to this, all devices and operations associated with channel signalling can be omitted in the echo canceller, which does not need to know how the signalling is routed. Additionally, the internal control of the telephone exchange enables a more accurate timing and a more effective operation of the echo canceller at various stages of a call. Brief Description of the Drawing The invention will be explained in the follow- ing in greater detail by means of a preferred embodi¬ ment with reference to the enclosed drawing, in which Figure 1 shows an illustrating block diagram of an arrangement according to the invention, in which the echo cancellers are integrated into the telephone exchange. Detailed Description of the Invention The arrangement of the invention can be applied in connection with a telephone exchange and an echo canceller of any type. Figure 1 shows a telephone exchange comprising four near end lines Al to A4 and four far end lines, preferably 2,048 Mbit/s PCM lines according to CCITT recommendation G.703, each line having 32 channels, 30 of which are telephone chan- nels. Between the channels of the lines Al to A4 and the channels of the lines Bl to B4, it is possible to switch transmission connections (calls) over a digi¬ tal switching unit 1 in a manner known per se. The operation of the telephone exchange is controlled and monitored by a call control computer 2. The exchange naturally also includes devices and software relating to the signalling to be used each time. To each PCM line Bl to B4 of the far end is se¬ ries-connected respective echo cancelling unit 4A to 4D, which carries out the echo cancellation of each channel of the PCM line separately, the channels be¬ ing 32 in number in the example case. Each echo can¬ celling unit 4A to 4D can thereby include a separate echo canceller for each channel. The operation of the echo cancellers 4A to 4D, especially switching on and off, is controlled by a computer 3 over a common con¬ trol channel 5 within the telephone exchange, the operation of which computer 3 is controlled by the call control computer 2 over a control channel 6. The control computer 3 thus provides an interface between the call control 2 and the echo cancelling units 4A to 4D. The control computer 3 comprises a software program knowing the control time slots of each echo cancelling unit 4A to 4D in the time-shared control channel 5 and delivers the commands for switching on or off the echo cancellation from the call control to respective echo cancelling units within said time slots over the channel 5. On the other hand, the call control computer 2 produces the commands for the con- trol of the echo cancellers on the basis of the echo cancellation signalling received or possibly on the basis of other call status data available to the call control, such as the answering of the called sub¬ scriber (off hook). Normally the echo cancellers 4A to 4D are al¬ ways on, and therefore, the call control 2 does not usually need to control them. However, if a connec¬ tion is established for instance in an international network having echo cancellers, the call control 2 switches off the echo canceller internally within the telephone exchange over the control computer 3 and the control channel 5. After the call, the call con¬ trol 2 commands the echo canceller in question back to normal mode of operation for next call. The figures and the related description are only intended to illustrate the present invention. As to the details, the method of the invention can vary within the scope of the attached claims.

Claims: Claims : 1. An arrangement for the control of an echo canceller, c h a r a c t e r i z e d in that the echo canceller (4A to 4D) is under direct control of a call control (2) of a telephone exchange over an internal control connection (3, 5) of the telephone exchange. 2. An arrangement according to claim 1, c h a r a c t e r i z e d in that the telephone ex¬ change comprises a computer (3) for the control of echo cancellation, which computer is connected be¬ tween the call control (2) and the echo canceller (4A to 4D). AMENDED CLAIMS [received by the International Bureau on 31 March 1993 (31.03.93); original claim 1 amended ; original claim 2 unchanged ( 1 page ) ] 1. An arrangement for the control of an echo can¬ celler, c h a r a c t e r i z e d in that the echo can¬ celler (4A to 4D) is under control of a call control (2) of a telephone exchange over an internal control connec¬ tion (3, 5) of the telephone exchange. 2. An arrangement according to claim 1, c h a r a c t e r i z e d in that the telephone exchange comprises a computer (3) for the control of echo cancel¬ lation, which computer is connected between the call con¬ trol (2) and the echo canceller (4A to 4D) .

Inventors: LAEHDEMAEKI HEIMO, SAERKIKANGAS VESA, SALONEN PERTTI, LAEHDEMAEKI, HEIMO, SAERKIKANGAS, VESA, SALONEN, PERTTI
Applicants: NOKIA TELECOMMUNICATIONS OY
Application year: 1992
Main classification: H04B3
IPC codes: H04B3, H04M3