Multiplex communications – Wide area network – Packet switching
Patent
1979-08-22
1982-10-12
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
179 2DP, H04J 312, H04M 1106
Patent
active
043542654
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a method and an apparatus, for use in a telephone system of the type wherein the amplitude values of speech signals are transmitted in digital form, which allows additional digital information to be transmitted without disturbing a speech communication in progress.
DESCRIPTION OF PRIOR ART
In PABX systems especially, it is desirable to be able to transmit certain digital information to a telephone set, for example to light up indicator lamps. Generally, this is accomplished by means of extensive wiring between the PABX-exchange and the telephone set in question, for example an operator's position, but if the transmission distance is long it might instead be advantageous to arrange a two wire data connection for transmitting the digital information serially in coded form.
SUMMARY OF THE INVENTION
In telephone systems of the type mentioned in the preamble of the claim it is possible to utilize the same kind of signal transmission as the one which is used for the speech signals also for the other information. In order to create a greater flexibility in the system it would naturally be advantageous if the use of an extra pair of wires to the apparatus in question could be avoided and instead the additional information could be transmitted on the telephone channel. The problem is to achieve such an information transfer without considerably disturbing a speech communication in progress. It is the purpose of the invention to solve this problem. The characteristics of the invention appear from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described more in detail by means of an embodiment and with reference to the accompanying drawings in which
FIG. 1 shows a block diagram of a telephone system in which the invention is applied;
FIG. 2 is a block diagram of an input unit for feeding other information onto a digital speech channel according to the invention;
FIG. 3 is a block diagram of an output unit for separating such other information being transmitted on the digital speech channel according to the invention; and
FIG. 4 shows a timing diagram illustrating the mode of operation of the units shown in FIGS. 2 and 3.
PREFERRED EMBODIMENTS
Either PCM or Delta modulation may be used to convert speech signals to digital form. Both types of modulation are in principle applicable to the invention but in the chosen embodiments Delta modulation is assumed. The digitalized speech signals are consequently transmitted as a bit stream where the variations of amplitude of the speech signals are represented by the transmitted bit pattern. A stream of alternating ones and zeros then represents a constant signal amplitude while a sequence of only ones or zeros corresponds to a considerable amplitude increase or amplitude decrease respectively. According to the invention transmission of additional digital information on the telephone channel is made possible by the fact that the digitalized speech signals are momentarily suppressed to create a time slot for the additional digital information.
At the receiving side this additional digital information must not reach the circuits for receiving the speech signals as it would give rise to a completely uncontrolled amplitude variation in the demodulated signal. The original suppressed digitalized speech signals cannot be restored at the receiving side and therefore they must be replaced by digital signals of a corresponding duration being so chosen that they, as far as possible, mask the discontinuity in the received signals. Practical tests have shown that a good masking effect is obtained if, according to the invention, a replacement signal is chosen which maintains the speech amplitude which was present immediately before the time slot was created as above. With Delta modulation, the replacement signal thus can comprise alternating ones and zeros. With PCM, a code which is identical with the one received immediately before the time slot would suitably have been used. As an alternative, however, it
REFERENCES:
patent: 3226482 (1965-12-01), Wright
patent: 3491206 (1970-01-01), Sheridan
patent: 3492429 (1970-01-01), Schroeder
patent: 3727005 (1973-04-01), Franaszek
patent: 3735048 (1973-05-01), Tomsa et al.
patent: 3978290 (1976-08-01), Sarma
Josefsson Kjell S.
Nyberg Karl F. L.
Olms Douglas W.
Telefonaktiebolaget L M Ericsson
LandOfFree
Method and an apparatus for transferring digital information in does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and an apparatus for transferring digital information in , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and an apparatus for transferring digital information in will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-226446