Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1999-12-17
2003-01-28
Pham, Chi (Department: 2734)
Pulse or digital communications
Bandwidth reduction or expansion
C375S220000, C379S093080, C370S535000
Reexamination Certificate
active
06512790
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to telecommunications systems in general, and in particular to the transmission of compressed signals in telecommunications system.
BACKGROUND OF THE INVENTION
Telecommunications has moved in the recent years towards digital networks carrying voice, facsimile and other signals. One known way in the art to increase the efficiency of such networks is to transmit the signals in a compressed form, thus using the available bandwidth for simultaneous transmission of more information.
U.S. Pat. No. RE 35,740 discloses a system for carrying voice, facsimile and non-facsimile voice band data. This system includes various compressing mechanisms and offers an improved detection of facsimile signals. Still, when speech, facsimile and other signals are subjected to several compression/decompression cycles, their quality degrades substantially, and at times, the signals may be received at a quality and delay that are unacceptable.
Some methods were suggested in the past to overcome this handicap. Cox et al., in International Conference on Communications, Vol. 1, June 1988, pp. 90-95, suggest a method to decrease the distortion and delay introduced while using low rate speech coding. It was suggested there that the receiving module, the compressor, searches the less significant bits of the input 64 Kb/s mu-law coded stream for the synchronization pattern. If it detects the pattern, it temporarily squelches the compressed signal and enables the de-compressor to begin padding rather than decoding. When the de-compressor is padding the low-rate frame, a new synchronization pattern is inserted into one of the non-used bits. When the far end compressor detects this new synchronization pattern it disables the squelch on its compressor and begins stripping the padded bits. However, when the compressor at the receiving end does not find the “robbed” less significant bits synchronization pattern in the 64 Kb/s stream, it will not proceed to the pad and strip state, and the de-compressor will insert the robbed bit synchronization pattern into the 64 Kb/s stream, going to the subscriber. One way of increasing the rate of the low rate bit stream suggested in this publication, is by inserting the low rate signal into the least significant bits of the mu-low word of the 64 Kb/s stream. The advantage of using such a method is that if by any chance the system treats the signal as mu-low coded speech, only low level noise signal would be noticed by the human listener.
However, one of the main drawbacks of the method described, is the fact that no other signals than voice signals can be transmitted along a transmission path comprising a number of operative compressing/decompressing devices. Furthermore, none of the methods described discloses a solution for the problem of handling a change in the type of the transmitted signals, while retaining the continuity of the communication session (e.g. switching from voice to fax during a communication session). Moreover, the traffic congestion in telecommunication networks is of a varying nature, and obviously for a system to operate efficiently it should also be adaptable to such variations.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a digital telecommunication station capable of efficiently transmitting signals originating from transmitting sources of various types.
It is another object of the present invention to provide a digital communication system utilizing efficiently the bandwidth available for communication transmissions while retaining a good quality of the signal and session continuity.
Yet another object of the present invention is to provide a method for efficient handling of various types of signals.
Further objects and features of the invention will become apparent to those skilled in the art, from the following description and the accompanying drawings.
In accordance with the present invention there is provided a digital telecommunication station adapted to receive at least two different types of signals, operative in a digital communication system, and comprising:
at least one detector operative to receive signals carried along a transmission path and determine their type;
at least one switch controlled by said at least one detector, adapted to channel said signals in accordance with the determination of their type;
first identifier for determining whether said signals received are of a digital compressed form;
second identifier for determining whether the transmission path includes at least one further operative de-compressor adapted for decompressing signals when being transmitted in their compressed form;
at least two pairs of compressing/decompressing devices, each adapted to compress/decompress a different type of signals;
said transmission path does not include at least one fur first transmitter operative in response to a determination made by said second identifier that ther operative decompressor adapted for decompressing the signals being transmitted in their compressed form; and
second transmitter operative in response to a determination made by said second indentifier that said transmission path does include at least one further operative decompressor adapted for decompressing the signals being transmitted in their compressed form into the decompressed digital output signals.
Preferably, said at least two different types of signals are selected from the group consisting of voice signals, fax signals, data signals, voiceband data signals and video signals. More preferably, the types of signals received by the digital communication station of the present invention include at least voice and fax types of signals.
According an embodiment of the present invention, the pairs of different compressing/decompressing devices are preferably selected from the group comprising:
encoder/decoder adapted to receive a voice signal and operate thereon;
modulator/demodulator adapted to receive a facsimile signal and operate thereon;
encoder/decoder adapted to receive a data signal and operate thereon;
voice-band data modulator/demodulator adapted to receive a voice band data signal and operate thereon; and
video encoder/decoder adapted to receive a video signal and operate thereon.
By a preferred embodiment, the digital telecommunication station of the present invention is adapted to receive a signal classification message denoting the type of digital signals received by that digital telecommunication station. More preferably, the signal classification message is transmitted to denote transmission of digital signals of a type, which differs from the type of their preceding digital signals transmitted by the station during a communication session. Typically, a signal classification message is a message that is included in a frame, block or the like, and characterizes the type of digital signals included in that same frame. Preferably, the signal classification message is included in a frame carrying digital signals sand precedes the compressed digital signals of a new type contained in that frame. However, as would be appreciated by a person skilled in the art, in systems which can tolerate delays in transmission, it would also be possible to have the signal classification message indicate that digital signals of a new type have already been transmitted. Furthermore, the signal classification message may denote a change in the signal type occurring in a neighboring frame (the one before or the one after the frame which includes that message) or even in non-neighboring frames. Of course, when the change occurs in a non-neighboring frame to that which comprises the signal classification message, the message should preferably also direct to the frame in which the new type of signals are introduced for the first time, e.g. by providing an indication to the number of frames separating between these two frames, etc.
Embedding in a frame the classification of the type of signals to follow has significant advantages that the present invention provides over the known art
ECI Telecom Ltd.
Nath&Associates PLLC
Novick Harold L.
Pham Chi
Tran Khanh Cong
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