Abstract: A first connection stage includes connecting by a switched network control device a call from a first terminal with a terminal selection device, noticing “there is no terminal to be connected” to the first terminal as a selected result from the terminal selection device when no terminal is selected, and disconnecting the call. A second connection stage includes connecting by the switched network control device a call from a second terminal with the terminal selection device, noticing “there is a terminal to be connected” and “a connection number of the first terminal” to the second terminal as a selected result from the terminal selection device when the first terminal is selected, and disconnecting the call.

Abstract: A variable length code system which is instantaneously decodable in both forward direction and backward direction is generated either in asymmetrical form or symmetrical form. The code thus generated has high transmission efficiency, and capable of backward reconstruction of video signals even when some bits are lost during transmission. The symbols to be encoded are prepared (1) with occurrence probability, and they are provisionally encoded to a non-reversible variable length code (2). Then, the provisional code is transformed to an asymmetrical reversible code (4) through equivalent transform process (9), reverse symbol tree process (10), and bit supplement process (12) when suffix condition is not satisfied. The provisional code is also transformed to a symmetrical reversible code (3) by assigning a symmetrical code word to each symbol on a symbol tree (FIG. 5). At least one of symmetrical code or a asymmetrical code is selected (5), and is provided as a final resultant code.

Abstract: A variable length code is converted to a new code in order to improve synchronization recovery capability without changing the length of each codeword. A short codeword with high occurrence probability is first selected as a seed. An object codeword, which is longer than the seed located at a leaf of a tree structure of the code, is exchanged with another node or leaf, which at the same is located depth as that of the object codeword in the tree structure, when a rear portion, called a suffix of said object codeword, coincides with the seed. The seed is also exchanged with another node or leaf on the same level as that of the seed, and the exchange of the object codewords is effected for the fresh seed in a similar manner as above. The final seed and the object codewords are determined so that the number of the codewords which coincide with the suffixes of seeds becomes maximum.

Abstract: A noise-shaping predictive coding system is disclosed, in which the deviation (i.e. correlation) of quantization representative values, which occurs when the coding noise resulting from predictive coding is frequency-shaped by a noise shaping filter, is used to perform an coding operation, so that the quantization entropy can be reduced simultaneously. According to another aspect of the present invention, the human visual characteristic may be combined with the deivation of quantization representative values.

Abstract: A predictive TV signal coding system is disclosed, in which a predictive value of a picture element to be coded is obtained from information of an already coded picture element, a representative quantization value of the picture element to be coded is determined in accordance with the magnitude of the predictive value, and a difference value between the representative quantization value and the predictive value is coded for transmission without quantization.

Abstract: A TV signal median prediction coding system in which a prediction value of a picture element to be coded is obtained from information of an already coded picture element and a difference between the prediction value and the value of the picture element to be coded is coded. In accordance with the present invention there is provided a storage section having a capacity large enough to store input TV signals of at least one frame at all times; an intrafield prediction section which, when supplied with a value X.sub.1 of the latest input picture element of the TV signal, produces a prediction value X.sub.1N of the latest input picture element using a value of a picture element of the same field as the latest input picture element, read out from the storage section; an interfield prediction section which, when supplied with the value X.sub.1 of the latest input picture element, produces a prediction value X.sub.

Abstract: An adaptive predictive coding system for television signals, in which noting the movement of a picture, adopts the inter-frame prediction value in a case of the picture being decided to be a still picture and, in other cases, compares the inter-frame, into-field and intra-field prediction values with each other in terms of magnitude taking into account the quantity of movement of the picture and adopts the prediction value which would not make the coding efficiency the worst, spo that a stable and high coding efficiency can be achieved.

Abstract: An inter-frame adaptive prediction system for television signals is disclosed in which a prediction value P.sub.1 for a picture element 1 in the current field is newly produced, through using prediction values P.sub.OPT and P.sub.MED obtained by the following two procedures.In a first procedure, the intra-field prediction (a prediction value X.sub.N), the inter-field prediction (a prediction value X.sub.K) and the inter-frame prediction (a prediction value X.sub.F) are performed for a picture element temporally ahead of the picture element in the current field F.sub.0, for instance, the picture element 2, and a prediction circuit which yields a prediction value closer to the picture element value X.sub.2 of the picture element 2 than the prediction values of any other prediction parts is selected, and a prediction value X.sub.1S for the picture element 1 obtainable from the selected prediction circuit is obtained and is used as the prediction value P.sub.OPT.