Abstract: The invention generally relates to a modem connected via a digital interface to a switched public telephone network and to a method for probing the line properties. The modem communicates with a second modem also connected via a digital interface to the same switched public telephone network. The public telephone network may incorporate voice compression devices (ADPCM G.726, G.723 etc.), digital pads (digital attenuators), robbed bit signalling and echo cancelling devices. The probing sequence of the invention uses large amplitude changes in a symbol sequence (each symbol having a duration of 125 ?s). After that single amplitude change, the signal may return to the previous value or continue with the new amplitude value for a number of symbols. The number of symbols is selected to be larger than any expected impulse response of a digital impairment of the channel.

Abstract: The communications system has a transmission network for transmitting useful data and control data. Call numbers are input at a subscriber terminal. A subscriber line unit with an adjustable transmission characteristic is connected between the subscriber terminal and the transmission network. A recognition unit connected to the transmission network recognizes particular call number patterns and outputs particular control signals corresponding to call number patterns. A control unit connected between the recognition unit and the subscriber line unit sets the transmission characteristic of the subscriber line unit depending on the control signals provided by the recognition unit.

Abstract: Codec circuit for increasing the data transmission rate in a modem transmission with a first programmable digital filter (13) which is connected into a transmission signal path of the Codec circuit, a second programmable digital filter (22) which is connected into a reception signal path of the Codec circuit, a modem signal detection device (31) for detecting whether the transmission signal which is output on the transmission signal path or the reception signal which is received on the reception signal path is a modem signal, the modem signal detection device (31) switching the first and second digital filters (13, 22) to a widened filter bandwidth when a modem signal is detected.

Abstract: Digital code words are transmitted via a digital communication network, e.g. from a digital modem (1) to an analog modem (5). Whenever an RBS technique is used for an RBS channel, a given bit, as a rule the LSB, of a corresponding code word is changed. In order to recognize and correct such RBS channels, training code words transmitted during a training phase are evaluated. If an RBS channel is detected, the given bit of the corresponding code word is set to a fixed value.

Abstract: A method is disclosed for generating a PCM code set for encoding data by a PCM encoder in a data transmission system having a digital modem with a PCM encoder, a digital signal transmission path, an analogue signal transmission path with a central office line interface portion, and an analogue modem. The method includes the step of determining a minimum signal level distance between adjacent PCM codes of the PCM code set, the minimum signal level distance enabling discrimination by the analogue modem. Then a line interface attenuation of the central office line interface portion is determined. Finally, the PCM code set on the basis of a power limit computed by adding the line interface attenuation to a central office line interface power limit is generated. The invention further relates to an analogue modem to be operated in such a data transmission system.

Abstract: The invention relates to a method for transmitting data between an analog modem (3) and a remote data terminal (4). The data can be transmitted at a variable sampling rate ≧8 kHz by means of a PCM modulation method from the analog modem (3) to a subscriber line module (5) that is provided with a coder/decoder device (50) with a corresponding sampling rate via an analog data transmission line (1). From the subscriber line module (5) at least two data transmission links K1, K2, . . . , Kn to the remote data terminal (4) can be established in parallel. The data transmission capacity properties of the data transmission line (1) during establishment of the link are determined. The maximally possible number mmax of data symbols Sxy that can be transmitted per data transmission link K1, K2, . . . , Kn is determined. A certain number n of switched data transmission links K1, K2, . . .

Abstract: A method and an apparatus for the transformation of a signal on a four-wire line are proposed where the signal comprises of discrete amplitude height levels that are intended for a conversion into a corresponding analog signal with amplitude height levels suitable for a two-wire line and the analog signal is intended for a data communication unit that connects to the two-wire line and which has a predefined amplitude resolution for the analog signal. The amplitude height levels of the signal on the four-wire line are transformed in such a way in the domain of the four-wire line that the number of amplitude height levels which the communication unit can discern in the analog signal match a presetable criterion.

Abstract: The S0-interface for ISDN base access connects a four-wire line with a receiver line pair and a transmitter line pair to an ISDN terminal device, subject to potential separation within the interface. Each of the receiver lines has a respective capacitor for potential separation and the transmitter lines have a transformer. An inductance is connected into each receiver line and each transmitter line on the interface side. Preferably, the receiver line pair is connected to a voltage amplifier on the device side. The voltage amplifier has a voltage amplification in the same ratio as the voltage amplification of the transformer in the transmitter line pair.

Abstract: An apparatus transmits digital signals between a higher-ranking station and one or more subordinate stations through transmission devices. A signal transit time is automatically measured in the transmission devices, differences in transit time are automatically compensated for and useful signals in the various subordinate stations are automatically synchronized with one another.

Abstract: A digital message switching system includes at least one digital message switching unit and a plurality of subordinate units each being coupled to the respective switching unit through a respective transmission link. In order to signal a request of a subordinate unit to transmit, that unit first sends at least one message of meaningless content to a higher-ranking unit and only then sends messages of meaningful content.