Abstract: A digital modem is connected to a CBX in a network. Data is transmitted to the digital modem in a data field of synchronous serial data frames. The digital modem converts the data into a digital signal corresponding to a time sampled analog signal representing the data. The converted digital signal is communicated to a digital to analog converter for transmission on a telephone line. Analog signals received on the telephone line are digitized, and then converted to data in the digital modem.

Abstract: A method of testing a communication network that comprises a first and a second multiport modem communicating with each other through a transmission channel, each of said modems being provided with a number of input/output interfaces and each of the interfaces on either modem being associated with a corresponding interface on the other modem. In accordance with the method of the present invention, a test request is applied to one of the interfaces on the first multiport modem, which responds thereto by generating a test configuration code identifying that interface. This modem is then caused to assume a so-called test configuration, in which only that interface to which the test request was applied is active, and a test command comprising an indication of the test to be performed and a link level identifier is applied to that interface. If the identifier designates the link level to which the first modem belongs, this modem will control the test specified in the test command.

Abstract: In a receiver for PSK modulated signals, carrier phase tracking is achieved by a feedback loop comprising a phase error predictor. Means are provided for adaptively setting the gain factor in the phase error predictor to an optimum value, in response to successive residual phase errors.