Abstract: A technique has been developed whereby an adaptive receiver may employ decision updating in a manner insensitive to RBS. One realization achieves nearly-ideal training of an adaptive equalizer of a modem during TRN1d training despite potential RBS in a digital portion of the PSTN. Updates in the exemplary realization are based upon the true value of the corresponding equalizer output (the decision) and insensitive to RBS. Adaptive equalizer realizations improve equalizer training by treating the received signal as a sequence of blocks of 24 symbols with 24 corresponding separate decision values. In an exemplary variation, equalizer training begins using a single pair of decision points for coefficient updating. After gross convergence of the equalizer coefficients is achieved the update broadens to include updating each of 24 decision points and the equalizer coefficients.

Abstract: Reliable detection of a call-waiting tone is provided by employing a correlation based technique. A modem or other device employing such a technique need not rely on carrier drop detection and is generally insensitive to other energy or noise on the line.

Abstract: The computational load imposed by communications software executed on a general purpose processor can be significantly reduced by exploiting periods during an active connection when no data is being received. In particular, execution of many receive path signal processing algorithms can be disabled when no data is being received. The transmit path continues output modulation as with a normal connection, so as to trick a remote communications device into believing the connection is still normal. However, substantial portions of the local receive path can be disabled, thereby reducing computational load on the general purpose processor and freeing additional compute cycles for application and/or operating system program use.

Abstract: Reliable detection of a call-waiting tone is provided by employing a correlation based technique. A modem or other device employing such a technique need not rely on carrier drop detection and is generally insensitive to other energy or noise on the line.

Abstract: A filter is implemented in software on a general purpose processor in a manner which reduces the number of memory accesses as compared to conventional methods. In some realizations, both application code and filter code are executed on a same general purpose processor. The filter code incrementally loads respective portions of input and coefficient vector data from addressable storage into respective registers of the processor and performs successive operations thereupon to accumulate output vector data into other respective registers of the processor. The filter code typically exhibits an execution ratio of less than two input and coefficient data loads per operation to accumulate. In some realizations, the filter code is callable from the application code and provides the application code with a signal processing facility without use of a digital signal processor (DSP).

Abstract: A technique is described for reliably determining whether a direct digital connection exists between a transmitting server modem and a receiving client modem. Such a determination is an essential part of the training procedure for modems that conform to ITU-T Recommendation V.90 but is also applicable to other data communications configurations and equipment. In some configurations in accordance with the present invention, segments of a modem training signal, L1 L2, are used to make the determination.

Abstract: A technique is described for reliably determining whether a direct digital connection exists between a transmitting server modem and a receiving client modem. Such a determination is an essential part of the training procedure for modems that conform to ITU-T Recommendation V.90 but is also applicable to other data communications configurations and equipment. In some configurations in accordance with the present invention, segments of a modem training signal, L1L2, are used to make the determination.

Abstract: Reliable detection of a call-waiting tone is provided by employing a correlation based technique. A modem or other device employing such a technique need not rely on carrier drop detection and is generally insensitive to other energy or noise on the line.

Abstract: Reliable detection of a call-waiting tone is provided by employing a correlation based technique. A modem or other device employing such a technique need not rely on carrier drop detection and is generally insensitive to other energy or noise on the line.

Abstract: A Finite Impulse Response (FIR) filter is implemented in software on a general purpose processor in a manner which reduces the number of memory accesses as compared to conventional methods.

Abstract: A Finite Impulse Response (FIR) filter is implemented in software on a general purpose processor in a manner which reduces the number of memory accesses as compared to conventional methods. In particular, an efficient implementation for a general purpose processor having a substantial number of registers includes inner and outer loop code which together make ##EQU1## memory accesses and KN multiply-accumulates, where L.sub.1 is the number of output vector elements computed during each pass through the outer loop and where L.sub.2 is the number of taps per output vector element computed during each pass through the inner loop. The efficient implementation exploits L.sub.1 +2L.sub.2 general purpose registers. For an embodiment in which L.sub.1 =L.sub.2 =8, inner and outer loop code make ##EQU2## memory accesses, which for filter implementations with large numbers of taps, approaches a 4.times. reduction in the number of memory accesses as compared to conventional methods.

Abstract: The computational load imposed by a software modem executed on a general purpose processor can be significantly reduced by exploiting periods during an active connection when no data is being received by the software modem. In particular, execution of many receive path signal processing algorithms can be disabled when no data is being received by the software modem. The transmit path continues output modulation as with a normal connection, so as to trick the remote modem (which may or may not be a software modem) into believing the connection is still normal. However, substantial portions of the software modem's receive path can be disabled, thereby reducing computational load on the general purpose processor and freeing additional compute cycles for application and/or operating system program use.

Abstract: A phase-splitting T/3 equalizer and echo canceller structure is computationally efficient because only one point per baud is calculated. However, there are two drawbacks to the structure: (1) since the equalizer performs both the phase-splitting function and channel response equalization, its convergence is slow, and (2) when training the echo canceller during half-duplex training, an answering modem needs an assumed equalizer in its receive path to train its echo canceller, because the adaptive equalizer has not yet been trained; however, after equalizer training the echo canceller needs to be retrained because equalizer coefficients have changed. In contrast, a fixed phase splitting filter can be used during training.