Abstract: In a multidrop data communication system operating at a first bit rate using the High-Level Data Link Control (HDLC) protocol, dial restoral of communications with a particular tributary at a second, lower bit rate is accomplished without requiring the system as a whole to back down to that lower bit rate. Specifically, the outgoing data is buffered in the dial restoral modem, which discards the data stored in the buffer upon receipt of the HDLC frame which follows any frame in which the so-called "poll" bit is set.

Abstract: The Transmission Control Protocol (TCP) is a connection-oriented transport layer protocol that offers a full duplex reliable virtual circuit connection between two endpoints. Each received TCP packet in an endpoint contains both control information and data. The complexity of processing this control information in an endpoint is reduced by only periodically processing the control information. In particular, control information in received packets are not processed in an endpoint until either a) a predetermined number of packets are received, or b) a timer expires, whichever occurs first. As a result, this overall decreases the amount of processing associated with the receipt of each TCP packet and improves the performance of the TCP protocol in a high-speed packet network.

Abstract: Announcements from a voice messaging system that either prompt a user for action or provide information to a user are constructed independent of the language in which the announcement is provided to the user. In particular, each announcement is treated as a "semantic expression" having an announcement identifier. This announcement identifier is mapped into a plurality of rules, each rule providing instructions on how to construct the announcement for a particular language. The rules can recursively call other rules to provide additional flexibility in constructing a particular announcement.

Abstract: The Electronic Industry Association (EIA) RS-232 interface signals are manipulated to additionally convey operating mode information from a piece of data communications equipment (DCE) to its respective data terminal equipment (DTE). In particular, in establishing a data connection, the data communications equipment may transmit information in either half-duplex mode or full-duplex mode. In order to convey which mode of transmission is being used, the data communications equipment manipulates the EIA RS-232 interface signals to provide a notification signal, which is representative of the particular mode, to the data terminal equipment. As a result of receiving this notification signal, the data terminal equipment can then switch to the same mode of operation.

Abstract: A high-speed convolutional decoder is constructed by performing the transition, or branch, metric calculations in reference to a subset of a constellation, which comprises a plurality of subsets. In addition, any subset can be chosen as the reference subset through the use of "modulo decoding." In a modulo decoder, the constellation space is folded into a modulo set area that is centered around the arbitrarily chosen reference subset. The branch, or transition, metrics are calculated within the modulo set area. As a result, the branch metric computations are only performed on a small area of the signal space, with the result that only one error is extracted, the branch metrics are easily computed, and one slicing is performed--thus reducing overall computation time.

Abstract: In many data communications systems, crosstalk is a significant channel impairment. If all transmitters in such a system must utilize the same shaping function, and if the transmitters are furthermore nominally Nyquist bandlimited, then the crosstalk generally cannot be mitigated by equalization. However, by extending the bandwidth of the transmitted signal in accordance with the principles of the invention, the resultant crosstalk can be efficiently mitigated by equalization. This extended bandwidth signal is produced by adding significant additional energy outside the traditional Nyquist band.

Abstract: In a time-division multiplexing communications system, which transmits information from various sources in different time-slots, additional information is transmitted by varying the pattern of time slot assignments in accordance with a set of rules. As a result, the assignment pattern by which time slots are assigned to each of the various sources of information, conveys additional information. Specifically, a High Definition Television (HDTV) transmission system is constructed in which picture information is transmitted by time-division-multiplexing between two different, and disjoint, signal point constellations. Additional information is conveyed by the rule for switching between the different signal point constellations.

Abstract: The data entry portion of a voice messaging system is constructed to be language, culture, or market segment independent. In particular, the design of the voice messaging system is based upon "semantic expressions," which are used to evaluate any language, culture, or market specific data that is entered by a user. In particular, each type of data entry is treated as a "semantic expression" having an identifier. This identifier is mapped into a plurality of rules, each rule providing instructions on how to interpret the input data for a particular language, culture, or market segment. The rules can recursively call other rules to provide additional flexibility in interpreting information that is entered by a user.

Abstract: A V.32 compatible modem provides a full-duplex mode of operation, while a 208B compatible modem provides a half-duplex mode of operation. The connect sequence of a V.32 compatible modem is modified so that it will automatically determine if the other modem, whether the originating modem or the answering modem, is a 208B type of modem or a V.32 type of modem. In one embodiment of the invention, the connect sequence of an originating V.32 modem is modified to detect either a 2100 Hz answer tone, which represents that the answering modem is a V.32 type of modem, or a 2021 Hz answer tone, which represents that the answering modem is a 208B type of modem. In another embodiment of the invention, the connect sequence of an answering V.32 modem is modified to transmit first a 2100 Hz answer tone and then, if no 1800 Hz V.32 signal "AA" is received from the originating modem, to transmit a 2021 Hz answer tone, thereby simulating a 208B modem has answered the data call.

Abstract: A business performs a credit check on a customer's credit card number by utilizing the D-channel of an Integrated Services Digital Network (ISDN) facility. The ISDN facility connects the business to a telecommunications network, which utilizes signaling system number 7 (SS7). Specifically, the ISDN Q.931 protocol is modified to allow the Q.931 FACILITY message to include: a) credit check request, b) a call reference number, and c) the customer's credit card number. This information is sent, via the ISDN D-channel, to the telecommunications network, which passes the information, via an SS7 Transaction Capability Application Part (TCAP) message, to a credit checking data base. A result from the credit checking data based is then passed back through the telecommunications network to the business on the D-channel of the ISDN facility.

Abstract: In the public switched telephone network, an originating modem can identify an answering modem, e.g., as to the type of modem it is, by detection of a low-level identification signal sent from the answering modem. The low-level identification signal is hidden within an industry standard "answer tone," e.g., a CCITT V.25 answer tone of 2100 Hz. If the low-level identification signal is detected by the originating modem, the industry standard "handshaking" procedure is terminated and a non-standard handshaking procedure is implemented. If the identification signal is not detected by the originating modem, the industry standard handshaking procedure is simply completed.

Abstract: The effect of non-linear distortion on a received signal point is reduced by the use of a circular limiter. In particular, the circular limiter computes the distance of the received signal point from the center of the signal point constellation. If this distance exceeds a desired limit, then both dimensions of the received signal point are reduced by the same factor to maintain the original phase. This reduction in the dimensions of the received signal point decreases the corresponding error signal that is calculated by a Viterbi decoder. As a result, this further reduces the value of the accumulated path metrics of the Viterbi decoder which results in an improvement in system performance. In addition, the circular limiter also realizes a slight improvement in system performance against additive white Gaussian noise. The value of the limiting distance can either be predefined, or determined adaptively to match channel conditions of the communications system.

Abstract: A re-authentication procedure between the modems of a public switched telephone network (PSTN) data connection, which is between a computer facility and a user, provides a secure method for protecting the computer facility against an active wire tap, or spoofing, by an intruder. In particular, the user's modem and the computer's modem perform a re-authentication procedure throughout the duration of the data connection. This re-authentication procedure is transparently performed on a side channel of the data connection. This side channel can either be an in-band channel or an out-of-band channel. The re-authentication procedure comprises an exchange of encrypted information between the two modems. If one of the modems detects the presence of an active wire tap, that modem simply interrupts the data connection.

Abstract: The decoding depth of a multidimensional trellis-coding scheme with X-fold time diversity is reduced, or minimized. As a result, an improvement in error rate performance is achieved for the multidimensional trellis code, which can then be favorably applied to a fading channel application.