Abstract: A robust tone detector is realized by applying a single taper, which provides a relatively narrow bandwidth filter, to a received signal and, then, performing a Discrete Fourier Transform of the tapered signal. The result of the Fourier transform is used to obtain an estimate of energy in the frequency domain of the expected tone. A prescribed selection algorithm based on the relationship of the received signal energy in the time domain and the energy estimate in the frequency domain is used to determine whether a valid tone has been received. Robustness of the tone detector is improved by performing a plurality of Discrete Fourier Transforms of the single tapered version of the received signal at a corresponding plurality of frequencies relative to the nominal frequency of an expected one or more tones. A further improvement in the tone detector is obtained by the dynamically adjusting tone acceptance thresholds based on a measure of channel impairments.

Abstract: An equipment unit protection switch from an in-service equipment unit to a standby equipment unit is realized prior to any movement of the active equipment unit about to be removed from an equipment frame in which it is inserted. This is achieved by advantageously incorporating apparatus for generating an equipment unit removal indication signal that enables a controller to anticipate the removal of the equipment unit from the equipment frame. To this end, the equipment units employ an equipment unit latch and an associated switch to generate the equipment removal indication signal. Initial movement of the latch causes the equipment unit removal indication signal to be generated prior to any movement of the equipment unit in the frame in which it is inserted.

Abstract: A switching architecture is disclosed which includes a dual access ring structure interconnecting the location of a customer, a primary central office, a backup central office and a remote central office (hub office) which does not directly serve the customer location. The architecture enables transport of a customer's communications traffic to be automatically restored in the event a failure occurs in the primary transport route of the traffic from the customer location to the hub office via the primary central office by automatically selecting a transport route free of a failure. Such a failure is detected whether caused by a so-called "hard" failure or a so-called "soft" failure. Optionally, each type of automatic network reconfiguration is executed in a manner such that as soon as it is possible to employ the original configuration, the network automatically reverts to the original configuration, thereby easing network maintenance activity.

Abstract: A plurality of M receivers are utilized to receive a plurality of N channels from various incoming multiplexed data signals, N.gtoreq.M, where each incoming data signal arrives on a separate wavelength and comprises several channels. Each of the M receivers, in sequence, receives a separate one of the N channels, thereby M of the N channels. The process then repeats for the next M channels, in the same sequence as the first M channels. The repetitions continue until all N channels are received.

Abstract: A modular growable packet switching arrangement is constructed from a plurality of packet switches and a novel interconnect fabric. The interconnect fabric includes a plurality of cell routers, for receiving data packets and routing them to a plurality of packet switches, where each cell router includes at least one connection to each packet switch. The interconnect fabric also includes a sorting network for receiving concurrently arriving data packets, sorting the data packets based upon their addresses, and sending the sorted data packets to the inputs of the cell routers. The sorted data packets are arranged such that all data packets which must be transmitted to the same packet switch are sent to different cell routers. Then, all packets which are destined for a common packet switch may be routed there, each from a different cell router.

Abstract: Heat dissipation performance of a pin fin heat sink is improved by utilizing a flow guide arrangement. Flow guide members are positioned relative to the outer rows of the pin fins and longitudinal to fluid flow through the pin fin field of the heat sink. A gap between a lower edge of each flow guide member and a base surface of the heat sink forms apertures allowing potentially stagnant fluid in an interior region of the pin fin field of the heat sink to communicate with fluid flowing around the exterior of the heat sink. This causes a so-called "pump" action in which the potentially stagnant fluid is drawn along with the fluid flowing around the exterior of the heat sink.

Abstract: The problems of buffer overflow and underflow encountered when employing actually variable or effectively variable bit-rate channels for communicating encoded video images are overcome by jointly controlling the number of bits employed to encode each video frame and the transmission bit-rate of the variable bit-rate channel as experience by the encoder. The selection of the number of bits employed to encode each video frame, and hence the encoder bit-rate, as well as the associated channel bit-rate are determined from the encoder buffer fullness, a determination of the decoder buffer fullness and any constraint imposed on the channel. The encoder is responsive to the selected encoder bit-rate and accordingly adjusts its encoding parameters so as to achieve the selected encoder bit-rate.

Abstract: A received digital signal is synchronized with a receiver in a communications network by employing a code word which is updated in accordance with a unique update technique. The synchronization arrangement receives the digital signal at a receiver, generates an error check code word over a prescribed portion of the received digital signal and compares the generated error check code word with an expected error check code word in the received digital signal. In response to the comparison result, the generation of the code word and the comparison is iteratged until synchronization is obtained. A new code word is generated as a function of a modified version of the last previously generated code word (previous code word), a function term based on a set of bits dropped from the prescribed portion of the received digital signal, and a set of bits added to the prescribed portion of the received digital signal. In one embodiment, a cyclic redundancy check (CRC) code word is employed.

Abstract: Asynchronous-synchronous digital signal conversion and vice versa are realized by employing a single synchronizing elastic store and associated phase detector. The signal smoothing and synchronization processes are achieved with a single elastic store by low pass filtering the elastic store write-read address separation signal from the phase detector to obtain a smooth stuff control signal. In turn, the smooth stuff control signal is employed to make a stuff decision for controlling the elastic store read clock signal. In a specific embodiment the low pass filtering is realized by first synchronously sampling the write-read address separation signal and, then, employing a digital low pass filter to obtain the aliasing free smooth stuff control signal.

Abstract: An original symbol rate of a transmitted modem signal which has been demodulated for digital transmission is recovered at a network receiver by obtaining an estimate of error between the original transmitted symbol rate and a known nominal symbol rate. This is realized at the network receiver by measuring an interval between blocks of data in a received signal having other than a known nominal number of data bits. This is achieved because each of the blocks of data is of a known fixed interval. The measured interval is proportional to the desired error estimate. The error estimate is then integrated and employed in an interpolator to adjust the symbol rate of a remodulated modem signal at the network receiver.

Abstract: An incoming data signal including so-called gaps is synchronized to a new outgoing clock signal by employing a single elastic store and a smooth write address. An elastic store write address is generated in response to an incoming clock signal and is inhibited from advancing during the gaps in the incoming data signal. A smooth clock signal is obtained by appropriately dividing the incoming clock signal by a value dependent on the duration of the gaps in a predetermined portion of the incoming data signal. The smooth clock signal is used to control a counter to generate a smooth write address. The smooth write address is supplied to a phase detector. An adjusted read address is generated in response to the new outgoing clock signal and is supplied to the elastic store and to the phase detector. A counter used to generate the adjusted read address is inhibited from advancing during intervals in which gaps are to appear in the output data signal from the elastic store.

Abstract: A new data communications architecture is disclosed in which high level communications services provided to a host processor are arranged into independent horizontal functions that are processed in parallel. Any conditional dependencies among the horizontal functions are resolved by a connector that interfaces the horizontal functions to an application layer of the host processor. Additionally, communication performance is enhanced by allowing adaptive specifications of a high-level protocol employed in the architecture for providing the high-level services. This adaptive specification may be initiated in response to changing user requirements or varying network parameters. Then, a high-level protocol specification is obtained by choosing appropriate values for parameters of the horizontal functions which are parametrically programmable.

Abstract: A dynamic channel allocation unit for specifying a bit rate for each video coder in a set of parallel video coders comprising an overall video coder is disclosed. The dynamic channel allocation unit is supplied from each individual video coder with an average from quantization step size for the previous frame and the average number of bits produced per pel. For the current image frame the dynamic channel allocation unit computes a set of channel sharing factors, i.e., the percentage of the total channel bandwidth to be allocated to a particular video coder. One channel sharing factor is computed for each individual video coder. Individual members of the set of channel sharing factors may be further refined to reflect the prior history of the channel sharing factor for their corresponding coder. Additionally, the set of estimates may be normalized to reflect the actual number of bits that can actually be produced by each individual video coder.

Abstract: A method for arranging components to be mounted on circuit packs to achieve improved cooling is disclosed. In accordance with one aspect of the invention, components are arranged such that the longer dimension of each component is substantially parallel to the flow of a heat carrier as it streams from an inlet to an outlet. In accordance with another aspect of the invention, those components having larger aspect ratios are substantially placed near the outlet via which the heat carrier is removed.

Abstract: A communications network comprising a plurality of "subnetworks" multiplexed onto a single communications medium. A separate group of NIU's communicate on each predetermined "subnetwork", and each NIU also includes a tunable transmitter for transmitting data to NIU's of other subnetworks. Data from a user equipment is transmitted via the tunable transmitter if it is destined for an NIU from another subnetwork, and via a fixed transmitter if it is destined for an NIU on the same subnetwork. In one embodiment, fiber optics is utilized in order to provide a high speed network with tunable lasers.