Abstract: Methods are provided for managing frequency channels in a shared spectrum available to a radio local access network (RLAN) access point (AP) in a wireless network. The methods may comprise receiving a request for channel availability from the RLAN AP to access the shared spectrum, computing, based on a plurality of parameters associated with the RLAN AP, an RLAN service area (RSA) associated with the RLAN AP, retrieving one or more incumbent protection contours (IPCs) associated with one or more incumbent users in the wireless network, identifying an IPC, among the one or more retrieved IPCs, that overlaps with the RSA associated with the RLAN AP, determining, based on the identified IPC, available frequency information corresponding to the received request for channel availability, and transmitting, to the RLAN AP, a channel availability response comprising the available frequency information.

Abstract: Disclosed is a system and method for providing program verify adaptation for flash memory. The method includes performing an adjustment iteration, which includes accessing error counts for respective N states of a plurality of memory cells, applying a weighting to the error counts based on a binary data coding for the N states, determining a state Smin of the N states having a minimum error count Emin from the error counts, determining a state Smax of the N states having a maximum error count Emax from the error counts, determining a difference between the Emax and the Emin satisfies an error count threshold, and adjusting, by a predefined value, a respective program verify offset of a lowest state from Smin and Smax, and of each state between Smin and Smax in the N states, wherein the adjusting is a decrement when Smin is less than Smax and an increment otherwise.

Abstract: This disclosure relates generally to methods and systems for real time unobtrusive monitoring of physiological signals of a subject confined to a bed. Output of single channel continuous wave (CW) radars are dependent upon distance of the subject from the radar. Dual channel IQ radars are more accurate but are costly and availability in the market is a constraint. The present disclosure provides a cheap and easily replicable pseudo IQ radar based system. The pseudo IQ radar comprises two CW radars placed at a calibrated distance from each other such that optimum points of one CW radar spatially overlaps null points of the other CW radar and phase imbalance is suppressed. Three such pseudo IQ radars are positioned in a predetermined configuration around the subject being monitored. A Supervised Complex Signal Demodulation (SCSD) method configured to suppress amplitude and DC imbalance is also provided for evaluating the physiological signals.

Abstract: Described embodiments provide systems and methods for providing remote application action feed cards. A ticket can be received from a client device. The ticket can be indicative of an action of a remote application and the remote application can be accessible by a group of users. The device can receive information about the action identified in the received ticket from at least one user of the group of users in response to provision of a determined key and the received ticket to the group of users. The device can provide the received information to client devices of user of the group of users to identify actions of other users of the group of users.

Abstract: Disclosed is a system and method for providing program verify adaptation for flash memory. The method includes performing an adjustment iteration, which includes accessing error counts for respective N states of a plurality of memory cells, applying a weighting to the error counts based on a binary data coding for the N states, determining a state Smin of the N states having a minimum error count Emin from the error counts, determining a state Smax of the N states having a maximum error count Emax from the error counts, determining a difference between the Emax and the Emin satisfies an error count threshold, and adjusting, by a predefined value, a respective program verify offset of a lowest state from Smin and Smax, and of each state between Smin and Smax in the N states, wherein the adjusting is a decrement when Smin is less than Smax and an increment otherwise.

Abstract: A system for providing remote assistance services using mixed and/or augmented reality visors includes the following apparatuses in combination: one or more smartphones/tablets of each user who requests assistance, connectable to any mixed/augmented reality visor on which a specific app is installed; one or more operator stations with PC/tablet configured to be able to communicate in real time with the devices of the user requesting assistance; at least one server configured to manage a database and to be connectable to and interfaceable with the smartphones/tablets of the users and the PCs/tablets of the operators; wherein the smartphones, tablets, PCs, visors and servers are connected to implement the following software components, which are all connectable to an Internet network: ADMINISTRATOR WEB FRONTEND, BACKEND, REAL TIME DATABASE, OPERATOR DESKTOP APP, RELATIONAL DATABASE, CLIENT MOBILE APP, OPTIP MIXED/AUGMENTED REALITY VISOR APP, EMAIL SERVICE.

Abstract: A processing system interconnect link training system includes a processing system that includes a secondary processing subsystem that is coupled to a first primary processing subsystem and a second primary processing system which are coupled to each other via a processing system interconnect that includes a plurality of processing system links. The secondary processing subsystem trains, during a boot operation and according to a first link configuration, the plurality of processing system links. Then the secondary processing subsystem determines that the training of the plurality of processing system links fails and, in response, retrains the plurality of processing system links according to a second link configuration that is a downgraded configuration relative to the first link configuration.

Abstract: Disclosed is a system and method for providing program verify adaptation for flash memory. The method includes performing an adjustment iteration, which includes accessing error counts for respective N states of a plurality of memory cells, applying a weighting to the error counts based on a binary data coding for the N states, determining a state Smin of the N states having a minimum error count Emin from the error counts, determining a state Smax of the N states having a maximum error count Emax from the error counts, determining a difference between the Emax and the Emin satisfies an error count threshold, and adjusting, by a predefined value, a respective program verify offset of a lowest state from Smin and Smax, and of each state between Smin and Smax in the N states, wherein the adjusting is a decrement when Smin is less than Smax and an increment otherwise.

Abstract: A method for analyzing a wireless link (3) of a wireless node of a customer premises equipment (CPE) device (1) during operation of the CPE device comprises: performing an active test, during which a data transmission is forced through the wireless link, to obtain a first set of parameters, and performing before or after the active test a passive test, which is a monitoring mode during which a data transmission of the CPE device is monitored, to obtain a second set of parameters. In particular, based on the first set of parameters, it is determined whether and to which extent the wireless link is in an uncertainty zone, and based on the second set of parameters, the decision is made to assign an observed decrease in a measured data rate to physics effects or to interference effects.

Abstract: An example remote control device includes an inertial sensor; one or more manipulable input devices; wireless communication circuitry; and control circuitry for controlling the wireless communication circuitry to communicate information about the inertial sensor and the input devices to an electronic device. The information is communicated at one or more communication intervals using a data format which permits a value associated with the inertial sensor and sampled at a given sampling time to be communicated in at least first and second different communications.

Abstract: Systems and methods are provided for powering Multimedia over Coax Alliance (MoCA) devices. An electronic device that is configured for use in a multimedia over coax alliance (MoCA) network may include a communication circuit operable to communicate multimedia over coax alliance (MoCA) based signals over coax cabling in the MoCA network, and one or more power circuits operable to support supplying and/or drawing power over the coax cabling in the MoCA network, to enable powering the electronic device and/or one or more other electronic devices in the MoCA network. The power circuits may include one or more of: a power regulator circuit that draws power from the coax cabling and/or regulates use of the power, a power source circuit that supplies power into the coax cabling, and a power management circuit that manages power related operations in the electronic device and/or in the MoCA network.

Abstract: A method implemented by a middlebox comprising registering a customer premises equipment (CPE) in the middlebox, wherein the CPE is coupled to the middlebox via an electrical line, and facilitating registration of the CPE in a central office (CO) equipment coupled to the middlebox.

Abstract: Novel tools and techniques are provided for implementing video qualification, which might include implementing video quality measurements at a subscriber premises and qualification of the subscriber premises for particular levels of video data transmission. In some cases, one or more customer premises equipment might comprise video quality chips that might perform measurements of the telecommunications links, and might send the results to a server associated with the service provider. The server might determine available video services, based on the results of the measurements, and might send the subscriber notifications indicating that the subscribers qualify for particular video services. In some cases, implementing video qualification might include the server determining that video service levels provided to a customer premises has been decreased or otherwise negatively affected.

Abstract: Described are an apparatus, system, and method for method for validating a broadband service for recommendation. The method comprises: collecting data associated with the broadband service; evaluating the collected data for service recommendations, the service recommendations including upgrades and downgrades to the broadband service; and validating broadband service recommendations, in response to evaluating the collected data, before presenting the broadband service recommendations to user of the broadband service.

Abstract: A communication system has a trunk extending from a network facility, such as a central office, with a plurality of distribution points positioned along the trunk. Each leg of the trunk defines a shared channel that permits peak data rates much greater than what would be achievable without channel sharing. As an example, the connections of each respective trunk leg may be bonded. Further, the same modulation format and crosstalk vectoring are used for each leg of the trunk. The crosstalk vectoring cancels both far-end crosstalk (FEXT) that couples between connections of a given trunk leg and crossover crosstalk that couples between one trunk leg and another. In addition, logic determines an amount of excess capacity available for each leg of the trunk and controls error correction based on the determined excess capacity.

Abstract: Described are systems and methods for implementing and operating a Device Abstraction Proxy (DAP). In one embodiment, the DAP includes a communications interface to connect the DAP to one or more access aggregation devices, each having a plurality of physical ports to provide Digital Subscriber Line (DSL) communication services to a plurality of remote DSL terminals via the plurality of physical ports. The DAP may further include a memory and processor to execute a virtual access aggregation device, in which a subset of the plurality of physical ports are allocated and linked to corresponding logical ports. The DAP may further include a global rule-set module to define operational constraints for the DSL communication services, and a management interface to allow at least one broadband access management system to manage the subset of physical ports allocated to the virtual access aggregation device subject to the operational constraints.

Abstract: The present invention discloses a smart ODN system of low power consumption, and the system is related to the ODN field and includes a smart management terminal, a master control management board, and several wiring management boards, where the smart management terminal is directly connected to the master control management board, and is also connected to the master control management board through the Internet and a mobile terminal, the master control management board is connected with several wiring management boards, each wiring management board includes a PMU and a PQU, which are independent from each other, the PQU is connected to a CPU of a wiring management board through a control line; the PMU is configured to collect and store information data of a port and communicate with the master control management board or the smart management terminal; the PQU independent from the CPU independently performs the query operation on a wiring port, and promptly obtains a port connection status.

Abstract: The combination device includes a first pair of series coupled first and second magnetically coupled coils, to which a first DSL line and a first DSL transmission line are electrically coupled, and a second pair of series coupled first and second magnetically coupled coils, to which a second DSL line and a second DSL transmission line are electrically coupled. A third DSL line is coupled to a first coupling element between the first and the second coils of the first pair, and to a second coupling element between the first and the second coils of the second pair. The combination device is located in a phantom injection module provided with at least five terminals respectively associated to the first DSL line, the second DSL line, the third DSL line, the first DSL transmission line and the second DSL transmission line.

Abstract: A method, computer program product, and system for a quality-of-service history database is described. Quality-of-service information associated with a first participant in a first electronic call is determined. The quality-of-service information is stored in a quality-of-service history database. A likelihood of quality-of-service issues associated with a second electronic call is determined, wherein determining the likelihood of quality-of-service issues includes mining the quality-of-service history database.

Abstract: The present disclosure relates to a method, a node, a system and a computer program for input impedance measurements in the form of return loss measurements, such as single ended line testing. The disclosure also relates to a communication system having a near-end terminal and at least one far-end terminal. The near-end terminal is capable of communicating instructions to the far-end terminal in order for the near-end terminal to perform echo impulse response measurements on subsequent states of impedance for comparing, analyzing and for enabling improved localization of faults.

Abstract: Prediction of a channel capacity is accomplished based on a TDR echo without explicitly estimating the topology of the line. The prediction is based on obtaining a measured TDR echo, determining a theoretical TDR echo for a plurality of loop lengths, estimating the equivalent TDR length based on an optimization, updating the equivalent TDR length and utilizing the updated TDR length to predict one or more of the upstream and downstream data rates.

Abstract: In a method of testing a residential broadband communication network, a residential gateway or set top box (STB) performs one or more single-ended parametric tests of the residential network that runs therebetween. The residential gateway or STB also performs one or more single-ended reflectometry tests of the residential network that runs therebetween. The residential gateway and the STB perform one or more dual-ended tests of the residential network that runs therebetween. The residential gateway dispatches the results of the foregoing tests to either: a device on the residential network, a device of another network that supplies broadband services to the residential network, or an intelligent device coupled to the residential gateway.

Abstract: A management device (100) for use in an access network (10, 19, 20, 30, 40, 100) including a plurality of data connections (18, 19, 20) between end user devices (10) and an aggregation transceiver device (20) where the connections (18, 19, 20) are aggregated for onward connection through the access network (20, 30,40), the access network storing in association with each data connection a Dynamic Line Management, DLM, profile which specifies a set of values for a plurality of parameters associated with the respective data connection, together with a stability level specifying a desired level of stability for the data connection.

Abstract: The present invention provides a method, an apparatus, and a system for reducing digital subscriber line interference. The method includes identifying at least one legacy digital subscriber line in a digital subscriber line DSL legacy line set, obtaining a target power spectral density mask value of the legacy digital subscriber line, and reducing power spectral density of a transmit signal on the legacy digital subscriber line according to the target power spectral density mask value.

Abstract: Using DSL modems as data collectors, the modems processes the data to, for example, allow easier interpretation of the line characteristics. In particular, the modems postprocess the data including calibration, filter compensation, determination of the SNR medley from the bits and gains tables and rate conversion. The interpretation process uses the postprocessed data and determines loop characterization, interferer detection, a data reduction estimation and a data rate estimation. The outputs of these determinations least allow for the characterization of the line conditions between the two modems.

Abstract: A test system for diagnosing twisted pair wiring includes a system processor in communication with a subscriber line interface module, which includes a codec and a SLIC (Subscriber Line Interface Circuit). The SLIC transmits a waveform having a frequency used for voice or baseband modem transmissions onto the twisted pair wiring. The system processor transmits a digital PCM (Pulse Code Modulation) stream to the codec, and the codec converts the digital PCM stream into the waveform transmitted onto the twisted pair wiring. In response to the transmitted waveform, the SLIC senses current on the twisted pair wiring. The codec generates an output waveform corresponding to the sensed current. The system processor receives the output waveform from the codec as a digital PCM stream, synchronizes the transmitted waveform and the output waveform at a single sample, and determines electrical properties of the twisted pair wiring from the output waveform.

Abstract: A method and a device for clustering lines of a wireline network in a number of virtual binders includes obtaining a noise value samples pertaining to different lines of the wireline network at substantially coinciding sampling moments, detecting corresponding features in these series, determining degrees of correlation between these features, and assigning the lines to one or more virtual binders on the basis of their mutual degrees of correlation.

Abstract: A probing signal transmitted on a twisted pair telephone line in a DSL system is reflected and received at a DSL device. An estimate of one of a DSL data transmission signal or DSL synch symbol transmission signal is removed from the received probing signal to recover the reflected probing signal. The recovered reflected probing signal is processed to determine characteristics information of the twisted pair telephone line.

Abstract: An integrated hybrid circuit includes a transmission unit, a transceiver coil, a transceiver circuit, a hybrid matching circuit, and a receiving circuit. The transmission unit generates a pair of upstream signals according to a user transmission signal. The transceiver coil transmits the pair of upstream signals to a central office through a pair of twisted pair, and receiving a pair of downstream signals from the central office through the pair of twisted pair. The hybrid matching circuit receives an adjustment signal to adjust selective impedances. The receiving circuit receives the pair of downstream signals from the central office, and generates the adjustment signal according to downstream and upstream rates and signals from the hybrid matching circuit. The transmission unit adjusts transmission power and bandwidth of the transmission unit and the receiving unit adjusts filter bandwidth of the receiving unit according to the adjustment signal for optimizing upstream and downstream rates.

Abstract: A diagnostic engine for remotely analyzing a fault of a telecommunication line includes a first measurement module adapted to be coupled to a termination of the line and adapted to measure first line characteristics according to a Metallic Line Testing measurement technique; a fault detection module to detect, based upon the first line characteristics, a fault on the line and to trigger thereupon a determining module; and a showtime module to be coupled to the termination to determine whether the line is in showtime mode and to inform thereupon the determining module accordingly. The determining module is adapted to trigger, in the event when the line being in showtime mode, activation of a second measurement module. The second measurement module is adapted to be coupled to the termination and to measure second line characteristics according to a Dual Ended Line Testing measurement technique.

Abstract: Using DSL modems as data collectors, the modems processes the data to, for example, allow easier interpretation of the line characteristics. In particular, the modems postprocess the data including calibration, filter compensation, determination of the SNR medley from the bits and gains tables and rate conversion. The interpretation process uses the postprocessed data and determines loop characterization, interferer detection, a data reduction estimation and a data rate estimation. The outputs of these determinations least allow for the characterization of the line conditions between the two modems.

Abstract: A method and apparatus for automatic processing of toll free call service alarms are disclosed. For example, the method receives a trouble ticket by a service provider for a toll free call service alarm, and retrieves a calling to number and a calling from number from the trouble ticket. The method determines if the service provider is a responsible organization for the toll free call service for the calling to number, and determines if a customer network for the toll free call service is active if the service provider is the responsible organization for the toll free call service. The method notifies a work center if the customer network is not active.

Abstract: The present invention relates to a method and an arrangement based on two-port network (TPN) theory that allows analytically estimating the loop transfer function from open and short-circuited input impedance measurements, e.g. single ended line transmission (SELT) measurements, by utilizing the fact that the line under test (LUT) can be considered reciprocal and by assuming that the LUT is symmetric. Hence, by using the present invention and an estimation of the noise on the line, the attainable bit rate at the customer premises can be determined by means of SELT measurements at the CO. The transfer function of a telephone copper-loop is estimated regardless of its topology by impedance measurements from the CO side. Specifically, such estimation is carried out from the calculation of the transmission parameters of loop, which are expressed only in terms of open and short-circuited input impedance measurements at the CO when reciprocity and symmetry is assumed.

Abstract: A probing signal transmitted on a twisted pair telephone line in a DSL system is reflected and received at a DSL device. An estimate of one of a DSL data transmission signal or DSL synch symbol transmission signal is removed from the received probing signal to recover the reflected probing signal. The recovered reflected probing signal is processed to determine characteristics information of the twisted pair telephone line.

Abstract: In one embodiment, a network device attaches a header including an identifier for an original call to an outgoing refer message and may also modify a table entry for a consultative call to include the identifier. The network device then monitors incoming invite messages for a header containing the identifier and observes that an incoming invite message containing the header correlates to the original call. When a header is not included, the network device extracts information from the incoming invite messages and compares the extracted information to the modified table entry to correlate one of the incoming invite messages to the original call.

Abstract: Systems and methods of selecting a media path for data packets bearing the media of a telephone call to traverse during a voice over Internet protocol telephone call include testing the call quality of multiple potential media paths immediately before a call is setup. The potential media path with the highest call quality is used as the initial media path for the call. If the call quality of the media path currently in use declines below a threshold value during a call, potential alternate media paths are identified and tested for call quality. If one of the alternate media paths has better call quality than the media path presently in use, the call is switched to the alternate media path with the highest call quality.

Abstract: A system for testing a conductor of a structure can include a test device connected to the conductor. The test device is configured to test an electrical characteristic of the conductor and to produce a test result based at least in part on the electrical characteristic. A service provider network may be configured to communicate with the test device to initiate a test and/or to obtain the test result. A customer may use a computing device to obtain information regarding the test result, as well as guidance for troubleshooting and resolving a problem detected with the electrical conductor, such as a fault.

Abstract: Existing and future standardized VDSL2 and other systems can be integrated into and used with a vectored DSLAM or other vectored or non-vectored DSL system, without a new user disrupting service to other users in the same or a nearby binder, in some cases by using transmit power, CARMASK and/or PSDMASK DSL capabilities to reduce both downstream and upstream training-signal levels so that training of a new DSL line is non-disruptive, despite a lack of knowledge of the pre-existing binder. For vectored systems, the crosstalk from that tone can be observed, learned and then added to the vectoring system so that any subsequent excitation on that tone would be eliminated by vector processing. A second tone then can be added in the same way, etc. In non-vectored DSLs that might be operating in a binder or line set, once these non-vectored lines are observed to be present, a vectored line set controller, such as a DSL optimizer, then can anticipate the potential interference from such non-vectored lines.

Abstract: A method and device for transmission line testing are provided. A particular modem device includes a transmission line interface to connect to a transmission line. The modem device also includes a memory to store a plurality of transmission line tests. The modem device also includes a controller coupled to the memory and to the transmission line interface. The controller selects one or more tests of the plurality of transmission line tests from the memory. The controller also performs the selected one or more tests on the transmission line and detects an electrical characteristic of the transmission line.

Abstract: An apparatus for estimating far-end crosstalk RDS-FEXT, i (fd) or an end (C1-2) of a communication line (C1) furthest from a transceiver (10-1) to which the communication line (C1) is connected. The apparatus is configured to: measure upstream noise RUS-Noise(fu) at an upstream frequency (fu), the upstream noise RUS-Noise(fu) induced in the communication line (C1) due to the crosstalk; select a downstream frequency (fd) for which the far-end crosstalk RDS-FEXT, i (fd) is to determined; and estimate the far-end crosstalk RDS-FEXT, i (fd)? as a function of the upstream Noise RUS-Noise(fu), the upstream frequency (fu) and the downstream frequency (fd). An apparatus reversing upstream and downstream features, a system, a computer readable medium and related methods are also described.

Abstract: Methods and apparatus to test a subscriber line for a broadband access service are disclosed. An example network interface device (NID) comprises a tone generator to transmit a tone on a subscriber line to characterize the subscriber line while a DSL modem is providing a DSL service via the subscriber line, the tone having a frequency occurring within a range of frequencies in use by the DSL modem to provide the DSL service, and a pair of terminals to couple the DSL modem and the tone generator to the subscriber line.

Abstract: One embodiment is a method for performing 2-wire line imbalance measurements. The method comprises receiving a probe signal and based on the probe signal, determining one of more of: an estimated transverse conversion loss (TCL) coupling transfer function and an estimated transverse conversion transfer loss (TCTL) coupling transfer function.

Abstract: A method includes identifying one or more second digital subscriber lines from one or more first digital subscriber lines based on historical performance data. The one or more second digital subscriber lines are identified based on degraded performance that is determined using first performance information for the one or more first digital subscriber lines. The method includes applying a line profile to the one or more second digital subscriber lines. The method includes storing second performance information associated with the one or more second digital subscriber lines. The method includes sending information to a remote computing device.

Abstract: Apparatus, methods and articles of manufacture to predict vectored digital subscriber line (DSL) performance gains are disclosed. A disclosed example method includes determining a model coefficient of a noise-to-margin ratio (NMR) model from performance data measured for a DSL subscriber loop prior to provisioning of vectoring for the DSL subscriber loop, computing, using the model coefficient, a first NMR value with disturbers enabled and a second NMR value with disturbers disabled, and estimating an expected vectoring performance gain for the DSL subscriber loop based on the first and second NMR values.

Abstract: An improper connection determination method includes a closed circuit forming step, a current detection step and a determination step. In the closed circuit forming step, a closed circuit from one of at least two contacts in a telephone connection terminal of a communication apparatus to another one of the at least two contacts in the telephone connection terminal is formed. In the current detection step, a current flowing in the closed circuit, when the closed circuit is formed in the closed circuit forming step, is detected. In the determination step, it is determined that the telephone line is improperly connected to the telephone connection terminal when the current is detected in the current detection step.

Abstract: A communication transfer apparatus and a communication transfer method can transfer communications at low cost without the need of requesting a global IP network to switch any port number. The local internet protocol address of the origin terminal of transfer described in a record relating to a transfer out of the records of the masquerade table that is utilized for an internet protocol masquerade is rewritten as the local internal protocol address of the destination terminal of transfer, while maintaining the global port number of the record.

Abstract: A method and a device are provided for data processing, including the steps of transmitting a first signal from a first instance to a second instance and sending a second signal from a third instance to the first instance, wherein the second signal corresponds at least partially to the first signal as received at the third instance.

Abstract: A portable signal testing system includes a transmitter, a first dynamically tunable receiver, a second dynamically tunable receiver, a first indicator and a second indicator. The transmitter transmits over a wired communications link a first signal having a corresponding first frequency representative of a first frequency range of the wired communications link, and transmits over the wired communications link a second signal having a corresponding second frequency representative of a second frequency range of the wired communications link. Signal losses for the first signal and second signal are measured, and indicators indicate whether the signal losses are acceptable.

Abstract: A method for analyzing the status of a subscriber loop belonging to an access network portion of a fixed network infrastructure, the subscriber loop not supporting a broadband service wherein the access network portion includes further subscriber loops, a set of which support broadband services. The method includes the steps of collecting attenuation measures associated with said set of subscriber loops supporting said broadband services; and processing said attenuation measures to obtain an estimation of a maximum bit rate that can be offered on the subscriber loop to be analyzed.

Abstract: An apparatus for estimating pair symmetry status for a communication line (Ci). The apparatus is configured to: obtain a value set indicative of a signal to noise ratio for the communication line (Ci) and at a receive band frequency (f); determine a crosstalk coupling length (Li) for the communication line (Ci); and estimate the pair symmetry status, based on the obtained value set indicative of the signal to noise ratio (SNRi(f)), the crosstalk coupling length (Li) and a predetermined symmetry indicator-value (qmax; ki,max). Related method and computer readable medium are also described.