Showing papers on "Loopback published in 1984"

An Echo-Cancellation-Based 4800 Bit/s Full-Duplex DDD Modem

Abstract: In this paper we describe an experimental 4800 bit/s fullduplex DDD modem which has been constructed at Bell Laboratories and AT&T Information Systems. The modem achieves full-duplex operation by using echo cancellation techniques. The main features of the modem's architecture and start-up procedure are discussed in the paper. We also study in detail the characteristics of an echo canceller structure which was found to be particularly attractive for this application. Finally, we present experimental performance results obtained over simulated channels in the laboratory and over telephone loopback facilities.

Method of detecting recovery from fault in a data transmission system which effects loopback control

Abstract: A looped data transmission system has a pair of looped transmission lines forming two transmission systems having different transmission directions, and a plurality of stations including at least one control station connected to said transmission lines of the two transmission systems If a fault occurs in the two transmission lines of the two transmission systems in the same section, a loopback configuration is established such that stations adjacent to the faulty section send signals from one system back to the other system With the loopback configuration being established, the stations which have received supervisory signals sent from a loopback end station send them back to the transmission line of the other system When one of the loopback end stations has received a supervisory signal from the direction of the faulty section, it is judged that a portion of the faulty section is recovered, and the result of the judgement is communicated to the control station

Communication circuit loopback test apparatus

Abstract: To perform a loopback condition for testing purposes, the present apparatus supplies a null signal from an end terminal on a communication link through a set of repeater stations to reinitialize the repeater stations. It then sends N+1 pulses of a frequency different than the data frequency through the repeater stations with each repeater station that receives more than two pulses disgarding one pulse and forwarding the rest. The repeater station or remote end terminal that receives only two pulses reconfigures itself to a loopback condition, returns a null signal back to the end terminal originally transmitting the N+1 pulses and then sends an acknowledgement pulse. Data signal testing can then be performed until a further null condition is sent thereby reinitializing the repeater stations to the data transmission configuration.

Switching system loopback test circuit

Abstract: This invention relates to a switching system testing arrangement which uses a looparound circuit, into which a test signal is injected and received to determine whether the loop is functioning properly. The system provides means for testing individual switches (or equivalent time division counterpart), individual loops and links between switching stages and the network, complete loops between peripherals, short loops between peripherals and their local control units, or any loop that can be set up within the system, without incurring loss of use of parts of the system which would otherwise be required to obtain the loop but are not of interest to test. The control data and test signals are applied, to set up the loop and into the loop respectively, via message transmission paths which are separate from the loop under test. Accordingly any part of the communication circuit system can be isolated for test, reducing substantially the time overhead for determining whether a switching element or stage, or link is operating properly.

Apparatus for providing loopback of signals where the signals being looped back have an overhead data format which is incompatible with a high speed intermediate carrier overhead format

Abstract: The overhead format for DS1C data must be removed and the data broken into two DS1 format data signals before being transmitted over DS2 or DS3 transmission lines. The present invention demonstrates a method whereby the stuff bit code for appropriate frames of a high speed transmission line can be violated and remotely detected whereby the signal is looped back at the destination end of the desired signal whether the remote signals are in the DS1C or DS1 data format.

Remote supervisory and controlling equipment

Abstract: PURPOSE:To allow a control station to discriminate whether a cause to a fault exists by providing the 1st means circulating a diagnostic signal to check the presence of a fault of an equipment in the control station and the 2nd means checking whether the fault exists in an outgoing/incoming line or in the equipment to be controlled. CONSTITUTION:A logical section 9-1 of a control station equipment 1 turns on a loopback relay 10-1 to form the loopback state of the route A. Then the logical section 9-1 outputs a diagnostic signal to a modulation section 5-1 to detect the diagnostic signal subject to loopback via a hybrid transformer 11-1, an attenuator 12 and a demodulation section 6-1. When a fault exists, the route A loopback is released and it is discriminated that it is the fault of the control station equipment 1. When no fault exists, the route A loopback is released, the route B loopback is executed and the logical circuit 9-1 of the equipment 1 outputs a diagnostic signal during that time. When the logical circuit 9-1 detects a fault of a loopback signal of the diagnostic signal, it is discriminate as a fault of the line side of the incoming line 7 or the outgoing line 8 and when no fault is detected, it is discriminated as a fault of the equipment 2 to be controlled.

Synchronizing system of digital multiplex transmission system

Abstract: PURPOSE: To receive data without changing a reception timing at a main controller by providing a phase control function to propagation delay to each terminal device connected to two pairs of cables in the form of multidrop. CONSTITUTION: A reference clock and a transmission data from a master clock oscillator 13 in the main controller are transmitted to a cable 3b via a signal transmission circuit 15. A signal reception circuit 10 of each terminal device receives the reference clock, a loopback pulse extracting circuit 6 separates a synchronous pulse and reception data and a reception PLL circuit 11 extracts the reception block. The synchronous pulse extracted from the circuit 6 becomes a loopback pulse, which is subjected to phase comparison with the reception block at a phase comparator circuit 7, the compared output is subjected to a delay in response to the propagation delay of a cable length by a variable delay circuit 8 to form a transmission clock at the terminal device. The transmission clock is transmitted to a cable 3a via a phase control pulse transmission circuit 5 and a signal transmission circuit 9. A signal reception circuit 12 of the main controller receives the synchronous pulse in the same phase from each terminal station. COPYRIGHT: (C)1986,JPO&Japio

Transmission system having detour

Abstract: PURPOSE:To prevent the permanent circulation of a specific small loop by counting the number of detours in an autonomous spread type double loop transmission system. CONSTITUTION:Terminal devices are connected to the double loop transmission line through transmission controllers 11-16 and 21-26. Either a large loop 1 or 2 is utilized normally for transmission. If a specific line or transmission controller is at fault a large loop check (for loop 1 or 2) and small loop check (check among adjacent transmitters, e.g., check of a small loop among devices 22, 23, 12 and 13) are executed to form automatically the loopback constitution. If transmitters 14, 21 are at fault detour transmission lines 200, 300 for the loopback take part in the transmission line and a packet is circulated permanently within this small loop. Thus, the packet is provided with an area counting the number of detours and when the number reaches a prescribed number or over, the transmission of the said packet is stopped.

A single-chip 300 baud FSK modem

Abstract: A 300-baud single-chip FSK modem implementing an RS-232 interface handshaking protocol is described. The device is a full duplex asynchronous modem that meets both Bell 103 and CCITT V.21 specifications. It incorporates the protocol required for automatic answer/originate, loss of carrier termination, and a 14-s abort timer. The device also implements analog and digital loopback capabilities for local and remote testing, respectively. The chip is implemented using a double-poly CMOS technology and uses a standard 3.58-MHz colorburst TV crystal. Inclusion of the handshaking protocol facilitates interfacing the modem to a standard RS-232 interface in stand-alone applications, or a UART in other applications, where the modem is integrated into the data terminal equipment.

Loop communication system

Abstract: PURPOSE:To attain such as linking and loop back processing of a node with high reliability in a short time by applying a signal to a main and a sub-transmission lines in opposite direction with each other and switching the transmission line based on the information about signal interruption of the main and sub- transmission lines at each node and the state of a communication control circuit of the node. CONSTITUTION:A communication station (control node) 1 performing system synchronism and the management of connecting state of communication stations (nodes) or the like and the nodes 2-4 are connected in a loop by the main transmission line 102 and the sub-transmission line 102. Signals are applied in opposite direction to the main and the sub-transmission lines 102, 102 respectively. The nodes 2-4 are provided with a signal detecting circuit supervising the state of transmission lines. Each node performs logical processing based on the information obtained from the signal detecting circuit and the information representing the state of the communication control circuit of the nodes. The changeover of the transmission lines is attained by the result.

Loop-back system

Abstract: PURPOSE:To reduce the constitution of hardware and to place the whole system in a loop-back state by exactly the same method as a normal data transfer method without stopping the system by connecting a transmission side to both transmission lines of a stand-by system and an operation system when a loop- back command is received. CONSTITUTION:A transmitter 4 is used as a data transmitter which monitors a loop or controls the system, and it is assumed that a new data transmitter is installed additionally between the data trasnmitter 1 and a data transmitter 2. A data transmitter 4 performs transmission firstly; to the frame data transmitter 1 which has a loop-back command (LOPBACKA) for connecting an operation system transmission line to a recetion side and a stand-by transmission line to a transmission side, and a frame receiving circuit 91 performs reception. The frame receiving circuit 91 confirms that this frame is addressed to this station (data transmitter 1) and receives the frame of the command LOOPBACK A. This frame is never supplied to the low-order station.

Loopback device for a data communication system on a multiplex link

Abstract: For each time window within which data are transmitted and received over the multiplex link, a loop control bit is set to one state to indicate whether the operating mode is normal or looped. This bit determines the transmission of data either to the link or to a test reception circuit, by logic based on four switches which are normally closed and two normally open. The bit is transferred to a register controlling the states of the switches and when a test loop is required, the first four switches are opened and the other two are closed accordingly. The bit is transferred to a register controlling the states of the switches and when a test loop is required the first four switches are opened and the other two are closed accordingly.