Showing papers on "Loopback published in 1991"

Full duplex digital transmission facility loop-back test, diagnostics and maintenance system

Abstract: A full duplex digital transmission, high-capacity digital, facility loop-back test, diagnostics and maintenance system having a digital transmission facility, transmission medium, and at least one microprocessor-based, full duplex facility loop-back diagnostics interface is located at predetermined end-user locations within the system. The system is capable of initiating a facility loop-back test and predetermined diagnostics for a predetermined digital transmission span and customer premises equipment at the location of the network interface for a specified end-user. The facility loop-back diagnostics interface has a performance monitoring mode of operation and a maintenance facility loop-back mode of operation. The diagnostics interface can be activated from a remote location and is compatible with and supports a particular protocol, specifically LAP-B protocol. The diagnostics interface has integral performance monitoring capabilities for nonintrusive multiple diagnostics testing and on-line monitoring of multiple predetermined performance characteristics for associated DS1 communications channels, or a specified DS1 communications channel, and customer premises equipment at the network interface. The microprocessor of the performance monitoring unit for the facility loop-back diagnostics interface is synchronized with an internal clock that is driven by conventional power. There is also a long-life battery for preventing historical performance data from being corrupted during a power loss. When the diagnostics interface is in the performance monitoring mode of operation, historical performance data pertaining to predetermined performance characteristics and criteria can be retrieved by utilizing the extended superframe, or superframe, embedded operations channel.

Generic encryption technique for communication networks

Abstract: A method and related cryptographic processing apparatus for handling information packets that are to be cryptographically processed prior to transmission onto a communication network, or that are to be locally cryptographically processed and looped back to a node processor. A special cryptographic preamble is included in each information packet that is to be subject to cryptographic processing. The cryptographic preamble contains an offset value pointing to the starting location of information that is to be processed, and completely defines the type of cryptographic processing to be performed. The cryptographic processor can then perform the processing as specified in the preamble without regard to a specific protocol. If the packet is to be transmitted onto the network, the preamble is stripped from the packet after cryptographic processing, so that the formats of packets transmitted onto the network will be unaffected by the preamble. Cryptographic processing modes include encryption of data for outbound transmission, encryption of a cipher key for loopback to the node processor, encryption or decryption of data for loopback to the node processor, and computation of an integrity check value for loopback to the node processor.

System for testing 2B1Q telephony loopback circuits and method therefor

Abstract: A system for testing 2B1Q private line data telephony circuits having 2B1Q modulation between the network channel termination equipment and the channel unit. 2B1Q modulation is provided over a single pair of wires connected to the E and M leads of the channel unit. The system can deliver testing signals from two different sources. The first source is from a remote testing system connected to a remote access system which in turn is connected to the T, T1, R, and R1 output leads of the channel unit. The remote testing system generates conventional testing signals which are converted into digital signals for directly communicating with the 2B1Q pair of wires. The remote testing system delivers conventional tests for testing the loopback of the channel connected to the single pair of wires and to the network channel termination equipment. Under a second source of tests, the interface of the present invention directly connects to the T1 carrier. Testing digital signals are delivered from a distant source into the interface which are then delivered to the 2B1Q channel between the channel unit and the network channel termination equipment for performing loopback testing of the private line data circuit there between.

Analog transmission radio equipment

Abstract: PURPOSE: To facilitate the discrimination of a fault location by integrating a fault self-diagnosis function (BITE) in the radio equipment with respect to the analog transmission radio equipment of a press-to-talk type making transmission reception with the same radio frequency. CONSTITUTION: The radio equipment is provided with a base band section 11 of a transmission system 1, a modulation section 12, a frequency conversion section 13, loopback switches 41-44 looping back an output of an RF section 14 respectively to a base band section 21 of a reception system 2, a demodulation section 22, a frequency conversion section 23, and an input of an RF section 24, an amplitude phase adjustment section 5 adjusting a signal SBOUT looped back by the loopback switches 41-44 and outputted from the base band section 21 of the reception section 2 so that the signal is equal to a test signal SBIN inputted to the base band section 11 of the transmission system 1, and a fault discrimination section 6 discriminating it to be the occurrence of a fault in a loopback path when a difference between the test signal SBIN and an output SBOUT from the amplitude phase adjustment section 5 exceeds a prescribed threshold level V th . COPYRIGHT: (C)1993,JPO&Japio

OAM mechanisms for BISDN UNI and access networks

Abstract: This paper clarifies operation and maintenance (OAM) requirements for broadband integrated services digital network (BISDN) customer access systems including user-network interface (UNI), and proposes basic OAM mechanisms. Access networks employ a logical networking architecture based on the asynchronous transfer mode (ATM) virtual path (VP) concept to provide all services efficiently, economically. Services are independent of the network's physical configuration. Thus, OAM functions for the access network are required to support physical and ATM layer capabilities. UNI physical performance and failure information flows to ensure user service quality are described. A fault localization mechanism is introduced that determines whether the failure lies on the network provider side or customer side. It uses failure information flows and loop back testing at the network terminator 1 (NT1). As connection-related virtual path connection (VPC) availability indication is necessary for user-to-network applications and user-to-user applications, two alternative VPC-related availability indication mechanisms are studied. Furthermore, basic performance monitoring mechanisms for ATM layer are described.

Operating system diagnostic system in duplex operation of terminal equipment block

Abstract: PURPOSE:To set active/standby state to a terminal equipment by recognizing an operating system of a terminal station equipment without changeover of the terminal station equipment with respect to the operating system diagnostic system diagnosing the operating system for a terminal equipment block through an I interface. CONSTITUTION:The system is the operating system diagnostic system in terminal equipment block configured in duplicate in which different data A,B are sent from two terminal equipments 2,3 of one station 1 to other station 5 via a terminal station equipment 4 through an I interface, after the other station 5 receives the data A by a terminal equipment 6, the data A are returned to the one station 1 via the terminal station equipment 4 through loopback, the two terminal equipments 2,3 of the one station 1 receive the data A, from which of the two terminal equipments 2,3 the received data A are sent is checked to diagnose the operating system as to which of the two terminal equipments 2,3 is the active system and which of them is the standby system.

Input restriction system in packet exchange network

Abstract: PURPOSE:To prevent overflow, to limit quantity of transfer delay, to use an output path efficiently and to warrant a throughput in response to a request of an input path by detecting an in-header address in a transfer packet with an output circuit, generating a relevant reply packet and outputting it to a loopback path. CONSTITUTION:An input circuit 10 is provided with a transmission control section 101 and a transmission reply packet number management section 102, an output circuit 16 transfers a packet, sent from the input circuit 10 to an output path, a reply packet generating section 163 detects an in-header address in a packet to generate a relevant reply packet and outputs it to a loopback path. The transmission reply packet number management section 102 of the input circuit 10 detects the reply packet and generates an output based on the transmission packet number and the reply packet number and the output allows the transmission control section 101 to apply the transmission control of the packet. Thus, overflow is prevented, the transfer delay is limited and the output path is used efficiently and the throughput in response to the request of the input path is warranted.

Optical fiber cable monitor system

Abstract: PURPOSE:To allow a terminal station to calculate the distance from the terminal station up to a fault point of an optical fiber cable between repeaters by sending a monitor signal from the terminal station to the opposite terminal station, sending a branched output to a loopback return path, superimposing the reflecting wave of a monitor signal from the fault point of an optical fiber cable and supplying the result to the loopback terminal station CONSTITUTION:A switch circuit 9 receives a monitor signal different from a transmission signal at monitor and is closed and loops back part of the monitor signal Then an analog signal pulse carrier shorter than one reciprocating propagation time of each relay block is sent at a longer period more than one reciprocating propagation time of the entire block being an object of monitor as a monitor signal from a terminal station 1 at a fault of an optical fiber cable Moreover, a superimposing signal causing a change in the waveform through the superimposition of a reflecting wave at a cable fault point reflected at a repeater just close to a fault point among a monitor signal group reflected at the switch circuit 9 is received by the terminal station 1 and a distance from the cable fault point is calculated from the timewise change in the superimposing signal Thus, the position of the fault point is calculated at the terminal station 1

Ring reconstitution method for network system

Abstract: PURPOSE:To reconstitute a ring from which a fault station is separated without requiring recognition of a caller address of a beacon frame by applying plural loopback operations through the changeover of main and sub rings in response to the reception state of own station beacon. CONSTITUTION:A transmission reception station 30 detecting a fault of an upstream transmission reception station 20 and starting the transmission of a beacon frame cannot receive own station beacon even after laps of a prescribed time, then 1st loopback 1 is applied to disconnect the station 20. Then a 2nd loopback 2 is applied to the station 20 by the interruption of a ring signal by the loopback 1. Succeedingly, after the end of loopbacks 1, 2, the ring for data transmission is switched from a main ring L0 to a sub ring L1 at each of transmission reception stations 40, 50, 60, 10 and beacon frame is sent by taking the downstream station with respect to the station 20 as the opposite station 10. When the station 10 cannot receive own station beacon even after laps of a prescribed time, 3rd loopback 73 is applied to disconnect the station 20 and a ring restored finally to the main ring is reconstituted and the reliability of system is improved.

High definition television signal decoding system

Abstract: PURPOSE:To improve the picture quality by combining an in-field interpolation processing and an inter-frame temporal filter processing eliminating loopback distortion due to an offset subsampling between frames at the encoder side appearing at a reproducing still picture CONSTITUTION:The interpolation for decoding a MUSE signal at the receiver side is only the in-field interpolation and as to the component of the band caused with loopback distortion by inter-frame offset subsample at encoder side, it is eliminated by using a temporal filter employing a frame memory That is, a difference between the current frame and the preceding frame is taken by a frame memory 3 and a subtractor, resulting that the difference output signal includes the loopback distortion due to the movement and the inter-frame offset subsample Suppose that the distortion exists in 4-8MHz in the MUSE signal, then it is extracted by a 4-8MHz BPF 4, then its output mainly includes the loopback component Then the component is subtracted from the current frame signal to reduce the loopback distortion

Time slot assignment method at loop disconnection of loop communication system

Abstract: PURPOSE:To prevent collision of communication even when a loop is integrated by assigning only a time slot assigned to a station belonging to the loop to the station belonging to the loop after the loop is opened. CONSTITUTION:When a fault takes place in plural locations of a loop communication system, loopback is applied by control candidate stations 33, 37 and normal stations 43, 47 and independent loops A, B are generated, only a preceding control station uses a standby slot fulfillment slot SSVS provided to the control station before loop opening in stations being a control station in each loop successively and a time slot returned from a station STN in the loop is a standby slot fulfillment slot SSVS in the opened loop during the operation of loop opening in other station becoming a new control station. Thus, when a faulty location is restored and the loop is integrated, since the slot of the same address is not in use, the collision of communication does not take place.

Clock synchronizing system at loopback

Abstract: PURPOSE:To prevent a phase locked oscillator from being oscillated by allowing a switching circuit to switch a clock from an N system into an E system with a loopback control signal at the loopback control. CONSTITUTION:A switching circuit 32 usually selects the clock of the N system and gives it to a phase locked oscillator 33. In this case, loopback is formed at the input section of a multiplex/demultiplex circuit 30 at loopback control because of the connection of input and output lines. On the other hand, the switching circuit 32 selects the E system clock from the N system with a loopback(LB) control signal. Since no clock loop through a clock path is formed at loopback, the oscillation of the phase locked oscillator 33 is prevented.

Fault processing method in loop communication system and connection sequence confirming method for station

Abstract: PURPOSE:To easily and surely implement the loopback processing by generating a loopback command, requesting loop connection state information from a control station, and releasing a loopback mode of each station by itself when each station is in the normal mode based on the reply information in response to the loop connection state information CONSTITUTION:When a line discontinuity takes place at a position E in transmission lines 4, 5, a control station 1 sends a loopback command signal simultaneously to stations 2, 3 via the transmission lines 4, 5 and the stations 2, 3 form the loopback loop to be in the loopback mode When the line discontinuity position E is recovered, the stations 2, 3 restore to the normal mode Then the control station 1 sends a command to collect the connection state information of the stations 2, 3 to the transmission line 4 and the stations 2, 3 sends the connection state information to the control station 1 via the transmission line 4 Then the control station 1 releases the loopback mode of the stations 2, 3 when they are in the normal bode based on the connection state information Thus, the loopback processing is easily and surely implemented

Switching control system for master equipment in duplicate loop network

Abstract: PURPOSE:To avoid malfunction of switching control of a master equipment due to a fault of reception of information automatically by providing the switching control depending on the presence of a loopback command in addition to the switching control of the master equipment according to the priority so as to apply relieve processing for the reception fault executed in the loopback control. CONSTITUTION:The system transits to the ACT(active) state without fault when a loopback commend of own node of own system is applied to plural master equipments N0, N1 connecting to nodes of 0, 1 systems of loop transmission lines in duplicate and the system transits the arbitration depending on the priority when no loopback command is given and the arbitration results in the ACT state or an SBY state. Thus, the switching control of the master equipments N0, N1 is implemented correctly without being affected by a reception fault of information.

Loopback data packet system for relay line

Abstract: PURPOSE:To revise a bypass or a data compression ratio, etc., dynamically by defining a loopback data packet on a relay line, transmitting or receiving the loopback data packet and measuring the delay time of the relay line. CONSTITUTION:In the case of the measurement of a delay value, a delay value measuring section A sends a loopback requesting packet 2 to a packet transmission circuit B, from which the packet is sent to a packet exchange G2 by using a local channel number set at every call. A packet reception circuit C of the exchange G2 analyzes a received data packet and generates a loopback reply packet 5 to the packet 2 and the packet is returned to a packet exchange G1 via the circuit B. The packet 5 is analyzed by the circuit C and the result is sent to the measuring section A as the loopback packet 7 to the loopback requesting packet from its own station, then when the measuring section A sends the packet 2, a start timer is stopped. The data being the result of measurement of the timer is outputted as a measurement delay value data 6.

Digital amplitude modulator

Abstract: PURPOSE:To prevent loopback distortion and to simplify the constitution by selecting the relation between carrier frequencies fC and fS2 to be fC=(n/4).fS2 ((n) is an optional number in 1, 3, 5). CONSTITUTION:The relation of 2.fS1=fS2 is selected between a sampling frequency fS1 of a digital modulation wave SD and a sampling frequency fS2 of a digital DSB modulation wave HC and the relation of fC=(1/4).fS2 is selected between a carrier frequency fC of a digital frequency WC and the sampling frequency fS2. Since the loopback component of an original signal component of the spectrum of the digital DSB modulation wave HC is overlapped in the same spectrum, in the same amplitude and the same phase, no loopback distortion is caused and it is not required to provide a loopback elimination filter between an A/D converter 30 and an amplitude modulator 34.

Ring type local area network

Abstract: PURPOSE:To ensure the communication as to a subsequent station located in advance from a area fault occurrence position by providing a standby management station so as to send a command of a loopback to the subsequent station disconnected of an input signal in the occurrence of a fault and allowing the standby management station to execute the loopback processing. CONSTITUTION:A standby management station 4 is connected to a management station 3 by a private line 5 and in the through state normally and releases its through state according to a command sent via the private line 5 from the management station 3 detecting a fault. Then a loopback command is sent to slave stations 1a-1d whose input signal is interrupted and the station 4 executes the loopback processing to reconstitute a new ring from that of the management station 3 while being arranged to a prescribed location in a ring. Thus, the communication between subsequent stations arranged before a fault occurrence location is ensured.

Multi-drop lan forming device

Abstract: PURPOSE:To obtain an inexpensive multi-drop LAN forming device rich in flexibility by providing a coupling/separation switch connecting plural LAN units in cascade, and connecting or disconnecting a common forward path and a common return path to/from an adjacent LAN unit. CONSTITUTION:In order to build up one group of a multi-drop LAN among 3 terminal equipments 14 corresponding to each of 3-stage of LAN units 20, the contacts 29-1, 29-2 of a coupling/separation switch 29 of the LAN unit 20 at the left end are opened. Moreover, the contacts 28-1, 28-2 of a loopback switch 28 of the right side LAN unit 20 are connected to the position of a loopback path 27. A transmission data from a terminal equipment corresponding to the central LAN unit 20 enters a data insertion section 26 through a data forward path 23. Thus, the grouping of the LAN is facilitated by the on/off of the contacts 28-1, 28-2 of the loopback path switch and the contacts 29-1, 29-2 of the coupling/separation switch 29 and the system easily copes with the extension of terminal equipments, as well.

Standby system channel loopback test system

Abstract: PURPOSE:To recognize the presence of occurrence of a fault of a standby system channel quickly by looping back a test data sent from a call processor via a network of a standby system and collating a received data and a test data in the call processor so as to discriminate the propriety of the standby system channel. CONSTITUTION:A loopback means 105 is provided between a demultiplex circuit 103 and a multiplex circuit 102 in a highway interface 101, a call processor 106 communicating a control signal with a line via a network 104 of a digital exchange sends a loopback command to the highway interface 101 of a standby system #1 via a network 104 of a digital exchange to form a loopback path. Moreover, a test data sent from the call processor 106 is looped back via the network 104 of the standby system and the received data and the test data in the call processor 106 are collated to discriminate the propriety of the standby system channel.

Subscriber circuit transmission characteristic measuring adaptor

Abstract: PURPOSE:To reduce a trouble of transmission characteristic measurement by looping back a speech line at a line loopback circuit so as to measure the transmission characteristic of a subscriber circuit when a transmission characteristic measuring equipment is connected to subscriber terminals side of two optional subscriber circuits in a subscriber circuit package. CONSTITUTION:A couple of subscriber circuits to be measured such as subscriber circuits 2a, 2b are selected, an output of an oscillator of a transmission measurement equipment 5 is connected to a subscriber line side of the one subscriber circuit 2a and a level meter of the transmission measurement equipment 5 is connected to a subscriber line side of the other subscriber circuit 2b. Simultaneously a loopback line designation section 1b of a subscriber circuit transmission changeover switch measurement adaptor 1 designates loopback of digital multiplex speech line from subscribers 2a, 2n. Thus, a line loopback circuit 1a loops back the speech line of the subscriber circuits 2a, 2n among digital multiplex speech lines 4 to connect the oscillator of the transmission measurement equipment 5 and the level meter via the two subscriber circuits 2a, 2b to measure the transmission characteristic.

Backup system for modem

Abstract: PURPOSE:To prevent disabled communication due to a fault of a MODEM by applying the operating test with an operation test means as to the MODEM not busy and using a switching control means to supply a switching command to a relevant switch tn response to the result of test CONSTITUTION:A state discrimination means 121 discriminates whether or not each MODEM 103 is busy based on state information outputted from a MODEM 103 An operation test means 122 conducts a test for the confirmation of operation such as a loopback test as to the MODEM 103 not busy to detect a faulty MODEM 103 A switch command is applied to a relevant switch 111 by a switching control means 123 and the relevant MODEM 103 is disconnected by the relevant switch 111 and a line 101 corresponding to the switch 111 is connected to a standby MODEM 104

Transmitter-receiver with loopback test function in its own station

Abstract: PURPOSE:To execute loopback test in its own station by mixing the transmission signal of output frequency of a transmitter coupled with a reception input of a receiver, with part of the output of a transmission local oscillator fed in place of the output of a reception local oscillator to convert the frequency, and outputting a reception signal of an intermediate frequency. CONSTITUTION:A transmission signal of the output frequency Ft of a transmitter 1 coupled with the reception input of frequency Fr of a receiver 2 by a coupling means 10 is mixed with part of the output of a transmission local oscillator 16 fed in place of the output of a reception local oscillator 26 with a switching means 20 at the time of testing, the frequency is converted and the reception signal of an intermediate frequency is outputted. Thus, the loopback test is executed in its own station in operation of the transmitter and the receiver without need of any special frequency converter.

Channel test system

Abstract: PURPOSE:To simplify the constitution of a test circuit and to reduce the number of signal lines by providing a channel test circuit outputting a test data, comparing it with a test data inputted from a sending end so as to verify the normality of a test object channel and a loopback circuit looping back an inputted data and outputting the data to receiving end. CONSTITUTION:The channel test system is provided with a channel test circuit 10 outputting a test data to a receiving end of a digital time division switch network 30, comparing it with a test data inputted from a sending end to verify the normality of a test object channel set between the subscriber circuit 20 or a trunk circuit, a loop back circuit 22 provided in the subscriber circuit 20 and the trunk circuit and looping back a data inputted from the sending end of the digital time division switch network 30 and outputting it to the receiving end. Thus, it is not required to provide a data insertion circuit, a branch circuit and a connection signal line inputting the test data for each subscriber circuit like a conventional channel test system and the channel is tested with simple circuit constitution.

Network changeover device and network control system

Abstract: PURPOSE:To attain quick maintenance processing by providing a loopback circuit between a network controller and a terminal equipment. CONSTITUTION:A loopback circuit 5a is provided between a changeover circuit 4a and an in-premises line 13. That is, the loopback circuit 5a is provided, which loops back a signal sent from a connected network controller to the network controller. Thus, the network controller receives a test signal sent from itself and discriminates whether or not the signal is correctly received thereby discriminating the normality of its own operation. When the communication is not implemented normally regardless of the normality, it is discriminated that a line or a terminal equipment 3 has a fault and it is informed to a center equipment. When it is faulty, it is informed to a remote equipment as faulty communication controllers 2, 2'. Thus, quick maintenance is implemented.

Loop type transmission line fault detection system

Abstract: PURPOSE:To detect a fault and to recognize a faulty terminal station equipment in a short time by allowing a terminal station equipment to compare its own terminal station equipment number with a received number, incrementing a numeral '1' to a number when they are coincident, sending the result to a control channel and allowing a central device to check the number on the control channel CONSTITUTION:A central device 1 gives a number to terminal station equipments 2-6 tied by transmission lines 7, 8 sequentially from number '1' When the numbers are sent from the central device 1 in the ascending order and the number equal to the linked terminal station equipment number is received, the system is normal When the line is faulty on its way, since the system is connected in loopback through the loop transmission line comprising adjacent terminal station equipments 2-6, the number of a faulty terminal station equipment is received by the reverse transmission line 8 Thus, since the central device 1 sends a terminal station equipment number 0 and the equipment number 0 is received through the normal transmission line, the number is distinguished from the number of the faulty terminal station equipment

Loop type optical data communication system

Abstract: PURPOSE:To reduce the number of optical fiber cables and to lower the price by providing a directional coupler to identify the directivity of an optical data signal, to execute the separation and coupling of the optical data signal and to detect the interruption of the optical data signal. CONSTITUTION:When a fault is generated between a terminal station C and a terminal station D, loopback function is immediately operated respectively in the terminal stations C and D themselves and the optical data signal is returned through one optical fiber cable 3. For example, at such a time, the terminal station C receives the optical data signal from a terminal station B through a directional coupler 5d, optical fiber cable 3 and directional coupler 5e. This signal is transmitted through the directional coupler 5e, optical fiber cable 3 and directional coupler 5d to the terminal station B. Accordingly, since a system can be composed only of one optical fiber cable including an auxiliary line for bypass, the cost can be reduced.

Optical loopback system

Abstract: PURPOSE:To confirm the quality assurance of a signal by applying optical loopback automatically on occurrence of a fault and varying a light attenuation factor with an optical attenuator provided to an optical loopback switch. CONSTITUTION:Each of loopback switches 11-14 is provided to each of optical repeaters 5-8 to locate a fault location on the occurrence of an optical transmission line by using the loopback switches 11-14 so as to bring the optical repeaters 5-8 at both ends of repeaters at the fault location into the optical loopback state. Then an optical attenuator is provided to the optical loopback switches 11-14 of the optical repeaters 5-8 to vary the light attenuation rate by the optical attenuator in the optical loopback state thereby self-diagnosing the quality of signal in the optical repeaters 5-8.

Traveling object exchange system

Abstract: PURPOSE:To execute communication outside of network by connecting two mobile sets with a couple of incoming outgoing talking paths of a channel switch and a loopback trunk, implementing simplex communication and looping back the call through the channel switch. CONSTITUTION:A transmission radio wave from a 1st mobile set 1 is received by a base receiver 3 and its voice signal is fed to a channel switch 5. An incom ing path assigned at call from a 1st mobile set 1 or a 2nd mobile set 2 is installed to the channel switch 5. A voice signal is looped back in a loopback trunk 7 connected to the channel switch 5 and fed again to the channel switch 5. The loopback voice signal is fed to the base transmitter 4 through an outgo ing talking path. The transmission radio wave from the base transmitter 4 is received by the 2nd mobile set 2. Moreover, in the case of the connection to an external network, the mobile set connects to an external connection trunk 6 via the channel switch 5 and the mobile set executes duplex communication with an external network telephone set.

Lan ring reconstitution system

Abstract: PURPOSE:To surely reconstitute a ring and to recover a fault even when a fault of a transmission control section in the transmission state of a consecutive fixed pattern by switching a downstream side loopback and an upstream side loopback in response to the reception state of own station beacon. CONSTITUTION:When a transmission reception station 50 detects a fault of an upstream transmission reception station 40 brought into the transmission state of consecutive fixed pattern due to a fault of at control section, the transmission of a beacon frame is started. When the reception of own station beacon is disabled even after laps of a prescribed time, the downstream side ring is subject to loopback 1 and a sub ring B is used for the station 40 to inform a transmission line fault command to apply loopback 2 of the upstream ring. When the station 50 cannot receive the own station beacon even after laps of a prescribed time, the loopback 1 is switched to loopback 3 of a downstream ring and loopback 4 of upstream ring is implemented by the upstream transmission reception station 30. Thus, even when a fault in the transmission station of the consecutive fixed pattern takes place in the transmission reception control section, the ring is reconstituted surely and the reliability is improved.

Packet transfer device

Abstract: PURPOSE:To execute reply reception to an external loopback command independently of a bus traffic by transferring the external loopback reply while an external loopback request sender acquires the bus so as not to acquire a token for each packet transfer. CONSTITUTION:A packet transfer device 11 and a packet transfer device 12 are connected to a bus arbiter 13 with an arbiter bus 14. The bus arbiter 13 makes arbitration to a transmission request from the packet transfer device 11 and the packet transfer device 12 to give a token and the packet transfer device 11 or the packet transfer device 12 acquiring the token transfers a data to the packet transfer device 11 or the packet transfer device 12 being a transmission destination via a packet bus 15. Since a means storing a transmission request of an external loopback request sender acquires a bus, it is not required to acquire the token for each packet transfer to transfer the external loopback request and the external loopback reply. Thus, the reply reception to the external loopback command is implemented independently of the traffic of the bus.