Abstract: A clock synchronization system synchronizes a clock of a slave node with a clock of a master node. The master node includes a packet transmitting unit that transmits a packet including a time stamp (TS) to the slave node. The slave node includes: a packet receiving unit that receives the packet transmitted from the master node; a packet filter unit that calculates as a value of delay of the packet a difference between a TS on the clock of the slave node when the packet is received and the TS of the packet received, corrects the value of the delay of the packet or a threthold for the delay of the packet, and performs filter processing on the packet received from the packet receiving unit based on the value of the delay of the packet and the threshold for the delay of the packet; and a phase synchronization unit that outputs the clock of the slave node based on the TS included in the packet employed.

Abstract: A node that configures a spanning tree over a network to which a plurality of nodes are connected generates a tree after a cost change using another LAN while continuing to operate the tree that existed before the change, and switches the tree that is used for forwarding after the new tree has been stable.

Abstract: A node that configures a spanning tree over a network to which a plurality of nodes are connected generates a tree after a cost change using another LAN while continuing to operate the tree that existed before the change, and switches the tree that is used for forwarding after the new tree has been stable.

Abstract: The clock synchronization accuracy between a master node and a slave node is stably measured. The slave node synchronizes its own clock with the clock of the master node by means of the packets transmitted from the master node. It reproduces the clock of the slave node by means of the transmitted packets, accumulates information on the transmitted packets and the clock of the slave node and performs clock synchronization on the basis of the accumulated information.

Abstract: For eliminating a reduction in throughput in a network as a whole according to optimum path transfer technique which is the expansion of spanning tree protocol, a frame switching unit of the network has an STP control unit for, when a port state of a spanning tree is changed, notifying a table control unit of an identifier of the spanning tree and a port number of a predetermined port among the respective ports, the table control unit for setting, in a forwarding table storage unit, a received port number of a predetermined port as an output port in an entry in which a node ID is equivalent to a spanning tree identifier, and a table search unit for determining an output destination from among output ports obtained by acquisition of received frame information from a frame analysis unit.

Abstract: A node to relay the Ethernet frame provided with means to insert, in the relay process of the frame, two or more VLAN tags into the frame at a time and to remove the inserted VLAN tags wherein a TTL area to show the frame survival time is provided in the VLAN tag to be inserted to the frame so that whether the survival time has been elapsed or not is checked by the value in the TTL area and the frame after elapse of the survival time is discarded without being relayed.

Abstract: In a communication system in which a plurality of communication terminals sequentially transfer data to a server during the respective transmission permissible periods assigned to the respective communication terminals, the communication terminal transfers a preamble for synchronization to the server at a time of starting the transmission permissible period, converts a data frame for every 8 bits into every 10 bit-code, and transmits to the server, the signal string with a code indicating the head added there, during the transmission permissible period, and turns a communication to the server into a zero signal state, during a period other than the transmission permissible period, while the server establishes a synchronization by reading the preamble for synchronization inserted into the signal string received from each of the communication terminals, converts a portion of the zero signal state of the signal string into a predetermined special code string, and inversely transforms the received signal string i

Abstract: A clock synchronization system includes a master node; a PSN (Packet Switched Network); and a slave node configured to synchronize a recovery clock signal in the slave node with a clock signal in the master node by using packets periodically received from the master node through the PSN.

Abstract: The frame switching unit 630 has the frame analysis unit 700, the frame rewriting unit 710, the frame transfer unit 720, the table search unit 730, the forwarding table 740, the MAC learning unit 750, the control frame distribution unit 760, the setting control unit 790, the STP control unit 780 which, when receiving a topology change message, converts an LT flag from 0 to 1 to indicate an entry as of before switching to leave the entry in the table, and the OAM control unit 770 which, upon an LT execution request before failure switching, transfers an LT frame according an output port in an entry whose LT flag is 1 among entries in the forwarding table 740.

Abstract: A node of a spanning tree system operating on a network connecting a plurality of nodes, comprises two transfer units which determines an output destination port, based on the destination MAC address of an input frame, two tree managers which configures a spanning tree according to a spanning tree protocol, and a virtual port of connecting the tree manager and the transfer unit.

Abstract: Provided in the EoE technique are the node, the network, the correspondence relationship generating method and the frame transfer program to avoid traffic concentration on a specific link to improve throughput of the network as a whole by realizing optimum path transfer. The frame switching unit includes the frame analysis unit for analyzing an input frame kind and the like, the table search unit for obtaining frame rewriting information and output port information, the forwarding table storage unit for managing an output port of a frame, the MAC learning unit for executing MAC address learning, the EoE-MAC learning unit for learning a relationship between a MAC address and an EoE-MAC address, the STP control unit for executing processing of a spanning tree, and the like.

Abstract: The invention enables protection of a ring frame transferred via an inter-ring bridge ring node when a fault occurs at the node in a multiring. Ring nodes form a ring protection domain to enable one ring node to be bypassed by using other ring nodes when a fault occurs at this ring node. The TTL value of ring frame to be transferred through the bypass is set to a value obtained by adding the number of hops h to the faulty ring node to a common initial value A in the same two-fiber ring to enable detection of a characteristic TTL value at a bypassing ring node. The bypass for the ring frame is selected with reference to the characteristic TTL value at the bypassing ring node.

Abstract: A node that configures a spanning tree over a network to which a plurality of nodes are connected generates a tree after a cost change using another LAN while continuing to operate the tree that existed before the change, and switches the tree that is used for forwarding after the new tree has been stable.

Abstract: The invention enables protection of a ring frame transferred via an inter-ring bridge ring node when a fault occurs at the node in a multiring. Ring nodes form a ring protection domain to enable one ring node to be bypassed by using other ring nodes when a fault occurs at this ring node. The TTL value of ring frame to be transferred through the bypass is set to a value obtained by adding the number of hops h to the faulty ring node to a common initial value A in the same two-fiber ring to enable detection of a characteristic TTL value at a bypassing ring node. The bypass fur the ring frame is selected with reference to the characteristic TTL value at the bypassing ring node.

Abstract: A network system in which a network adopting a node redundancy protocol and a network adopting an STP protocol as other protocol for managing a state of a port coexist, which is configured to manage, by the STP protocol as other protocol, a state of a port which belongs to a master node 10 and a backup node 20 forming the network adopting the STP protocol and is under the management of the node redundancy protocol and also under the management of the STP protocol, and in which the master node 10 or the backup node 20 transmits a Hello message as a control frame for monitoring a node and a link to all or a part of nodes connected to the port under the management of the node redundancy protocol, as well as transmitting a Flush message as a control frame for rewriting a forwarding database to all or a part of nodes connected to the port under the management of the node redundancy protocol at the time of switching to a master mode.

Abstract: A packet communication system is constructed with a plurality of terminal side devices and a network side device including a dynamic identifier assigning portion 141 and a time slot allocation portion 1242. The dynamic identifier assigning portion 141 transmits an identifier information assigned to the respective terminal side devices in an initial setting state to the respective terminal side devices by means of a control signal. When an identifier assignment release request is received from an identifier control portion 100 of the terminal side device in a usual state, the dynamic identifier assigning portion changes the state of an identifier assigned to the terminal side device to the non-assigned state.

Abstract: A base node (100) and a base node (101) transmit a keep alive frame broadcast by a relay node forming a communication medium (106) and a communication medium (107) from a port 1 and a port 2, monitor an arrival state of the keep alive frame at each port, and in normal operation, assume the two communication media connected to the port 1 and the port 2 as one node to expand a communication band and at failure detection, continue communication by using only a communication medium connected to a port at which no failure is detected.

Abstract: A communication system includes a server and a plurality of terminals. The server repeatedly assigns transmission periods to the terminals in a regular order, each of the terminals being permitted as a current terminal to transmit data stored in a buffer thereof to the server during an assigned transmission period assigned thereto by the server as a current transmission period. The communication system includes: a transmission controller provided in each of the terminals for transmitting a release request notification to the server in a case where the terminal finishes data transmission before the end of the assigned transmission period assigned to the terminal, and a transmission period assigning portion provided in the server for assigning a next transmission period following the current transmission period to a next terminal different from the current terminal, in response to the release request notification.

Abstract: The present invention comprises a plurality of terminal-side apparatuses each having a buffer, a queue length notification module, and an output control module, and a network-side apparatus having a fairness guarantee/high efficiency hybrid time slot assignment control module (FG/HE HTSAC module). The FG/HE HTSAC module assigns time slots to all or a part of the terminal-side apparatuses in accordance with a fairness criteria. If the number of the time slots assigned exceeds a queue length for one or more terminal-side apparatuses, leftover time slots are reassigned among the terminal-side apparatus(es) where the number of the time slots assigned thereto does not exceed a queue length. The result of reassignment is notified to an output control circuit that controls output of cells from the buffer.

Abstract: In a communication network, end-user systems are connected via a common transmission medium to a timeslot assignment unit. Each end-user system has a buffer for storing packets, and a queue length detector for detecting a queue length of the stored packets. The end-user system forwards packets on assigned timeslots to the network and transmits a signal for indicating the detected queue length to the assignment unit. The timeslot assignment unit maintains timeslot records to store count numbers of assigned timeslots, determines a total count number of timeslots assigned to each end-user system during a period corresponding to the delay time of the unit, and receives a queue length signal from each end-user system. From the total count number and the queue length a virtual queue length is determined for indicating the number of packets to which timeslots are still not assigned. Based on the virtual queue length, timeslots are assigned to each end-user system.