Abstract: A transmitting unit includes a plurality of ports, and transmits a monitor packet from a port corresponding to a target network to be monitored. An extracting unit extracts transmitted monitor packet from received packets. A judging unit judges whether a loop is formed in a network that is configure by connecting a plurality of communication devices, based on a transmission-source address of extracted monitor packet. A blocking unit blocks, when it is judged that the loop is formed in the network, the port from which the monitor packet has been transmitted.

Abstract: Network monitoring device and method whereby the user can be given an alarm before a guaranteed limit of packet routing is exceeded. Counting section counts the number of nodes based on packets exchanged between the nodes, and comparing section compares the node count with an allowable value. If the node count is larger than the allowable value, alarm output section outputs a message that the node count is excessively large.

Abstract: A ring network has first and second network connecting offices for connecting ring networks together and for dropping a signal from a terminal office. Each node of the ring network recognizes whether it is the first network connecting office based upon channel setting information. A first node, which has been recognized as being the first network connecting office, executes a squelch-table creation procedure between itself and other nodes based upon the channel setting information, thereby identifying a second node, which is the second network connecting office. The first node embeds office identification information in a squelch table of a protection channel and sends this information to the second node. The second node recognizes that it itself is the second network connecting office based upon the office identification information.

Abstract: Network monitoring device and method whereby the user can be given an alarm before a guaranteed limit of packet routing is exceeded. Counting section counts the number of nodes based on packets exchanged between the nodes, and comparing section compares the node count with an allowable value. If the node count is larger than the allowable value, alarm output section outputs a message that the node count is excessively large.

Abstract: A ring network has first and second network connecting offices for connecting ring networks together and for dropping a signal from a terminal office. Each node of the ring network recognizes whether it is the first network connecting office based upon channel setting information. A first node, which has been recognized as being the first network connecting office, executes a squelch-table creation procedure between itself and other nodes based upon the channel setting information, thereby identifying a second node, which is the second network connecting office. The first node embeds office identification information in a squelch table of a protection channel and sends this information to the second node. The second node recognizes that it itself is the second network connecting office based upon the office identification information.

Abstract: A protocol conversion system is provided to secure a highly reliable and smooth data communication between different two types of networks whose protocols differs in types from each other. A protocol conversion between such networks is realized by replacing headers added to communication data. Information indicating that sending data was success or failure in transmission is included in the headers, thereby sending results being recognized. A serial interface intervenes between the self and party systems in order to detect states of the party system. Further, for data communication, without processing (or terminating) layers up to an application layer, only lower layers, that is, a transport layer and layers lower than it, are processed (or terminated) to raise reliability in data communication.