Networks have complex systems comprised of subsystem components like servers for various kinds of service and DCE (Data Communication Equipment) such as routers and switches. As each system operates constantly, it is hard to know exactly how the whole network operates. The network monitoring system, therefore, is required, in addition to monitoring and checking the network under steady operation, to detect system failures, weigh the situation and investigate into the cause. In this paper, we propose a method that we convert the three kinds of data, data by polling the server externally, data from computer resource of the server, and data from log information of the network server, into an integrated format, and then assemble them as generalized log format, so that we can extract the abnormal events without providing the monitoring system with any data such as key words, in advance. Firstly, we identify the patterns of frequency of the words by text-mining of the log information. Secondly, by means of signal processing of the frequency, periodically appeared patterns are figured out. Lastly, these patterns are associated with each other to presume the cause of the abnormal events. Our proposed method should support network administrators greatly in detecting system failures and investigating into the cause, and also reduce a lot of workload in monitoring log information.

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Conventional TCP suffers throughput deadlocks over congested ATM (Asynchronous Transfer Mode) networks due to retransmission timeouts caused by cell loss at ATM level under heavy congestion. A modified congestion control algorithm for TCP is proposed to improve the effective throughput of IP over ATM UBR even in a situation such that an external CBR pressure exist at the same port of the ATM switch. When TCP faces congestion then TCP will reset its retransmission timer. In the proposed algorithm, the MSS (maximum segment size) is reduced from 9140 bytes, the recomended value in RFC 1612, at the same time. When TCP is in fast retransmit machine phase, the MSS is reduced to 512 bytes. A considerable improvement in the effective throughput of TCP has been achieved by these two modifications under relatively small switch buffer size and high CBR stream pressure. The idea, called “Dynamic Granularity Control (DGC)”, have been implemented and evaluated on the Linux kernel.

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We propose a new framework for stateless auto-configuration of IPv6 site-local addresses with “zero configuration.” When a router is connected to a link as the first router, it becomes the link leader and generates an address prefix with randomly generated 16-bit subnet ID for the segment. In order to assure the uniqueness of the prefix addresses, we show a protocol, which is an extension of RIPng, for detecting prefixes conflicts. When a conflict is detected, it is notified to its segment leader immediately. The segment leader generates a new prefix and renumber to new one via IPv6 address renumbering scheme. And, exploiting the IPv6 feature that multiple addresses can coexist on an interface, we realize such a routing algorithm that can protect the connections using old addresses for a fixed time.

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