This letter proposes a practical scheme that can estimate ADSL link rates. The proposed scheme allows us to estimate ADSL link rates from measurements made at the NOC using existing communications protocols and network node facilities; it imposes no heavy traffic overhead. The proposed scheme consists of two major steps. The first step is to collect measured data of round trip times (RTT) for both long and short packets to find their minimum values of RTTs by sending Internet Control Message Protocol (ICMP) echo request messages. The second step is to estimate the ADSL down- and up-link rates by using the difference in RTT between long and short packets and the experimentally-obtained correlated relationships between ADSL down- and up-link rates. RTTs are experimentally measured for an IP network, and it is shown that the down- and up-link rates can be obtained in a simple manner.

We describe a scheme of secret communication over the Internet utilizing the potentiality of the TCP/IP protocol suite in a non-standard way. Except for the sender and the receiver of the secret communication it does not need any entities installed with special software. Moreover it does not require them to share any key beforehand. Such features of the scheme stem from the use of IP datagrams with spoofed source addresses and their related error messages for the Internet Control Message Protocol (ICMP) induced by artificial faults. Countermeasures against IP spoofing are deployed in various places since it is often used together with attacks such as distributed denial of service (DDoS) and SPAM mailing. Thus we examine the environment where the scheme works as an intention and also clarify the conditions to obsolete the scheme. Furthermore we estimate the amount of secretly communicated data by the scheme and storage requirements for the receivers and those for the observers who monitor the traffic to detect the very existence of such a secret communication. We also discuss various issues including the sender anonymity achieved by the scheme.

Network traffic contains many symptoms of various network faults. Symptoms of faults aggregate and are manifested in the aggregate traffic characteristics generally observed by a traffic monitor. It is very difficult for a manager or an NMS (Network Management Station) to isolate the symptoms manifested in the aggregate traffic characteristics. Especially, transit networks, like a backbone network, deal with many types of traffic. So, symptom isolation must be efficient. In this paper, we propose a powerful algorithm for symptom isolation. This algorithm is based on the popular SNMP-based RMON technology. Using dynamically constructed aggregate, fresh symptoms can be isolated efficiently. We apply the algorithm to two operational transit networks which connects some LANs and WANs, and evaluate it using trace data collected from these networks. The results show a significant improvement in the fault management capability and accuracy. Furthermore, the characteristics of fault symptoms and the various factors for effective system configuration are discussed.