Network applications such as FTP, WWW, Mirroring etc. are presently operated with little or no knowledge about the characteristics of the underlying network. These applications could operate more efficiently if the characteristics of the network are known and/or are made available to the concerned application. But network characteristics are hard to come by. The IP Performance Metrics working group (IETF-IPPM-WG) is working on developing a set of metrics that will characterize Internet data delivery services (networks). Some tools are being developed for measurements of these metrics. These generally involve active measurements or require modificationsin applications. Both techniques have their drawbacks. In this work, we show a new and more practical approach of estimating network characteristics. This involves gathering and analyzing the network's experience. The experience is in the form of traffic statistics, information distilled from management related activities and ubiquitously available logs (squid access logs, mail logs, ftp logs etc. ) of network applications. An analysis of this experience provides an estimate of the characteristics of the underlying network. To evaluate the concept we have developed and experimented with a system wherein the network characteristics are generated by analyzing the logs and traffic statistics. The network characteristics are made available to network clients and administrators by Network Performance Metric (NPM) servers. These servers are accessed using standard network management protocols. Results of the evaluation are presented and a framework for efficient operation of network operations, using the network characteristics is outlined.

Providing a fair allocation of bandwidth among different connections over the Internet without affecting link efficiency has been a challenging issue in the area of network performance improvement. Congestion signaling is essential for the purpose. Conventional TCP uses packet loss as an implicit indication of congestion. Several enhancements to TCP have been proposed for faster congestion recovery and thus to improve the network performance. However, packet loss reduces TCP goodput and adds large delay. Also the variance in the share of bandwidth obtained by each connection may become unaccepatbly high. To the contrary, Explicit Congestion Notification (ECN) indicates a congestion explicitly before it actually occurs. Therefore, ECN facilitates a faster congestion detection and contributes to the network performance improvement. In this paper, we consider the performance implications of employing different ECN strategies along with several TCP enhancement schemes. We also introduce a new ECN packet marking strategy FIM and evaluate its relative performance and suitability for deployment along with different TCP enhancements. Simulation results show the superiority of FIM over other existing marking strategies with different TCP enhancement schemes by providing the best fairness without hampering link efficiency. We also observe FIM maintains a more consistent delay bound than other strategies and as such, is more suitable for application in practical purposes.