Internet protocols currently use packet-level mechanisms to detect and react to congestion. Although these controls are essential to ensure fair sharing of the available resource between multiple flows, in some cases they are insufficient to ensure overall network stability. We believe that it is also necessary to take account of higher level concepts, such as connections, flows, and sessions when controlling network congestion. This becomes of increasing importance as more real-time traffic is carried on the Internet, since this traffic is less elastic in nature than traditional Web traffic. We argue that, in order to achieve better utility of the network as a whole, higher level congestion controls are required. By way of example, we present a simple connection admission control (CAC) scheme which can significantly improve the overall performance. This paper discusses our motivation for the use of admission control in the Internet, focusing specifically on control for TCP flows. The technique is not TCP specific, and can be applied to any type of flow in a modern IP infrastructure. Simulation results are used to show that it can drastically improve the performance of TCP over bottleneck links. We go on to describe an implementation of our algorithm for a router running the Linux 2.2.9 operating system. We show that by giving routers at bottlenecks the ability to intelligently deny admission to TCP connections, the goodput of existing connections can be significantly increased. Furthermore, the fairness of the resource allocation achieved by TCP is improved.

In the management of a modern LAN or campus network, two issues are of key importance, namely network performance and capacity planning. In this paper we report on results from an experimental programme which aims to quantify the performance that can be achieved with a real distributed application running over a range of different network technologies, including Ethernet, ATM, FDDI, and a 100 Mb/s packet-switched LAN. In particular we analyse the contribution of each of the various application and network components to the overall performance experienced by applications.

In the management of a modern LAN or campus network, two issues are of key importance, namely network performance and capacity planning. In this paper we report on results from an experimental programme which aims to quantify the performance that can be achieved with a real distributed application running over a range of different network technologies, including Ethernet, ATM, FDDI, and a 100 Mb/s packet-switched LAN. In particular we analyse the contribution of each of the various application and network components to the overall performance experienced by applications. This information will facilitate planning and management of new networks, and permit the identification of "hidden costs" which prevent currently deployed applications from fully exploiting high bandwidth networks.

An approximate model of an asynchronous transfer mode (ATM) multiplexer is constructed and used to compare the performances of static and dynamic resource allocation schemes. Static allocation parameterizes a source at connection setup only, whereas dynamic allocation requires a source to inform the multiplexer whenever its bandwidth requirements change. A simple dynamic renegotiation protocol is analyzed, and bounds on the performance of an optimal dynamic protocol are derived. Markovian source models parameterized from working applications are used to contrast the behavior of the three control schemes.>