The END : Exploring QoS Issues in Adapter

A new class of applications with stringent quality of service (QoS) requirements on communication (e.g., bandwidth, delay) are being made possible by the advent of high-speed networks. End-to-end communication performance is largely determined by a variety of factors, such as the underlying network technology, the end-host operating system, and the interface between the host and the network. As network speeds increase, the performance bottleneck tends to shift to the end host, especially to the hardware/software components of the communication subsystem. In this paper , we focus on the design of one such component, the network adapter, and how it interacts with the host communication software to provide QoS guarantees. In particular, we explore QoS issues in adapter design via an Emulated Network Device (END) that interfaces to a real communication protocol stack. The END can emulate all the operations required of a network adapter, without interfacing to a real network. This allows us to model the behavior of a host and its interaction with a network model of our choice. In general, network device emulation permits designers to experiment with network adapter and host interface design, including the partitioning of functionality between the host communication software and the hardware//rmware on the network adapter, before actually developing a prototype implementation of the adapter. More importantly, the experimentation can be carried out on the target host platform, thus accounting for software overheads and host architectural features that innuence communication performance. We present the design and implementation of END and demonstrate its utility by studying the performance of our implementation of real-time channels, a model for provision of QoS guarantees in packet-switched networks. Any opinions, ndings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reeect the views of the funding agencies.