We present the design and implementation of the Emulated Network Device (END), a network adapter design tool that facilitates accurate evaluation of alternative adapter designs. Using device emulation, the END permits designers to couple a representative model of an adapter with a real host and its communication software. Different adapter designs can be evaluated and compared accurately in a realistic setting, i.e., while capturing host-adapter concurrency and interaction overheads, before building a prototype. We present the architectural framework adopted by the END and demonstrate its feasibility via a case study of a commercial network adapter. Several design improvements to alleviate performance bottlenecks are realized and evaluated using the END, highlighting its utility as a network adapter design tool.

We propose architectural mechanisms for structuring host communication software to provide QoS guarantees. We present and evaluate a QoS sensitive communication subsystem architecture for end hosts that provides real time communication support for generic network hardware. This architecture provides services for managing communication resources for guaranteed QoS (real time) connections, such as admission control, traffic enforcement, buffer management, and CPU and link scheduling. The architecture design is based on three key goals: maintenance of QoS guarantees on a per connection basis, overload protection between established connections, and fairness in delivered performance to best effort traffic. Using this architecture we implement real time channels, a paradigm for real time communication services in packet switched networks. The proposed architecture features a process per channel model that associates a channel handler with each established channel. The model employed for handler execution is one of "cooperative" preemption, where an executing handler yields the CPU to a waiting higher priority handler at well defined preemption points. The architecture provides several configurable policies for protocol processing and overload protection. We present extensions to the admission control procedure for real time channels to account for cooperative preemption and overlap between protocol processing and link transmission at a sending host. We evaluate the implementation to demonstrate the efficacy with which the architecture maintains QoS guarantees on outgoing traffic while adhering to the stated design goals.

We propose architectural mechanisms for structuring host communication software to provide QoS guarantees. In particular, we present and evaluate a QoS sensitive communication subsystems architecture for end hosts that provides real time communication support for generic network hardware. This architecture provides services for managing communication resources for guaranteed QoS (real time) connections, such as admission control, traffic enforcement, buffer management, and CPU and link scheduling. The design of the architecture is based on three key goals: maintenance of QoS guarantees on a per connection basis, overload protection between established connections, and fairness in delivered performance to best effort traffic. Using this architecture we implement real time channels, a paradigm for real time communication services in packet switched networks. We evaluate the implementation to demonstrate the efficacy with which the architecture maintains QoS guarantees while adhering to the stated design goals. The evaluation also demonstrates the need for specific features and policies provided in the architecture.