An Ada Runtime System Implementation of the Ravenscar Profile for High Speed Application-Layer Data Switch

The Top Layer Networks AppSwitch is a coordinated hardware and software Layer 7-application switch designed to provide User and Application Quality of Service (QoS) and Operational Automation for data communication networks by automatically prioritizing network traffic according to the application to which the traffic belongs. The AppSwitch software was developed in Ada95 (A companion paper describes how that software was built [1]). The nature of the application and the need for efficiency has dictated that the use of multiple task communication and synchronization be kept simple and straightforward. As a result, the communication and synchronization needs are very similar those defined in the Ravenscar Profile. Top Layer Networks found it necessary to construct an Ada runtime system that efficiently supported the Ravenscar Profile. The construction strategy was to tailor the GNAT runtime system in three ways: (1) Simplify the functionality of the Ada specific layer of the runtime system to support only the Ravenscarlike profile; (2) Reduce number and the “thickness” of layers in GNAT runtime system; and (3) Construct a POSIX-compatible “kernel” that is simplified for bare machine execution. The paper will describe the details of Ravenscar Profile runtime design and will summarize the impact of this runtime system on the performance of AppSwitch software.