QoS management at the transport layer

This work reports on further implementation and testing of the Application Oriented Transport Protocol (AOTP). AOTP is an experimental protocol above IP that provides end-to-end transport service with functionality to trade off reliability, throughput and/or jitter in order to support the application layer with the required quality of service. Our protocol, based on QoS tradeoffs, can favor application and/or user-specific QoS characteristics of importance, at the expense of others, less significant. We outline the protocol's specification and mechanisms. AOTP provides an adjustable partially reliable service, priority-based error recovery strategy and dynamic playback management. We have tested the mechanisms using a video transmission application and a simulated, low-bandwidth environment with variable error characteristics. We characterize the tradeoffs associated with these mechanisms; we argue that the application layer can yield significant QoS achievements even within the confines of given environmental constraints, when the transport layer utilizes efficiently the tradeoffs developed in the communication system.