Design, implementation, and evaluation of a software-based real-time Ethernet protocol

Distributed multimedia applications require performance guarantees from the underlying network subsystem. Ethernet has been the dominant local area network architecture in the last decade, and we believe that it will remain popular because of its cost-effectiveness and the availability of higher-bandwidth Ethernets. We present the design, implementation and evaluation of a software-based timed-token protocol called RETHER that provides real-time performance guarantees to multimedia applications without requiring any modifications to existing Ethernet hardware. RETHER features a hybrid mode of operation to reduce the performance impact on non-real-time network traffic, a race-condition-free distributed admission control mechanism, and an efficient token-passing scheme that protects the network against token loss due to node failures or otherwise. To our knowledge, this is the first software implementation of a real-time protocol over existing Ethernet hardware. Performance measurements from experiments on a 10 Mbps Ethernet indicate that up to 60% of the raw bandwidth can be reserved without deteriorating the performance of non-real-time traffic. Additional simulations for high bandwidth networks and faster workstation hardware indicate that the protocol allows reservation of a greater percentage of the available bandwidth.