RETHER: A Software-Based Real-Time Ethernet Protocol


TTzi-cker Chiueh
Computer Science Department, SUNY at Stony Brook

RETHER is a software-based token passing protocol that provides bandwidth guarantee over off-the-shelf Ethernet hardware. It switches between the CSMA mode and the token-passing mode transparently depending on whether there are real-time connections on the Ethernet segment. Each user application can dynamically reserve a distinct amount of bandwidth. RETHER provides a race-condition-free distributed admission control mechanism for network resource management. In addition, by carefully tuning the total real-time bandwidth allocation, the performance impacts on non-real-time traffic is reduced to the extent that won't disturb high-level protocols. In the past year, we have improved the original RETHER implementation by porting it over a Fast Ethernet link, as well as extending it to a switched Ethernet environment that consists of multiple heterogeneous 10-Mbps and 100-Mbps Ethernet segments. We have found several interesting issues during this process, including fault tolerance, token overhead estimate, and switch scheduling. At this point, we have a fully operational RETHER network running it the lab, and we have applied it to the Stony Brook Video Server to provide an end-to-end bandwidth guarantee from the server's disk subsystem, through the multi-hop RETHER network, to the clients' displays. In this presentation, I will discuss the lessons we have learned in this project, how it can serve as a building block for RSVP, and outline the ongoing work in extending RETHER to wireless LANs and in implementing a RETHER-based Ethernet switch.