Design and implementation of a real-time switch for segmented Ethernets

Providing network bandwidth guarantees over an Ethernet requires coordination of the network nodes for traac prioritization such that real-time data can have deterministic access to the network. We have shown previously how RETHER, a software-only token passing protocol can eeciently provide real-time support over a single shared Ethernet segment. This work extends the token passing mechanism into a switched, multi-segment Ethernet environment. This paper describes the detailed design issues involved in supporting bandwidth guarantees across multiple segments, their solutions, and a fully operational implementation built into the FreeBSD UNIX kernel. By testing the protocol independently and as the underlying network protocol of the Stony Brook Video Server, we have veriied that the bandwidth guarantees are successfully provided, with relatively low run-time overhead, for real-time connections crossing multiple Ethernet segments. In this paper, we present our implementation experiences as well as the results of a comprehensive performance evaluation of the prototype system.