Performance modeling and optimization of interconnected ethernets

An internetwork of LANs is modeled as a graph with LAN segments as edges and transparent bridges and repeaters as nodes. The graph model leads to a simple expression for the effective load on an arbitrary LAN segment, which takes into account the overhead traffic due to the learning mechanism of the transparent bridges. Simplifying assumptions for the operation of the medium access control (MAC) layer protocol lead to a simple expression of the average end-to-end delay in terms of the effective loads on the LAN segments. The problem of optimally locating bridges and repeaters on the nodes in order to minimize the average delay is studied. This problem is equivalent to the set partitioning problem which can be readily solved with state-of-the-art algorithms. Minimizing cost subject to a constraint on average end-to-end delay is discussed. Locating bridges and repeaters on a linear topology, as typically found in an office building with a large number of floors, is also studied.