On Using Circuit-Switched Networks for File Transfers

High-speed optical circuit-switched networks are being deployed to support highly demanding applications in the eScience research community. File transfers were identified as an ideal application for high-speed circuits because such transfers can utilize any rate, limited only by end-host capabilities. This paper addresses the question of how a circuit-switched network can be shared efficiently amongst many users for file transfers. Specifically, we study the question of how much bandwidth should be allocated per file transfer so that the system performance averaged across all flows is optimal in terms of mean response time. We explore a heterogeneous bandwidth-allocation scheme, in which bandwidth is allocated based on file sizes, as well as a homogeneous scheme, in which all transfers are allocated the same amount of bandwidth. Our analytical results show that bandwidth allocation should be based on loading conditions. Under low loads, we recommend a homogeneous scheme and each call should be allocated a high-bandwidth circuit. However, under high loads, small files should be allocated low-bandwidth circuits and large files high-bandwidth circuits; this heterogeneous bandwidth-allocation scheme results in a one-to-three orders of magnitude reduction in mean response time.