Guaranteed periodic real-time communication over wormhole switched networks

In this paper, we investigate how to efficiently implement TDMA (Time Division Multiple Access) on a wormhole switched network using a pure software solution in the end nodes. Transmission is conflict free on the time-slot level and hence deadlock free. On the sub-slot level, however, conflicts are possible when using "early sending," a method we propose in order to reduce latency while still not hazarding the TDMA schedule. We propose a complete system to offer services for dynamic establishment of guaranteed periodic real-time virtual channels. Two different clock synchronization approaches for integration into the TDMA system are discussed. Implementation and experimental studies have been done on a cluster of PCs connected by a Myrinet network. Also, a case study with a radar signal processing application is presented to show the usability. A best-case reduction of the latency of up to to 37 percent for 640 Byte messages by using early sending in Myrinet is shown in the case study. Source routed wormhole switching networks are assumed in the work but the results are applicable on some other categories of switched networks too.