Evaluation of open-loop sequence control schemes for multi-path switches

Modern packet switches and routers are commonly designed using a multi-path architecture, in which the capacities of multiple switch cores are aggregated in order to build a higher capacity system. The local parallelism within such systems has been found to be the biggest contributing factor to packet re-ordering within the network. This motivates the employment of localized sequence control mechanisms that maintain the ordering of packets, belonging to the same flow, which are forwarded through different paths of the switch. The protocol chosen for this purpose has to maintain a low overhead and exhibit a favorable behavior under arbitrary dispatch patterns and differential delays. We analyze the performance of the sequence controller of a generic multi-path switch, and establish a sufficient condition which guarantees the stability of the system. Furthermore, we compare the behavior of three practical open-loop sequence control schemes using packet-level simulations. The results presented can be used as a reference to choose an appropriate protocol under the assumed traffic conditions.