Abstract
Traffic load balancing in data centers is an important requirement. Traffic dynamics and possibilities of changes in the topology (e.g., failures and asymmetries) make load balancing a challenging task. Existing end-host-based schemes either employ the predominantly used ECN or combine it with RTT to get congestion information of paths. Both congestion signals, ECN and RTT, have limitations; ECN only tells whether the queue length is above or below a threshold value but does not inform about the extent of congestion; similarly, RTT in data center networks is on the scale of up to few hundreds of microseconds, and current data center operating systems lack fine-grained microsecond-level timers. Therefore, there is a need of a new congestion signal which should give accurate information of congestion along the path. Furthermore, in end-host-based schemes, detecting asymmetries in the topology is challenging due to the inability to accurately measure RTT on the scale of microseconds. This paper presents QLLB, an end-host-based, queue length-based load balancing scheme. QLLB employs a new queue length-based congestion signal that gives an exact measure of congestion along the paths. Furthermore, QLLB uses relative-RTT to detect asymmetries in the topology. QLLB is implemented in ns-3 and compared with ECMP, CONGA, and Hermes. The results show that QLLB significantly improves performance of short flows over the other schemes and performs within acceptable level, of CONGA and Hermes, for long flows. In addition, QLLB effectively detects asymmetric paths and performs better than Hermes under high loads.