Bonded deficit round robin scheduling for multi-channel networks

摘要

In order to increase the link capacity in telecommunication networks the bandwidth of multiple channels can be aggregated by transmitting on them simultaneously. The latest data-over-cable service interface specification (DOCSIS 3.0) for hybrid fiber coax networks defines a mechanism for channel bonding at the link layer. Thus, the scheduler at the cable modem termination system, which distributes the packets on the network, not only has to support per-flow queuing but also has to distribute the packets to one modem over possibly several channels. In this article we propose two downstream multi-channel packet scheduling algorithms designed to support scheduling amongst flows possibly using different numbers of channels. Both algorithms are based on the deficit round robin (DRR) scheduler. The bonded deficit round robin (BDRR) algorithm, has complexity dependent only on the number of the channels and requires only one queue per flow. It is shown that the algorithm is a latency-rate server and the latency is derived. Furthermore, BDRR bounds the packet reordering and the maximum bounds on the packet delay and the reorder buffer needed at the receiver are calculated. The paper explores also a second algorithm which has more similarities with load balancing algorithms. It uses fully independent channel schedulers thus avoiding the need for modification in the single channel DRR algorithm. The transmission channel for a packet is selected upon its arrival. However, the algorithm does not bound the latency and packet reorder for flows assigned to receive on multiple channels. Flows for which such bound is needed should be assigned on a single channel.