Bonded deficit round robin scheduling for multi-channel networks Dessislava Nikolova ⇑ , Chris Blondia PATS Research Group, Dept. Math. and Computer Science, University of Antwerp, Middelheimlaan, 1, B-2020 Antwerp, Belgium Interdisciplinary Institute for BroadBand Technology (IBBT), Belgium article info Article history: Received 9 May 2010 Received in revised form 13 January 2011 Accepted 7 July 2011 Available online 22 July 2011 Keywords: Scheduling Multiple channels Access networks Wired networks DOCSIS3.0 Channel bonding abstract 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 possi- bly 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 chan- nels. 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 reor- dering 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 simi- larities 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. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction One of the currently most deployed wired broadband access network solutions is the hybrid fiber coax (HFC) network. It uses the legacy community antenna television cables and is a point-to-multipoint network with tree topology. The terminal equipment placed at the root of a HFC network is referred to as a cable modem termination system (CMTS). It is connected via coaxial or both optical and coaxial cable to cable modems (CM) situated at the customer premises. There is a family of data-over-cable service interface specifications (DOCSIS) which standardize the physical and the medium access control (MAC) layers and also the QoS support. The speed of a DOCSIS-based network depends on the modulation used on the physical layer. For example a network based on the DOCSIS 2.0 standard [1] offers effective downstream bandwidth (from the CMTS to the CMs) of approximately 40 Mb/s provided 256QAM modulation is used. Increasing further the modu- lation would increase the speed but is technologically expensive. Another access network technology, the FTTx (fiber- to-the-home, fiber-to-the-business or fiber-to-the-curb), uses optical fiber and has gained lots of momentum in the recent years. The most promising fiber network is considered the passive optical network (PON). There exist a number of different PON types like ATM PON (APON) 1389-1286/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.comnet.2011.07.007 ⇑ Corresponding author at: London Center for Nanotechnology, Gordon Street 17-19, WC1H 0AH, London, UK. Tel.: +44 7980 589518. E-mail address: dessie.nikolova@gmail.com (D. Nikolova). Computer Networks 55 (2011) 3503–3516 Contents lists available at ScienceDirect Computer Networks journal homepage: www.elsevier.com/locate/comnet