Wireless Interface Bonding Supporting In-Order Delivery and Automatic Load Balancing

Wireless interface bonding is an important technique in multiradio systems, where multiple radios can be combined to establish a fast link between nodes. However, existing interface bonding modules are not well-suited for wireless interfaces due to lack of functionalities to cope with varying channel capacity. Variance in throughput and delay of the individual radios can cause significant degradation of transmission control protocol throughput due to suboptimal scheduling and out-of-order delivery. Since condition of wireless channels is dynamic, capacity of each channel cannot be predicted offline which makes the packet scheduling challenging. Naive queue management for in-order delivery could also be hazardous to the throughput due to long dwell time of packets at the receiver queue. This paper presents an extension to Linux bonding driver called the new load balancing (NLB) mode, which is designed to combine multiple WLAN interfaces into a single virtual interface. The NLB mode supports automatic load balancing and in-order delivery, and together, they make a multichannel link that behaves like a single link with aggregated bandwidth. Automatic load balancing is done using receiver measurements on interarrival time of consecutive packets. In-order delivery is implemented using a receive queue and a fast loss detection scheme which prevents long dwell time of packets at the queue. The NLB mode does not require modifications to physical network device drivers which makes it usable with devices from any vendor. Performance evaluations using OpenWrt-based wireless devices show that the NLB mode can efficiently aggregate bandwidths of channels under various conditions.