NATO Narrowband Waveform (NBWF) - network layer flow control protocols

NATO has an ongoing activity with the objective to develop a narrowband waveform (NBWF) standard for the VHF/UHF band. This is a single-channel mobile ad-hoc network (MANET) which shall serve voice and data traffic simultaneously over a 25 kHz radio channel. As a member of the NBWF working group, FFI is working on a proposal for a network layer flow control protocol in multihop networks. A narrowband network has low throughput capacity, and to experience network congestion during usage must be regarded as an ordinary event. Therefore it is important to have a robust flow control protocol that prevents network collapse. The first part of this document addresses the challenges we are faced with in a multihop network when the current NBWF link layer is used. Then we propose two flow control protocols and implement these protocols in the NBWF network simulator. The solutions proposed are based on a cross layer design where we also consider services at the lower layers, their buffer structure and the layer interface flow control. A number of simulation experiments are conducted with the objective to study protocol behaviour under different conditions. This report concludes that NBWF must implement a network layer flow control protocol, that is, some signalling between adjacent nodes is required. However, which of the two flow-control protocols to select demands further study. Based on the simulation experiments, we conclude that the link layer must implement an additional function (LLC exponential backoff) as a countermeasure to the hidden-node problem.