Measuring the Available Bandwidth (ABW) is an important function for traffic engineering, and in software-defined metro and wide-area network (SD-WAN) applications. Because network speeds are increasing, it is timely to re-visit the effectiveness of ABW measurement again. A significant challenge arises because of Interrupt Coalescence (IC), that network interface drivers use to mitigate the overhead when processing packets at high speed, but introduce packet batching. IC distorts receiver timing and decreases the ABW estimation. This effect is further exacerbated with software-based forwarding platforms that exploit network function virtualization (NFV) and the lower-cost and flexibility that NFV offers, and with the increased use of poll-mode packet processing popularized by the Data Plane Development Kit (DPDK) library. We examine the effectiveness of the ABW estimation with the popular probe rate models (PRM) such as PathChirp and PathCos++, and show that there is a need to improve upon them. We propose a modular packet batching mitigation that can be adopted to improve both the increasing PRM models like PathChirp and decreasing models like PathCos++. Our mitigation techniques improve the accuracy of ABW estimation substantially when packet batching occurs either at the receiver due to IC, DPDK based processing or intermediate NFV-based forwarding nodes.more »
Utilizing JANUS for Very High Frequency Underwater Acoustic Modem
JANUS is a physical layer communication standard for underwater acoustic communications published by North Atlantic Treaty Organization (NATO) in 2017. Instead of the nominal frequency band of 9440 – 13600 Hz specified in the standard, we adopt the JANUS packet for a high frequency band spanning from 96 kHz to 134 kHz. We also add cargo packets in the same frequency band using JANUS fast mode with a symbol rate of 23 ksps. Experiments were conducted in a swimming pool and the JANUS 3.0.5 Matlab version of the example receiver program was used to process the JANUS packets. We found that the example receiver program uses many fix(), round() and floor() functions which lead to synchronization errors. After modifying the simple rx code and fixing the error, our JANUS decoding results show that the adopted JANUS fast mode successfully achieves carrier and frame synchronization in all cases despite some bit errors remaining in the JANUS packet in severe multipath scenarios.
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