6LoWPAN’s fragmentation mechanism enables transport of IPv6 datagrams with the required minimum MTU of 1280 bytes over IEEE 802.15.4-based networks. Testbed experiments showed disastrously bad datagram success rates for a collection traffic scenario with large, 6LoWPAN-fragmented datagrams, which significantly differed from the simulation results for a comparable scenario. In this paper we present an experimental setup that enables capturing the MAC and transceiver states of participating nodes in realtime. The results of our experiments show, that for the given fragmentation/collection scenario, the usage of the extended operating mode of the transceiver hardware, which provides CSMA/CA, ACKs and retransmissions in hardware, is responsible for nearly all datagram losses. Therefore, we strongly advise against using such hardware-assisted modes of operation in similar traffic scenarios.
