  Power-line communications (PLC) are becoming a key component in home
networking, because they provide easy and high-throughput connectivity. The
dominant MAC protocol for high data-rate PLC, the IEEE 1901, employs a CSMA/CA
mechanism similar to the backoff process of 802.11. Existing performance
evaluation studies of this protocol assume that the backoff processes of the
stations are independent (the so-called decoupling assumption). However, in
contrast to 802.11, 1901 stations can change their state after sensing the
medium busy, which is regulated by the so-called deferral counter. This
mechanism introduces strong coupling between the stations and, as a result,
makes existing analyses inaccurate. In this paper, we propose a performance
model for 1901, which does not rely on the decoupling assumption. We prove that
our model admits a unique solution for a wide range of configurations and
confirm the accuracy of the model using simulations. Our results show that we
outperform current models based on the decoupling assumption. In addition to
evaluating the performance in steady state, we further study the transient
dynamics of 1901, which is also affected by the deferral counter.
