Power-line communications are becoming a key component in home networking. The dominant MAC protocol for high data-rate power-line communications, 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 introduces strong coupling between the stations, and, as a result, makes existing analyses inaccurate. In this paper, we propose a new performance model for 1901, which does not rely on the decoupling assumption. We prove that our model admits a unique solution. We confirm the accuracy of our model using both testbed experiments and simulations, and we show that it surpasses current models based on the decoupling assumption. Furthermore, we study the tradeoff between delay and throughput existing with 1901. We show that this protocol can be configured to accommodate different throughput and jitter requirements, and give systematic guidelines for its configuration.