We discusse PLC efficiency when multiple users contend for the medium. To resolve contention conflicts, PLC uses carrier sense multi- ple access with collision avoidance (CSMA/CA) on the MAC layer. The stations have to sense the medium before they transmit, and to wait for a random interval of idle-medium time slots before they transmit. The PLC CSMA/CA protocol is similar but more complex than that of Wi-Fi. We present the IEEE 1901 CSMA/CA protocol and certain MAC-layer processes, such as the priority resolution for QoS classes, inter-frame spaces, and frame aggregation. We discuss the new features of HomePlug AV2 compared to IEEE 1901 and the differences between Wi-Fi and PLC MAC layers.

We evaluate the performance of the PLC CSMA/CA protocol by analysis, simulations and testbed measurements. We explain the impact of each parameter on performance and the motivation behind the design choices for PLC. Both throughput and short-term fairness are discussed and modelled. Short-term fairness is achieved when all users share equally the medium over a short time horizon. If short-term fairness is not guaranteed, there exists high delay-deviation that harms certain delay-sensitive ap- plications. We provide fundamental evidence about performance trade- offs of the PLC CSMA/CA. Our study suggests that PLC parameters should be judiciously selected in order to exploit the tradeoff between throughput and fairness and to achieve high QoS for best-effort and delay-sensitive applications. This chapter also presents a cross-layer PHY/MAC evaluation of contending links and investigates the challenges of stations with different rates and hidden terminals.

In this chapter, we summarize the content of our book and we discuss current limitations of PLC technology. Buidling on these limitations, we highlight new research areas for residential and enterprise PLC networks.

The IEEE 1905.1 standard aims at making interoperability between different technologies (Wi-Fi, PLC, MoCA) easier and more flexible. By introducing an abstraction layer between the MAC and IP layers (layer 2.5) and a common interface, it enables a device to seamlessly use or alternate between two or more technologies, depending on the network conditions. Its goal is also to make the management of heterogeneous networks simpler, by providing end-to-end QoS, autoconfiguration, common secured authentication and setup methods.

In this chapter, we present different standardized solutions for heterogeneous net- works. We describe in particular the IEEE 1905.1 standard. We also present algorithms that can be used in heterogeneous networks to improve performance.