This work deals with the performance analysis of a particular type of AMI: the RF-mesh based smart meter network. The system implements a MAC access with a time-slotted ALOHA with the Frequency Hopping Spread Spectrum (FHSS) to reduce co-channel interference by other users. We developed the PeRF-mesh analytic tool to study the performance of such systems, taking into account the combined effects of ALOHA access and of FHSS on the performance. The tool allows the evaluation of currently deployed systems and can also help in the design phase of new ones.