  Communication protocols and techniques are often evaluated using simulation
techniques. However, the use of formal modeling and analysis techniques for
verification and evaluation in particular for Wireless Sensor Networks (WSN)
becomes a necessity. In this paper we present a formal analysis of the backoff
procedure integrated in the medium access control protocol named ECo-MAC
designed for WSN. We describe this backoff procedure in terms of discrete time
Markov chains (DTMCs) and evaluated using the well known probabilistic model
checker PRISM. After checking the different invariants of the proposed model,
we study the effect of contention window length (in number of time contention
unit) on the acceptable number of simultaneous senders in a neighborhood of a
given receiver. The obtained quantitative results confirm those provided by the
simulation using OPNET tool and justify the validity of the adopted value for
the time contention unit TCU.
