  We introduce and analyze a new Markov model of the IEEE 802.11 Distributed
Coordination Function (DCF) for wireless networks. The new model is derived
from a detailed DCF description where transition probabilities are determined
by precise estimates of collision probabilities based on network topology and
node states. For steady state calculations, we approximate joint probabilities
from marginal probabilities using product approximations. To assess the quality
of the model, we compare detailed equilibrium node states with results from
realistic simulations of wireless networks. We find very close correspondence
between the model and the simulations in a variety of representative network
topologies.
