In this paper, the analytic model for single class broadcast based frame transmission by IEEE 802.11 MAC is presented. A Markov chain is used to derive a transmission probability that a station may transmit a frame in a random time slot. The collision probability is calculated based on the transmission probability. After that the per-node throughput is calculated based on the stationary transmission probabilities. With the proposed analytic model, we studied the network QoS performances in terms of message success probability, network throughput and channel access delay for both emerging and routine messages. The proposed analytic model was verified by simulations, which shows very high accuracy.