The paper investigates the performance of the contention-free period (CFP) repetition rate (CFPRate) for real-time and non real-time IP traffic over IEEE 802.11. We show that variations on the length of CFPRate affects negatively the mean transmission delay for an 802.11 frame, increasing the effective latency for IP-mobility; on this basis we argue that performance of IP traffic is tracked by the size of CFPRate. We further derive lower bounds of CFPRate with respect to minimum frame delay, under different signalling rates by means of simulations.