A transmission initiation interval timing structure is used in combination with a lower layer timing structure, e.g., physical layer timing structure. A device selects a subset of packet transmission initiation intervals and then limits initiation of packet transmission to those intervals thereby reducing the potential for collisions. Packet transmission may occur outside the initiation interval in which the transmission is initiated. In some embodiments, packet transmission length is intentionally limited to sizes which can be transmitted in a fraction of the amount of time the physical layer allows a single device to continuously transmit, e.g., in an amount of time which is equal to or less than the duration of a packet transmission initiation interval. This increases the probability that multiple devices will be able to successfully transmit small packets at short intervals on a regular basis even when carrier sensing techniques are used.