A Dynamic Threshold Rule is provided for sharing of bandwidth of a shared medium between multiple devices. In one embodiment, a device determines a measure of available bandwidth of said medium; reserves bandwidth up to the available bandwidth; receives a request from a device for bandwidth of a specified amount; and honors the request when relinquishing the specified amount results in preserving an equal or greater percentage of bandwidth available at a time of reserving bandwidth. Different classes of devices may be distinguished, where the percentage for devices of a particular class is greater than for devices not of that particular class, or for which at least one class of device is exempt from the requirement to relinquish bandwidth.