Bandwidth control in a packet-based data system

摘要

A data system, such as a computer network or a telecommunications system, has a base station and a number of nodes called network interface units (NIUs). Each NIU is assigned to one of a number of groups of NIUs. The base station transmits special data to the NIUs indicating which groups of NIUs are currently authorized to transmit upstream messages to the base station, where only the authorized NIUs are allowed to transmit upstream messages. When message collisions in the upstream direction becomes a problem, the base station can reduce the number of NIU groups that are authorized at any given time to transmit upstream messages, in order to attempt to reduce the rate of message collisions. In one possible embodiment, each NIU is assigned horizontal and vertical group words that identify to which group it is assigned. The special data contain additional horizontal and vertical code words that are monitored by the NIUs. If the bits in the downstream code words appropriately match the corresponding bits in the NIU's assigned group words, then the NIU recognizes that it is authorized to transmit upstream messages to the base station. Otherwise, it is not. The horizontal and vertical code words correspond to two-dimensional patterns that indicate which subset of NIU groups are authorized at any given time. By cycling through a series of 2D patterns, the base station ensures that each NIU is authorized at least some of the time. Depending on the number of bits in the code words, a back-off scheme can be designed with different back-off levels, each of which authorizes a different number of groups to transmit. The base station can progressively decrease the rate of upstream transmission by selecting back-off levels with fewer and fewer NIU groups authorized to transmit.