Communicating packetized data over a channel using a dual leaky bucket priority scheme for assigning priorities to ports assigned to channels in a channel bank

This invention relates generally to a system and method for communicating packetized data over a time division multiplexed communications system. In the early 1970's, telephone began using a time division multiplexed (TDM) communications system, known as D4, that used a channel bank to multiplex and communicate time division multiplexed (TDM) voice signals over a communications link, such as a T link. The channel bank typically carried 24 digital voice signals between central telephone offices using only one pair of wires in each direction instead of the normal 24 pairs of wires required to communicate the 24 voice signals in analog form. This capability was achieved by digitizing and time division multiplexing the 24 analog voice signals into 24 channels or timeslots. In the TDM system, each of the channels is allocated a predetermined, equal amount of time (corresponding to a predetermined bandwidth) within each frame of the T link to communicate any data. Each channel is always allocated its predetermined amount of time, even if that channel has no voice data to transmit. In addition to communicating voice signals, these systems may also communicate digital data because the D system was designed to handle digital data. The systems are still widely used today to carry voice traffic between central telephone offices. Therefore, the communications hardware and the network necessary for this D system are readily available. A priority scheme is based on an amount of preallocated bandwidth unused by channel unit ports. A first water level in a first bucket is associated with an amount of allotted bandwidth unused by the channel unit and a second water level in a second bucket is associated with an amount of unused allotted bandwidth exceeding an overflow level of the first bucket. A priority value is derived from the first water level when the first water level is above zero. The priority value is derived from the second water level when the first water level is below or equal to zero. In another aspect of the invention, the high priority value is determined by tracking a percentage utilization of allocated bandwidth for a predetermined number of time increments comprising a measurement time period.