AT&T Labs Research — Leading Invention, Driving Innovation

A method and apparatus is provided for allocating bandwidth and reducing jitter in an upstream transmission in a shared-media packet-switched access network with multiple upstream channels offering integrated Internet Protocol voice and high-speed data services. To allow multiple simultaneous CBR (constant-bit-rate) voice connections to be supported by a cable modem, when only a single channel can be accessed at a time, a method to select an upstream channel and assign to each connection a time slot in the upstream channel is provided. Jitter, i.e. packet delay variation, results when packets associated with a voice connection are not received at expected intervals. To maintain jitter within predetermined tolerances, the sequence of mini-slots in an upstream channel is divided into frames. Each frame will have a sequence of voice and data-only regions, and the voice region is divided into non-overlapping jitter windows of generally equal length. Even when an upstream channel change is required, each active voice connection is maintained in one of the jitter windows, thereby limiting jitter to the duration of a jitter window.

A communication system includes a plurality of devices, such as cable modems, in communication with a station, such as a cable modem termination system, that provides efficient upstream bandwidth sharing.

A system and method are described for assigning downstream and upstream communication pathways in broadband access networks, such as networks based on the hybrid fiber-coax architecture. In the upstream direction, frequency channel and time slot assignments use a packing opposite methodology, which is dependent on the type of service request. The system assigns the lowest time slot in the lowest frequency available for a DSO service request and the highest time slot in the highest frequency which has the next four contiguous time slots available for an H0 service request. To optimize upstream bandwidth efficiency, a H0 channel occupying the space of four contiguous time slots is used to carry up to six simultaneous voice conversations. A method is described that governs such use of H0 channels by NIUs according to their offered loads. In the downstream direction, network interface units are automatically assigned frequencies in response to the expected load across the available frequency channels and are made to spread evenly the load across all downstream frequency channels. In one embodiment, assignments are based upon each individual network interface unit load, each network interface unit group load, the capacity of each network interface unit group and the blocked load. An assignment will be made to the group having the maximum idle capacity, i.e., the group which has the greatest blocked load differential. That is, assignments are made if moving an individual NIU from a first NIU group to a second NIU group results in a blocked load differential greater than the cost ratio R, where R represents the cost of moving an NIU divided by the cost.