Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-09-04
2001-11-27
Ton, Dang (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S470000
Reexamination Certificate
active
06324184
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the transmission of data in a layered data communication scheme, and is particularly applicable to the transmission of upstream messages in a hybrid fiber coaxial network. The invention is useful, for example, in allowing subscriber units to communicate messages to a central controller (e.g., cable television headend) for Internet access, videoconferencing, audio communication or the like. Bandwidth is dynamically allocated to subscribers of the network by the central controller according to the overall available bandwidth, the amount of bandwidth which is currently being used by each subscriber, and the number of current subscribers, among other factors.
In the past, cable television systems have utilized coaxial cable to carry signals from a headend to individual subscriber units. With the advent of new digital television services as well as the desire to carry data to and from subscriber units, the increased bandwidth provided by fiber optic cable has become attractive. Implementation of optical fiber networks all the way from the headend to individual subscriber units is not currently a practical alternative due to the high cost of building an optical fiber plant in which fiber is run all the way to individual homes. As a compromise, hybrid fiber coax (HFC) plants are being implemented. In HFC systems, fiber is run from the headend to neighborhood hubs. Existing coaxial cable is then coupled to receive the signals from the optical fiber, for distribution to individual homes.
Various interactive services to be provided by digital transmission systems require a bi-directional link between the central controller and individual subscriber units. One way to provide a return path from the subscriber units back to the central controller is to rely on existing telephone lines. However, it would clearly be advantageous to provide bi-directional communication over the same plant, such as an HFC plant, in which the downstream television signals are provided to the subscriber units. In order to accomplish this, proposals have been made to develop robust upstream communication networks over HFC plants. For example, single carrier frequency and time division multiple access (F/TDMA) have been proposed to provide a low risk, high capacity approach which offers suitable characteristics for upstream modulation over an HFC system.
In order to efficiently implement a practical upstream channel, it would be advantageous to allow the central controller to allocate bandwidth on an upstream channel according to the current subscriber demands. The central controller should have the capability to provide a minimum bandwidth to each subscriber, and to distribute bandwidth among users in an equitable manner. The central controller should also have the capability to provide priority to selected users, such as those who pay an additional fee. The scheme should be applicable to virtually any type of network, including networks which communicate television and/or other data signals, and should operate in a manner which is transparent to the subscriber units.
The present invention provides a communication scheme enjoying the above and other advantages.
SUMMARY OF THE INVENTION
A method and apparatus are presented for allocating bandwidth in a layered data communication network in which a plurality of subscriber units communicate with a central controller, e.g., for Internet access, videoconferencing, or voice communication.
The method includes the step of maintaining a running total of unallocated bandwidth in successive control intervals. A traffic count is determined for each subscriber unit, for example, by counting the number of slots used in a control interval. The slot usage rate corresponds to a bandwidth.
The assigned bandwidth of the subscriber units is then adjusted according to the traffic count. For example, the assigned bandwidth may be decreased when the currently assigned bandwidth exceeds the traffic count, e.g., by a programmable amount which is greater than or equal to zero. The assigned bandwidth can be set to equal the traffic count for each particular subscriber unit. Generally, bandwidth utilization is optimized by tailoring the assigned bandwidth to the subscriber unit's required bandwidth.
Optionally, to ensure that each subscriber unit is allocated a non-zero bandwidth, the assigned bandwidth may be set to the greater of (a) the traffic count for the particular subscriber unit, and (b) a minimum bandwidth, R
min
. The running total of unallocated bandwidth is then incremented by the decrease in the assigned bandwidth for each subscriber unit. The running total of unallocated bandwidth carries over to subsequent control intervals (e.g., time intervals), where the assigned bandwidth is again adjusted.
Alternatively, a ratio of the traffic count to the assigned bandwidth for the particular subscriber unit may be determined, and the assigned bandwidth may be decreased when the ratio is at or below a lower utilization threshold, T
1
.
The assigned bandwidth may be increased for particular subscriber units according to the running total of unallocated bandwidth when the traffic count is at or near the currently assigned bandwidth. This may be accomplished by marking particular subscriber units for an increase in assigned bandwidth, and distributing the unallocated bandwidth among the marked subscriber units. For example, the unallocated bandwidth may be distributed equally to the marked subscriber units. Optionally, the assigned bandwidth for the subscriber units may be determined according to a subscriber unit hierarchy. For example, users who pay an additional fee may be granted various benefits, including priority access to unallocated bandwidth and/or a higher maximum (e.g., ceiling) bandwidth allocation. Additionally, assigned bandwidth may be based on a subscriber unit bandwidth usage history, time of day, or other factors.
Alternatively, a ratio of the traffic count to the assigned bandwidth for the particular subscriber units may be determined, and the assigned bandwidth may be increased when the ratio is at or above an upper utilization threshold, T
2
.
The bandwidth may be allocated in a transmission path between the subscriber units and the central controller, or in a transmission path between the central controller and another communication network.
A corresponding apparatus is also presented.
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Fellows Jonathon A.
Hou Victor T.
General Instrument Corporation
Lipsitz Barry R.
McAllister Douglas M.
Nguyen Toan
Ton Dang
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