Time slotted logical ring

Details Time slotted logical ring Time slotted logical ring

1998-11-02

2003-06-17

Ton, Dang (Department: 2666)

Multiplex communications

Channel assignment techniques

Combining or distributing information via time channels...

C370S403000

Reexamination Certificate

active

06580723

ABSTRACT:

BACKGROUND OF THE INVENTION
A cable modem network includes a head end located at a cable company central location. The head end distributes cable services to different local areas of subscribers. Subscriber stations are terminated by cable modem boxes that are connected to the subscriber's computer through a conventional data interface such as serial or Ethernet. The cable modem boxes allow the subscribers to transmit data back upstream on the cable network to the head end. For example, if a subscriber wishes to order a pay-for-view movie, the subscriber enters a selection that is transmitted by the cable modem back over the cable network to the head end. The head end then transmits a downstream signal to the subscriber with the selected movie.
With the installation of more subscribers on cable modem networks, it becomes more important to allocate bandwidth more efficiently on the cable return path. For example, different types of transmissions, such as voice traffic may require a higher priority than data traffic. Alternatively, certain subscribers may need to purchase more bandwidth or higher priority than other subscribers. Current cable modem systems do not efficiently allocate cable bandwidth over the return path.
Accordingly, a need remains for a cable access system that allows multiple users to both send and receive information in an orderly and efficient manner.
SUMMARY OF THE INVENTION
Communications between a head end and multiple subscribers on a cable network are scheduled using a Time Slotted Logical Ring protocol (TSLR). Data is broadcast from the head end to the subscribers over a downstream path of a broadcast media, such as a combination of a fiber optical link and coaxial cable. The TSLR protocol allocates bandwidth to subscribers on an upstream path of the broadcast media by assigning the subscribers to time slots on different logical ring levels. The time slots on a first ring level represent the total available bandwidth for the upstream path. The portion of the bandwidth allocated to one or more of the time slots on the first ring level are distributed between multiple time slots on lower ring levels that represent different user bandwidth requirements.
The TSLR protocol rotates selection of the time slots around the first ring level allowing the subscriber assigned to the selected time slot to transmit data upstream to the head end. When the selected time slot opportunity on the first ring level is allocated to a lower ring level, the TSLR protocol allows the subscriber assigned to the selected time slot on the lower ring level to transmit. The TSLR protocol then rotates assignment of another time slot on the lower ring level to the time slot on the first ring. Thus, each subsequently lower TSLR ring level allocates relatively smaller portions of upstream bandwidth to the subscribers.
The head end sends time tick identifier (TTI) frames to the subscribers assigned to the currently selected time slots. The TTI frames are used to notify the identified subscriber to transmit frames upstream back to the head end. After receiving the TTI frame, the subscriber sends back either a data frame or a heart beat frame to the head end. The heart beat frame is sent when the subscriber has no data to transmit or when transmitting a reduced sized data frame. The heartbeat frame is used by the head end to assign the subscriber to different ring levels. For example, subscribers sending only heartbeat frames back to the head end for a specified time period are assigned to lower frame levels than subscribers sending back data frames.
The subscribers are assigned to different ring levels and, in turn, sent TTI frames at different rates according to different scheduling criteria. In one embodiment of the invention as mentioned above, the subscribers are assigned to different ring levels according to the number of data frames sent back from the subscribers to the head end within specified time periods. The subscribers can also be assigned to classes. The TSLR then meters out a maximum number of TTI frames to individual subscribers within a fixed time period according to the assigned subscriber classes. The subscribers can also be allocated time-bandwidth credits. The credits allocated to each subscriber are reduced upon receiving TTI frames and TTI frames are no longer sent to subscribers with zero credits. The credits for the subscribers are then increased after selected time intervals.
Bandwidth efficiency is improved by releasing early TTI frames after the head end receives a subscriber heart beat frame. Efficiency is also improved by aggregating multiple subscriber data frames together and sending the aggregated frames all at one time to the head end. To prevent allocating too much bandwidth to low bit rate subscribers, the highest ring level assigned to individual subscribers is controlled according to a maximum transmission rate of the individual subscribers.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.


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