Multiplex communications – Channel assignment techniques
Reexamination Certificate
1997-08-27
2001-08-14
Ton, Dang (Department: 2661)
Multiplex communications
Channel assignment techniques
C370S421000
Reexamination Certificate
active
06275497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and system for of sub-channelizing a broadband medium and assigning predefined protocols to respective subchannels thereof. More particularly, it relates to a method and system for sharing sub-channels based on the nature of the data to be transferred in a multi-channel communication network.
2. Background of Related Art
The general trend of the prior art has been to establish high bandwidth channels for the transmission of data to improve performance. For instance, recent improvements in dial-up modems has been the migration from 28.8 Kb/s to 56 Kb/s. It is conventionally assumed that larger bandwidths provide better performance. In the case of shared channels, as the bandwidth of channels increases, so does the complexity of the channel, including the protocol used. Moreover, larger bandwidths increase the possibility that noise at a particular frequency will erode the reliability of communications.
In a shared channel environment, media access protocols involve contention or polling to gain channel access. For instance, U.S. Pat. No. 5,563,883 discloses a controller which periodically broadcasts a polling message simultaneously to a plurality of cable modems over a shared downstream communication channel. The cable modems then contend for access to a single upstream channel. If messages of more than one modem collide with one another, a binary search method implemented in a media access controller arbitrates between and isolates colliding modems. However, only one upstream channel is available for the colliding modems to communicate upstream back to the controller. Thus, all modems assigned to a particular upstream channel must not only contend for channel access to respond to the downstream broadcast poll, but any subsequent data transmission must also contend for the same single upstream channel. This leads to congestion and lower performance.
U.S. Pat. No. 4,829,297 discloses a communication method wherein the same polling technique is used in two channels. While this increases performance only because it provides two upstream paths rather than just one, it fails to segregate busy users from inactive or idle users.
U.S. Pat. No. 4,754,426 teaches the prioritized polling technique of placing a higher priority on some users, and thus polling those higher priority users more frequently. However, all upstream communications remain on a single channel. Thus, the performance of the higher priority users is increased, but at the expense of the non-high priority users.
Other patents such as U.S. Pat. No. 5,572,517 to Safadi discourage the use of a polling scheme in a shared network environment altogether.
SUMMARY OF THE INVENTION
The present invention exploits the beneficial aspects of both contention and polling protocols by employing dynamic allocation of upstream channels to move users of a network between diverse channels utilizing different protocols selected to maximize data transfer based on the instantaneous transmission status of the user and/or a user's detected or requested payload data transfer needs.
For instance, non-responding users (e.g., user equipment that is powered down) are assigned to a first group of channels utilizing a contention-only protocol in the upstream direction. After detection by a media access controller, the status of responding and active users are reclassified to use a second group of channels utilizing a polling protocol that is maximized for low latency, e.g., a limited-1 polling scheme. Users demanding heavy usage with lengthy transmissions reclassified to use a third group of upstream channels, called burst channels, that are maximized for high throughput, e.g., channels that have an exhaustive polling or approximately exhaustive polling scheme. The media access controller is capable of switching the users' upstream channels dynamically and intelligently on a packet-by-packet basis. Rules based on payload data activity level of the user are implemented to determine when the user is to switch between channel groups. The user can transmit on any of a plurality of upstream channels or sub-channels, utilizing either a contention-based protocol, or any of a plurality of polling-based protocols, on a per-packet basis.
Contention based algorithms work well when there are a large number of subscribers but only a few of them are active at any time (i.e. in light traffic), while polling based algorithms work well in heavy traffic. The present invention utilizes the efficiencies of both protocols. First, by initially assigning non-responding users (e.g. powered-down users) to a channel chosen at random out of the group of contention mode channels. Once it becomes active, the user is moved to a first level polling mode channel selected from a first group of polling mode channels operating with a polling protocol that is maximized for low is latency. Then, as necessary, the user is moved again to a higher level polling mode channel selected from a second group of polling mode channels operating with a polling protocol that is maximized for maximum throughput, the burst mode channel. Additional levels of polling mode channel groups blending a mix of low latency and maximum throughput, e.g., greater than limited-1 type polling, although adding to the complexity of the overall protocol, can add further efficiencies to the communication system. In another aspect of the invention, the communication mode of the channel itself may dynamically be changed, e.g., between polling and contention modes, based on user loading.
Ranging and synchronization between the media access controller and the users are not necessary according to the present invention because of the use of contention mode and polling mode channels.
Moreover, the present invention makes intelligent use of an expanded number of smaller bandwidth channels formed from a smaller number of larger bandwidth channels. It is found that there is a greater likelihood of having a larger number of usable smaller bandwidth upstream channels than there is of having an equivalent amount of usable larger bandwidth upstream channels due largely to the noise characteristics in the upstream path of a cable TV facility. Commonly assigned U.S. patent application Ser. Nos. 08/702,932 and 08/735,110 disclose the sub-channelization of a communication channel and are explicitly incorporated herein by reference.
In view of the foregoing, it is an object of the present invention to maximize the throughput and reliability of a plurality of upstream channels from a plurality of users to a host computer or controller.
It is a further object of the present invention to intelligently pass packet data from a single user to a host computer or controller over a selected one of a plurality of upstream channels operating with different protocols chosen based on the data itself.
It is also an object of the present invention to maximize the performance of an overall polling scheme by providing classifying a plurality of sub-channels into a plurality of groups, each group utilizing a different polling scheme.
It is a further object to provide a protocol which switches upstream communications between different polling mode channel groups based on optimized performance criteria.
This summary is not intended to limit the invention to any extent beyond that defined in the appended claims.
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p
Enns Frederick
Varma Subir
Hybrid Networks, Inc.
McIntyre Harbin & King
Sam Phirin
Ton Dang
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