Electrical computers and digital processing systems: processing – Processing architecture – Vector processor
Reexamination Certificate
1997-11-26
2004-01-20
Srivastava, Vivek (Department: 2611)
Electrical computers and digital processing systems: processing
Processing architecture
Vector processor
C712S007000, C375S240160
Reexamination Certificate
active
06681315
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the bi-directional transport of digital data between a digital network and devices in customer premises, either residence or business. More specifically, the present invention relates to the management of concurrent accesses to the cable TV digital network by multiple devices so that the devices can share the data transport medium, which is a mixture of optical fiber and coaxial cable media.
BACKGROUND OF THE INVENTION
Background Art
Interactive residential broadband/multimedia services are expected to be the next main event in the cyberspace experience. Services like video on demand (where people will choose movies to their liking to watch at any time they choose), effective telecommuting (by bringing the full power of one's familiar office computer interface to one's home), remote learning, teleshopping, ever-increasing on-line newsgroup interactions, Web surfing, remote video game playing, and so on are waiting to jump into people's homes as soon as the 28.8 kb/s barrier of today's fastest modems is toppled tenfold or by a new breed of communication technologies.
The large excess bandwidth (well over 300 MHZ) available in today's cable TV (CATV) hybrid fiber/coaxial (HFC) plants is an ideal candidate to provide the underlying communications infrastructure for interactive digital services to the home. Cable operations that have not yet upgraded their all-coaxial plants to HFC are quickly moving in this direction.
In order to maintain compatibility with today's analog TV channels, the spectrum (of an HFC CATV plant) between 54 MHZ and 450 MHZ will not be affected by the new services. The spectrum between 5 MHZ and 42 MHZ will be used for “upstream” transmissions (i.e., from the home to the CATV headend station) and from there to the rest of the world, while the spectrum between 450 MHZ and 750 MHZ will be used for “downstream” transmissions (from the CATV headend station to the home). Since the theoretical frequency bandwidth of the cable is on the order of 1 GHZ, future generations of this technology may have a different split and different frequency ranges between upstream and downstream transmissions.
To cope better with power limitations, cost, channel error characteristics, system management, and so forth, the downstream and upstream spectra will be further subdivided into a number of channels, for example, 1-2 MHZ wide for each upstream channel, and about 6 MHZ wide for each downstream channel. Each of these channels, using appropriate modulation techniques, will be capable of carrying possibly from 2 to 10 Mb/s (or more) of digital data upstream (shared by up to a few thousand stations) and 30-40 Mb/s (or more) downstream (a broadcast channel).
Due to the “peculiarities” of the CATV tree-and-branch topology (e.g., the splitting of the receive and transmit frequencies), the various stations cannot directly listen to the upstream transmissions from other stations; hence, they are incapable of detecting collisions and ultimately coordinating their transmissions all by themselves. On the other hand, since the headend station is the focal point of the tree-and-branch topology, it can play a major role in coordinating the access to the upstream channel. In addition to coordinating upstream transmissions, since the downstream channels are broadcast (one-to-many), the headend station also has complete control of the downstream transmissions as well.
Various protocols are becoming available for controlling the transmission of upstream data and requests. Of primary interest is the formation of the IEEE 802.14 working group, which has been formed with the responsibility of standardizing the medium access control (MAC) layer protocols for HFC networks. The MAC level access protocol (MLAP) is a MAC-level protocol for the HFC environment that has been formally submitted to the IEEE 802.14 working group for consideration. MLAP is the protocol used by the present invention and is described in more detail hereinafter.
The prior art deals with management techniques and systems that control the contention between a number of devices sharing a bi-directional digital network, so that all the devices can access the shared media.
In U.S. Pat. No. 5,634,485, “Media Access Control for Digital Data,” by Buckland, et al., Buckland teaches a method for controlling the contention for use of a digital network between a broadband network headend unit and network devices. Each device contributes a portion of an upstream signal to the broadband network headend unit. The upstream signal comprises a series of frame intervals. A frame interval has two major components: request slot packets and cell slot packets. Request slot packets are allocated one for each device. There is an arbitrary number of cell slot packets. The request slot packets transmit requests for cell slots to the broadband network headend unit. The broadband network headend unit decodes the requests, determines which to grant, and responds to the requesting device with a downstream signal that identifies which cell slots are allocated to the device. Buckland teaches a protocol for use over cable TV and similar networks that is similar to the MLAP protocol used by the present invention. However, Buckland's protocol applies only to fiber-to-the-curb (FTTC) network topology and is a unique protocol that is different than the MLAP protocol used by the present invention to hybrid fiber-coaxial (HFC) networks. FTTC topology provides the fiber network much closer to each customer premise than HFC does and allows a separate coaxial cable to be run to each premise. On the other hand, the HFC topology is more standard and more difficult to deal with, since the cables are run a greater distances and each coaxial handles the traffic to and from many premises sharing the same coaxial cable. Thus, the HFC topology generates contention by all users for the use of the coaxial cable and requires a more sophisticated protocol. In addition, Buckland does not use special-purpose hardware to assist in the implementation of his protocol as the present invention does.
In U.S. Pat. No. 5,353,285, “Time Slot Management System,” by Van Der Plas et al., Van Der Plas teaches another system for controlling the sending of upstream data from various stations to a headend station. The substations send data as packets during time slots as assigned by the headend station. Part of the time slots are reserved for management information and used by the substation to inform the headend station about the bandwidth required to transfer upstream information. Accordingly, the headend station allocates time slots and informs the substations thereof. This is very similar to the request slot packets and cell slot packets taught by Buckland in U.S. Pat. No. 5,634,485 and discussed previously. Van Der Plas does not teach the MLAP approach and does not use special-purpose hardware to assist in the implementation of his protocol as does the present invention.
In U.S. Pat. No. 5,572,517, “Configurable Hybrid Medium Access Control for Cable Metropolitan Area Networks,” by Sadadi, Sadadi teaches yet another media access control (MAC) system having unique characteristics. Sadadi combines four of the popular MAC concepts into a system which is configurable to the type of communication required to support a desired service or application. The MAC system analyzes the services requested from each premise or client and determines the best MAC concept to use from four supported candidates, including plain old polling (POP) to three different versions of time division multiplexing. Sadadi does not use the MLAP format used by the present invention, nor does he use special-purpose hardware to assist in the implementation of his protocol as is done by the present invention.
In U.S. Pat. No. 5,541,921, “Isochronous Serial Time Division Multiplexer,” by Swenson et al., Swenson teaches a method and controller for filling time slots of a plurality of serial data streams by multiplexing time slots from a pluralit
Hilts Paul John
Youngman Brian Alan
Cockburn Joscelyn G.
Munoz-Bustamante Carlos
Srivastava Vivek
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