The desired solution for high speed data communications appears to be cable modem. Cable modem is capable of providing high data throughput rates, and is thus suitable for high speed file transfer, video teleconferencing and pay-per-view television. Further, cable modems may simultaneously provide high speed Internet access, digital television (such as pay-per-view) and digital telephony.
Although cable modems are used in a shared access system, wherein a plurality of subscribers compete for bandwidth over a common coaxial cable, any undesirable reduction in actual data rate is easily controlled simply by limiting the number of shared users on each system. In this manner, each user is assured of a sufficient data rate to provide uninterrupted video teleconferencing or pay-per-view television, for example.
Cable modem systems typically include one or more head ends or cable modem termination system (CMTS) devices that engage in bidirectional communication with the various subscribers' cable modems. Both the cable modems and the CMTS devices include modulators to transmit data (either upstream from the cable modems to the CMTS devices, or downstream from the CMTS devices to the cable modems), as well as demodulators to receive and demodulate the incoming data. Such system are preferably flexible to accommodate varying numbers of subscribers (typically an ever-increasing number).
MAP information is transmitted on one or more downstream channels by the cable modem termination system to all of the cable modems on a given frequency channel. As is well known in the art, MAP information covers all time periods on an upstream channel. MAP information typically consists of the combination of one or more of the following: request regions (i.e., the contention area that a modem can request new band width), request/data regions (where both data and request can be transmitted), initial maintenance regions (where new modems have the right to try and sign on), station maintenance regions (for modems that are in operation), and short and long data grant regions (for transmitting data). The short and long data grants may either be based on a request or can also be unsolicited grants. The MAP will consist of a combination of these regions, all as decided by the MAP generator.