Apparatus and method for digital data transmission over a catv system

Abstract

A method and apparatus for carrying an ATM communication protocol on a hybrid fiber coax CATV system. Point to point communication is supported by use of synchronous code division multiplexing on the physical and by assigning on the MAC layer one or more orthogonal SCDMA codes exclusively for use by pairs of devices needing to communicate such the head end and any customer premises equipment. Quality of service or guaranteed bandwidth availability is implemented by controlling the code space at the MAC layer such that certain CPEs having in use peripherals which cannot tolerate interruptions in data flow may reserve one or more SCDMA codes for use exclusively by them. Standard ATM cells are modified by the addition of a two byte virtual link header which identifies to which CPE a particular ATM packet is destined. This virtual header also makes possible broadcast and multicast of packets from the head end to all CPEs. Each byte in each ATM cell has 8 bits of data and a 9th bit which is encoded with to indicate where the ATM cell starts and includes CRC data for error detection and correction. Bandwidth is allocated by the head end computer which executes algorithms on the MAC layer to collect actual bandwidth usage information and requests for bandwidth and prioritize them in accordance with the channel allocation/reservation scheme currently use. The channel allocation/reservation scheme can be changed on the fly and reallocation calculations to adjust bandwidth allocations are calculated every 10 milliseconds and the new allocations are distributed in downstream messages which are transmitted to all CPEs.