Methods for Supplying Interactive Services on Broad-Band Communication Networks
The features and limitations of time- and frequencydivision miltiplexed (TDM and FDM) systems for providing interactive services on broad-band communication networks are considered. We find that TDM systems make efficient use of bandwidth for digital signal rates below 10 kbits/s while FDM systems are efficient for analog signals and digital signal rates above 1 kbit/s. Although TDM and FDM systems can employ static allocation in which fixed channels are assigned to subscribers, dynamic allocation increases the efficiency of bandwidth usage by an order of magnitude. A TDM interrupt scheme appears to be the most efficient way to identify requests and process control signals in a dynamic allocation system, but introduces a problem of interference between simultaneous signals (not present with a polling technique for request identification).