By James R. Cherry and Tony Chen-tung Li, Oak Communications Inc.
The need of the subscriber to simultaneously operate multiple TV sets and/or VCR's from his cable service has led to significant use of multiple home terminal units (HTU). If a subscriber pays a lower fee for a secondary HTU that is authorized to receive the same premium service as his primary unit a risk exists that the unit will be sublet to a neighbor. For addressable cable systems using out-of-band data carriers, a master/slave configuration is proposed as a solution to the problem of subletting secondary units. The master/slave consists of two HTU's: the master used with the primary set and the slave used with the secondary sets. The slave unit does not function unless its address-control channel is protected by a master HTU. Thus, if the slave unit is used in a neighbor's home without its master, the secondary, or slave, unit will not function. Both master and slave HTU's can still respond with all addressable features. The uniqueness of the scheme lies in the selective blocking, by the master unit, of deauthorize commands directed at all slave HTU's. A high level of security is maintained without the requirement for complex, handshaking duplex data communications between the two HTU's.