The well-accepted advantages of an off-premises, star-switched distribution system, like MH-II, include security of signal and reduction of equipment theft. These advantages have prompted many cable operators to plan system expansions in a theft-prone environment such as Multiple Dwelling Units (MDUs) by using the star-switched technology. This paper reviews the issues of compatibility for implementing a hybrid addressable system comprised of conventional addressable set-top units and star-switched distribution nodes.
The design of a Mass Descrambling System (MDS) that alleviates the need for a clear trunk option is described. MDUs can be placed at strategic points in the franchise area to provide clear signals to nodes where Local Distribution Units (LDUs) are located. The MDS descrambles up to eight channels and then upconverts them to unused channel slots in the distribution system's frequency spectrum. Because the frequency table in an LDU is software downloadable, the up-conversion process is transparent to subscribers. The hardware design objectives for the MDS are performance transparency, cost effectiveness, and universality of the descrambling approach.
The paper includes a discussion of integration issues involved in implementing headend control and communication functions for two systems in a hybrid environment.