 a total of 16K channels multiplied over 8 cards comprising an advanced services in the BT network. odd/even pair on all four shelves. Members of the DMS family are characterised by their ability to With up to 16 (8 pairs) crosspoint cards per shelf, this gives the meet new application and reliability requirements, and to incorpor- total of 128K channels in eight streams of 16K. ate new technology in their design. New technology in turn provides Each incoming call will appear on eight of the crosspoint cards, increased capability and reliability at reduced cost. serving the 16K stream within which it originates. One of these The DMS family can evolve because modular design techniques cards switches the call to one of the pair of horizontal buses (H-bus) are used in the development of both its software and its hardware. available on its shelf. The call is then switched by the appropriate Modularity may be thought of as the implementation of a complex card on the same shelf and the same H-bus serving the 16K stream system through a set of functional units or modules connected by containing the destination port. Since any incoming call appears on well defined interfaces. As a result of proper module and interface both the odd and even card on each shelf via the mated V-bus arrays, design, the various units can be connected, disconnected, modified, it may be switched to any other crosspoint card via the appropriate or improved, without affecting either the operation of other modules H-bus. The second crosspoint card simply passes the incoming 2K in the system or the system as a whole. stream from the H-bus to the speech link interface for demultiplex- There are two generations of DMS. The second generation is ing into four separate DS512 speech link ports. A call between two known as DMS SuperNode and provides increased processing and channels in the same 16K stream is switched twice on the same call handling capacity at reduced size and with improved reliability. crosspoint card. This is the current product and, exc