| 摘要 |
<p>A subscriber multiplexing device comprising a time-division user data bus (33) and a message-based signalling channel (34) between subscriber interface units (32) and a multiplexing unit (31), the signalling channel being common to all the subscriber interface units. A 'message based' signalling channel means that signalling is transferred in discrete protocol data units (PDU), or messages, comprising at least a destination address and the actual signalling data. Each unit connected to the signalling channel receives the message and compares the destination address of the message to its own address. When the addresses match, the unit concerned identifies the message as being addressed to it. If there is no match, the unit rejects the message. Each unit sends a signalling message only when needed, on event basis, in response to an internal change in state or to a message received from another unit, for example. In other words, information about changes is only signalled further through the signalling channel (34).</p> |
