In a broadband switching system for the switching of asynchronously transferred cells of data, a dynamic bandwidth controller (DBC) controls the application of data cells to an input port of the system, the data cells being supplied by a number of transmitting end-systems. When an end-system begins transmitting data cells, the DBC
detects the presence of incoming cells and requests bandwidth from a connection admission control (CAC) forming part of the system. The switching system stores a table associating a number of signal sources connected to the input port with respective predetermined maximum transmission times and maximum transmission rates for the sources. When arrival of cells at the input port from one of the source is detected, the DBC and CAC operate together to allocate sufficient bandwidth in the switching system to allow the respective message size to be transmitted within the respective maximum transmission time.
A guaranteed minimum rate of transmission is also guaranteed for the source.