Controller for ATM segmentation and reassembly

摘要

A header and a payload in a cell are separated for transfer between a cell interface and a host memory. The header is transferred to a control memory. For transfer to the host memory, the control memory initially provides a host-memory region address and the region length. The payload is recorded in such region. The control memory also provides a second host-memory region address, and length, when the payload length exceeds the payload length in the first address region. For transfer from the host memory to the cell interface, the control memory provides a host memory region address and the header combines the header and the payload and passes the combination to the cell interface. Cells from different sources (i.e. terminals) are scheduled at table positions dependent upon their individual transfer rates. The cells at the scheduled positions are normally transferred in time slots corresponding to such positions. When more than one (1) cell is scheduled at the same position, one (1) cell is transferred on a preset priority basis to the corresponding time slot. The other cells are delayed for transfer subsequently in idle time slots (i.e. no cell normally scheduled) in the same or other priorities. The cell delays for each source are accumulated to a maximum preset value. When the cell delays accumulated for a source exceed the normal time spacing between cells from that source, a cell the source transfers a cell in an idle time slot prior to the normally scheduled time slot to compensate for such delay.