Flow control system to reduce memory buffer requirements and to establish priority servicing between networks

摘要

The invention is a system and method to allow precise control of the transmit packet rate between two different networks and to optionally introduce a priority servicing scheme across several related output ports of a switch engine. The invention employs flow control circuitry to regulate data packet flow across a local interface within a single device by asserting back-pressure. Specifically, flow control is used to prevent a switch port from transmitting a data packet until a subsequent processing stage is ready to accept a packet via that port. The downstream node only permits transmission of packets from the switch when its buffer is available. An interface block effectively multiplexes together multiple switch ports by maintaining constant back-pressure on all of the ports and then releasing the back-pressure, one port at a time, to see if a port has a packet to transmit. This use of back-pressure to control the flow of data packets also allows a priority servicing scheme to be implemented by controlling the sequence of releasing back-pressure to the ports and also the number of packets allowed out of a port when it is allowed to transmit.