Link-Level Flow Control
Packet discarding: If a packet arrives at a switch and there is no room in the buffer, the packet is discarded
- no communication between switches, requires higher level protocol
Flow control: between pairs of receivers and senders; use feedback to tell the sender when it is allowed to send the next packet
- Choke packets: aka “rate-based”; Each packet received by busy switch in warning state sent back to the source via choke packet. Source reduces traffic to that destination by a fixed % (ATM Forum) Back-pressure: separate wires to tell to stop
- high water, low water (stop & go back to source switch) (Myrinet)
- Window: give the original sender the right to send N packets before getting permission to send more (overlap the latency of the interconnection with the overhead to send and receive a packet)