Under certain conditions, packets sent from the source to the destination can overwhelm the destination endpoint. The destination is not able to process all packets at the rate that they are sent, leading to retransmits or dropped packets. Most scenarios have a fast source endpoint and a slower destination endpoint; this could be due to processing power or several source endpoints interacting with a single destination. Flow control is implemented to manage the rate of data transfer between these IP endpoints, providing an option for the destination to control the data rate, and ensuring the destination is capable of processing all the packets from the source.
The IEEEs 802.3x standard defines an Ethernet Flow Control mechanism at the Data Link Layer. It specifies a pause flow control mechanism through MAC Control frames in full-duplex link segments. For flow control to be successfully implemented, it must be configured throughout the network hops that the source and destination endpoints communicate through. Otherwise, the pause flow control frames are not recognized and are dropped.
By default, PowerScale OneFS listens for pause frames but does not transmit them, meaning it is only applicable when a PowerScale node is the source. In the default behavior, OneFS recognizes pause frames from the destination. However, pause frames may be enabled for transmit, depending on the NIC.
Most network devices today do not send pause frames, but certain devices still send them.