IEEE 802.3x Flow Control, which is the process of pausing the transmission based on received pause frames, is supported on Fast Ethernet, Gigabit Ethernet, and 10-Gigabit Ethernet (SFP+) ports. In the transmit direction, the Ethernet ports generate pause frames if the buffer occupancy reaches critical values or if port FIFO buffers are overloaded. Pause frame generation is automatically handled by the Ethernet Adapter card when the system-wide constant thresholds are exceeded. The generation of pause frames ensures that newly arriving frames still can be processed and queued, mainly to maintain the SLA agreements.
If autonegotiation is on for an Ethernet port, enabling and disabling of IEEE 802.3x Flow Control is autonegotiated for receive and transmit directions separately. If autonegotiation is turned off, the reception and transmission of IEEE 802.3x Flow Control is enabled by default and cannot be disabled.
Ingress flow control for the 6-port SAR-M Ethernet module is Ethernet link-based and not port-based. When IEEE 802.3x Flow Control is enabled on the 6-port SAR-M Ethernet module, pause frames are multicast to all ports on the Ethernet link. There are two Ethernet links on the 6-port SAR-M Ethernet module: one for ports 1, 3, and 5, and one for ports 2, 4, and 6. Pause frames are sent to either ports 1, 3, and 5, or to ports 2, 4, and 6, depending on which link the pause frame originates.