Brocade Communications Systems FastIron Administration Manual page 68

About XON and XOFF thresholds
About XON and XOFF thresholds
An 802.3x PAUSE frame is generated when the buffer limit at the ingress port reaches or exceeds the
port's upper watermark threshold (XOFF limit). The PAUSE frame requests that the sender stop
transmitting traffic for a period of time. The time allotted enables the egress and ingress queues to be
cleared. When the ingress queue falls below the port's lower watermark threshold (XON limit), an
802.3x PAUSE frame with a quanta of 0 (zero) is generated. The PAUSE frame requests that the
sender resume sending traffic normally.
Each 1G, 10G, and 40G port is configured with a default total number of buffers as well as a default
XOFF and XON threshold. The defaults are different for 1G ports versus 10G or 40G ports. Also, the
default XOFF and XON thresholds are different for jumbo mode versus non-jumbo mode. The defaults
are shown in
TABLE 8
1G ports
Total buffers 272
XOFF
XON
10G ports
Total buffers 416
XOFF
XON
40G ports
Total buffers 960
XOFF
XON
If necessary, you can change the total buffer limits and the XON and XOFF default thresholds. Refer
to Changing the total buffer limits
69, respectively.
Configuration notes and feature limitations for symmetric flow control
Note the following configuration notes and feature limitations before enabling symmetric flow control.
• Symmetric flow control is supported on FCX and ICX devices only. It is not supported on other
FastIron models.
• Symmetric flow control is supported on all 1G,10G, and 40G data ports on FCX and ICX devices.
• Symmetric flow control is not supported on stacking ports or across units in a stack.
68
About XON and XOFF thresholds.
XON and XOFF default thresholds
Limit when Jumbo disabled / % of buffer limit Limit when Jumbo enabled / % of buffer limit
240 / 91%
200 / 75%
376 / 91%
312 / 75%
832 (87%)
720 (75%)
on page 70 and
272
216 / 82%
184 / 70%
416
336 / 82%
288 / 70%
960
832 (87%)
720 (75%)
Changing the XON and XOFF thresholds
FastIron Ethernet Switch Administration Guide
on page
53-1003625-01