8-6 User Guide for the Avaya P580 and P882 Multiservice Switches, v6.1
Chapter 8
There are four flow control options on Gigabit Ethernet Ports.
■Disable
■Enable
■Enable – Send Only
■Enable – Respond Only
The Disable option disables flow control (the default).
The Enable option enables IEEE802.3X (XOFF/XON) Flow Control on the
line. The Avaya Multiservice Switch is the sender of pauses based upon
inbound traffic and the Avaya Multiservice Switch is the receiver of pauses
based upon outgoing traffic (and the ability of att ached equi pment to use th e
protocol).
With Gigabit links, you can:
■Enable IEEE802.3X for both send and receive (the “Enable”
setting)
■Only send pause (XOFF/XON) signals (the “Enable – Send Only”
option)
■Only respond to the pause signals (the “Enable – Respond Only”
option).
With 10/100 links you can use the Enable with Aggr es sive Backof f opti on
to enable Active Backpressure (creation of a collision) on a link. Active
Backpressure only applies to HD links so that when a 10/100 link is in FD,
options 2 and 3 are identical.
If you enable flow control, the switch manages the inbound buffers with
flow control (IEEE 802.1X XOFF, or Backpressure) applied when a high
water mark is reached. Thus, no matter which flow control option is chosen,
outgoing pauses or backpressure are only applied to the port on which the
parameter is set based upon the inbound traffic for that port in the default
queuing mode.
Flow control is not applied across the switch itself. Ther efore, if you have a
server sending data on one port at 100MB and a client receiving the data at
10MB, the switch will not throttle the data at the Server’s input based on
outgoing buffer backup on the client’s port in this default queuing mode.