Flow Control

There are three flow control options on 10/100 Ethernet ports:

• Disable
• Enable
• Enable with Aggressive Backoff

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 attached equipment to use the 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 Aggressive Backoff option 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. Therefore, 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.