Allied Telesis AT-9400, User Manual

Page: 71 / 668

AT-S63 Management Software Menus User’s Guide
Section I: Basic Operations 71
Configuring Flow Control and Back Pressure
A switch port uses flow control to control the flow of ingress packets from
its end node when operating in full-duplex mode.
A port using flow control issues a special frame, referred to as a PAUSE
frame, as specified in the IEEE 802.3x standard, to stop the transmission
of data from an end node. When a port needs to stop an end node from
transmitting data, it issues this frame. The frame instructs the end node to
cease transmission. The port continues to issue PAUSE frames until it is
again ready to receive data from the end node.
The default setting for flow control on a switch port is disabled.
Back pressure performs much the same function as flow control. Both are
used by a port to control the flow of ingress packets. Flow control applies
to ports operating in full-duplex; back pressure applies to ports operating in
half-duplex mode.
When a twisted pair port on the switch operating in half-duplex mode
needs to stop an end node from transmitting data, it forces a collision. A
collision on an Ethernet network occurs when two end nodes attempt to
transmit data using the same data link at the same time. A collision causes
the end nodes to stop sending data.
When a switch port needs to stop a half-duplex end node from transmitting
data, it forces a collision on the data link, which stops the end node. After
the switch is ready to receive data again, the switch stops forcing
collisions. This is called
back pressure .
The default setting for back pressure on a switch port is disabled.
To set up flow control or back pressure, perform the following procedure:
1. From the Main Menu, type 1 to select Port Configuration.
The Port Configuration menu is shown in Figure 13 on page 62.
2. From the Port Configuration menu, type 1 to select Port Configuration.
The following prompt is displayed:
Enter port-list ->
3. Enter the number of the port to be configured. You can configure more
than one port at a time. You can specify the ports individually (for
example, 5,7,22), as a range (for example, 18-23), or both (for
example 1,5,14-22).
The Port Configuration menu is shown in Figure 15 on page 65.