Setting the desired operational mode – Enterasys Networks 6000 User Manual
Page 66
Managing the Module
2-47
The Device View
Duplex
This field specifies Half Duplex or Full Duplex mode for the port.
Flow Control
Flow control allows Ethernet devices to notify attached devices that congestion is
occurring and that the sending device should stop transmitting until the congestion can be
cleared. There are two commonly used methods of flow control: Frame-based (operates on
Full Duplex links) and Backpressure (operates on Half Duplex links).
Ports set to Full Duplex mode have frame-based flow control, using pause control
frames. Frame-based flow control options are:
Symmetric
The port is able to both receive and transmit pause control frames.
Asymmetric RX This option appears only for Gigabit Ethernet ports. The port will
receive pause control frames, but will not transmit its own.
Asymmetric TX This option appears only for Gigabit Ethernet ports. The port is
capable of sending pause control frames, but will not acknowledge
received pause control frames.
Disabled
Disables flow control on the port.
Auto Negotiate
Ports configured to operate in auto negotiation mode will only use
pause control frames if the negotiation process determines that the link
partner supports them. Both ends of the link must support auto
negotiation and a common mode of operation.
Ports set to Half Duplex mode use Backpressure flow control. Backpressure flow control
simply asserts the carrier sense signal out the port causing the device transmitting to detect
a collision, stop transmitting data, and send the jam signal. Backpressure flow control
options are enabled or disabled.
Setting the Desired Operational Mode
For any 100Base-TX port, you can configure operational modes, or you can select Auto
Negotiate mode, which allows the port to negotiate with its link partner to find the highest
mutually available bandwidth and flow control. If you select Auto Negotiate mode, you
must also choose which of the port’s bandwidth and flow control capabilities you wish to
advertise to the link partner (refer to
100Base-FX ports do not support auto negotiation for bandwidth or flow control
capability, so you must choose between 100Base-FX Half Duplex and 100Base-FX Full
Duplex mode, and set the flow control option. However, you must still be sure that both
link partners are set to the same operational mode, or the link will be unstable.
For 1000Base-SX/LX/CX ports the speed and duplex modes are always configured at
1000MB Full Duplex. However, you can select Auto Negotiate mode, which allows the
port to negotiate with its link partner to find the highest mutually available bandwidth and
flow control. If you select Auto Negotiate mode, you must also choose which of the port’s
bandwidth and flow control capabilities you wish to advertise to the link partner (refer to
).