Specifications

Appendix B IR-ETH/QV Interface Module FOM-40 Installation and Operation Manual

B-6 Installation and Operation

Backpressure and Flow Control

DIP switch SW1/4 enables or disables both backpressure and flow control.

When the IR-ETH/QV is set to half-duplex, backpressure is active, and when the

IR-ETH/QV is set to full-duplex, flow control is active.

Full-duplex flow control activation requires autonegotiation to be enabled.

Backpressure is the term given when the buffer is filled from the LAN faster than it

is able to transmit to the WAN. In order to prevent packet loss, collisions are

forced into the LAN, which causes the link partners to go into back-off before

attempting to retransmit. This reduces traffic passing through the interface.

Flow control is active only in full-duplex mode. When the buffer is filled from the

LAN faster than it is able to transmit to the WAN, pause frames are sent to the

LAN, ordering the LAN to stop for a time interval indicated by the pause frame

until transmission starts again.

To use the flow control option, the link partners (switches, etc.) should support flow

control.

LED Indicators

Table B-4 lists the IR-ETH/QV LED indicators and describes their functions.

Table B-4. IR-ETH/QV LED Indicators

LED Color Function

LINK Green ON – LAN is connected

ACT Yellow Blinks – Transmit/receive activity is detected on the

Ethernet link

100M Green ON – LAN is operating at 100 Mbps

Connecting the LAN

Use either a straight cable or a cross-cable for the LAN connection.

Use a cross-cable when connecting to a port that does not implement the

crossover function internally. Otherwise, use a straight cable.

Hubs usually implement the crossover function internally, while NICs and other

devices do not.

Note