3Com Network Jack NJ2000
Page 15 of 44
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Speed/Duplex
The Speed and Duplex settings for the port are set by a single drop-down list. The possible values are:
Auto
- Speed and duplex settings are auto-negotiated.
10HDX
- 10 Mbps, half-duplex
10FDX
- 10 Mbps, full-duplex
100HDX
- 100 Mbps, half-duplex
100FDX
- 100 Mbps, full-duplex
1000FDX
- 1000 Mbps, full-duplex
Note: Auto
is the default setting and need not be changed unless you are experiencing problems
establishing link with a connected device (i.e. the front-panel LEDs or
STATUS > Overview
page
indicate that the link is down when there is a cable connecting a device to the switch).
Note: Auto
causes the switch to negotiate the link speed and duplex settings with the connected device;
this is called Auto-negotiation. All of the other settings cause Auto-negotiation to be turned off.
Note:
In full-duplex mode, both ends of a connection can send traffic at the same time which effectively
doubles the available throughput. In half-duplex mode, only one end of the connection can send traffic at
any one time.
Flow Control
When
Flow Control
is selected on a port (by clicking on the tick-box in the
Flow Control
column), the
switch will attempt to slow incoming traffic down when traffic levels are high. It does this by sending
special Pause packets on full-duplex connections or creating back-pressure (deliberately causing
collisions) on half-duplex connections. This can increase traffic throughput by reducing the number of
dropped packets and, as a result, the number of resends that are required. However it is not appropriate in
all circumstances.
