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C
HAPTER
2: O
PTIMIZING
B
ANDWIDTH
If the devices at either end of a link do not support auto-negotiation,
both ends must be manually set to full duplex or half duplex accordingly.
Ports operating at 1000 Mbps support full duplex mode only.
Flow Control
All Switch ports support flow control, which is a mechanism that
minimizes packet loss during periods of congestion on the network.
Packet loss is caused by one or more devices sending traffic to an already
overloaded port on the Switch. Flow control minimizes packet loss by
inhibiting the transmitting port from generating more packets until the
period of congestion ends.
Flow control is supported on ports operating in half duplex mode, and is
implemented using the IEEE 802.3x standard on ports operating in full
duplex mode.
Auto-negotiation
Auto-negotiation allows ports to auto-negotiate port speed,
duplex-mode (only at 10 Mbps and 100 Mbps) and flow control. When
auto-negotiation is enabled (default), a port “advertises” its maximum
capabilities — these capabilities are by default the parameters that
provide the highest performance supported by the port.
You can disable auto-negotiation on all fixed ports on the Switch, or on a
per port basis. You can also modify the capabilities that a port
“advertises” on a per port basis, dependent on the type of port.
For auto-negotiation to work, ports at both ends of the link must be set
to auto-negotiate.
Ports operating at 1000 Mbps support full duplex mode only.
If auto-negotiation is disabled, the ports will no longer operate in
auto-MDIX mode. Therefore, if you wish to disable auto-negotiation you
must ensure you have the correct type of cable, that is cross-over or
straight-through, for the type of device you are connecting to. For more
information on suitable cable types, please refer to the Getting Started
Guide that accompanies your Switch.
Smart Auto-sensing
Smart auto-sensing allows auto-negotiating multi-speed ports, such as
10/100 Mbps or 10/100/1000 Mbps, to monitor and detect a high error
rate on a link, or a problem in the “physical” interconnection to another