Overview
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Duplex Mode Duplex mode refers to how an end node receives and transmits data. If an
end node can receive or transmit data, but not both simultaneously, it is
operating in what is referred to as half-duplex mode. If an end node can
both receive and transmit data simultaneously, the end node is said to be
operating in full-duplex mode. Naturally, an end node capable of operating
in full-duplex can handle data much faster than an end node that can only
operate in half-duplex mode.
The twisted pair ports on the AT-9000/28 Gigabit Ethernet ecoSwitch can
operate in either half-or full-duplex mode. They are IEEE 802.3u-
compliant and use Auto-Negotiation to set the duplex mode setting for you
automatically.
For Auto-Negotiation to operate properly on a switch, the end nodes
connected to the switch should also use Auto-Negotiation. If an end node
does not have this feature and has a fixed duplex mode of full-duplex, the
result will be a duplex mode mismatch between the end node and a switch
port. A port on the Gigabit Ethernet switch connected to an end node with
a fixed duplex mode of full-duplex will operate at only half-duplex. This
results in the end node using full-duplex and the switch port using half-
duplex. This can produce network performance problems. If you
encounter this situation, you must configure the port on the end node to
use Auto-Negotiation or, if it lacks that feature, to half-duplex.
AutoMDI/MDI-X
The auto-MDI/MDI-X feature on the twisted pair ports automatically
configures the MDI/MDI-X setting when a link is established with an end
node. Available when a port is at the default setting of Auto-Negotiation,
this feature allows you to use a straight-through twisted pair cable when
connecting any type of network device to a port.
Disabling Auto-Negotiation on a port and setting the speed and duplex
mode manually also disables the auto-MDI/MDI-X feature. A port where
Auto-Negotiation has been disabled defaults to MDI-X. Disabling Auto-
Negotiation may require manually configuring a port’s MDI/MDI-X setting
or using a crossover cable. For instructions on how to configure a port,
refer to the AT-S100 Management Software User’s Guide.
Store andForward
The AT-9000/28 Gigabit Ethernet ecoSwitch uses store and forward as
the method for receiving and transmitting frames. When a Ethernet frame
is received on a switch port, the switch does not retransmit the frame out
the destination port until it has received the entire frame and stored the
frame in a port buffer. It then examines the frame to determine if it is a
valid frame. Invalid frames, such as fragments or runts, are discarded by
the switch. This insures that only valid frames are transmitted out the
switch ports and that damaged frames are not propagated on your
network.
Back Pressureand Flow Control
To maintain the orderly movement of data between the end nodes, an
Ethernet switch may periodically need to signal an end node to stop