AT-GS900/8POE Gigabit Ethernet Switch Installation Guide
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end node can receive or transmit data, but not both simultaneously, the
end node 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-GS900/8POE Gigabit Ethernet switch
switch 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.
Note
Because the ports on the AT-GS900/8POE Gigabit Ethernet switch
operate in Auto-Negotiate mode only, the end nodes connected to
the switch must also be configured to operate in the Auto-Negotiate
mode. If an end node is configured to a specific duplex setting in a
manual mode, it will not respond to the Auto-Negotiate protocol from
the AT-GS900/8POE Gigabit Ethernet switch. (The speed is
determined from the link pulses, however, so the speed is always
detected correctly.) As a result, the port setting on the switch will end
up at half-duplex. If the end node is manually configured to full-
duplex, there will be a duplex mismatch and data will be lost. If the
end node is manually configured to half-duplex, both ports will have
the speed and duplex match up correctly.
Store and
Forward
The AT-GS900/8POE Gigabit Ethernet switch 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.
