Allied Telesis AT-GS950/8 - Manual (Page 23)

AT-GS950/8 Gigabit Ethernet WebSmart Switch Installation Guide
23
Duplex Mode The term 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, the end node is operating in half-duplex mode. If an end
node can both receive and transmit data simultaneously, the end node is
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-GS950/8 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 is 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-GS950/8 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 in a manual mode, it will not
respond to the Auto-Negotiate protocol from the AT-GS950/8 switch.
(Since the speed is determined from the link pulses, the speed is
always detected correctly.) As a result, the port setting on the switch
becomes half-duplex. If the end node is manually configured to full-
duplex, there is a duplex mismatch and data is lost. If the end node
is manually configured to half-duplex, both ports have the speed and
duplex match up correctly.
Store and
Forward
The AT-GS950/8 switch uses store and forward as the method for
receiving and transmitting frames. When a Ethernet frame is received by a
switch port, the switch does not retransmit the frame from the destination
port until it has received the entire frame and stored the frame in a port
buffer. Then it examines the frame to determine if it is a valid frame. Invalid
frames, such as fragments or runts, are discarded by the switch. This
ensures that only valid frames are transmitted from the switch ports and
that damaged frames are not propagated on your network.