Allied-telesis AT-GS900/8E User Manual download pdf (Page 23)

AT-GA900/8 and AT-GA900/8E Gigabit Ethernet Switches Installation Guide

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-GS900/8 and AT-GS900/8E switches 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. Should 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

Since the ports on the AT-GS900/8 and AT-GS900/8E switches

operate in Auto-Negotiate mode only, the end nodes connected to

the AT-GS900/8 or AT-GS900/8E 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-GS900/8 or AT-GS900/8E 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 AT-GS900/8 or AT-GS900/8E 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-GS900/8 and AT-GS900/8E switches use 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.

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Allied-telesis AT-GS900/8E User Manual Page 23

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