Allied Telesis AT-8088/xx (MT and SC) - Manual (Page 41)

AT-8000 Series Fast Ethernet Switches Installation Guide
41
If the switch receives a packet with a destination address that is on the
same port on which the packet was received, it discards the packet
without forwarding it on to any port. Since both the source end-node
and the destination end-node for the packet are located on the same
port on the switch, there is no reason for the switch to forward the
packet.
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,
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-8000 Series Switches can operate in
either half- or full-duplex mode. The twisted pair ports are IEEE 802.3u-
compliant and will Auto-Negotiate the duplex mode setting for you.
By allowing the switch to configure the duplex mode for each port itself,
you will not need to change the setting for a port on the switch should
you replace an end-node with an end-node that has a different duplex
mode capability. With Auto-Negotiation, the switch will automatically
reset the port to a new duplex mode setting for you.
If desired, Auto-Negotiation on the switch ports can be disabled so that
you can set the duplex mode manually through the switch’s
management software.
Note
In order for a switch port to successfully Auto-Negotiate its duplex
mode with an end-node, the end-node should also be using Auto-
Negotiation. Otherwise, a duplex mode mismatch can occur. A
switch port, using Auto-Negotiation, will default to half-duplex if it
detects that the end-node is not using Auto-Negotiation. This will
result in a mismatch if the end-node is operating at a fixed duplex
mode of full-duplex. Consequently, when connecting an end-node
with a fixed duplex mode of full-duplex to a switch port, you should
use the AT-S39 management software to disable Auto-Negotiation
on the port and set the port speed and duplex mode manually.