Allied Telesis AT-CM70S - Manual (Page 59)

Converteon Media Converter Line Cards Reference Guide
59
without forwarding it on to any port. Because both the source end node
and the destination end node for the packet are located on the same port
on the line card, there is no reason for the line card to forward the packet.
Duplex Mode
Duplex mode refers to the manner in which 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 Converteon™ line cards 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 line card to configure the duplex mode for each port, you
will not need to change the setting for a port on the line card should you
replace an end node with an end node that has a different duplex mode
capability. With Auto-Negotiation, the line card automatically resets the
port to a new duplex mode setting.
If desired, you can disable Auto-Negotiation on the line card ports so that
you can set the duplex mode manually through the management software.
In order for a line card 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 line card port, using
Auto-Negotiation, defaults to half-duplex if it detects that the end node is
not using Auto-Negotiation. This results in a mismatch if the end node is
operating at a fixed duplex mode of full-duplex.
Consequently, when you connect an end node with a fixed duplex mode of
full-duplex to a line card port, you should use the AT-S70 management
software to disable Auto-Negotiation on the port and set the port speed
and duplex mode manually.
Store-and-
Forward
The bridging media converter line cards, for example the AT-CM20x
Series, AT-CM2K0S, and CM212x/1 Series line cards, use store-and-
forward as the method for receiving and transmitting frames. When an
Ethernet frame is received on a line card port, the line card 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 line card. This ensures that only valid frames are
transmitted out the line card ports and that damaged frames are not
propagated on your network.