Duplex Mode; Store And Forward; Backpressure And Flow Control - Allied Telesis AT-8024 Installation Manual

Product Description

Duplex Mode

Store and
Forward
Backpressure
and Flow
Control
38
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
node is said to be operating in full-duplex mode. Naturally, a node
capable of operating in full-duplex can handle data much faster than a
node that can only operate in half-duplex mode.
Each twisted pair port on an AT-8024 and AT-8024GB 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. If the end node connected to a twisted pair port on the switch is
capable of full-duplex operation, the switch sets the twisted pair port to
full-duplex. If the end node is capable of only half-duplex, the port is set
automatically to half-duplex.
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 a 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.
These Fast Ethernet 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.
In order for an Ethernet switch to maintain the orderly movement of
data between the end nodes that are connected to its ports, it may
periodically need to signal an end node to stop sending data. This can
occur under several circumstances. For example, if two end nodes are
operating at different speeds, the switch, while transferring data
between the nodes, might need to instruct the faster end node to stop
transmitting data to allow the slower end node to catch up. An example
of this would be when a server operating at 100 Mbps is sending data to
a workstation operating at only 10 Mbps.