Allied Telesis AT-S62 - Manual (Page 76)

Chapter 5: Port Parameters
76 Section I: Basic Operations
Broadcast Filter
Most frames on an Ethernet network are usually unicast frames. A
unicast frame is a frame that is sent to a single destination. A node
sending a unicast frame intends the frame for a particular node on the
network. For example, when a node sends a file to a network server
for storage, the node sends the file in unicast Ethernet frames
containing the destination address of the server where the file is to be
stored.
Broadcast frames are different. Broadcast frames are directed to all
nodes on the network or all nodes within a particular virtual LAN.
Broadcast packets can perform a variety of functions. For example,
some network operating systems use broadcast frames to announce
the presence of devices on a network.
The problem with broadcast frames is that too many of them traversing
a network can impact network performance. The more bandwidth
consumed by broadcast frames, the less available for unicast frames.
Should the performance of your network be impacted by heavy
broadcast traffic, you can use this parameter to limit the number of
broadcast frames forwarded by the switch and so limit the number of
broadcast frames on your network.
When you activate this feature on a port, the port discards all egress
broadcast packets. That is, if the port has a broadcast packet to
transmit, it instead discards the packet.
It should be noted that the filtering takes place only on egress
broadcast packets—packets that a port is transmitting. This filter does
not apply to ingress broadcast packets.
Possible settings for this parameter are:
Enabled The port will not transmit any broadcast frames.
Disabled The port will transmit broadcast frames. This is the
default setting.
Back Pressure
Sets backpressure on a port. This option only applies to ports
operating in half-duplex mode. A switch port uses backpressure to
control the flow of ingress packets.
When a twisted pair port on the switch operating in half-duplex mode
needs to stop an end node from transmitting data, it forces a collision.
A collision occurs when two end nodes attempt to transmit data using
the same data link at the same time and causes the end nodes to stop
sending data. The switch stops forcing collisions when it is ready to
receive data again. This is called backpressure.
The default setting for backpressure on a switch port is disabled.