Allied Telesis AT-S39 - Manual (Page 188)

Section II: Local and Telnet Management
188
Broadcast Storm Control Overview
Most frames on an Ethernet network are usually unicast frames. A
unicast frame is a frame sent to a single destination. The node sending a
unicast frame intends the frame for a particular node on the network. For
example, when a node needs to send a file to a network server for
storage, it sends the file in a unicast Ethernet frame 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 the 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 the AT-S39 management software to limit
the number of broadcast frames forwarded by the switch and so restrict
their number.
To accomplish this, you specify the maximum number of broadcast
frames you want the switch to forward within a specified time interval.
Broadcast frames that exceed the maximum on a port during the time
interval are not forwarded and are discarded by the switch.
In order to use this feature, you must set two values: the interval timer
and the maximum broadcast frame limit.
The interval timer defines the time period used in counting the number
of forwarded broadcast frames on a port. There are two interval timers.
One timer is for ports operating at 10 Mbps or 100 Mbps. The second
timer is for 1000 Mbps ports. The timer interval for 10 and 100 Mbps
ports is measured in milliseconds. The timer interval for 1000 Mbps ports
is in microseconds. A time interval setting applies to all ports operating
at the corresponding speed on the switch.
The maximum broadcast frame limit specifies the maximum number of
broadcast frames a port will forward during the timer interval. Broadcast
frames received once the maximum has been exceeded are not
forwarded by a port and are discarded. You can specify a different
maximum for each port on the switch.