Peavey MediaMatrix NION Hardware Manual page 69

A network topology, such as either of the examples in the Commonly used fault tolerant
techniques for CobraNet networks (on page 64) section, is in use and functioning properly
with redundant links having been removed by STP. A link between switches is then
broken. STP creates a new path and the network continues to work properly. Later, the
bad link is repaired. When the link is reestablished, a loop is momentarily created until
STP removes it.
Rapid Spanning Tree (RSTP) is a newer variant of Spanning Tree (STP) in which
management of the links is accomplished an order of magnitude faster than standard
Spanning Tree. The net effect of this operating characteristic is that a network using RSTP
can experience data storm like events in the course of its normal operation while resolving
loops.
What we know
CobraNet modules can crash in the presence of excessive network traffic (data storms).
Excessive traffic is almost always caused by the presence of a loop but can, in some cases,
be a consequence of normal operation.
Loops, in conjunction with the use of Spanning Tree or an analogous feature such as
RSTP, MSTP or Meshing (a proprietary HP protocol), can be intentionally used to create
fault tolerant network topologies.
Different topologies can cause loop effects.
Loops and use of Spanning Tree will typically only apply to networks that use more than
one switch. Use of more than one switch is common.
Mitigation
Do not use topologies that intentionally employ loops when their use can be avoided.
Check for the presence of, and remove any, unintended loops.
Do not use Rapid Spanning Tree (RSTP or MSTP). Use STP.
Use switches that allow port based bandwidth throttling or data storm control. The
configuration of a throttling feature will be switch vendor specific. Configure each port
directly connected to a CobraNet device to limit the amount of traffic allowed to go from
the port to the CobraNet device.
Data storm control often consists of severely limiting or stopping multicast data. Be
sure that this feature is not configured to prevent the passage of normally occurring
multicast CobraNet data which includes beat packets, reservation packets and
multicast bundles.
A good rule is to limit traffic going to a CobraNet device to 50 megabits. Less traffic
may be acceptable and safe depending on the number of bundles and channels received
by a device. More than 50 Mbit of bandwidth will seldom be required when using
CM-1 modules.
The specific bandwidth to allow should be the amount of received data plus
approximately 10 to 15 megabits
A CM-1, when fully configured to receive 32 channels of 48 kHz sample rate audio
data at standard latency, will receive approximately 32 Mbit of audio data + beat
packets + SNMP + serial or packet bridge. The additional 10~15 Mbit is intended to
accommodate data other than audio bundles.
Additional requirements for bandwidth will be created by the use of:
Lower latencies – approx +10% per decrease in latency
96 kHz sample rate - doubles the required bandwidth per channel
Packet bridge – use dependant
Serial bridge – use dependant
September 30, 2010 Version 1.6.1.0
NION Hardware Manual
65