Extended Cp-Limit - Avaya 8800 Planning And Engineering

Extended CP-Limit

The Extended CP-Limit feature goes one step further than CP-Limit by adding the ability to
read buffer congestion at the CPU as well as port level congestion on the I/O modules. This
feature protects the CPU from any traffic hitting the CPU by shutting down the ports that are
responsible for sending traffic to CPU at a rate greater than desired.
To make use of Extended CP-Limit, configuration must take place at both the chassis and port
level. The network administrator must predetermine the number of ports to be monitored when
congestion occurs. Extended CP-Limit can be enabled on all ports in the chassis, but when
congestion is detected, Extended CP-Limit monitors the most highly utilized ports in the
chassis. The number of highly utilized ports monitored is configured in the MaxPorts parameter.
When configuring Extended CP-Limit at the chassis level, the following parameters are
available:
• MinCongTime (Minimum Congestion Time) sets the minimum time, in milliseconds, during
which the CPU frame buffers can be oversubscribed before triggering the congestion
algorithm.
• MaxPorts (Maximum Ports) sets the total number of ports that need to be analyzed from
the may-go-down port list.
• PortCongTime (Port Congestion Time) sets the maximum time, in seconds, during which
the bandwidth utilization on a port can exceed the threshold. When this timer is exceeded,
the port is disabled – this parameter is only used by SoftDown.
• TrapLevel Sets the manner in which a SNMP trap is sent if a port becomes disabled.
- None—no traps are sent (default value)
- Normal—sends a single trap if ports are disabled.
- Verbose—sends a trap for each port that becomes disabled.
When configuring ext-cp-limit at the port level, the following parameters are available:
• HardDown disables the port immediately after the CPU frame buffers are congested for
a certain period of time.
• SoftDown monitors the CPU frame buffer congestion and the port congestion time for a
specified time interval—the ports are only disabled if the traffic does not subside after the
time is exceeded. The network administrator can configure the maximum number of
SoftDown ports to be monitored.
• CplimitUtilRate defines the percentage of link bandwidth utilization to set as the threshold
for the PortCongTime—this parameter is only used by SoftDown.
The following figures detail the flow logic of the HardDown and SoftDown operation of Extended
CP-Limit.
Planning and Engineering — Network Design
Extended CP-Limit
November 2010 37