Cabletron Systems CSX1000, CSX1200 manual Overload Condition Monitoring

USER’S GUIDE

The throughput monitor feature constantly monitors the use of the connections and looks for the following conditions:

•The overload condition, which indicates that demand exceeds the current aggregate capacity of the WAN connections. The system can add more bandwidth when this occurs.

•The underload condition, which indicates that demand falls below a target capacity that is low- er than the current aggregate capacity. The system can release any previously added band- width when this occurs.

•The idle condition, which indicates that the last connection remaining is no longer needed.

The following sections explain each of these conditions in greater detail. Following the condition explanations, a throughput monitoring example is provided for further clarification.

OVERLOAD CONDITION MONITORING

The overload condition is monitored by comparing the samples to an upper threshold. The sample is marked as a true condition if either the transmit or the receive byte count exceeds the threshold. When the number of true samples in the window reaches the configured limit, the overload condition has occurred.

The overload threshold is configured as a utilization percentage of the aggregate bandwidth for a group of connections between two Systems.

If the system determines that the bandwidth can be increased, it will add a new channel into the connection group. At this time, the system adjusts its upper threshold for the new aggregate capacity and resets its counters. If the new capacity still cannot satisfy the transmit demand, the system will again detect the overload condition.

Similarly, when bandwidth is decreased, the system will remove a channel from the group of connections. The system adjusts its threshold accordingly, resets its counters, and begins monitoring for the overload condition against the lower aggregate capacity.

UNDERLOAD CONDITION MONITORING

The underload condition is monitored by comparing the samples with a lower threshold. The sample is marked as a true condition if both the transmit and the receive byte count fall below the threshold. When the number of true samples in the window reaches the configured limit, the underload condition has occurred.

The purpose of detecting this condition is to decide if connections can be released. Therefore, an underload threshold is defined in terms of a target bandwidth that is less than the current aggregate bandwidth. The underload condition indicates that the target capacity can satisfy the traffic demand.

When only one circuit remains in a group, the underload mechanism determines if a lower bandwidth circuit would satisfy the demand. For example, if one 384Kbps circuit remained, a target of 64Kbps could be specified and the above described mechanisms will identify when the 64Kbps circuit would satisfy the demand.

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