Cabletron Systems CSX1000 - Manual (Page 316)

USER’S GUIDE
316 CyberSWITCH
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.
O VERLOAD C ONDITION M ONITORING
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.
U NDERLOAD C ONDITION M ONITORING
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.