Cabletron Systems CyberSWITCH CSX150 User Manual

Also see for CyberSWITCH CSX150: User guide Quick start guide

Contents

USER’S GUIDE298 CyberSWITCHThe throughput monitor feature constantly monitors the use of the connections and looks for thefollowing conditions:• The overload condition, which indicates that demand exceeds the current aggregate capacityof 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 conditionexplanations, a throughput monitoring example is provided for further clarification.O VERLOAD CONDITION M ONITORINGThe overload condition is monitored by comparing the samples to an upper threshold. The sampleis 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 overloadcondition has occurred.The overload threshold is configured as a utilization percentage of the aggregate bandwidth for agroup of connections between two Systems.If the system determines that the bandwidth can be increased, it will add a new channel into theconnection group. At this time, the system adjusts its upper threshold for the new aggregatecapacity and resets its counters. If the new capacity still cannot satisfy the transmit demand, thesystem will again detect the overload condition.Similarly, when bandwidth is decreased, the system will remove a channel from the group ofconnections. The system adjusts its threshold accordingly, resets its counters, and beginsmonitoring for the overload condition against the lower aggregate capacity.U NDERLOAD C ONDITION MONITORINGThe underload condition is monitored by comparing the samples with a lower threshold. Thesample is marked as a true condition if both the transmit and the receive byte count fall below thethreshold. When the number of true samples in the window reaches the configured limit, theunderload condition has occurred.The purpose of detecting this condition is to decide if connections can be released. Therefore, anunderload threshold is defined in terms of a target bandwidth that is less than the current aggregatebandwidth. The underload condition indicates that the target capacity can satisfy the trafficdemand.When only one circuit remains in a group, the underload mechanism determines if a lowerbandwidth circuit would satisfy the demand. For example, if one 384Kbps circuit remained, atarget of 64Kbps could be specified and the above described mechanisms will identify when the64Kbps circuit would satisfy the demand.