The ONL NPR Tutorial

NPR Tutorial >> Filters, Queues and Bandwidth

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UNDER CONSTRUCTION (50% DONE)

Monitoring With Formulas

In the bandwdith displays of UDP flows, one plot can hide other displays. We describe how to display incremental bandwidth using the Parameter => Add Formula feature in monitoring charts. We will use the dumbbell network shown to the right. The UDP senders n1p1, n1p2 and np3 each send at 200 Mbps to n2p1, n2p2 and n2p3 respectively. The senders begin sending using a 5-second staggered start with n1p1 starting first and n1p3 starting last. Each flow is given an equal share of the 300 Mbps bottleneck bandwidth by mapping each flow to a separate queue at port 1.4.

The bandwidth displays that we have been using would show that each flow would receive 100 Mbps. Their plots in the contention interval would fall on top of each other so that two of the plots would be hidden. But we can show each plot separately if we showed the bandwidth in an incremental manner by showing the following bandwidths: 1) bandwidth to n2p1; 2) combined bandwidths to n2p1 and n2p2; and 3) combined bandwidths to n2p1, n2p2 and n2p3. The second and third plots would show the bandwidth over and above the preceding plot.

======================= NEED INCREMENTAL BW FIG ============================

For example, the figure (right) shows the bandwidths coming from each of the three senders labeled as "1.1 rx", "1.2 rx" and "1.3 rx". These plots use the Monitoring => RXBYTE menu item in the port menu and the Parameter => Add Formula menu item in the monitoring chart. The chart is easier to read because the "1.2 rx" plot appears to be stacked on top of the "1.1 rx" plot, and the "1.3 rx" plot appears to be stacked on top of the "1.2 rx" plot. Similarly, the figure shows the bandwidth going to each of the three receivers as the stacked plots labeled "2.1 tx", "2.2 tx" and "2.3 tx" (also shown as dashed curves).

We now describe how to construct an incremental bandwidth chart. In the figure (right), we laid down the base "1.1 rx" plot in the standard manner by monitoring the bandwidth received by port 1.1 (Port 1.1 => Monitoring => RXBYTE). Now, we want to add two more lines each stacked on top of the "1.1 rx" line and then repeat the process for the three "2.n tx" (n = 1, 2, 3) lines that measure the bandwidth transmitted out of the NPR 2 ports 1-3. In order to display the bandwidth in incremental format, we select the Parameter => Add Formula menu item in the display panel and the Add Formula dialogue box appears.

The Add Formula feature acts just like a calculator. Suppose that the three plots of 1.n (n = 1, 2, 3) are represented by the three time series X[], Y[] and Z[] where X[] represents the sequence X[0], X[1], .... In effect, we would like to display X[i], X[i]+Y[i] and X[i]+Y[i]+Z[i] for i = 0, 1, 2, .... However, in our example, we visually indicate the time series by selecting the monitoring items instead of the time series X[], Y[] and Z[].

The recipe for creating the +1.2 plot (after the 1.1 plot) is:

The traffic chart will look like the figure (right). Now, you can change the monitoring units to Mb/s by selecting the plot label and selecting Mb/s from the Units menu. Now, repeat the above procedure to add the other incremental bandwidth plots.

NPR Tutorial >> Filters, Queues and Bandwidth	TOC