Overview… histograms, counting packets
Histograms analyze a stream of packets, either at the transmit side or the receive side of a port, and classify them into a number of buckets, counting how many packets go into each bucket.
Histograms complement the statistics, which just provide aggregate counts, and capturing, which provides per-individual-packet information.
Like transmitting and capturing, histograms are explicitly started and stopped:
A histogram is defined in terms of its source and its range.
The source specifies which packets should be analyzed and for which parameter, such as: transmitted packet length, received packet inter frame gap, received packet latency, etc.
Please note the difference between inter frame gap and latency: inter frame gap is the time elapsed since the previous packet was encountered, whereas latency is the time this packet itself has been in transit. Inter frame gap times are converted to the equivalent number of bytes, whereas latency is measured in nano-seconds.
The range specifies an offset and the bucket size, and thereby the resolution of the counted parameter:
Once a histogram is started, the XenaManager provides a graphical display of the counts:
All the buckets start off empty, and as packets are encountered (according to the source) they are counted (according to the range), and a picture emerges. Hovering the mouse over a particular vertical bar pops up a little window with the exact numbers for that bucket. The bucket counts can also be saved to a file for more detailed analysis.
With a partial picture you can click three zoom buttons to quickly adjust the range settings and restart the histogram:
You can also zoom in by dragging the mouse across a section of the histogram.