Curious BBQM graph

Last night I had to download some data from work - nearly 12GB. It went very well (thanks Be!) and completed in just shy of 3 hours which is good for my 12Mb/s connection. Out of curiosity I had a look at the quality monitor and it seems a bit odd:

My Broadband Ping

Why does the average latency drop off like that? The data being downloaded was SharePoint databases so it was half a dozen large files. I'd have thought a steady graph all the way through would make more sense.

Maximum on a 12 Meg sync would be around 16GB, so it is feasible that it was not saturating the connection for the full download period. i.e. was bursting to 12Mbps, then down to 8Mbps, all in the course of a second or so, which might not even be obvious if using monitoring tools, which generally average over 1 second.

In reply to a post by Andrue:

Last night I had to download some data from work - nearly 12GB. It went very well (thanks Be!) and completed in just shy of 3 hours which is good for my 12Mb/s connection. Out of curiosity I had a look at the quality monitor and it seems a bit odd:

My Broadband Ping

Why does the average latency drop off like that? The data being downloaded was SharePoint databases so it was half a dozen large files. I'd have thought a steady graph all the way through would make more sense.

Were all of the downloads in parallel or sequential? Were they all the same size?

In reply to a post by MHC:

In reply to a post by Andrue:

Last night I had to download some data from work - nearly 12GB. It went very well (thanks Be!) and completed in just shy of 3 hours which is good for my 12Mb/s connection. Out of curiosity I had a look at the quality monitor and it seems a bit odd:

My Broadband Ping

Why does the average latency drop off like that? The data being downloaded was SharePoint databases so it was half a dozen large files. I'd have thought a steady graph all the way through would make more sense.

Were all of the downloads in parallel or sequential? Were they all the same size?

My client was set to allow up to four concurrent downloads. According to Explorer properties 10 files, 10.2GB. They would be in pairs - a big file (1GB+) and a little file (couple of meg).

In reply to a post by MrSaffron:

Maximum on a 12 Meg sync would be around 16GB, so it is feasible that it was not saturating the connection for the full download period. i.e. was bursting to 12Mbps, then down to 8Mbps, all in the course of a second or so, which might not even be obvious if using monitoring tools, which generally average over 1 second.

That's possible. Having done the calcs it seems like it averaged 1MB/s so that's only 80% of my normal throughput. It was also coming from the US.

Have a close look at the graph and there does appear to be a series of steps ... As one file finishes there is less overhead both traffic and processing so the Ping response can occur fractionally faster.

And from experience, I have seen four big downloads started a few seconds apart. With one it get 100%, with two maybe a 60:40 split, with three 45:35:20 and four 40:25:20:15 or similar - they often seem to run at different speeds - which could explain the steps and one finishes ...