[Sephiroth]

TH might be giving me too much credit!

The yellow means the maximum ping time recorded. It can be just one ping in an hour, but it'll show like that. However, if the blue bit, the average ping, follows the yellow, then the yellow is regular as a high.

Into the mix comes the peak time added activity in your network segment. This will produce increased blue and yellow.

The high yellow is abnormal though. What did the engineer say he'd done? Did he actually think he'd fixed it? If everything's off except the SH, what could the SH be putting out or doing? Have you tried turning the Firewall off for a while and using Windows firewall in your PCs?

Incidentally the reason why you can get these strange graphs but download speed seems unaffected is that the pings are at low priority as compared with TCP or UDP network traffic that you'd be generating/receiving.