DUT

While investigating a separate network issue at work, we observed unexpected Ethernet link behavior on an embedded ARM system. During boot, the switch port facing it reports link up at 100 Mbps, then down, then up at 100 Mbps again, three times in total, before finally settling at 1 Gbps once the operating system is up. Before proceeding, we needed to determine whether the cycling was related to the issue at hand or independent behavior that could be ruled out. ...

I wanted to measure how much latency a network device adds to a path, precisely enough to characterize a DUT (Device Under Test) that adds less than a microsecond. The instrument is a quad-port Intel i350, which does per-packet hardware timestamping and exposes a PTP hardware clock per port. The DUTs: a Netgear FE104 repeater hub, a Netgear FS105 10/100 switch, and a Netgear GS305 gigabit switch. Results up front: ...