John He from DualComm Technology was kind enough to send me one of his company's port-mirroring switches, namely the DCGS-2005 pictured with its box at left.
In the figure, I have port 1 going to a computer I want to monitor. Port 2 is going to the uplink (or access switch) for that computer. Port 5 (at the far right) is going to a sensor.
The idea behind this device is to provide a plug-and-play alternative to network taps. I thought this system was interesting because it acts somewhat like a port aggregating tap, in the sense that two ports are used for accessing the network but only one port is needed by the sensor.
Note that only port 1 is mirrored to port 5. (The manual confirms this, and I did some limited testing. The words on the tap imply ports 1 - 4 are all mirrored.) This is a one-for-one copy. If you connect to ports 2 and 3, 2 and 4, or 3 and 4, you will not see any unicast traffic on port 5.
This device is also different in that in requires a USB connection for power.
Probably the biggest advantages of this device include low cost and simple use. I think the single USB power connection is the biggest disadvantage. I'd also like to know more about the software on the switch itself.
Thanks again to John for sending me this device. Check out DualComm for more information!