TRENDnet TW-H6W1IR - Manual (Page 28)

TW-H6W1IR ISDN Remote Router
20 Installation
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If uplinking more than two hubs together, observe the 5-4-3 rule:
no signal, in order to go from one end node to another, must ever
pass through more than five twisted-pair cables, four repeaters
(that is, hubs), and three uplink cables. This is the maximum signal
path in twisted-pair Ethernet. Also be sure never to allow a signal
loop to form.
Note that you can connect an end node through the Uplink jack,
but to do so you must use a cross-wired cable or cable
converter.
Step 6 - Powering Up Devices for Initial Configuration
Plug in the included 18V DC, 750 mA power adapter into the power
jack on the router’s rear panel.