hardware loop on 1000Base-T

[Scorpio99]

I've a problem :
How make a hardware loop on a connection with RJ45 on an GbE (1000base-T) electrical interface.
There are 4 pair with 250Mbit on this sort of link.
Wich are the interconnection for making a single cabling loop ?
This is for making a test in loop back with a GbE tester on long distance.
On the other side (where is connected my tester), I've a fiber connection on 1310nm.  :?: