Unlike other cheap ethernet/RJ45 "splitters" sold and other sites, this splitter/combiner actually allows two devices to use and communicate over one CAT5e/6 ethernet cable simultaneously.

Other solutions simply map the 8 data lines of two ethernet jacks to the same 8 data lines of one ethernet cable to "share" the cable, but only one at a time, similar to old serial switch-boxes.  So, those other solutions are only 2-to-1 splitters that require one device to be off while the other device is on.  Two devices cannot use the same ethernet cable at the same time.

This solution achieves this by utilizing the fact that every ethernet cable has 8 data lines, but ethernet TCP/IP networking only actually uses 4 of those 8 data lines.  So, one pair in this kit combines two 8 line ports in your network switch into one ethernet cable, then the other pair on the other side at the location of the devices splits that ethernet cable's 8 data lines into the 4 data lines necessary for each of the two ethernet cables to work 100% independently.

This has many uses, but the most obvious is to avoid spending hundreds or thousands of dollars paying an ethernet cabling contractor or an IT person to run secondary CAT5e/6 ethernet cables to locations that suddenly require two instead of one.  The most common reason we've seen for this in the past 10 years has been the move to VoIP, requiring a second line for the phone.  Some users simply don't want or can't use wireless or to daisy-chain their computer to their VoIP phone, for performance or other reasons.  Another use is for outdoor PoE camera applications so you can avoid running both power and ethernet cables while protecting them from the environment.

Where wireless network access is not reliable, it offers unacceptable performance, or it simply isn't possible (many devices require ethernet and do not even have wireless), this is a low cost alternative to the high price and inconvenience of running more network cables.