ATS 10/100 Base T Splitter Adapters
Last updated: 8/20/03

"no luck" recently posted the following question in our forums:

"What is the best and hopefully cheapest way I can use two computers on one RJ45 outlet. The RJ45 outlet goes to a router."

"Radioshack has a Y network cable splitter but I presume you can only use one computer at a time."

This question has been posted in our forums a few times, so I decided to take a closer look.

The 10/100BASET Ethernets only use four of the eight wires in a CAT5 cable. T Splitter Adapters (also known as Modular Y adapters) combine two RJ45 8-wire Ethernet jacks (ports) into one 8-wire jack at one end of a cable and split them apart at the other end.

Most of the splitters I've seen are spec'd for 10BASE T. ATS, Inc. says their's are rated CAT 5e and claims they will work with 100BASET: "The ATS 10/100 Base T Splitter Adapters convert one RJ45 4-pair Jack into 2-pair Jacks while still maintaining 10 and 100 Base T system performance. The use of this adapter will allow two 10/100 Base T HUB ports to function on one horizontal cabling run (minimum 2 adapters required), we will include one 2" Patch cord."

I asked ATS for a couple of their T-splitters for testing. They arrived the other day. Of course, I had to take one apart to see what makes it tick. I didn't see anything unusual inside, such as as extra twist that some CAT 5 jacks put in pairs inside the jack. In fact some of the pairs are untwisted more that the half an inch specified for CAT5/5e jacks, plugs, and patch panels. (The jack contacts in the below picture are actually shiny gold.)

To test the units, I used them to connected two computers at each end of a single CAT 5e cable running from my shop in a converted garage to my Wife's office at the other end of our house, or about 120 wire feet. I had the computers at one end simultaneously send files to the computers at the other end. Each sending computer and the corresponding computer receiving the files at the other end were on an entirely separate network than the other sending a receiving pair.

The only things in common between the two networks were the T-splitters and the long cable. I measured how long it took one computer to send the Windows 98 upgrade cab files (80 files, 91.5 MBytes, while the other computer at the same end was constantly sending files. I then removed the T-splitters and a computer at each end and sent the cab files again over the same cable. The time, 20 seconds plus or minus a second (which is about as fast as the computers can transfer data given the Ethernet and operating system overhead, and disk drive speeds, etc.), was the same in both cases. So, using the splitters and the same cable for two simultaneous data streams resulted in no slow down, and apparently no data corruption from interference, which would have resulted in packet retransmissions and slower rates.

Conclusions. The ATS T-splitters work as advertised. You can use two computers at the same time on the same line without any noticeable degradation. If you search google.com with "t splitter," you should find them. Larry