Splitters in Category 5 networks

Q: A large percentage of our buildings here on station are wired with Category 5 unshielded twisted-pair (utp) cable. We know that Category 5 cable is capable of carrying 100 megabits per second, but right now 10 Mbits/sec is the most we are carrying. In the near future we plan to implement Asynchronous Transfer Mode and Fast Ethernet. But we are finding that people have taken it upon themselves to install splitters on their utp jumpers running from the jacks to their PCs. These splitters appea

Q: A large percentage of our buildings here on station are wired with Category 5 unshielded twisted-pair (utp) cable. We know that Category 5 cable is capable of carrying 100 megabits per second, but right now 10 Mbits/sec is the most we are carrying. In the near future we plan to implement Asynchronous Transfer Mode and Fast Ethernet. But we are finding that people have taken it upon themselves to install splitters on their utp jumpers running from the jacks to their PCs. These splitters appear to be standard phone splitters used to split house lines.

My question is: How will this affect the cable as to its Category 5 rating? Will it affect near-end crosstalk or impedance? Will it cause more collisions, or have any effect at all on the network? Could it cause problems at the hubs and, in essence, crash the system? Please let me know so we can put a stop to this "creative networking" before it gets too far out of hand.

Chuck Travis

Naval Undersea Warfare Center--Division Keyport

Keyport, WA

A: As is true of a chain only being as strong as its weakest link, cabling is only as good as its least-capable component. The splitters you mention are most likely Category 2 components. So, according to the tia/eia-568a standard of the Telecommunications Industry Association (Arlington, VA), you have a Category 2-rated channel. Yes, this practice will have a detrimental effect on the network, but it is not likely to crash a 10Base-T network. You see, the Institute of Electrical and Electronics Engineers (ieee--New York) designed the 10Base-T network to run over twisted-pair telephone wire and even to share the sheath with a telephone line. This is why the ieee used pairs 2 and 3, leaving pair 1 available for the telephone line.

This will not be the case when you move to a faster network--one requiring a 100-megahertz-compliant channel. Then the splitters will have to go.

In the early 1980s here at the University of Texas, all the helpful Harrys and Hannahs would run from location to location, adding and removing the terminating resistors in the LocalTalk trunk networks because they didn`t want to bother the technicians--just because Sally couldn`t see the printer. And the next thing they knew, no one could see anything. After we explained to them the problems they were causing, most of the Harrys and Hannahs retired as network troubleshooters.

I suggest that you first focus on why the splitters are being used. Is there insufficient cabling from the telecommunications closet to the work areas to support the voice, data, and video needs of the users? Or are additional cables available but insufficient hub ports? Find the person who is plugging these devices into your network and see what problem he or she is attempting to solve.

Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: ballast@utexas.edu.

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