Tec-Alert Newsletter

The Search for the perfect Datacom Tone & Probe Set

Network Tone & Probe SetLink lights on switches and hubs have been around forever. Those little LEDs, blinking away incessantly as traffic runs to and fro. Basically, warming the heart of any network person, realizing that if the LED is working, the switch probably is too. These LEDs have always reminded me of the robot on "Lost in Space", blinking away indicating some higher artificial intelligence.

Today, these LEDs are getting smarter, or at least are helping the network technician work smarter. With the right tester, these LEDs can be used to identify the exact location of a user in the switch closet by giving a friendly rhythmic blink rate in that port. Doesn't sound too incredibly smart but neither did Carl Sagan with that odd accent. Here is how it works.

There are several test devices on the market right now that, among other things, transmit a link signal. This link signal will activate the link light (i.e. make it blink). If the activating tester regulates this signal into a distinctly different pattern from the usual chatter, enough to distinguish it from all the other stuff, then it can be used for ID purposes. Pretty simple concept.

Now why would anyone care? I shouldn't even have to ask this question. If you have been in cabling for any period of time you are familiar with what I call rat's nest cabling. You know the ones, nothing labeled, and even if they were labeled initially, they aren't now! The bottom line is: Lots of cabling jobs are not labeled well or at all and many don't survive long after the user takes over and move-adds-changes start.

In the past, two methods of ID have been used on active networks to identify where these wall plates are connected; traditional audible toners and the plug-unplug method.

The first method, traditional toners, are not suited for tracing active wiring for many reasons. First, they send a tone down a cable trying to set up a cross talk field for the probe to detect. That works great on POTS wiring but Cat 5 and Cat 6 cables are highly twisted to prevent this type of cross talk and signal loss. The tone generator tries to fight this signal loss but the cabling usually wins.

Second, toners do not work into shorts. The tone dies when a loop is formed and many switches act as if there is a loop on the end. Consequently, no tone appears. Finally, even if a tone does appear, it bleeds over to other ports. Good luck at that point. In addition, the traditional toner wasn't built for LAN work, the RJ connector is an RJ-11. If that doesn't scream telephony as opposed to LAN, I don't know what does.

The plug-unplug method requires 2 technicians, a lot of time and a lot of guts. Do you really want to accidentally unplug the CEO?

Now don't throw out your old toner just yet. It is still the method of choice for telecom wiring. But for Datacom installations tracing both disconnected (Dead) wiring and active (Alive) cabling, you need something more.

The most complete Datacom test kit is a toner with both a link light activator and a RJ-45 split pair tone generator. You will also need a tone probe for receiving the tone. A Tone & Probe with these features will prove invaluable in any cabling ID situation the network technician faces.).

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