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Beware the "Channel-Certified" Dodge

"Channel compliant" usually means "Non-compliant"

A while ago we wrote about Cat 6 and 6a cables on the consumer market -- we had tested a number of cables offered by online and brick-and-mortar vendors, and found that 80% failed their applicable certification standards while 55% failed even to pass the much easier Cat 5e certification. This led to a bit of discussion online about certification for Ethernet cables, and one issue came up repeatedly that seems to be the focus of a lot of misinformation: the notion that there are two "levels" of certification for Ethernet patch cables, usually referred to as "channel" certification and "component" certification. Vendors of noncompliant Chinese products would pop up in these discussions and argue that while their cables might fail the "component" certification, they would still pass the easier "channel" certification, ergo, all is well.

There's a simple answer to this proposition, which we'll explain below. First, though, the simple answer: There is no such thing as a "channel-certified" Ethernet patch cord. If a patch cord fails the patch cord spec, it fails and is noncompliant, plain and simple.

The explanation is not hard to understand, though the spec documents themselves are a bit of a handful. The basic spec for Ethernet cabling is TIA 568-C.2, and the spec doesn't just govern patch cords -- it governs horizontal cable between jacks, as well as the jacks and plugs themselves, and it governs the whole connection run between two devices. The object of the specification is to ensure that a connection between two devices in a network will function, and to do this, the spec must take into account all of the losses which may occur between two devices. The specification which determines what levels of loss are acceptable between two compliant devices is the "channel" specification -- a kind of "loss budget" for the entire device-to-device connection.

But a channel, of course, is composed of multiple elements. In a typical installation, a patch cord will run from one device to a jack; that jack will be wired through a run of horizontal cable to another jack; and into that jack will be plugged another patch cord, which will run to the other device. This said, it's obvious why the "channel" specification isn't much good for certifying a patch cord. A patch cord which uses up all or most of the allowable losses for the whole channel, once coupled to horizontal cable and another patch cord, will result in a channel which exceeds the channel's loss budget.

To avoid this result, the specification contains additional, more stringent, specifications for patch cords and for that jack-to-jack horizontal cable run (which, in specification terminology, is called a "permanent link"). The idea is that if each component in this signal chain meets or beats its spec limits, then they should, when strung together, meet the "channel" limit. But, of course, this means that the requirements for each component must be considerably more stringent than the "channel" limits. Compliant components, strung together, make a compliant channel. "Channel-certified" components that fail their respective specifications, strung together, will ordinarily make a noncompliant channel.

There is no suggestion, anywhere, in the spec that there are two "levels" of certification for patch cords. There is, in fact, only the one set of limits for return loss and crosstalk in patch cords, and ONLY a test against these patch-cord-specific limits results in a "certified" cable. As ought probably to be needless to say, when we test a cable we test it against the actual, applicable patch cord limits. When a vendor offers to sell you a "channel-compliant" patch cord, there is a simple translation: he means to sell you a "non-compliant" patch cord.

For a demonstration of testing, plus a short discussion of other discrepancies between the channel test and the patch cord test, see this helpful video from Fluke: Certifying a Cat 6a Patch Cord.

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