Feeder cables with 10 Gig?

Feeder cables with 10 Gig?
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Subject Author Date
Feeder cables with 10 Gig? BJ 07-25-2006
Posted by BJ on July 25, 2006, 12:15 pm
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We're about to rewire our office with a high-grade, shielded Cat6 cable that
is supposed to support 10gig up to 55 meters (yes, I know there's no
guarantee since there's no ratified standard yet). Our hope is that this
high-grade wire will eliminate the need to do another network rewire for at
least another 10-15 years. But there's a good chance that our server room
may move from it's current location in the next couple of years. We could
always use feeder cables to extend all the cable runs from the old server
room to the new, but my question is, should we?

If we hope to someday run 10 gig over this copper, will a properly-done
feeder cable be as good as a single unbroken run of the same cable over the
same length? Do I run the risk of performance loss, increased exposure to
EMI, or any other problems by using feeder cable in this scenario, or would
I need to do another complete rewire to get the cable integrity I'd need for
10gig? I realize I'm trying to predict the future of a technology that
barely even exists today, but I'm hoping someone with particular expertise
or experience in this area can tell me, on a gut level, what they think.
I'd like to make the choices now that stand the best chance of serving us
well for the future. In case it matters, we'll be running PoE over this
wire today, and I can't image that 10gig networks won't try to do the same
thing.

All comments appreciated, and thanks in advance.

Bryan



Pure Networks
Posted by Walter Roberson on July 25, 2006, 1:29 pm
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>If we hope to someday run 10 gig over this copper, will a properly-done
>feeder cable be as good as a single unbroken run of the same cable over the
>same length? Do I run the risk of performance loss, increased exposure to
>EMI, or any other problems by using feeder cable in this scenario, or would
>I need to do another complete rewire to get the cable integrity I'd need for
>10gig?

I have no expertise in wiring, let alone wiring for very high speed,
so the following might be wrong or irrelevant:

What I have read is that often the greatest challenge for high
bandwidth is in the connectors, as it is at the connectors that
signal reflections are generated, and at which impedence matches
become an issue, and at which phase distortions are most sharply
introduced into signals.

This would suggest that if your aim is cutting-edge bandwidth,
that you would be better off with an unbroken run.

I've read the odd tidbit about very high speed wire networks; one of
the suggestions I've seen is that in the future, cable interconnects
might no longer be passive electromechanical systems, and might instead
require some amount of electronics (I don't recall if they would
be passive or active), such as in order to reduce echoes. It wasn't
a "repeater" as such, in that the signal would not be regenerated,
but it was more than a simple capacitor.

Posted by BJ on July 25, 2006, 5:52 pm
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Great info, thanks; I may forward it to my cabling guys for their reactions,
and post them back here.

BJ

>
>>If we hope to someday run 10 gig over this copper, will a properly-done
>>feeder cable be as good as a single unbroken run of the same cable over
>>the
>>same length? Do I run the risk of performance loss, increased exposure to
>>EMI, or any other problems by using feeder cable in this scenario, or
>>would
>>I need to do another complete rewire to get the cable integrity I'd need
>>for
>>10gig?
>
> I have no expertise in wiring, let alone wiring for very high speed,
> so the following might be wrong or irrelevant:
>
> What I have read is that often the greatest challenge for high
> bandwidth is in the connectors, as it is at the connectors that
> signal reflections are generated, and at which impedence matches
> become an issue, and at which phase distortions are most sharply
> introduced into signals.
>
> This would suggest that if your aim is cutting-edge bandwidth,
> that you would be better off with an unbroken run.
>
> I've read the odd tidbit about very high speed wire networks; one of
> the suggestions I've seen is that in the future, cable interconnects
> might no longer be passive electromechanical systems, and might instead
> require some amount of electronics (I don't recall if they would
> be passive or active), such as in order to reduce echoes. It wasn't
> a "repeater" as such, in that the signal would not be regenerated,
> but it was more than a simple capacitor.



Posted by glen herrmannsfeldt on July 26, 2006, 1:28 am
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Walter Roberson wrote:


>>If we hope to someday run 10 gig over this copper, will a properly-done
>>feeder cable be as good as a single unbroken run of the same cable over the
>>same length? Do I run the risk of performance loss, increased exposure to
>>EMI, or any other problems by using feeder cable in this scenario, or would
>>I need to do another complete rewire to get the cable integrity I'd need for
>>10gig?

> I have no expertise in wiring, let alone wiring for very high speed,
> so the following might be wrong or irrelevant:

> What I have read is that often the greatest challenge for high
> bandwidth is in the connectors, as it is at the connectors that
> signal reflections are generated, and at which impedence matches
> become an issue, and at which phase distortions are most sharply
> introduced into signals.

Well most people (except ethernet engineers) use coaxial cable
when they need high bandwidth. It isn't so hard to make an
impedance matched coax connector if the connector parts have the
appropriate diameter. It is somewhat harder for UTP.

> This would suggest that if your aim is cutting-edge bandwidth,
> that you would be better off with an unbroken run.

I agree, though it might be that with good connectors the
reduction in length is not so big.

> I've read the odd tidbit about very high speed wire networks; one of
> the suggestions I've seen is that in the future, cable interconnects
> might no longer be passive electromechanical systems, and might instead
> require some amount of electronics (I don't recall if they would
> be passive or active), such as in order to reduce echoes. It wasn't
> a "repeater" as such, in that the signal would not be regenerated,
> but it was more than a simple capacitor.

Active terminators are popular for SCSI termination. I suppose that
could soon be true for network cabling.

-- glen


Posted by William P.N. Smith on July 25, 2006, 1:47 pm
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>We're about to rewire our office with a high-grade, shielded Cat6 cable

Why shielded?

>If we hope to someday run 10 gig over this copper, will a properly-done
>feeder cable be as good as a single unbroken run of the same cable over the
>same length?

It can't be as good, as there'll be another couple of sets of
connectors and a patch cable between them (or at least a Cat6 splice).

>In case it matters, we'll be running PoE over this
>wire today, and I can't image that 10gig networks won't try to do the same
>thing.

An unknown spec for 10G, unknown PoE interactions, adding splices,
"10G PoE midspans" (whatever they might look like), I think you are
planning too far into the unforseeable future.

I can't even buy 1G PoE midspans today...

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