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From what I heard, cat5e ethernet cables are fully capable of supporting gigabit ethernet at full speed. However, I have also heard that gigabit speeds are not fully unlocked until you use cat6 or cat6e cables.

Can someone explain that the differences are between these specifications, and under what circumstances would I care about using a cat6/6e cable? Or is cat5e indeed capable of taking full advantage of all that gigabit ethernet has to offer?


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"fully unlocked" made me lol. cat6 acquired ACHIEVEMENT UNLOCKED – Nic Jun 8 '11 at 22:45
@melee Haha, glad you liked that! – hpy Jun 8 '11 at 23:17
up vote 11 down vote accepted

Gigabit Ethernet is really pushing the limit of Cat5e cabling. Cat6 is superior to Cat5e when it comes to insertion loss, near end crosstalk (NEXT), return loss, and equal level far end crosstalk (ELFEXT).

Consequently, Gigabit Ethernet over Cat6 could be marginally faster than Cat5e, by the amount of errors produced over Cat5e, even though the networking equipment on either end still operates at the same 1 Gbit. This difference will vary based on other factors in your environment, and also networking equipment. In real world terms, the difference is probably too small too measure without sophisticated tools, and so small as to be made non-existent when other delays introduced by operating systems, switches, routers, and end-user applications are considered.

Most companies are installing Cat6 now for new installations (some reports say as much as 90%). That is mainly for future proofing, since the labor to run cabling can often exceed the cost of cabling itself. I would recommend Cat6 for all new installations, but not to replace existing Cat5e.

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1000BASE-T was designed and tested by the Institute of Electrical and Electronics Engineers (i.e. the IEEE standards body) for 1000 megabits per second performance over up to 100 meters of Cat 5 (not even Cat 5e) cable. See the IEEE 1000BASE-T specifications within the 802.3 spec, currently in IEEE802.3-2008, clause 40.1. And it gets that without problem. You need to site your source on your claim that it's "pushing the limits" of 5e when it was designed and tested for, and successfully deployed worldwide on, up to 100 meters of plain old Cat 5 just like 100BASE-TX (Fast Ethernet) used. – Spiff Jun 8 '11 at 23:41
The problem is not that what the standards say, it is usually the method of installation of cat5e cables that cause them to lose integrity and ability to reach gigabit speeds. When properly installed, sure, they'll do that, but how often do cabling techs bend the rules? In my experience, it is often. Cat6 is more robust and built to handle bad cabling jobs much better. Specifications for cabling are not always real-world applicable. – MaQleod Jun 9 '11 at 3:55
@MaQleod @bwall A reference or it didn't happen. I know it's easy for me to say this, but you can't put forward an opinion without any evidence. – sblair Jul 15 '11 at 2:38
@sblair, there are reasons that the GR-1275, TP76300, i72202, 77350 and other such documents exist. If installation of cabling didn't affect network speeds and integrity, they wouldn't all have cabling sections outlining such things as bending radius and tightness of a stitch. – MaQleod Jul 15 '11 at 3:15
@Rushino, I didn't say you couldn't run 1000BASE-T over Cat5, nor was that the OP's question. The OP asked what the differences were, and under what circumstances one would want to use Cat6 over Cat5. It's a fact that at 1000BASE-T speeds, Cat5/5e can run into more errors and consequently more re-transmits and slower speeds than Cat6. There is not much room for error since the ANSI/TIA/EIA-568-A spec for Cat5e only requires 100 Mhz performance per wire, but 1000Base-T requires 125 Mhz per wire. See here (This info is from TIA) – bwall Oct 14 '11 at 18:03

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