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| Big Test MFG says our Ethernet Chip violates the IEEE standard - are they right? |
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| wraper:
--- Quote from: tooki on October 21, 2021, 03:06:47 am ---Nope. It’s a common misconception that gigabit requires Cat 5e. It does not. --- End quote --- It's not a misconception. CAT5 cable is not up to spec for gigabit ethernet. It should work for shorter runs or even may be as good as 5e spec but nothing is guaranteed. |
| rsjsouza:
--- Quote from: nctnico on October 21, 2021, 01:30:43 pm --- --- Quote from: tooki on October 21, 2021, 03:06:47 am --- --- Quote from: nctnico on October 20, 2021, 08:51:41 pm --- --- Quote from: tooki on October 20, 2021, 12:24:42 pm ---- Gigabit requires Cat 5 cable, but requires 4 pairs. --- End quote --- AFAIK Cat 5E actually. I had to redo a lot of wiring to replace plain CAT5 because it didn't work for 1Gbit. --- End quote --- Nope. It’s a common misconception that gigabit requires Cat 5e. It does not. --- End quote --- Well, I have seen CAT5 cables fail at 1Gbit where CAT5E worked. The failing cables where only a few meters long. So explain that to me... --- End quote --- That is my experience as well. The standard may say one thing, but for about a decade or so doing Eth evaluations in various scenarios I can tell that, in practice, GigE with anything longer that your run of the mill freebie-accessory length (1m or 1.5m) is extremely flaky with Cat5 and even ultra-cheap Cat5e. Reasonable quality Cat5e creates solid GigE connections. |
| ve7xen:
--- Quote from: tooki on October 21, 2021, 03:06:47 am ---Nope. It’s a common misconception that gigabit requires Cat 5e. It does not. --- End quote --- When 1000base-T was specified, Cat5e didn't exist. So the standard references plain Cat5, but stipulates additional requirements that were not part of the Cat5 standard. These requirements were ultimately rolled into Cat5e. So while 1000base-T spec doesn't call out Cat5e, it does require cable that is more stringently specified than Cat5, and Cat5e meets those requirements. The new requirements were regarding return loss and several forms of crosstalk. I find it somewhat hard to believe that people had actual problems with Cat5 patch cables because they were not Cat5e, since most would be compliant anyway, and you can't really get them anymore even if you wanted to, but the specs don't offer any guarantees (without the specified RL/crosstalk parameters of the cable), I suppose. IME problems with cabling are practically always due to poor termination or damaged cable. |
| helius:
--- Quote from: ve7xen on October 19, 2021, 08:23:01 pm ---The only IEEE 802.3 PMA supporting Cat3 that would be relevant is 10base-T. Clause 14.5.1 of 802.3-2018 (in the 10base-T MDI section) says: --- End quote --- 100baseT4 also operates over Category 3 cable (using 4 pairs). |
| tooki:
--- Quote from: Ranayna on October 21, 2021, 12:19:40 pm ---Wasn't there some change in the specs some years ago? I always heard that CAT 5e was essentially "backported" into CAT 5, making CAT 5e obsolete. --- End quote --- No, the other way around: the Cat 5 standard was deprecated, meaning that the Cat 5e standard effectively replaced the Cat 5 standard. --- Quote from: wraper on October 21, 2021, 02:02:52 pm --- --- Quote from: tooki on October 21, 2021, 03:06:47 am ---Nope. It’s a common misconception that gigabit requires Cat 5e. It does not. --- End quote --- It's not a misconception. CAT5 cable is not up to spec for gigabit ethernet. It should work for shorter runs or even may be as good as 5e spec but nothing is guaranteed. --- End quote --- It is a misconception: as ve7xen said, the Cat 5e standard didn’t even exist when gigabit was created! Clearly, 5 is being pushed to its limits on gigabit, and it wouldn’t surprise me at all if low grade cables didn’t actually meet their claimed Cat 5 standard, which would explain those cables failing. (Noncompliant cables remain extremely widespread in the computer industry, and it’s only because we often are nowhere near length limits that some cables work at all.) Also, even a compliant cable could become noncompliant if mechanically abused, so this is another source of potential bad cables. It’s all academic anyway, since practically all Ethernet cable these days is Cat 5e, 6, or 7. --- Quote from: ve7xen on October 21, 2021, 07:31:20 pm --- --- Quote from: tooki on October 21, 2021, 03:06:47 am ---Nope. It’s a common misconception that gigabit requires Cat 5e. It does not. --- End quote --- When 1000base-T was specified, Cat5e didn't exist. So the standard references plain Cat5, but stipulates additional requirements that were not part of the Cat5 standard. These requirements were ultimately rolled into Cat5e. So while 1000base-T spec doesn't call out Cat5e, it does require cable that is more stringently specified than Cat5, and Cat5e meets those requirements. The new requirements were regarding return loss and several forms of crosstalk. I find it somewhat hard to believe that people had actual problems with Cat5 patch cables because they were not Cat5e, since most would be compliant anyway, and you can't really get them anymore even if you wanted to, but the specs don't offer any guarantees (without the specified RL/crosstalk parameters of the cable), I suppose. IME problems with cabling are practically always due to poor termination or damaged cable. --- End quote --- Thanks for the info! |
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