5 ms·

Around 2010 I designed the "computer room" for a 3 story apartment building that had computers for the residents to use. It was all very basic. The only complex

Around 2010 I designed the "computer room" for a 3 story apartment building that had computers for the residents to use. It was all very basic. The only complexity was that the ethernet run was across the whole building and 3 stories from the 3rd story computer room to the first story utility room. The day came when it was time to test it out. All the Ethernet lights came on, but throughput was on the order of less than a few kbps. I let the project manager know that something was wrong with the cabling. He got back to me a week later. The electrician who ran the line ran out mid way and used wire nuts to splice another length of cable. The fix was to simply terminate each end correctly on a splice connector. IIRC they might have even just re-ran one single length. But the instinct not to trust electricians to run CAT5/6 was 101% correct!

walshemj 6y ago
They did use the correct wiring standard T-568B ? and the runs where < 90m
- MaxBarraclough 6y ago
  > and the runs where < 90m What happens if you somewhat exceed the 100m limit? The only sources I can find boil down to just don't do that but I can't find a chart showing what happens to performance/frame loss. Would it help to have a heavily shielded cable?
  - WalterBright 6y ago
    It may work if you run it over RG6 coax.
    - walshemj 6y ago
      10BASE2 uses Rg58 :-) not even sure if you can buy adaptors that could use Rg6
  - biktor_gj 6y ago
    It depends a lot on cable quality, what you have on either side and the connectors in between. At work we had to repurpose a pair 170ish meter cat 6 cables for some cameras and it has worked nicely for three years (with PoE even). We tried again with a 100m cable rated for exterior (plus female + patch cords) and it wouldn't even link at 100mbps
  - folmar 6y ago
    It helps to have a good combination of hardware on both ends. Some switches happily do 200-300m but others don't.
  - slavik81 6y ago
    The 100m eithernet distance restriction used to be to ensure that if two machines tried to start talking on the same line, they would hear the noise from the other before they finished sending their packet, and could therefore know there was a transmission error. That is, at least, what was described to me in Computer Networks I back in 2006. I'm sure things have changed as we've moved to always using full-duplex wiring and fully-switched networks.
    - chokeartist 6y ago
      It is really about the modulation scheme limits (distance v noise). Most ethernet networks have been full-duplex on an individual link level since the early 2000s.
  - toast0 6y ago
    > What happens if you somewhat exceed the 100m limit? The only sources I can find boil down to just don't do that but I can't find a chart showing what happens to performance/frame loss. It depends on your system. If you're running old school shared medium Ethernet (with hubs, not switches, for cat5), or even just half-duplex mode, if your run length is too long, the big issue is that you've lost guarantees about collision detection; in that case, receivers may see collisions that senders don't, and you're left with transport layer resends (if any) instead of Ethernet layer resends. This is because of transmission speed, minimum packet lengths, and the length of the cable mean that one sender could finish transmission before seeing the second sender's preamble. If you're running full-duplex dedicated medium, collision detection is a non-issue, there are no collisions. GigE transmits and receives on all four pairs simultaneously and uses echo cancellation to remove the echo'd send that comes back from the far end, the extra distance will make the echo come back later than expected, and that might be outside the ability of the network cards' signal processing to adjust. Assuming that's not a problem, you would have more resistance, and probably more? capacitance, which may make signal recovery more challenging. 100BaseTx would probably be more likely to work than GigE, in my opinion, but I'd certainly try both. Ethernet autonegotiation runs on a single pair at 1Mbps, so it's quite possible that the cards will negotiate to 1G, and then not be able to actually communicate at that speed because of the wiring parameters. One important thing to consider is that Ethernet wiring specifications are such that minimum standard wiring will work at a very low error rate at maximum length when in a bundle with many other ethernet cables/other low voltage signaling cables. If you don't have a lot of bundled cables, you have a bit more wiggle room. Of course, if you run the wires parallel and close to AC wires, you have a lot less wiggle room.
    - toast0 6y ago
      Oh, and one more thing. If there's a midpoint somewhat accessible, there are two-port PoE powered switches you can drop in the middle of the span; some of them even will chain PoE; I think i've seen something that would let you put in three of the chainable switches between the power source and your endpoint (you could probably chain a couple more if the endpoint is also a powered switch). It would certainly make network engineers cry, but you have to work with the site and wiring you have, and only sometimes is it easy or convenient to run new cabling.
EvanAnderson 6y ago
The same goes for telco technicians. Just as I've caught electricians wire-nutting UTP cables I've also caught telco technicians putting "Scotch Lock" splice connectors on cables to "extend" them.
core-questions 6y ago
I was confused as all get-out about what a "wire nut" is, turns out Marettes are not what everyone calls 'em!
- dylan604 6y ago
  without looking it up, sounds like you are referring the brand name or the manufacture/distributor of wire nuts available at your local hardware store.
  - minitoar 6y ago
    It's actually based on the name of the inventor, a Canadian, and is commonly used in Canada as a generic name.
dkdk8283 6y ago
Electricians are bad at low voltage wiring. There’s a different contractor license for low voltage work in many states. Electricians also almost always use the wrong colors when wiring speakers with something like a 16/4. I have ran into this a lot.
- spicybright 6y ago
  Spot on with the colors. Why don't they pay more attention to that?
  - vinceguidry 6y ago
    My dad’s an electrician. I worked for him once upon a time and later I did low voltage electrical construction. He says that the standards change too often, and it’s different enough to be considered a totally different field. When I went to do low voltage later I realized what he meant. Stereo and security installations just isn’t something you want your electrician, whose knowledge mostly revolves around huge, 1000+ amp panels, to be doing. There’s way more money in commercial installs, so most electricians only do residential work to tide them over. My dad doesn’t even want to terminate anything more complicated than 4 conductor phone wire, and would pull me into a job just for that reason.

walshemj 6y ago

They did use the correct wiring standard T-568B ? and the runs where < 90m

MaxBarraclough 6y ago
> and the runs where < 90m What happens if you somewhat exceed the 100m limit? The only sources I can find boil down to just don't do that but I can't find a chart showing what happens to performance/frame loss. Would it help to have a heavily shielded cable?
- WalterBright 6y ago
  It may work if you run it over RG6 coax.
  - walshemj 6y ago
    10BASE2 uses Rg58 :-) not even sure if you can buy adaptors that could use Rg6
- biktor_gj 6y ago
  It depends a lot on cable quality, what you have on either side and the connectors in between. At work we had to repurpose a pair 170ish meter cat 6 cables for some cameras and it has worked nicely for three years (with PoE even). We tried again with a 100m cable rated for exterior (plus female + patch cords) and it wouldn't even link at 100mbps
- folmar 6y ago
  It helps to have a good combination of hardware on both ends. Some switches happily do 200-300m but others don't.
- slavik81 6y ago
  The 100m eithernet distance restriction used to be to ensure that if two machines tried to start talking on the same line, they would hear the noise from the other before they finished sending their packet, and could therefore know there was a transmission error. That is, at least, what was described to me in Computer Networks I back in 2006. I'm sure things have changed as we've moved to always using full-duplex wiring and fully-switched networks.
  - chokeartist 6y ago
    It is really about the modulation scheme limits (distance v noise). Most ethernet networks have been full-duplex on an individual link level since the early 2000s.
- toast0 6y ago
  > What happens if you somewhat exceed the 100m limit? The only sources I can find boil down to just don't do that but I can't find a chart showing what happens to performance/frame loss. It depends on your system. If you're running old school shared medium Ethernet (with hubs, not switches, for cat5), or even just half-duplex mode, if your run length is too long, the big issue is that you've lost guarantees about collision detection; in that case, receivers may see collisions that senders don't, and you're left with transport layer resends (if any) instead of Ethernet layer resends. This is because of transmission speed, minimum packet lengths, and the length of the cable mean that one sender could finish transmission before seeing the second sender's preamble. If you're running full-duplex dedicated medium, collision detection is a non-issue, there are no collisions. GigE transmits and receives on all four pairs simultaneously and uses echo cancellation to remove the echo'd send that comes back from the far end, the extra distance will make the echo come back later than expected, and that might be outside the ability of the network cards' signal processing to adjust. Assuming that's not a problem, you would have more resistance, and probably more? capacitance, which may make signal recovery more challenging. 100BaseTx would probably be more likely to work than GigE, in my opinion, but I'd certainly try both. Ethernet autonegotiation runs on a single pair at 1Mbps, so it's quite possible that the cards will negotiate to 1G, and then not be able to actually communicate at that speed because of the wiring parameters. One important thing to consider is that Ethernet wiring specifications are such that minimum standard wiring will work at a very low error rate at maximum length when in a bundle with many other ethernet cables/other low voltage signaling cables. If you don't have a lot of bundled cables, you have a bit more wiggle room. Of course, if you run the wires parallel and close to AC wires, you have a lot less wiggle room.
  - toast0 6y ago
    Oh, and one more thing. If there's a midpoint somewhat accessible, there are two-port PoE powered switches you can drop in the middle of the span; some of them even will chain PoE; I think i've seen something that would let you put in three of the chainable switches between the power source and your endpoint (you could probably chain a couple more if the endpoint is also a powered switch). It would certainly make network engineers cry, but you have to work with the site and wiring you have, and only sometimes is it easy or convenient to run new cabling.

EvanAnderson 6y ago

The same goes for telco technicians. Just as I've caught electricians wire-nutting UTP cables I've also caught telco technicians putting "Scotch Lock" splice connectors on cables to "extend" them.

core-questions 6y ago

I was confused as all get-out about what a "wire nut" is, turns out Marettes are not what everyone calls 'em!

dylan604 6y ago
without looking it up, sounds like you are referring the brand name or the manufacture/distributor of wire nuts available at your local hardware store.
- minitoar 6y ago
  It's actually based on the name of the inventor, a Canadian, and is commonly used in Canada as a generic name.

dkdk8283 6y ago

Electricians are bad at low voltage wiring. There’s a different contractor license for low voltage work in many states. Electricians also almost always use the wrong colors when wiring speakers with something like a 16/4. I have ran into this a lot.

spicybright 6y ago
Spot on with the colors. Why don't they pay more attention to that?
- vinceguidry 6y ago
  My dad’s an electrician. I worked for him once upon a time and later I did low voltage electrical construction. He says that the standards change too often, and it’s different enough to be considered a totally different field. When I went to do low voltage later I realized what he meant. Stereo and security installations just isn’t something you want your electrician, whose knowledge mostly revolves around huge, 1000+ amp panels, to be doing. There’s way more money in commercial installs, so most electricians only do residential work to tide them over. My dad doesn’t even want to terminate anything more complicated than 4 conductor phone wire, and would pull me into a job just for that reason.