Long network cable damages devices?? bs?? - Page 1
Forum section: electronics / general

author: The Soulman
author_rank: Super Contributor
timestamp: October 09, 2018, 10:18:44 pm
content: Today I heart a new one (from a guy that builds custom hardware), to long of a Ethernet/network cable not only gives a poor connection/dropped packages but will also damage or even cook the network devices??I´m certainly no expert on this, but is it even possible to damage (proper) hardware with to to long of a cable run?

author: jmelson
author_rank: Super Contributor
timestamp: October 09, 2018, 10:34:07 pm
content: Quote from: The Soulman on October 09, 2018, 10:18:44 pmLightning0induced transients are proportional to loop area of the wires. So, the power wires in the walls and power cords to the equipment, plus the network cable, can form a loop that intercepts some amount of magnetic flux from a nearby lightning strike. (And, nearby can mean 500 m+!)So, longer cables CAN actually make this particular case worse. Ethernet is galvanically isolated by transformers, but if enough voltage is developed, it will arc over the transformer and pop the network chips.Without lightning or other very energetic electromagnetic events, then I don't think this is valid.Jon

author: Halcyon
author_rank: Unknown
timestamp: October 09, 2018, 11:03:16 pm
content: Quote from: jmelson on October 09, 2018, 10:34:07 pmSpot on.Although I will add that Ethernet (just like anything) does have upper limits in terms of cable length. 90-100 metres of either shielded or unshielded (STP/UTP) Cat 5/6 is generally the quoted figure for maximum cable lengths. Anything more than that and signal starts to degrade and your devices may start to negotiate link speeds of 100 Mbps instead of 1 Gbps and increased packet errors might result. Of course this depends on the environment in which its installed, the quality of the terminations etc...It won't cause damage to any of your devices, but you will start to see degraded link performance/reliability.

author: PlainName
author_rank: Super Contributor
timestamp: October 10, 2018, 05:17:47 am
content: QuoteI think you'll find that the length issue is caused by handshaking. Specifically, the time it takes a signal to propagate down the line and be detected by another station wanting to transmit. Over 100m the signal arrives after the second station has given up listening and assumed the line is free, thus causing a collision. The two stations then hold off for random times and retry, so the data gets through eventually but the throughput is reduced. From a top of system viewpoint it mightseemlike cable attenuation of an analogue signal, but it ain't.

author: Berni
author_rank: Super Contributor
timestamp: October 10, 2018, 06:06:09 am
content: Packets simply start getting garbled on too long cable due to loss and noise. Collisions should not be a problem because modern networks use only point to point links where the pairs only transfer data in a single direction (One for Tx one for Rx in 100Mbit) Its the old school Ethernet hubs that get collisions or the old coax networking.As said before only case where a long cable could fry something is a lightning strike or similar surge. When the two network devices are really far apart (and potentially in two different buildings.) it makes it easier for a lightning strike to lift the earth wire in your mains installation to 10kV for a few microseconds. If both network devices are in the same rack they will ride the transient together and will see no voltage between them. But if the other device is on the other end of the building it might stay at 0V. As a result the insulation transformer in the network card (That is there for these very cases) could get overwhelmed and arc over sending those 10kV into the rest of the device and killing it. However this has nothing to do with the 100m spec for Ethernet.Networking problems can sometimes be a pain to diagnose so just stick to what the spec says and for long runs use a switch along the way or use fiber.So this is the equivalent of saying that having a badly adjusted antenna on your TV and getting a fuzzy picture would damage the TV.

author: PlainName
author_rank: Super Contributor
timestamp: October 10, 2018, 06:10:49 am
content: Fair enough. Maybe I am thinking of the number of hubs allowed between endpoints, and that also indicates which generation of Ethernet I come from

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 10, 2018, 06:35:01 am
content: Does this guy run his cables the whole way bundled with mains or higher power cable or something?

author: Berni
author_rank: Super Contributor
timestamp: October 10, 2018, 06:36:07 am
content: Well technically you can still use a passive hubs with modern network gear and then you would cause collisions happen, the longer the cable the more likely a collision becomes. But that should cause network cards to fallback to 10Mbit Ethernet so makes little sense to do use such hubs now. People used hubs a lot back then because they needed little to no electronics inside so it made them really cheap compared to a proper switch that actually had a little computer inside that cost a pretty penny back then.Yet these days they make magical ethernet switch chips for $1 in quantity that are basically a bunch of ethernet cards with dedicated network routing logic. Collisions no longer happen on the wire but inside the routing logic where there is RAM buffering to delay them until the destination port is free. So since switches are so cheap now everyone uses them and hubs have become forgotten (And its for the best).

author: Halcyon
author_rank: Unknown
timestamp: October 10, 2018, 08:38:46 am
content: Quote from: dunkemhigh on October 10, 2018, 05:17:47 amAs others have touched on, collisions haven't been a think since switches were invented. The handshake has nothing to do with other stations on the network, rather attenuation over the cable. This is why you don't see "collision" LEDs on ethernet switches.

author: The Soulman
author_rank: Super Contributor
timestamp: October 10, 2018, 09:50:20 am
content: Without sharing to much details on the device used (and I don't know anything about its hardware anyway),It normally connects to a switch about 30 meters (100ft) away and worked like a charm many times before.However yesterday that switch and its further network connections were unavailable ().So I had to patch the device thru some additional cable (all dual shielded cat6 btw) to the next available switch.Total cable length was around 100 meters (300ft) at that point, but had a good connection tested with a laptop.But the mystical device refused to connect so I suggested a additional "dumb" network switch halfway down the line.Then he (the creator and operator of the device) asked how much cable length was leading up to his precious, about 100m,and he was likeThat could blow up network hardware!Then he tells one of his precious devices went up in smoke previously on a outdoor event running 120m of cable to a house.I didn't asked him if they where running on a non-grounded generator, but that most likely must have been it.I'm not a networking expert and certainly don't want to be one (with all respect to those that are) but this was something I wanted to double check here.Thanks guys.btw. inserting the "dumb" switch halfway fixed the issues we were having.

author: mariush
author_rank: Super Contributor
timestamp: October 10, 2018, 10:07:10 am
content: A small note:A lot of cheap ethernet cable out there is CCA (copper clad aluminum, aluminum core wire coated with copper) which has poorer performance compared to regular copper cable.... and if you bend this cable a lot or step on it a lot, the thin copper coating can break and you're left with just the aluminum wire.With big lengths of such ethernet cable, some modern network cards in combinations with some switches can have problems because by default the ethernet drivers enable "green mode" or "power saving" modes where they reduce the transmission power to save a few tenths of a watt or something like that. So if you're over let's say 40-50 meters and you experience some packet loss, it may be worth playing with those settings before assuming it's a poorly installed connector or problem somewhere in the cable.

author: jmelson
author_rank: Super Contributor
timestamp: October 10, 2018, 08:18:47 pm
content: Quote from: dunkemhigh on October 10, 2018, 05:17:47 amModern twisted-pair Ethernet does not HAVE collisions. Also, the round trip time of a maximum-length Ethernet cable is about 200 ns maximum. 100m is too long for signal degradation reasons, more like 100' or 30m. I haven't seen a non-switched Ethernet hub since I migrated off of thinwire coax Ethernet. Ethernet switches only send packets destined for the specific node(s) on any particular port. And, if broadcast packets are sent at the same time, the switch buffers them until they can be sent without collision.Jon

author: ogden
author_rank: Super Contributor
timestamp: October 10, 2018, 08:31:50 pm
content: Quote from: jmelson on October 10, 2018, 08:18:47 pmHuh? What exactly you are talking about? Please explain in more details.

author: Mr. Scram
author_rank: Super Contributor
timestamp: October 10, 2018, 09:03:44 pm
content: Quote from: The Soulman on October 10, 2018, 09:50:20 amThis sounds like a ghost story, to be honest. I've seen entire buildings directly wired to switches with network cables around those lengths without issue. Lots of older gear with plenty of time to stew and cable ducts with mains running next to the network cables too.

author: Halcyon
author_rank: Unknown
timestamp: October 10, 2018, 09:57:27 pm
content: Quote from: jmelson on October 10, 2018, 08:18:47 pmFirstly, frame collisions have really nothing to do with the physical cabling, twisted pair or not. It's about how end-points (switches, hubs, clients) handle data. With hubs, they are essentially just a dumb repeater, they take packets of data from one port and just broadcast it over every other port andCSMA/CDcomes into play. As you said, switches on the other hand direct the packets out a single port based on the destination instead of out to all ports, they also have data buffers to prevent collisions.Hubs are still available brand new and some cheap/nasty home networking installers still use them (presumably because they don't care about the quality of their services or don't know any better).100 metres isn't too long for decent Ethernet gear (good quality switches and network cards). It's at the limit of where 1 Gbps, full-duplex over Cat 6 becomes viable. Longer runs aren't unheard of but mileage may vary. In a large building, many 10's of metres of Cat 6 isn't uncommon. Where I am currently sitting, there is about 30-40 metres of Cat 6 between my machine and the switch and it handles 10 Gbps just fine (it's not the recommended solution, but we aren't about to start ripping up cabling to replace it with Cat 6A). Some switches will even detect the cable length and adjust the power accordingly, if it doesn't need to communicate at maximum power output, it won't to save energy. Ethernet is actually quite resilient.

author: thm_w
author_rank: Super Contributor
timestamp: October 10, 2018, 10:48:21 pm
content: Quote from: Mr. Scram on October 10, 2018, 09:03:44 pmIndoor sure, outdoor no way. Notice how he said the issue only occurred outside: "one of his precious devices went up in smoke previously on aoutdoor eventrunning 120m of cable to a house."You do not want to run CAT5 outside without it being properly shielded/metal conduit/whatever. Unless its some DIY project and its not a major issue if it goes down.I've had many failed units from lightning surges (or similar, no way to know what the actual source was). After seeing photos of how end users wire up stuff outside, most often with no surge protection, its not surprising.

author: Berni
author_rank: Super Contributor
timestamp: October 11, 2018, 05:49:54 am
content: Quote from: The Soulman on October 10, 2018, 09:50:20 amYes the dumb switch halfway simply acts as a repeater since it receives the packets, does MAC routing to them and then sends them out, so whats coming out of the switch is again a perfect clean signal.And yes if this was an outdoor generator setup then you can get into all sorts of strange electrical problems. Especially if the people wiring things up don't know what they are doing. Things might not be grounded properly and if you suddenly connect and disconnect very large loads on generators that can cause significant voltage spikes as the generator can't respond instantly to the load change.Its even a bad idea to run ethernet like this between two separate buildings due to them having separate grounding systems. It usually wouldn't cause trouble, but lightning would likely eventually fry something. For these applications fiber is the way to go. Not only is it electrically isolated so it doesn't care about floating a few kilovolts above everything else, but is also immune to noise while having less attenuation over distance so it has no problems working for >1km. Yes it costs more than just running a CAT6 cable but boxes that convert 1Gbit ethernet to fiber and back are not all that terribly expensive.(And if you run 10Gbit you probably are used to paying a pretty penny for your network gear, fiber converter are no exception)

author: jmelson
author_rank: Super Contributor
timestamp: October 11, 2018, 08:30:49 pm
content: Quote from: ogden on October 10, 2018, 08:31:50 pmThe original Ethernet was a coax cable, and all nodes sent packets to all other nodes on the cable. There was a "jabber" enforced at the end of every packet to make sure the packet was long enough so any collision would trip the collision detector on all the taps on the cable. It was possible for two short packets sent from opposite ends of a long segment to collide in the middle, but appear fine at each end, so the senders would be unaware that a collision occurred.Thinwire Ethernet had pretty much the same issue.A long time ago, when twisted pair was really new, they had hubs, which reflected all incoming packets to all ports. Quickly, these were replaced with switches, and I suspect you will have great trouble today finding an unswitched hub. If you DO find one, I STRONGLY suspect it will be a 10 mbit ONLY hub, and probably 20+ years old.Switches are actually routers. They observe packets from all the ports to learn what nodes are at those ports. Then, they use that info to direct packets to the ports that need to see them, ONLY. Also, almost all TP Ethernet is full-duplex, meaning there are wires for sending and separate wires for receiving.Because all packets are managed by the logic in the switch, there are no collisions. Each node connected to a switch sends packets whenever it wants to, and the switch sends packets as time is available to the node. If two packets destined for one node arrive at different ports at the same time, one will be buffered (delayed) until the port to that node is available.You can read up on all of this, there should be PLENTY of places where this is discussed.Jon

author: ogden
author_rank: Super Contributor
timestamp: October 11, 2018, 09:39:43 pm
content: Quote from: jmelson on October 11, 2018, 08:30:49 pmDuplex mismatch is all you need to have collisions on Modern twisted-pair Ethernet, so technically your statement was incorrect. Anyway collisions are no concern in talk about long twisted-pair cables.Quote from: thm_w on October 10, 2018, 10:48:21 pmExactly. Copper Ethernet is kind of bad idea to connect buildings or tower to building. Many think that direct lightning hit is only way it can damage anything and they are so wrong. You can guard against lightning-induced (EMI) surges by installing surge suppressors on both ends of the cable, but it does not help in case of direct hit into one of buildings or hit into building/tree somewhere close. In such case ground potential rise may burn everything conductive between buildings.