Gigabit Switch performance issues

xar

Well-known Member
Hi all,

Looking for some input on an issue I am having. Setup is:
  1. BT FTTP (Fibre to the Premises) at 500mb into a Smart Hub 2
  2. Smart Hub runs into a 'TP-Link 8-Port Gigabit Ethernet Switch'
  3. Cat 5 running from above switch to various other things, but for this issue it runs into another switch (same one) in my home office
  4. In the home office the 2nd switch has 2 computers and a BT home hub disc (the main disc) connected
The problem is that my computer (2018 iMac) regularly drops from circa 500 download speeds to circa 80-90, sometimes as low as 20. If I unplug the cable into the iMac it sometimes jumps back to 500 straight away, other times it does nothing and stays at the speed for days before going back. I have tried a hard reset on the Smart Hub which sometimes sorts it, but other times not.

If I remove the switches from the equation and plug the iMac direct to the router there are no issues, so the switches are obviously doing something to kill the speed, but I have no idea what. Its not like the kids come home from school and they jump on the iPad and it drops all of a sudden, it can be when its just me using the iMac and no one else is using anything.

I assume with them be unmanaged there is little I can actively do, but it anyone has any ideas I am open to them!
 
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cjed

Well-known Member
If you are sure it's the switch then I'd just replace it with another (preferably from another manufacturer, say Netgear or Zyxel). An 8 port unmanaged gigabit switch is less than £20.
 

xar

Well-known Member
Thanks - the thing is I am assuming its the switch, purely as removing them from the chain stops it happening. Concern would be that I get new switches and the same things happens, but no idea how to cater for that...
 

mickevh

Distinguished Member
I would run some tests using local transfers and not Internet downloads, which will give evidence as to whether the switches or your Internet link are culpable. It could even be something in your source or sink devices that is culpable (like they've caught some malware for example.) With "the world" upstream of your ISP link, literally anything could be happening out there, so it's best to test local issues locally.

Set up some tests using some DVD of BR rips to copy around so you've got something that will run for a while (unlike speed tests like NetIO of iPerf which only last few seconds,) warn the household and unplug your Internet link (leave the router running so it continues to service DHCP requests) and run some tests and see what difference it makes.

I agree that with switches only costing GBP 20 or so, if that's not a big amount of money to you, you could just say "what the hell" and buy some new ones, but I'd not be happy yet that there's adequate evidence that the switches are culpable. (It could be your network cables are broken or dirt in the ports or some of the other causes I've described.)
 
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xar

Well-known Member
Thanks. Good advice. I have noticed a slowdown in transfers between my iMac and the NAS drive when the speeds are down, suggesting it is the switches not the internet in general. This would be supported by the fact that my iPhone gets at least 200mbs over Wi-Fi consistently.

interim plan is a new 20m cat5 cable direct from router to my iMac, separate from the switches.
 

mickevh

Distinguished Member
That would certainly provide some good evidence. Prevailing traffic levels on the network are also another factor. Each lobe on your network is a resource with finite capacity and once it's full it's full and you get congestion and collisions - just like the road network.

If you really wanted to go the whole hog by way of testing, you could create "lab" test by taking each switch out of use, cable it up with just itself and a source and sink device (you'll need to assign IP addresses manually - which for a NAS is no bad idea in any case) and pound it with some file copies and see what the results are like. Thusly, you're running some tests free from any influences of everything else on your network.

I've no experience of it but I have heard of so-called "green" switches (that institute various low power states when idle) causing problems.

It may even be worth unplugging/re-plugging al the network cables - sometimes if they have gotten dirty of corroded, so doing cleans up the contacts a bit a might coax them back into life.

In an ideal world, we'd also have a look at the error rates on the ports, but unfortunately cheap "unmanaged" switches such as one uses in SOHO deployments generally lack such reportage.
 

xar

Well-known Member
Thanks for the info. That all sounds a bit more advanced than I could effectively manage, so I think a physical ’bypass’ with a separate cat5 cable will do the trick. The rest of the network can glitch as long as the main iMac gets full juice.
 

oneman

Well-known Member
If it is just your Mac having the problem then isn't it more likely that is the cause of your issues. Plug it in to the first switch switch and see what happens.

In 20+ years I would by far the biggest cause of problems is O/S or driver issues rather than hardware. Now is it a Mac so should be better than windows but they still can have problems.

One quick question, you said Cat5 between the switches, did you mean Cat5e ?
 

xar

Well-known Member
I did mean Cat5e indeed. It’s a fair point about it potentially being the OS, but I have ensured that the memory has been cleaned, there aren’t any time machine backups or virus updates happening (AVG, no firewall enabled), memory jogs like iTunes are closed etc when testing the speed. I also try a full reset every few days, sometimes that works, other times not.

My new cable comes today, so will test it for a few days direct to the router and see what happens. If that works I might try it from the first switch to see if that makes a difference
 

oneman

Well-known Member
It is odd that only device is having a problem. Is there any spare cable to a TV or something you can quickly try or a laptop you can plug in place of the iMac ?
 

xar

Well-known Member
I don’t have spare laptop unfortunately, only an older Mac but it runs pretty slow generally, so wouldn’t be a good measure. Will see how this new cable works out (due today) then report back.
 

xar

Well-known Member
No sky in the house. The first switch has cables into:

1. the 2nd switch in the office, which has an iMac (the problem machine), wife’s work laptop, and the main BT Wi-Fi disc (of which there are 4 round the house)
2. The 3rd switch in the garage cinema room (which has 10 items plugged in - amp, blu ray, 2 x NAS units, projector, IKEA home hub, Alexa device, BT disc, shield tv, few other things) 3. Devolo main plug (for two devolo adapters, one of which has a 4th switch connecting a tv, PS4, Sonos)
 

ChuckMountain

Distinguished Member
Some things like Sonos and sky q can cause issues so if it happens again rather than connecting directly, try removing the other devices from the switch.
 

xar

Well-known Member
Received the new Cat5e cable last night, plugged it into the router, and instant 500mbs + download speed. While I would like to get to the bottom of the problem, its not much effort to run the new cable round the outside of the house to the office, so will go with that plan for now...


Screen Shot 2021-04-03 at 09.00.55.png
 

xar

Well-known Member
Router
 

xar

Well-known Member
Not tried that yet. Will do in a bit
 
D

Deleted member 24354

Guest
Some of those cheap 8 port switches, have a limited backplane in them and although they can deliver Gigabit at each port individually the backplane that they are connected to only supports a gigabit in total. Given that you may have a lot of devices hanging off your wif, your switch maybe prioritising traffic to the BT hub when it gets ‘busy’. Try connecting the BT disc to the router with the long cable and try plugging the Mac back into your TP Link switch
 

xar

Well-known Member
That’s interesting and makes a lot of sense, especially with the main BT disc hanging off it. Will try your suggestion tomorrow
 

ChuckMountain

Distinguished Member
Some of those cheap 8 port switches, have a limited backplane in them and although they can deliver Gigabit at each port individually the backplane that they are connected to only supports a gigabit in total.
Not seen any for a long time that have that little switching capability, most backplanes these days are just a multiple of the total number of ports
 

mickevh

Distinguished Member
With SOHO kit, I've find it challenging to dig out what the backplane capacity is. Not that I've tried often, but even when I have I find it's rarely stated.
 

ChuckMountain

Distinguished Member
Take this cheap £11 5 port switch from tp link.

Here are the specs from its sheet

Gigabit Expansion Solution
· TL-SG1005D equips 5 10/100/1000Mbps ports, providing up to 10Gbps switching capacity

So full duplex switching for all 5 ports, I do think you would struggle these days to find one that doesn’t
 

oneman

Well-known Member
Some of those cheap 8 port switches, have a limited backplane in them and although they can deliver Gigabit at each port individually the backplane that they are connected to only supports a gigabit in total. Given that you may have a lot of devices hanging off your wif, your switch maybe prioritising traffic to the BT hub when it gets ‘busy’. Try connecting the BT disc to the router with the long cable and try plugging the Mac back into your TP Link switch
Give it a try, tp-link
With SOHO kit, I've find it challenging to dig out what the backplane capacity is. Not that I've tried often, but even when I have I find it's rarely stated.
I found TP Link is pretty good at finding specs, had a quick look and all their 8 port switches seem to have at least 10gb switching with 11m packets per sec.
 

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