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Smarty/Three 5G tethering: great speeds, then slows to a crawl

wriggles

Member
Hi,

As the title suggests, I'm with Smarty (Three) on an unlimited plan, which I use tethered for 5G home internet.

I get excellent speeds of around 400 Mbps when I connect but, after a time (maybe 20-30 minutes), the speed drops right down to perhaps 3-5 Mbps and latency increases. If I reconnect by quickly enabling then disabling airplane mode, speeds jump right back to 400 Mbps again, only for the slowdown to repeat itself in another 20 minutes or so.

Can anyone suggest why this keeps happening? Are there particular tests I can run to diagnose what's happening? This is what I have considered so far:
  • Tethering is allowed, and there is no throttling or data shaping according to Smarty.
  • I've checked the cell ID of the mast I am connected to - that stays constant whether speeds are good or bad, so it doesn't look like I'm simply connecting to a slower mast.
  • The fact that the connection returns to full speed as soon as I reconnect seems to rule out network congestion, I think.
  • I have tried various APN settings - smarty.net, 3internet, 3secure, three.co.uk - the result is the same with each.
Thank you for any advice.
 
I don't see this issue I'm with smarty too, sounds like signal issue maybe, have you checked with three service status page to see if it shows any issues?
 
Hi,

The signal strength remains pretty constant (full bars) even as the download speed slows down. I don't think it's the signal. And there are no service issues reported.
 
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I take it you are tethered to your mobile phone. Could it be a phone issue, have you tried another phone?
 
I don't have another phone to try, but this one is a Samsung S21 used only for tethering. I'm pretty sure the phone works perfectly, but are there any settings I should check?
 
Don't know about the settings for tethering an S21 but it sounds from your description that you are being throttled, either by your SIM(Smarty) or your phone possibly overheating. 20+ minutes of 400Mhz 5G may be causing the modem in the phone to get a bit to warm, worse if you're charging the battery at the same time. This is just my guess but until you try the SIM in another phone or modem you will not know
 
Are you sure the phone is still connected to the 5G band when that slow down happens? In some areas, going from 400Mbps to 5Mbps is just what happens when going from Three's 5G to 4G.

You can't trust the "5G" icon on a phone as that is displayed even when a 5G band isn't being used. On Android, you can use apps like NetMonster to see this. For example, 5G actually connected to 5G (3500 = band n78):

1.png


And "5G" while not using 5G at all:

2.png


On my phone I can prioritise 5G by selecting "NR/LTE" as the preferred network type and this makes the phone stay on 5G for longer. To access this menu, I type *#*#4636#*#* on the phone app and then:

JXFojcr.png


I don't know if the same option exists on a Samsung. On some devices you have "Smart 5G", which drops you to 4G when not doing anything intensive to save power, but you want that to be disabled in this case.

Even by doing this you can't really stop a phone from downgrading to 4G. You can force 5G on some 5G routers, but not all support that. The network also plays a part here. Three/Smarty seems to be fine with me being on 5G all the time, but EE sometimes only gives me 4G and 5G only becomes available when I'm actually using a lot of data.

I don't think it's a overheating problem. I've seen degraded performance when the phone is hot, but it needs to cool down before getting better speeds and in your case it's fast again after a network reconnect (which probably connects you to 5G again).

Just be sure it's not a hotspot issue, you can try to disable/enable the SIM or at least disable/enable mobile data instead of using turning on Airplane mode. Airplane mode turns off everything, so it also resets your hotspot. Doing this would keep the hotspot on and if it's fast again, then you know it's not a hotspot problem.
 
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I don't have another phone to try, but this one is a Samsung S21 used only for tethering. I'm pretty sure the phone works perfectly, but are there any settings I should check?
Samsung always issues with tethering! Except iphone! Don't ask me why?

Samsung a70 tethering to PC link speed 150Mbps
Samsung a53 5G tethering to PC link speed 433Mbps
Samsung a54 5G tethering to PC link speed 600Mbps
 
Samsung always issues with tethering! Except iphone! Don't ask me why?

Samsung a70 tethering to PC link speed 150Mbps
Samsung a53 5G tethering to PC link speed 433Mbps
Samsung a54 5G tethering to PC link speed 600Mbps
Tethering via cable? The Samsungs are all USB 2. They'll also generally have lower quality hardware, antennas etc.
 
Samsung modems are trash. Shannon modems need to get in the bin. I've not experienced this issue with my Snapdragon based phone, and I tether quite often.
 
Samsung always issues with tethering! Except iphone! Don't ask me why?

Samsung a70 tethering to PC link speed 150Mbps
Samsung a53 5G tethering to PC link speed 433Mbps
Samsung a54 5G tethering to PC link speed 600Mbps
I would be interest to know if others see that the report of this issue with low-end Samsung A mobiles also impacts the high-end Samsung S mobiles.

 
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This sounds like fairly typical traffic shaping. Only way you're going to resolve this is by switching networks to one that isn't as heavily traffic managed - like Vodafone.
 
Hi all, thanks for your replies - apologies for not responding earlier, I wasn't receiving notifications about your replies.

One thing I have tried in the meantime is to use an iPhone to tether with the same SIM. Although I have only a 4G iPhone to test with (getting around 40Mbps downloads), the performance is good and I haven't noticed the same drops in speed that I do while using the Samsung.

Smarty claims (publicly and officially) they don't do any kind of throttling or traffic shaping, so I tend to assume that's true, though a test with another network would help to settle that question.

I will also look into the NetMonster app to see if I am getting reconnected to a 4G signal while on the same mast (though even if that's the case, the performance when "throttled" is much worse than the constant 4G on my iPhone).

Given the more consistent performance using the iPhone, I am tending at the moment to think this is something to do with overheating or CPU management/throttling on the Samsung. It does feel much hotter than the iPhone when tethering. I am going to do some more tests where I will try to disable as much throttling as I can.

My Samsung is the S21 with USB-3. It can perform very well when it chooses to but it's a black box in terms of configuration, especially compared to an iPhone.
 
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