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tw31ve
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R11e-LTE PAcket Loss

Tue Jul 09, 2019 1:18 pm

Hi All,

I have an SXT LTE Kit router with the R11e_LTE modem and am getting severe packet loss which is preventing me from getting a stable VPN connection to my workplace. Packet loss is consistently between 18% and 28%. When I put the sim in my phone it drops to 0%. I am on the three network in the UK.

I have updated the modem to the latest firmware (MikroTik _CP_2.160.000_v012) and am using routerOS 6.45.1. I have no site to site VPNs or other configurations set up, its currently just the LTE connection, a DHCP server and the firewall. The CPU never gets over 5% utilised.

Does anybody have any suggestions I can try to improve the situation as im getting to the point where I will need to try an alternative router as I cant work from home currently!

Thank you.
 
robpeng
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Re: R11e-LTE PAcket Loss

Tue Jul 09, 2019 4:03 pm

Hi tw31ve,

Ireland here, on Three network also

Have you tried 3g only? un-ticking LTE under /interfaces > LTE
 
tw31ve
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Re: R11e-LTE PAcket Loss

Tue Jul 09, 2019 4:59 pm

Hi Rob,

I currently only have LTE channel 3 selected and all the others switched off as I found that was only way to get any decent performance. I will try 3g when im home tonight and report back. Clearly its not a long term option due to decreased speed but it will be interesting to see if the packet loss disappears, im also not sure if my local mast supports 3g, from memory its 4g only but i could be wrong!
 
robpeng
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Re: R11e-LTE PAcket Loss

Tue Jul 09, 2019 5:13 pm

Sure, let me know when you get to to, also be useful to know

* What LTE band does it select if you allow natural selection? (no band selected).
* Have you tried locking it to band 20? I know Three use band 3 and 20.
* Have you set the APN?

Also, you may need to tick "allow roaming" as I've seen 3g here is still coming up as owned by O2 but Three bought them out ages ago
 
uldise
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Re: R11e-LTE PAcket Loss

Tue Jul 09, 2019 9:56 pm

Try to reduce Max MTU size, to something like 1360 or so..
 
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krafg
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Re: R11e-LTE PAcket Loss

Tue Jul 09, 2019 9:57 pm

How much is your reception signals?
If you want to know my network, you can find it here.

Image
 
tw31ve
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 12:09 am

Hi All,

I'm definitely meant to be on band 3, nothing else works. I tried 3g only which reduced the packet loss slightly but as you expected also dropped the speed from 40x20mb down to 6x2mb!

Uldise, reducing the MTU has helped considerably, packet loss now averages 10% instead of 20% or so. Do I just experiment with different numbers until I get the best fit?

Signal wise I'm seeing -105dbm, -8.5 RSRQ, -9 SNSR

Thanks for your help everyone, it's heading the right way!
 
robpeng
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 12:45 am

Interesting, -105dbm for the rsrp is a little poor, I usually get from -90 to -70, have you the SXT outside and pointed towards the cell tower? or in the general direction?

I'm not sure if the signal would equate to packet loss, does the connection ever just drop?

Would you mind putting up a screenshot of the packet loss up? I have a few SXTs in the wild now and have never seen packet loss or what it looks like
 
tw31ve
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 11:32 am

Right, I had a bit more of a play with the MTU numbers and it seems to be the cause. I dont know exacty what the 'right' number is but im currently on 1488 and the packet loss has dropped to 1% which is good enough for a stable VPN connection. Being picky I would still like it to get down to 0% so any further tips greatfully received but in the main I think this is resolved now. Thank you.

Rob, currently the SXT is on top of one of my kitchen cabinets pointed in the direction of the tower but with no clear line of sight. I want to get it running reliably before mounting it on the wall of the house. I cant upload pictures from the office but basically if I am running a ping from the terminal on the router to an outside IP around 20% of them will timeout. Its not really a huge issue for day to browsing as everything still works but for VPNs its a nightmare.
 
flynno
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 12:22 pm

You should get somebody to hold it in the direction of the tower outside the house, then run your tests.
 
robpeng
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 12:49 pm

My MTU is 1480 if you want to try that

Yeah I feel your pain, I had mine inside a window for sometime before mounting it outside, the signal drastically improves outside and doesn't need to be line of sight with the mast

The SXT has a 60 degree antenna so pointing it in the general direction should be good enough and you can use the signal strength guide in 'Quick Set' to help
 
mkx
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Re: R11e-LTE PAcket Loss

Wed Jul 10, 2019 4:01 pm

Interesting, -105dbm for the rsrp is a little poor, I usually get from -90 to -70, have you the SXT outside and pointed towards the cell tower? or in the general direction?

I'm not sure if the signal would equate to packet loss, does the connection ever just drop?

LTE works quite fine down to RSRP of -110dBm. Can work even down to -125dBm, but it requires fair RSRQ (signal/noise ratio), at least -10dB. Which is hard to get with low RSRP due to uncorrelated RF noise. Absolute minimum is set by thermal noise. Surely throughput drops with reduced RSRP.
What can happen is that LTE connection breaks because of lack of Tx power from customer's device (can happen if Tx power from cell tower is set too high).

Anyways, if RSRP gets lower, then all the LTE L1 machinery kicks in: RRC and RLC retransmissions etc., which means that IP (running on top of LTE data bearer) only observes longer average RTT and increased RTT jitter, but IP packets should not get dropped just like that. Well, IP packets do get dropped, but the throughput gets really low by that time (because of massive retransmissions on RLC timing out). Definitely much lower than 40/20 observed by @tw31ve ... Mind that all the mentioned LTE machinery is transparent to IP data ... and that machinery makes LTE more resilient to interference than any 802.11 stuff.
BR,
Metod
 
tw31ve
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Re: R11e-LTE PAcket Loss

Thu Jul 11, 2019 12:06 pm

That's interesting, I was on an MTU of 1480 previously and 1488 has improved the situation somewhat, I'm still running at between 2 and 3% which is higher than when I use my phone but survivable.

I have already experimented with moving the router around and I can increase the maximum speeds but it makes no difference to the packet loss.

I'm tempted to get another router to experiment with to see if I can pin it down to the sxt or some other as yet unknown external factor. Once again thanks for the input.
 
uldise
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Re: R11e-LTE PAcket Loss

Thu Jul 11, 2019 6:54 pm

i have SXT LTE Kit, and on band3 with MTU 1480. but for my LTE interface MTU is 1200.
and -105 RSRP is really bad, you are on the cell Edge..
with band3 you should place your device with direct visibility to tower to improve signal.

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