Issues with P25 via home internet

Help with P25 issues
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vk2faeu
Posts: 4
Joined: Fri Apr 24, 2020 2:06 am

Issues with P25 via home internet

Post by vk2faeu »

Having a really strange issue with P25 via an MMVDM hotspot running on a raspberry pi 3 zero w.

When my hotspot is connected to my home internet (NBN Cable, 50 down, 20 up) via an ethernet adapater (10/100), a particular station that I talk to regularly receives garbled audio from me during certain times of the day. Other stations listening at the same time on the same talk group via their hotspots (TG 10400) receive my audio perfectly fine.

To add to this, if I connect my hotspot instead to a Telstra 4G modem (a knighthawk), bypassing my home NBN internet connection, my audio is received perfectly by everyone.

Finally, to add to the confusion - the issue seems to rectify itself without any intervention from myself after a period of time (generally speaking 30 minutes to an hour).

I should add too that this particular station is able to receive P25 audio from TG10400 from other stations perfectly fine during group chats. It's just me that seems to be sending him garbled audio.

I've listened to the audio via the phone that he gets - it sounds as though data is arriving in the wrong order (packet re-ordering). Again, the issue is only occurring sometimes (possibly during peak internet usage times), and will resolve itself.

The issue occurs on both TG 10400 and TG 10700

I do not encounter these issues with other stations, and I don't encounter the issue when using DMR via the same hotspot.

Any ideas?
KE7FNS
Pi-Star Team
Posts: 1830
Joined: Wed Apr 17, 2019 11:11 pm

Re: Issues with P25 via home internet

Post by KE7FNS »

vk2faeu wrote: Tue Aug 18, 2020 5:41 am I've listened to the audio via the phone that he gets - it sounds as though data is arriving in the wrong order (packet re-ordering).
With UDP there is no guarantee that your packets will arrive in order or even if they will arrive at all. If they are using standard UDP mechanics, out of order packets are discarded and not used at all.

I would expect if the problem existed between your ISP and the server everyone is listening to, they all would be hearing the same thing, and since they aren't it makes me suspicious that maybe its really your buddies problem.

Maybe you both should contact your individual ISPs and open up support tickets and see if they will work together and look into it.
If someones previous actions are any indication of their future actions, then I predict the deletion and removal of access will happen at any moment. 7-11-2020.

"07/13/20 This Website Has Been Taken Down" ... again :lol:
vk2faeu
Posts: 4
Joined: Fri Apr 24, 2020 2:06 am

Re: Issues with P25 via home internet

Post by vk2faeu »

I would expect if the problem existed between your ISP and the server everyone is listening to, they all would be hearing the same thing, and since they aren't it makes me suspicious that maybe its really your buddies problem.
This is the main issue when troubleshooting. My thoughts are:

I'm user A. I've got user B and user C listening to me.

If user B reports 5/5 and user C reports garbage, the issue is clearly with user C (as im sending good audio)

If users B and C report garbage - its either me sending poor audio, the reflector having an issue, or users B and C having internet issues).

To add to this, the person who reports issues with my audio is using a Quantar repeater. I'm told that the Quantar will drop the audio on receiving bad packets.

From my point of view, if 1 other person can hear me fine - i'm sending good audio.
KE7FNS
Pi-Star Team
Posts: 1830
Joined: Wed Apr 17, 2019 11:11 pm

Re: Issues with P25 via home internet

Post by KE7FNS »

vk2faeu wrote: Tue Aug 18, 2020 11:48 pm This is the main issue when troubleshooting.
Yeah, theres very little you can do, thats why I suggested opening support tickets and see if you can get the network engineers to figure out what the issue is.

My guess is the traffic is not being prioritized at one of the hops because it isn't a common/frequently used UDP packet like skype, zoom or some other VOIP packet would be.

My ISP had the same sort of issue a few years ago where VOIP audio was warblely and robotic. They had upgraded some hardware and the problem became widespread in multiple locations. Luckily one of the network engineers was also a ham, and he was able to troubleshoot and solve the issue.
If someones previous actions are any indication of their future actions, then I predict the deletion and removal of access will happen at any moment. 7-11-2020.

"07/13/20 This Website Has Been Taken Down" ... again :lol:
vk2faeu
Posts: 4
Joined: Fri Apr 24, 2020 2:06 am

Re: Issues with P25 via home internet

Post by vk2faeu »

traffic is not being prioritized at one of the hops
Yeah you're probably on the money there. This would make sense too where at "peak" times of the day it gets worse.

I'm going to leave the hotspot connected to my 4G modem. Seems to work perfectly fine there :)

In case anyone is reading this - my ISP here in Sydney Australia is TPG.
KK6RQ
Posts: 13
Joined: Mon Feb 22, 2021 9:32 am

Re: Issues with P25 via home internet

Post by KK6RQ »

Here's another possibility, that absolutely affected a friend of mine: His cable modem suddenly started using some frequencies right smack in the 420-450MHz range after previously not using any below about 600MHz (hence the cable modem was being jammed by his onsite 100w UHF repeater periodically). Comcast was reportedly useless trying to change the frequency range while talking to tech support, but a hard power reboot (unplugged for 10 min) set it back to the 600MHz range, solving the problem...

Might be a good idea to look at the cable modem frequencies in use for those DOCSIS channels...
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