Fritz 7340 6.06 broken codec G722.HD on analog FON1

cybermaus

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I have a 7340 (also tried this on 7270v2) with 6.06, and have recently been troubled with many bad connections.
Well, recently, it started about a year ago and is increasing in frequency.

After a long experimental search, I strongly suspects this is due to the following facts conspiring together:
- Fritz only supports G711 when going to/from analog FON1 (it supports many other codes, but only G711 on analog)
- Over the last few year G722 is becoming more widespread in use for cell phones. In NL at least.
- There is some bad codec negotiation between incoming line and Fritz, when it concerns G722. In this old 6.06 at least.

Basically, if I have an incoming line, and the originator is on GSM, they cannot hear me.
Fritz is reporting it as G711, but I think the GSM still thinks it is G722, and thus fails to decode.
Something along the lines of Fritz negotiating "G722? Yeah, I support that" And then forgets the FON hardware puts out a 711 stream.

I (seem to) have worked around it by forcing Fritz in /var/flash/voip.cfg to allow only *one* codec. Only PCMA (G711a)
And now I have had no bad line for 48 hours already.

Can anyone confirm/reject my suspicion?
Or tell me if newer OS maybe do better on this.
Or any other tips on how I could make Fritz do G722 on FON1
 

KunterBunter

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G.722 will never work with an analog phone connected to FON1 since it is a 7 kHz Wideband audio codec.
 

cybermaus

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True, as in you will never get wideband audio quality from an analog line.
But the analog line itself is without any codec, so you can still encode it in any codec you want for compatibility sake, even if it is a little overkill.

Or at the very least, should negotiate the codec properly to the cell phone.
Rather then end up with a broken connection.
 

sonyKatze

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  1. Which network operator do you use in the Netherlands?
  2. Does that issue happens constantly with one of your callers or is it sporadic? Which mobile network does your caller use?
/var/flash/voip.cfg to allow only […] PCMA
Glad you found a workaround and shared that with the community. Your issue is more complex because I tried to reproduce it with a FRITZ!Box 7270v2 at FRITZ!OS 6.06 and failed. When an analogue phone starts the call, FRITZ!OS does not offer G.722 (or G.711 HD). When an analogue phone answers an incoming call, FRITZ!OS does not include G.722 (or G.711 HD) as possible audio codec. When I force just G.722 (and G.711 HD), the call is not established at all.

FRITZ!OS allows to capture the network traffic by going for fritz.box/html/capture.html
There, select the first Internet connection. After you face a call with no audio, end the capture, and feed Wireshark. In Wireshark, you filter for ‘sdp’. Then, you have a look at the line m=audio … RTP/AVP … in the first SIP INVITE and the resulting SIP OK. A good example can be found here. The numbers after the RTP/AVP would be interesting for us. If one of the numbers is higher than 95, all subsequent lines are interesting. If the numbers are all below 96, just share the numbers with us.
newer OS maybe do better on this
Diffilcut to say without knowing the exact cause.
AVM updates a lot and backports some of their fixes even to older FRITZ!OS versions. However, FRITZ!OS 6.06 is terrible old. And because not all interoperability fixes get backported, the best would be the current FRITZ!OS 7.2x as comparison, like in the FRITZ!Box 7430 ~ 35 € in eBay.
 

sunnyman

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But the analog line itself is without any codec, so you can still encode it in any codec you want for compatibility sake, even if it is a little overkill.
Not only that. There seem to be ATAs and CPE supporting to put the 7 kHz bandwidth signal onto the analog line.
The next question is: is the POTS phone's circuitry and speaker/mic able to deal with that frequency range?

I found a proof-of-concept, where an Arris CPE was able to put the wideband audio onto the POTS line and a Gigaset DECT handset supported that via a beta firmware:

Also look here:

Quote: "Gigaset later reported that any of their SIP/DECT systems could be upgraded to support HDVoice via the analog line with only a firmware update."
 

cybermaus

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  1. Which network operator do you use in the Netherlands?
  2. Does that issue happens constantly with one of your callers or is it sporadic? Which mobile network does your caller use

Originally, the issue happened with budgetphone.
We now moved to cheapconnect, and the issue presists.

It was sort of random. Too often to call sporadic. But if it happens with a caller, it happens for that particular caller nearly repeatedly.
(often they call 2 or 3 times before we manage to call them back with an apology)
We did not get info from them what provider they are on, but it is clear it is always an incoming mobile number.

Please also understand it is not actually me or my company, but my brother, who is ... non-technical. To put it politely.
So getting a good description of what exactly went wrong in what way is sometimes hard.


When an analogue phone starts the call, FRITZ!OS does not offer G.722 (or G.711 HD). When an analogue phone answers an incoming call, FRITZ!OS does not include G.722 (or G.711 HD) as possible audio codec. When I force just G.722 (and G.711 HD), the call is not established at all.

Indeed, the call log never claims it negotiated G.722. For any line to and from the FON1, it only shows G.711 as the negotiated protocol
However, I am guessing their is somehow a miscommunication between both sides, and though Fritz believes G711 is negotiated, the other side believes something else.
This is a guess though.

At first I tried to prefer G722, until I realised that is never supported on FON1, so then I went back to not only prefer, but enforce PCMA/G711 by making that the only availible codec
This seems to work. Again seems, because non-technical user.
But any errors that still occur seems less frequent, and different. For all I know, they may be unrelated, people hanging up.


FRITZ!OS allows to capture the network traffic by going for fritz.box/html/capture.html
There, select the first Internet connection. After you face a call with no audio, end the capture, and feed Wireshark. In Wireshark, you filter for ‘sdp’. Then, you have a look at the line m=audio … RTP/AVP … in the first SIP INVITE and the resulting SIP OK. A good example can be found here. The numbers after the RTP/AVP would be interesting for us. If one of the numbers is higher than 95, all subsequent lines are interesting. If the numbers are all below 96, just share the numbers with us.
Diffilcut to say without knowing the exact cause.
AVM updates a lot and backports some of their fixes even to older FRITZ!OS versions. However, FRITZ!OS 6.06 is terrible old. And because not all interoperability fixes get backported, the best would be the current FRITZ!OS 7.2x as comparison, like in the FRITZ!Box 7430 ~ 35 € in eBay.

Good info, Thanks, if it turns out it is still a actual problem despite my workaround, I will check this out a bit better.


I considered a new fritz, but also considered that the use of FON1 itself may be as antiquated as the 6.06 OS.
So I worry that the FON1 related code may not have changed at all.

Was it for me directly, I would indeed simply try a €35 Fritz. But I also worry about upsetting the status quo. If I make a visually obvious change (change box) then for the weeks thereafter, *everything* is because I did something (printer does not print, maybe because you did something to the fritz, can you have a look?)
 

cybermaus

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...The numbers after the RTP/AVP would be interesting for us. ...share the numbers with us...

So you seem very knowledgeable about this, as well as motivated to dig out deep details.
Which is very positive. But who is "us"? Are you with AVM? Or part of some core group here on IP-FORUM?

I did not report to AVM directly as this box is obviously long out of support.
And also I usually find I get better help in communities of enthusiast then companies, as the latter usually only talk on layman consumer skil level.
 

sonyKatze

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The AVM support is quite sophisticated but won’t help you here indeed, because your FRITZ!OS is out of support. And yes, AVM does tarpit style in their support channels. However, when you overcame that, they are quite good when you are about a bug. Anyway, when it comes to software bugs in telecommunications, you should go for several ‘attacks’ in parallel. That means, confronting AVM and your network operator and the community. In you case, AVM won’t move. Therefore, I recommend to go for a new FRITZ!Box.

‘Us’ is just ‘us’, the reader and writers at IP-Phone-Forum. Somebody else might answer, somebody else might see something, I might be offline. So it is ‘us’. In other words, you do not have to post your whole SIP traffic (privacy concerns?) to analyze your situation further; just those RTP payload type numbers are needed right now.
 

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