[asterisk-users] Voice broken during calls (again...)

Luca Bertoncello lucabert at lucabert.de
Tue Jun 23 02:06:39 CDT 2020

Am 23.06.2020 08:43, schrieb Luca Bertoncello:

And another thing, I discovered right now...

> Could you suggest me something to restrict the problem?
> Currently, I think the problem can be:
> 1) on Asterisk
> 2) on my Gateway/Firewall

A couple of years ago I added this entry in my firewall:

/sbin/iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS  

since I had the problem downloading data from an Internet site using my 
I found this site explaining that:


I really forgot this entry, but now I checked all entries in my 
Firewall, and I see it, with my remark...
Now, the last line of the HowTo:

# iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 

This sets the MSS of passing SYN packets to 128. Use this if you have 
VoIP with tiny packets, and huge http packets which are causing chopping 
in your voice calls.

Could it be the problem? Right now I'm not at home, so I cannot test it, 
but maybe I can add an entry like:

iptables -A FORWARD -p tcp -m multiport --ports 5060,<my high port for 
SIP> --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 128

and change the previous entry like:

iptables -A FORWARD -p tcp -i intlan0 --tcp-flags SYN,RST SYN -j TCPMSS  

to limit the behaviour on the internal LAN...

Your opinion?

Thanks a lot!
Luca Bertoncello
(lucabert at lucabert.de)

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