Asterisk set QOS internally but because it doesn’t not run as the root user these settings are not applied to outbound packets. You would need to create rules in iptables to specifically tag the SIP/RTP packets. There are many examples you can Google.
Thanks for reply
As I use an ADSL line , the voice is ok unless I use some P2P connections
Even a very low P2P throughput 2-3 KBps leads to voice deterioration
So I need to do something about voice prioritization…
Two cisco 877 are used to tunneling voice between two asterisk machines…