The consumer-grade SFR Box 7 has a feature that is activated by default: SIP ALG.
It has been observed that bad call quality occurs with Aircall (jitter and packet loss), as well as other VoIP applications, when this setting is enabled.
Here is a screenshot of the setting and where it is located on the Admin page of the SFR Box 7 :
This setting is causing issues due to how "SIP ALG" is implemented on this particular equipment (seemingly systematic scanning of usual Voice UDP/RTP ports + usage of the CPU resources of the equipment).
It is not due to the SIP ALG mechanism itself, which works OK with Aircall on most other router equipment that strictly applies SIP ALG (Aircall application doesn't use SIP TCP port 5060 or UDP Port 5060).
Once the change is applied, reboot the Box and computer.
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