SRX5308 VoIP over VPN

Hello,

We've been using two SRX5308s (previously two FVX538s) to establish a VPN tunnel (over the Internet) between our two remote offices. These have been working fine for several years. We also run VoIP over this tunnel (using two Panasonic IP-PBX devices) to provide VoIP services between the two offices. This also has been working (mostly) fine. However, we do experience occassional (but regular) call quality issues (most notably sound quality) beyond what we'd otherwise expect from VoIP in this configuration.

We've been troubleshooting all other aspects of the network to help isolate what might be triggering these occassional quality issues. To further diagnose this we'd like to further configure the SRX5308 endpoints to establish precedence for all VoIP traffic through the VPN tunnel. I've been running through the SRX5308 manual but can't isolate exactly what and how I need to do this.

Is this type of traffic conditioning over the tunnel possible? If so, what exactly is required to configure the SRX5308 to provide this?

Thx,