VOIP Delay...traffic marking for Qos?

Hi, thanks for the reply.

I already have the VOIP system behind a QoS capable router with a public IP address, but the router is behind the Comcast gateway.

We're using the Comcast connection for all our internet needs as well....

Are you saying I need to ditch the Comcast gateway all together and buy a modem that also supports Qos? 

If your Comcast modem is in passthrough mode and you are using your own router, it sounds like you are already setup how Comcast_John was recommending. If you are not in passthrough mode and are using double NAT, that would be the first thing to correct.

You may be able to control QoS on your own router to make sure traffic is prioritized going out your router, but Comcast does not provide any kind of QoS once you reach their network/Internet and even if they did, your traffic is likely routed through other networks and QoS is not guaranteed to be honored. Inbound QoS is even more complex. High end business Internet service sometimes do guarantee QoS, but you aren't going to find that with $100-$250 service from Comcast cable.

I deal with VoIP systems from Vertical. QoS is normally tagged by the devices, not the router. Routers job is to recognize and prioritize the traffic. So that would be the question I'd ask Mitel, is the traffic being tagged and are you saying the routers need to prioritize those QoS queues. If that is the case, as I suspect it is, you aren't going to get Comcast to do any more prioritizing than is already happening.

My favorite config is Comcast in passthrough with a pfsense firewall. With that I can prioritize outbound traffic to make sure RTP (VoIP packets) are being prioritized as much as possible. I'm also able to setup limits on bandwidth use by other protocols such as HTTP or just other LAN devices to make sure no other device takes up all the bandwidth. This has generally made VoIP reliable (although currently I'm having jitter issues).

Also, you may want to find out how your traffic is being routed. If you can find out from Mitel what IP or hostname the RTP packets are coming from, you can do a tracert to see how your traffic is being routed. Comcast often has some interesting routing with traffic sometimes traversing the country before reaching it's destination. I don't know if there is anything that can be done about that though.