I have a very typical scenario where I would like to protect IP phones traffic from high RTT, packet delay variation and packet loss on congested links. I fully understand, that QoS would help only in case of very short congestion. To make matters worse, my ISP does not support QoS so there is no way I can prioritize certain traffic from end-to-end. Overall topology can be seen here:
(Usually) the short traffic congestion happens in ISP PE router where the traffic policers are. I tried Priority Queuing(VoIP traffic has known bandwidth so it's safe to use) in Cisco 2801 routers where IP phones traffic was set to "high" queue both in Fa0/0 and Fa0/1 in egress direction, but this did not have a noticeable affect. On the other hand, it was somewhat expected as I configured queuing before the congested link(policer in PE router)? Is there any technique which helps to protect the traffic between two IP phones in case of short-term traffic bursts other than increasing the policer in PE routers?