Scenario: Small office; an ADSL (8meg x 512k) Internet connection provided by an 877, also terminating a VPN link to a main office. There is VOIP traffic only over the VPN tunnel (protected GRE).
While providing QOS for outbound VOIP (over VPN) has not proven difficult, inbound eludes me. What is an effective procedure that will mitigate the effects of flooded inbound connection on the VOIP quality? From time to time, a burst of download activity severely disrupts the voice traffic.
The effective procedure is to configure QoS on the egress of the device that provides your ingress traffic. However, most likely your Internet provider won't do so. In that case, and assuming what's causing your inbound transient congestion is TCP traffic, you can rate limit non-voice inbound TCP traffic to attempt to preserve available bandwidth for your VoIP. And/or, you can shape outbound TCP ACKs to shape inbound data packets. Both work, but both also will still allow transient bursts. To mitigate those, you often need to set a much lower inbound traffic target than your ingess bandwidth capacity. Initially try regulating ingress traffic to 1/4 to 1/2 inbound capacity.