QOS for VOIP Inbound 877

Answered Question
Aug 4th, 2008

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.

Thanks!

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Correct Answer by Joseph W. Doherty about 8 years 5 months ago

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.

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sadbulali Fri, 08/08/2008 - 14:40

To ensure voice quality, you must use QoS in all areas of the enterprise network. To make a proper QoS configuration, you must first identify the points where QoS is a concern, then choose the appropriate QoS tools to use, and deploy to the devices in the network.

Correct Answer
Joseph W. Doherty Sun, 08/10/2008 - 17:41

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.

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