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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:

network topology

(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?

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    If your ISP doesn't provide some type of QOS, I would A) Consider changing providers to one that does and/or B) Tell them this is a requirement for your continued business. They should be able to readily implement it with any modern hardware, and then charge you a fee for it. It's win/win as you get protection for your traffic and they get more money... – Brett Lykins Jan 23 '14 at 17:46
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    The problem lies with your ISP, so as @Brett Lykins says, you need to get your ISP to prioritize traffic for you. Unless they do, or you switch to one that does, there's not much you can do from your end to protect voice traffic. – Ron Trunk Jan 23 '14 at 19:51
  • Could you tell us what rate the PE is policing traffic to? It's relevant because there are workarounds for the problem, but you have a platform with somewhat limited horsepower – Mike Pennington Jan 23 '14 at 21:34
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    Are you buying a regular internet line and pushing the VoIP traffic over that link? Ideally, you should buy something like MPLS where the SP will guarantee QoS. You could then on your main site have a regular internet line and a router to handle traffic. – Jan Jan 23 '14 at 22:42
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    Martin, have you solved this problem? If so, please update the question. If not, are you still interested in us helping to solve it? – Mike Pennington Apr 24 '14 at 1:41
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The only place you have control of is up to the output queue where you transmit the packet to the provider. If you are using policing here, you need to convert it to Hierarchical Queuing Framework (HQF) or whatever name they have given it now. Inside of this you can set policing values, but your VoIP would be put into the Priority queue to receive low latency transmit priority for packets that match that class (RTP/SIP/SCCP or whatever you define, an ACL perhaps).

This will make sure the voice traffic is transmitted before any other queues and will help on short congestion. Indeed if you convert your policing to traffic shaping, you may see an overall performance increase for everyone, but for sure get that voice in the priority queue. (Shaping vs Policing)

This will only help if your output queue is lightly congested and will have no effect on any internet transport in the middle. If this is where your problem exists, investigate alternative providers or a small dedicated point to point circuit.

Edit: ps set your shaping on CE egress just smaller than the PE ingress with shaping and priority that way you control what gets dropped first.

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