I'm testing ASA phone proxy (connecting IP phone to my local DSL provider) and having an issue with the voice quality. quality is bad sometimes. I'm thinking to use router so as to provide QoS for voice but would DSL provide give priority to the QoS marked voice packets? should QoS be end-to-end? or will I have to pay extra bucks to have them give priority to marked voice packets?
From my experience, I have never seen ADSL provider even bother to inspect QoS marking as they are selling the service as best effort. But you can certainly check with your provider whether they support QoS or not.
Only if they support then it would make sense to do the marking. Or you need to buy some special service off them, provided they offer one.
You likely won't get your DSL provider to look at DSCP tags and treat the traffic accordingly, but you still may be okay over the link if you do this:
* Police (since the ASA can't shape) the outbound direction on the outside interface to the *upload speed* of the connection. It is useful to run a bandwidth speed test that tests upload speed to find out the actual upload speed (instead of theoretical or published/marketed speed) of the link.
* Apply a QoS policy to the policed interface with a priority queue for the size you want to handle RTP traffic for.
* Strip all DSCPs outbound, unless the provider confirms they will treat DSCP with specific priority.
I use this same concept for my home Internet SIP trunk on a cable connection, and have no issues with outbound voice quality, even during link congestion.
Note that if this is a VPN, make sure you classify traffic before it hits the encryption.
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