Re: Does QOS on an 828 or 837 actually achieve anything?

"John Rennie" <john@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:bo2sg1l67b0a06vlthhf02to3agkum90m4@xxxxxxxxxx
> We have a number of customers using VOIP through an ADSL to ADSL or SDSL
to
> SDSL VPN, and inevitably they occasionally get sound quality problems. Am
I
> right in thinking that implementing QOS on the 837 (ADSL) or 828 (SDSL)
> routers isn't going to help?
>
> My reasoning is:
>
> - all the public Internet routers between the two sites will ignore any
QOS
> settings on packets I generate
>
> - because it's a VPN the same public routers will just see ESP packets and
> won't even get to see any VOIP settings made by the PBXs
>
> If I understand correctly I can use QOS on the router to control how the
> router prioritises packets sent from my LAN out through the ADSl or SDSL
line.
> However if the latency problems are due to the intervening public Internet
> routers there is nothing I can do about it. Is this a reasonable summary?
>
> Thanks,
>
> John Rennie

John,

You are thinking along the right lines, but there is more to it. Yes, you
definitely want to prioritize for packets leaving your network in case you
are filling up the outgoing pipe, even though you can't control the public
internet. However, you can make sure that the qos is carried end to end -
not obeyed by the public routers, but used by your end site. You can always
reclassify the traffic when it comes in the other end, but the better
solution is to use 'qos pre-classify' with the vpn tunnel. That means that
the packets inside the esp packets will be assigned the qos tag. When the
other end breaks down the esp packet, it will have the qos information
available. Here is a good article:

http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800b3d15.shtml

Hope that helps,

Jim


.

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