[Asterisk-Users] QOS / Cisco / Asterisk

[Jeffrey C. Ollie]

Sorry for the late, late reply, but I don't follow the -users list
closely.

On Tue, 2005-01-04 at 10:43 -0600, rsenykoff at harrislogic.com wrote:
>
> What's wrong with doing it by port? If it is possible that something
> else out there may use the same TOS flags as Asterisk, by prioritizing
> port 4569 (IAX2 protocol) you know for sure that the only packets in
> that queue are VoIP traffic. Also, what about your incoming traffic?
> Are the TOS flags correct there? I'm not saying that TOS is bad, just
> that as you've seen, it can get changed along the way. I'm using port
> number to separate traffic and it is working great. 

Well, in a sense, we are both correct.  You are looking at the problem
from the perspective of an edge router.  At the edge of your network,
you can't trust the incoming QOS markings, so you need to use an ACL of
some sort to differentiate priority traffic from non-priority traffic.

However, inside the network, when you can (mostly) trust that packets
have been generated with the correct QOS markings by the orginating
device, internal routers/switches can use the QOS marking (be it the
TOS, DiffServ markings, 802.1p priorities, etc.) to prioritize traffic.

I'd be willing to bet that switches (and maybe even some routers) can
prioritize based upon QOS markings more efficiently that they can run
packets through ACLs.  This is especially needed where traffic volumes
are large.

So, inside your network you need to examine the configuration of pretty
much every device to make sure that they don't mess with the QOS
markings where they aren't supposed to.

Jeff


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