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QoS for voice traffic

 
 
michikrall@hotmail.com
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      06-07-2006
Hy guys,
can anyone explain in some simple sentences what these config lines
exactly do?

ip access-list extended VOICE
permit ip any any dscp af31
permit ip any any dscp cs5

I got it out of an QoS conf on a Cisco Router.
I am interested in what "af31" and "cs5" is and what voice traffic is
matched when this lines are used. What does "dscp" mean and do I need
to mark a packet with this value before I can match it? I need to match
voice traffic from a Alcatel pabx, so maybe I will need to match other
traffic (I got a whitepaper from Alcatel where app. 300ports are
mentioned...).

If anyone can help, please do so.
Thx Mike

 
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SAto
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      06-07-2006
> I got it out of an QoS conf on a Cisco Router.
> I am interested in what "af31" and "cs5" is and what voice traffic is
> matched when this lines are used. What does "dscp" mean and do I need


Differentiated Services Code Point
A way to classify packets in QoS.

CS5 is the same as IP precedence 5.

Normally I think call setup traffic is marked as AF31 and rtp traffic
marked with precedence 5.

So your access list matches both controlsignaling and voice traffic.

> to mark a packet with this value before I can match it? I need to match
> voice traffic from a Alcatel pabx, so maybe I will need to match other
> traffic (I got a whitepaper from Alcatel where app. 300ports are
> mentioned...).


Some but not all makers of VoIP systems mark their traffic, to see if
this is the case with the Alcatel you could just apply this access list
to the port the pbx is connected to and see if the counters go up.

Or you could classify the packets yourself.

-SAto

 
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michikrall@hotmail.com
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      06-08-2006
Thanks a lot Sato,
you gave me the right hints! So this is part of an QoS config, where
voice traffic is prioritised "after" the DiffServ - method?

Cheers, Mike

 
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SAto
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      06-08-2006

http://www.velocityreviews.com/forums/(E-Mail Removed) skrev:
> Thanks a lot Sato,
> you gave me the right hints! So this is part of an QoS config, where
> voice traffic is prioritised "after" the DiffServ - method?


Yes, but depending on where this access list is actually used it can be
used to reclassify or prioritize.

-SAto

 
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anybody43@hotmail.com
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      06-08-2006

SAto wrote:
> (E-Mail Removed) skrev:
> > Thanks a lot Sato,
> > you gave me the right hints! So this is part of an QoS config, where
> > voice traffic is prioritised "after" the DiffServ - method?

>
> Yes, but depending on where this access list is actually used it can be
> used to reclassify or prioritize.
>
> -SAto


"depending on where this access list is actually used "
Or not at all.

VOICE is just an arbitrary label and
for QoS the access-list can be applied to a 'policy map'
and then that in turn applied using a 'service-policy'
statement to an interface.

'voice traffic is prioritised "after" the DiffServ - method'

Are you thinking of "after" as in later than?

It is not later than.

I would say:-
'voice traffic is prioritised using the DiffServ - method'

The other BIG one to look out for is that by default
some network equipment resets the diffserv bits to zero
as the traffic passes through it.

 
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michikrall@hotmail.com
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      06-12-2006

(E-Mail Removed) wrote:
> SAto wrote:
> > (E-Mail Removed) skrev:
> > > Thanks a lot Sato,
> > > you gave me the right hints! So this is part of an QoS config, where
> > > voice traffic is prioritised "after" the DiffServ - method?

> >
> > Yes, but depending on where this access list is actually used it can be
> > used to reclassify or prioritize.
> >
> > -SAto

>
> "depending on where this access list is actually used "
> Or not at all.
>
> VOICE is just an arbitrary label and
> for QoS the access-list can be applied to a 'policy map'
> and then that in turn applied using a 'service-policy'
> statement to an interface.
>
> 'voice traffic is prioritised "after" the DiffServ - method'
>
> Are you thinking of "after" as in later than?
>
> It is not later than.
>
> I would say:-
> 'voice traffic is prioritised using the DiffServ - method'
>
> The other BIG one to look out for is that by default
> some network equipment resets the diffserv bits to zero
> as the traffic passes through it.


Hi,

> I would say:-
> 'voice traffic is prioritised using the DiffServ - method'


You're right, my English unfortenetely is not the best

> The other BIG one to look out for is that by default
> some network equipment resets the diffserv bits to zero
> as the traffic passes through it.


Generally speaking, what equipment does that (a special brand)?
That means, if I want to match the mentioned dscp's, I (or the pbx)
first has to
mark it?

Thanks a lot

 
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anybody43@hotmail.com
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      06-12-2006

(E-Mail Removed) wrote:
> (E-Mail Removed) wrote:
> > SAto wrote:
> > > (E-Mail Removed) skrev:
> > > > Thanks a lot Sato,
> > > > you gave me the right hints! So this is part of an QoS config, where
> > > > voice traffic is prioritised "after" the DiffServ - method?
> > >
> > > Yes, but depending on where this access list is actually used it can be
> > > used to reclassify or prioritize.
> > >
> > > -SAto

> > 'voice traffic is prioritised using the DiffServ - method'
> > I would say:-
> > 'voice traffic is prioritised using the DiffServ - method'

> You're right, my English unfortenetely is not the best
> > The other BIG one to look out for is that by default
> > some network equipment resets the diffserv bits to zero
> > as the traffic passes through it.

>
> Generally speaking, what equipment does that (a special brand)?
> That means, if I want to match the mentioned dscp's, I (or the pbx)
> first has to
> mark it?


I am not absolutely sure about this since my experience is limited
however I suspect that unless specifically configured
to do so Cisco switches will

I am not absolutely sure about this since my experience is
limited however I believe that Cisco switches will clear any
diffserv (or TOS) bits. To avoid that they have to be specifically
configured.

 
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