QoS for voice traffic

Discussion in 'Cisco' started by michikrall@hotmail.com, Jun 7, 2006.

  1. Guest

    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
    , Jun 7, 2006
    #1
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  2. SAto Guest

    > 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
    SAto, Jun 7, 2006
    #2
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  3. Guest

    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
    , Jun 8, 2006
    #3
  4. SAto Guest

    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
    SAto, Jun 8, 2006
    #4
  5. Guest

    SAto wrote:
    > 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.
    , Jun 8, 2006
    #5
  6. Guest

    wrote:
    > SAto wrote:
    > > 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
    , Jun 12, 2006
    #6
  7. Guest

    wrote:
    > wrote:
    > > SAto wrote:
    > > > 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.
    , Jun 12, 2006
    #7
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