From: Victor Cappuccio (cvictor@protokolgroup.com)
Date: Thu Jan 05 2006 - 10:50:47 GMT-3
Hello Leigh,
Maybe this like cold help u a little bit more
http://www.cisc.com/en/US/products/sw/iosswrel/ps1834/products_feature_guide
09186a0080080466.html
the AFny PHB defines four AF classes: AF1, AF2, AF3, and AF4. Each class is
assigned a specific amount of buffer space and interface bandwidth,
according to the SLA with the service provider or policy map.
Within each AF class, you can specify three drop precedence (dP) values: 1,
2, and 3.
Assured Forwarding PHB can be expressed as shown in the following example:
AFny
In this example, n represents the AF class number (1, 2, or 3) and y
represents the dP value (1, 2, or 3) within the AFn class.
In instances of network traffic congestion, if packets in a particular AF
class (for example, AF1) need to be dropped, packets in the AF1 class will
be dropped according to the following guideline:
dP(AFny) >= dP(AFnz) >= dP(AFnx)
where dP (AFny) is the probability that packets of the AFny class will be
dropped. In other words, y denotes the dP within an AFn class.
In the following example, packets in the AF13 class will be dropped before
packets in the AF12 class, which in turn will be dropped before packets in
the AF11 class:
dP(AF13) >= dP (AF12) >= dP(AF11)
The dP method penalizes traffic flows within a particular BA that exceed the
assigned bandwidth. Packets on these offending flows could be re-marked by a
policer to a higher drop precedence.
An AFx class can be denoted by the DSCP value, xyzab0, where xyz can be 001,
010, 011, or 100, and ab represents the dP value.
Also I have this formula that could be usefull for anything
8X + 2Y
Af11 == 8(1) + 2(1) = 10
Af41 == 8(4) + 2(1) = 34
-----Mensaje original-----
De: nobody@groupstudy.com [mailto:nobody@groupstudy.com] En nombre de Leigh
Harrison
Enviado el: jueves, 05 de enero de 2006 8:57
Para: FORUM
Asunto: QoS AF priorities
All,
I've had a little dig and can't seem to find the answer to my question.
If you have traffic is the following classes:-
af11 af12 af13
af21 af22 af23
af31 af32 af33
af41 af42 af43
I know that af41 is top of the shop and af 13 is at the bottom. My
question is:-
Which order will the packets get dropped off? i.e. will af43 be dropped
before af31?
I'm not sure if they degrade 41, 42, 43, 31, 32....etc, or if they go
41, 31, 21, 11... etc, or any other order.
LH
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