From: Scott Morris (swm@emanon.com)
Date: Wed Mar 17 2004 - 08:59:02 GMT-3
DSCP per the RFC treats the first 6 bits of the TOS field as one value, so
you get things from 0 to 63. Later RFCs (2597, 2598) where we started
defining the PHB (per hop behavior) stuff to give everyone a common
guideline to implementation changed things to a "class" (which strangely
enough was just like the old RFC791 version of IP Precedence!) followed by a
drop threshold. While you have classes like AF11, AF22, etc. These are not
read as AF "eleven" or AF "twenty-two". It's more of Assured Forewarding
Class 1 Drop Threshold 1 (low), or Assured Forewarding Class 2 Drop
Threshold 2 (medium).
The actual codepoints though are still referred to in DSCP format, or 0-63.
AF11 = DSCP 10. AF22 = DSCP 20.
All in all though, it's the same 6 bits in the IP TOS field that we've
always had, we're just referring to them in a different way in order to try
to give a common approach to QoS throughout a network (or perhaps across
multiple networks).
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIS, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@emanon.com/smorris@ipexpert.net
http://www.ipexpert.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of wang
jun
Sent: Wednesday, March 17, 2004 6:17 AM
To: ccielab@groupstudy.com
Subject: RE: question of qos
QoS can be quantified by one of the following indicators:
!* CoS!*A 3-bit value (0-7) that is carried along with packets in a trunk
!* IP Precedence!*A 3-bit value (0-7) that is carried within each packet!/s
IP header
!* DSCP!*A 6-bit value (0-63) that is carried within each packet!/s IP
header
The DSCP codepoint is made up of the following two parts:
!* Class Selector!*A 3-bit value that specifies a class of service
!* Drop Precedence!*A 3-bit value that specifies how likely a packet is to
be dropped (when
necessary)
0--7 or 0--63 ?
>From: "Lee Donald" <Lee.Donald@bacs.co.uk>
>Reply-To: "Lee Donald" <Lee.Donald@bacs.co.uk>
>To: "Richard Dumoulin" <richard.dumoulin@vanco.es>, "wang jun"
<waloowmoon@hotmail.com>, <ccielab@groupstudy.com>
>Subject: RE: question of qos
>Date: Wed, 17 Mar 2004 10:02:49 -0000
>
>My mistake, 0-7.
>
>8 Classess.
>
>
>
>-----Original Message-----
>From: Richard Dumoulin [mailto:richard.dumoulin@vanco.es]
>Sent: 17 March 2004 10:00
>To: Lee Donald; wang jun; ccielab@groupstudy.com
>Subject: RE: question of qos
>
>
>
>Correction I think IP Precedence has 8 classes ,
>
>Regards
>
>--Richard
>
>-----Mensaje original-----
>De: Lee Donald [ mailto:Lee.Donald@bacs.co.uk]
>Enviado el: mi(&rcoles, 17 de marzo de 2004 10:47
>Para: wang jun; ccielab@groupstudy.com
>Asunto: RE: question of qos
>
>
>DSCP is Differential Services Code Point. This includes 64 categories to
class
>traffic as opposed to IP Precedence which has 6.
>
>AF & EF are some of those categories, look up DSCP on Cisco.com for a
complete
>listing of categories.
>
>I hope this helps.
>
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [ mailto:nobody@groupstudy.com]On Behalf Of
wang
>jun
>Sent: 17 March 2004 09:22
>To: ccielab@groupstudy.com
>Subject: question of qos
>
>
>hi everybady.
>
> i don't understand the mean of "DSCP" and "AF&EF".could you explain
it?
>thanks
>
> paul
>
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