7-7
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 7 Marking Traffic
IP Differentiated Services Code Point Marking
Again, vendor-specific mechanisms need to be configured to implement these PHBs. For more
information about EF PHB, see RFC-2598. To implement the PHBs, you must configure vendor-specific
mechanisms. For more information, see the appropriate RFC as indicated in
Table 7-4 on page 7-8
.
Assured Forwarding
There are four assured forwarding (AF) classes, AF1x through AF4x. The first number corresponds to
the AF class and the second number (x) refers to the level of drop preference within each AF class. There
are three drop probabilities, ranging from 1 (low drop) through 3 (high drop). Depending on a network
policy, packets can be selected for a PHB based on required throughput, delay, jitter, loss, or according
to the priority of access to network services. AF allows for a committed information rate between
multiple classes in a network according to desired policies.
Table 7-3
provides the DSCP coding and drop probability for AF classes 1 through 4. Bits 0, 1, and 2
define the class; bits 3 and 4 specify the drop probability; bit 5 is always 0.
Expedited Forwarding
The expedited forwarding (EF) PHB is used to build a low-loss, low-latency, low-jitter, assured
bandwidth, end-to-end service through differentiated services (DiffServ) domains. This PHB appears to
the endpoints like a point-to-point connection or a virtual leased line. EF PHB, also referred to as a
premium service
, is suitable for applications such as Voice over IP (VoIP).
The recommended code point for the EF PHB is 101110.
Class Selector Code Points
The router also supports class selector (CS) code points, which is a way of marking the six DSCP bits
so that the code points are identical to IP precedence values. These code points can be used with systems
that only support the IP precedence. The CS code points have the form
xyz
000, where
x
,
y
, and
z
represent
a 1 or 0.
For more information, see the appropriate RFC as indicated in
Table 7-4 on page 7-8
.
Table 7-3
Assured Forwarding DSCP Code Points
Drop Probability
Class 1
Class 2
Class 3
Class4
Low Drop
001010
AF11
DSCP 10
010010
AF21
DSCP 18
011010
AF31
DSCP 26
100010
AF41
DSCP 34
Medium Drop
001100
AF12
DSCP 12
010100
AF 22
DSCP 20
011100
AF32
DSCP 28
100100
AF42
DSCP 36
High Drop
001110
AF13
DSCP 14
010110
AF23
DSCP 22
011110
AF33
DSCP 30
100110
AF43
DSCP 38
