Assured Forwarding; Expedited Forwarding; Class Selector Code Points - Cisco 10000 Series Configuration Manual

Quality of service configuration guide

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Marking Traffic

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

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.

define the class; bits 3 and 4 specify the drop probability; bit 5 is always 0.

Drop Probability

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.

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 xyz000, where x, y, and z represent

For more information, see the appropriate RFC as indicated in

provides the DSCP coding and drop probability for AF classes 1 through 4. Bits 0, 1, and 2

Assured Forwarding DSCP Code Points

IP Differentiated Services Code Point Marking

Table 7-4 on page

Cisco 10000 Series Router Quality of Service Configuration Guide

Table 7-4 on page

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