User`s guide

XSR User’s Guide 211
Chapter 10 Mechanisms to Provide QoS
Configuring Quality of Service
The following table describes typical traffic classification:
The XSR provides a class-based traffic classifier that creates traffic policies
and attaches them to interfaces, sub-interfaces, and virtual circuits such as
Frame Relay DLCIs. A traffic policy contains a traffic class and one or more
QoS features. A traffic class is used to classify traffic, while the QoS features in
the traffic policy determine how to treat the classified traffic. Traffic policy
cannot be applied to multilink PPP interfaces at this time.
NOTE
A Dialer interface is similar to a virtual interface in that only after it dials on
a resource from a dialer pool is it able to receive and send data. A policy
map applied to a dialer interface is automatically pushed to the resource
(Serial or ISDN interface) that the dialer called on. When the connection is
cleared, the policy map is automatically removed from the resource.
Table 10 Traffic Classification
Classification
Criteria
Description
Additional
Comments
IP Precedence bits
in IP header (IP
only)
Simple classification for IP packets only. IP Precedence bits reside
inside the TOS byte of the IPv4 header and are 3-bits long,
providing up to 8 levels of QoS classes.
Simple, IP
traffic only
DSCP (DiffServ
Code Point) bits in
IP header (IP only)
Simple classification for IP packets only. This QoS signaling
method is defined by the IETF DiffServ group providing a
scalable QoS solution. It is 6-bits long and can provide 64
different traffic classes. DSCP overlaps with the IP Precedence
bits in the IP header and can be considered a super set of IP
Precedence.
Simple, IP
traffic only
Multiple-Field
Classification
This classification generally looks at the L3 header (source and
destination IP addresses), L4 header (TCP/UDP port numbers to
identify the nature of applications as FTP, Telnet, Web, etc.), and
in some cases, look at fields beyond the L4 header (e.g., to
differentiate Web access to certain Web pages from other Web
accesses), to narrow the classification and choose traffic from a
particular application.
Most
versatile
but CPU
intensive.