Cisco cBR 8 Configuration Guide

Each service flow is assigned a single service class, but the same service class can be assigned to multiple
service flows. Also, a cable modem can be assigned multiple service flows, allowing it to have multiple traffic
flows that use different service classes.
Packet Classifiers
In DOCSIS 1.0 networks, a cable modem used only one set of QoS parameters for all of its traffic, so the
CMTS simply had to route packets to and from the appropriate cable modems. In DOCSIS 1.1 networks,
however, cable modems can be using multiple service flows, and each service flow can be given a different
level of service. To quickly assign upstream and downstream packets to their proper service flows, the CMTS
uses the concept of packet classifiers.
Each packet classifier specifies one or more packet header attributes, such as source MAC address, destination
IP address, or protocol type. The classifier also specifies the service flow to be used when a packet matches
this particular combination of headers. Separate classifiers are used for downstream and upstream service
flows.
When the CMTS receives downstream and upstream packets, it compares each packet’s headers to the contents
of each packet classifier. When the CMTS matches the packet to a classifier, the CMTS then assigns the proper
SFID to the packet and transmits the packet to or from the cable modem. This ensures that the packet is
assigned its proper service flow, and thus its proper QoS parameters.
Figure below illustrates the mapping of packet classifiers.
Figure 1: Classification Within the MAC Layer
Cisco cBR Series Converged Broadband Routers Quality of Services Configuration Guide for Cisco IOS XE
Fuji 16.7.x
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DOCSIS 1.1 for the Cisco CMTS Routers
DOCSIS 1.1 Quality of Service

Cisco cBR 8 Specifications

General

Brand	Cisco
Model	cBR 8
Category	Network Router
Language	English