Model D.2 Definition; Model F Definition - Cisco 10000 Series Configuration Manual

Chapter 1 Quality of Service Overview

Model D.2 Definition

This model is equivalent to the ATM-DSL model where shaped virtual circuits (VCs) terminate on an
interface, without shaped virtual paths (VPs). In this model all QoS control is maintained at the
broadband remote access server or network processing engine (BRAS / NPE) and none at the DSLAM.
The traffic to each subscriber line is shaped to less than or equal to the DSLAM modem train rate. This
shaping at the BRAS / NPE accounts for the ATM overhead on the DSLAM-to-CPE link, even though
the downstream interface on the BRAS / NPE is an Ethernet interface.
The subscriber line is represented by individual or groups of IP or Point-to-Point Protocol (PPP)
sessions. The policy for per class policing or marking is applied per PPP or IP session.
The key components of Model D.2 are shown in
Figure 1-2
Upstream and downstream
per subs/session per class:
• 1 rate 2 color policer
Downstream per
subscriber line:
• shape/min bw
• per class PQ +
CBQ+ WRED
bw = bandwidth
PQ = Priority Queue
CBQ = Class Based Queue
WRED = Weighted Random Early Detection

Model F Definition

This model is functionally equivalent to the ATM model with shaped virtual paths (VPs) and shaped
virtual circuits (VCs). Similar to the Model D.2, this model has all QOS control at the broadband remote
access server or network processing engine (BRAS / NPE) and none at the DSLAM.
The traffic to a group of subscriber lines is shaped to a defined rate, equivalent to a virtual path in ATM.
In the case of residential services, a group of subscribers is represented by a VLAN, and for business
services a group of subscribers is represented by the outer 802.1q tag.
The traffic to individual subscriber lines is shaped to less than or equal to the DSLAM modem train rate.
The subscriber line for business services is identified by the inner and outer 802.1q tag. The subscriber
line is represented by individual or groups of IP or PPP sessions.
QoS Model F requires 3 levels of shaping, queuing and scheduling –Subinterface / Session / Class
queues.
The key components of Model F are shown in
OL-7433-09
Key Components of Model D.2
Treated as any other
trunk" network:
Could use per class
PQ+CBQ, or
overprovision
BRAS
Figure 1-2.
PE-AGG / UPE
Figure 1-3.
Cisco 10000 Series Router Quality of Service Configuration Guide
No QOS supported
E-DSLAM
QoS Models
CPE
1-7