Table 30: Header Lengths For Atm Encapsulation; Byte Adjustment For Frame Shaping Of Vdsl Traffic Overview; System Calculation For Byte Adjustment Of Adsl And Vdsl Traffic - Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual

Table 29: Header Lengths for Ethernet Encapsulation (continued)
Table 30 on page 295 lists the header lengths for the ATM encapsulation, which
represents the B-RAS protocol overhead. The interface stack is PPPoA over ATM 1483
with LLC Mux. The ATM AAL5 trailer is considered cell tax and is not part of the byte
adjustment calculation.

Table 30: Header Lengths for ATM Encapsulation

The byte adjustment calculation for these encapsulations is:

Byte Adjustment for Frame Shaping of VDSL Traffic Overview

Packet fragmentation can occur at a DSLAM because of the associated segment
header that is added for VDSL2 in frame mode. Because the segment header is not
included in the ANCP rate report, the forwarding rate on an E Series router can be
higher than the DSLAM rate, which can result in packet loss.
You can use a QoS parameter expression with the frame byte-adjustment application
to reduce the forwarding rate so that it matches the rate at the DSLAM. To adjust
rates for interfaces with frame shaping mode, apply the frame byte-adjustment
application (qos-frame-byte-adjustment).
When you apply a parameter with the qos-byte-adjustment application to an interface
with frame shaping mode, you adjust shaping rates to account for different layer 2
encapsulations only.

System Calculation for Byte Adjustment of ADSL and VDSL Traffic

You can create parameter instances for the cell byte-adjustment application and the
frame byte-adjustment application on the same system. The system performs the
byte adjustment calculation based on the shaping mode specified. The byte adjustment
can have both a positive and negative value.
Table 31 on page 296 lists the final byte adjustment value that the system uses
depending on the configured shaping mode and the value that you configured for
the byte adjustment applications.
Chapter 29: Configuring Byte Adjustment for Shaping Rates with QoS Parameters
Header Number of Bytes
34 bytes
Total
Header Number of Bytes
ATM AAL5 LLC 4 bytes
PPP 2 bytes (2-protocol id)
6 bytes
Total
Byte Adjustment for ADSL and VDSL Traffic Overview
295