Byte Adjustment For Frame Shaping Of Vdsl Traffic Overview; System Calculation For Byte Adjustment Of Adsl And Vdsl Traffic; Table 30: Header Lengths For Atm Encapsulation; Table 31: Byte Adjustment Values For Frame And Cell Shaping Modes - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - QUALITY OF SERVICE CONFIGURATION GUIDE 2010-09-22 Configuration Manual

Byte Adjustment for Frame Shaping of VDSL Traffic Overview

System Calculation for Byte Adjustment of ADSL and VDSL Traffic

Copyright © 2010, Juniper Networks, Inc.
Chapter 29: Configuring Byte Adjustment for Shaping Rates with QoS Parameters
Table 30 on page 277 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

Header Number of Bytes
ATM AAL5 LLC 4 bytes
PPP 2 bytes (2-protocol id)
Total 6 bytes
The byte adjustment calculation for these encapsulations is:
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.
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 277 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.

Table 31: Byte Adjustment Values for Frame and Cell Shaping Modes

Configured
Shaping Mode qos-frame-byte-adjustment
on Port 0 Value
Cell Any value
Cell Any value
Configured Final Byte
qos-byte-adjustment Adjustment
Value Value
-4 -4
Undefined 0
277