Calculation And Example Of Byte Adjustment For Cell Shaping; Figure 65: Byte Adjustment Calculation For Ethernet And Atm Encapsulations; Encapsulations; Table 29: Header Lengths For Ethernet Encapsulation - Juniper JUNOSE 11.1.X - QUALITY OF SERVICE CONFIGURATION GUIDE 3-21-2010 Configuration Manual

JUNOSe 11.1.x Quality of Service Configuration Guide
To adjust the shaping rates to account for different layer 2 encapsulations as well as
the ATM cell pad, header, and trailer on interfaces, apply a parameter with the cell
byte-adjustment application (qos-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.

Calculation and Example of Byte Adjustment for Cell Shaping

The system counts the bytes transmitted to track the shaping rate. Instead of counting
the actual packet size, the system uses the CPE packet size. You can configure the
byte adjustment so that the shaping rate matches the CPE bandwidth.
By default, the byte adjustment is set to 0. If the overhead between the access node
and CPE is 0, you do not need to configure the byte adjustment value.
Figure 65 on page 294 displays an example of an Ethernet encapsulation and an ATM
encapsulation.

Figure 65: Byte Adjustment Calculation for Ethernet and ATM Encapsulations

Table 29 on page 294 lists the header lengths for the Ethernet encapsulation, which
represents the CPE protocol overhead. The hierarchy is PPPoE over S-VLAN over
Ethernet.

Table 29: Header Lengths for Ethernet Encapsulation

294
Byte Adjustment for ADSL and VDSL Traffic Overview
Header Number of Bytes
EnetHeader 14 bytes (6-SA, 6-DA, 2-ethertype)
Vstack 8 bytes (2-vmanTci, 2-ethertype,
2-vlanTci, 2-ethertype)
PppoeHeader 6 bytes (1-version/type, 1-code,
2-session id, 2-length)
Ppp 2 bytes (2-protocol id)
FCS 4 bytes