QoS and L2TP TX Speed AVP 24 Overview

You can configure the router to use QoS settings to calculate the transmit connect speed of the subscriber’s access interface reported for an L2TP tunneled session. The router reports the transmit connect speed in L2TP Transmit (TX) Speed AVP 24. During the establishment of an L2TP tunneled session, the LAC sends AVP 24 to the LNS to convey the transmit speed of the subscriber’s access interface.

Logical Interfaces and Shared-Shaping Rates

You can configure QoS to control the rate for any of the logical interfaces of the following interface columns:

• ATM 1483 subinterface over ATM VP over ATM interface
• PPPoE subinterface over Ethernet interface
• PPPoE subinterface over VLAN subinterface over Ethernet interface

For those logical interfaces with a rate controlled by QoS, QoS reports this configured rate as the transmit connect speed for that interface. For the logical interfaces that do not have a QoS-configured rate, QoS reports the speed of the underlying physical port as the transmit connect speed.

For each logical interface, QoS determines the rate of the interface using either the shaping rate or the shared-shaping rate, if one is configured. The numeric value of the shaping rate or shared-shaping rate is determined as the result of a provider-specified arithmetic expression in a scheduler profile. This expression can either be a constant value, such as 1,000,000, or an expression using QoS parameters, with values supplied by RADIUS or statically in non-volatile storage (NVS).

If the QoS profile or the QoS parameters are configured in RADIUS, these values are used in computing the rate at the time of login. The system can subsequently modify the value of parameters through change of authorization (CoA), Service Manager, or L2C. Modifications are not reflected in the rate QoS reports because they might take place after the LAC has sent the message that contains AVP 24.

Shaping Mode

When the QoS shaping mode is set to cell for an interface, QoS reports the ATM rate. In cell mode, user-specified rates account for cell headers and trailers, which are ATM native rates; therefore, QoS does not convert the rates for AVP 24.