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    Transmission of the Subscriber Access Interface Speed to LNS Using the RX Connect-Speed AVP

    The L2TP access concentrator (LAC) conveys the speed of the subscriber access interface to the L2TP network server (LNS) through the transmit (TX) Connect-Speed attribute-value pair (AVP) [24] and receive (RX) Connect-Speed AVP [38] in the Incoming-Call-Connected message, during the establishment of an L2TP session. By default, the receive speed of the access interface is set equal to the calculated transmit speed and the generation of RX Connect-Speed AVP is suppressed.

    The RX Connect-Speed AVP is generated when the receive speed of the access interface is set equal to the calculated transmit speed by issuing the l2tp rx-connect-speed-when-equal command. In this scenario, the LAC transmits the same value for transmit and receive connect speeds that are sent to the LNS through the TX Connect-Speed AVP and RX Connect-Speed AVP in the Incoming-Call-Connected message.

    The advisory receive speeds of Ethernet VLANs and ATM1483 circuits can be configured using the vlan advisory-rx-speed and atm atm1483 advisory-rx-speed commands. When the advisory receive rate is configured, the LAC transmits the configured advisory receive rate to LNS through the RX Connect-Speed AVP. If the advisory receive rate is configured, the transmission of the advisory receive rate in the RX Connect-Speed AVP takes precedence over the transmission of the calculated transmit speed in the RX Connect-Speed AVP even when the l2tp rx-connect-speed-when-equal command is issued.

    The transmission of the layer 2 control (L2C) RAM actual upstream rate to the LNS can be enabled using the l2tp rx-connect-speed-upstream-rate command. Since there is no integration between L2C and L2TP, the actual upstream rate is sent from the L2C to AAA, which sends the rate with tunnel parameters to the LAC during the creation of the L2TP tunnel. The LAC transmits the actual upstream rate to the LNS through the RX Connect-Speed AVP. If the actual upstream rate transmission is enabled, the transmission of the actual upstream rate in the RX Connect-Speed AVP takes precedence over the transmission of the configured advisory receive rate and transmission of the calculated transmit speed in the RX Connect-Speed AVP.

    The transmission of the actual upstream rate is applicable only for the interface in which L2C is configured. If the interface does not have L2C configured, the actual upstream rate is not transmitted. Instead, one of the following actions is taken:

    • The advisory receive rate is transmitted in the RX Connect-Speed AVP, if the advisory rate is configured.
    • The calculated transmit speed is transmitted in the RX Connect-Speed AVP, if the l2tp rx-connect-speed-when-equal command is issued and the advisory rate is not configured.
    • The RX Connect-Speed AVP value is transmitted as 0, if the advisory rate is not configured and the l2tp rx-connect-speed-when-equal command is not issued or the no l2tp rx-connect-speed-when-equal command is issued.

    Note: The actual upstream rate is independent of any QoS parameterization since it does not influence any QoS factor.

    Published: 2014-08-13