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Transmission of Tx Connect-Speed and Rx Connect-Speed AVPs from LAC to LNS
An L2TP access concentrator (LAC) uses Incoming-Call-Connected (ICCN) messages to send the attribute-value pair (AVP) 24 (which represents the transmit connect speed) and the AVP 38 (which represents the receive connect speed) to the L2TP network server (LNS).
The value of speed in AVP 24 and AVP 38 is typically not greater than the value that is enforced by CoS on the LAC side of the network. Any difference between the speed reported in these AVPs and that enforced by CoS can occur because of differences between the CoS configuration (of the source that is used to enforce a downstream speed) and the transmit connect speed method used to establish these AVPs.
When you include the tx-connect-speed-method statement at the [edit services l2tp] hierarchy level, the transmit connect speed method selected for the downstream speed, AVP 24, also applies to the selection of the upstream speed , AVP 38. You can configure the transmit and receive connect speeds to be derived from Point-to-Point Protocol over Ethernet (PPPoE) intermediate agent tags that are sent from the digital subscriber line access multiplexer (DSLAM) to the LAC, the Access Node Control Protocol (ANCP) settings of the underlying interface, or the recommended (advisory) shaping rate. When the method you specify as ANCP, PPPoE intermediate agent tags (PPPoE IA tags), or advisory shaping rate does not support an upstream speed, the static or advisory speed is used.
A fallback method is adopted to derive the transmit and receive connect speed values when these values cannot be determined from any of the configured methods, such as from the ANCP settings, the PPPoE IA tags, or the advisory shaping rate, or if the speed value is determined to be 0 from any of the configured methods.
If you configure the ANCP method to calculate the connect speed, the following sequence of events takes place:
- The upstream and downstream connect speed values are derived from ANCP.
- If the values cannot be derived from ANCP, the PPPoE IA tags are used to determine the values. If the PPPoE IA tags are present for either or both transmit and receive connect speeds, these values are used.
- If the values cannot be derived from the PPPoE IA tags, the recommended (advisory) shaping rate configured on the PPPoE logical interface is used. If the advisory shaping rate is present for either or both transmit and receive connect speeds, these values are used.
- If the values cannot be derived from the advisory shaping rate, the configured or default port speed is used for transmit and receive connect speeds.
If you configure the PPPoE IA tags method to calculate the connect speed, the following sequence of events takes place:
- The upstream and downstream connect speed values are derived from PPPoE IA tags.
- If the values cannot be derived from the PPPoE IA tags, the recommended (advisory) shaping rate configured on the PPPoE logical interface is used. If the advisory shaping rate is present for either or both transmit and receive connect speeds, these values are used.
- If the values cannot be derived from the advisory shaping rate, the configured or default port speed is used for transmit and receive connect speeds.
If you configure the static or advisory downstream shaping rate method to calculate the connect speed, the following sequence of events takes place:
- The upstream and downstream connect speed values are derived from the advisory shaping rate.
- If the values cannot be derived from the advisory shaping rate, the default port speed is used for transmit and receive connect speeds.
The transmit connect speed, AVP 24, is set in the ICCN messages on the basis of the method for determining the transmit connect speed configured using the tx-connect-speed-method statement at the [edit services l2tp] hierarchy level. You can configure the method for determining the transmit connect speed in the following order of precedence:
- ancp—The speed is derived from the configured ANCP value for the underlying interface. You can change this speed after a subscriber has logged in, but those changes do not affect the actual speed used by the LNS.
- pppoe-ia-tags—PPPoE IA tags sent from the DSLAM to the LAC. This speed value is transmitted when a subscriber logs in and it cannot be subsequently changed. This value is used when the ancp value is not available. This speed does not apply to the subscribers that are already logged in; it is effective only for subscribers that log in after this setting has been saved.
- static—The speed is derived from the recommended (advisory) shaping rate configured on the PPPoE logical interface underlying the subscriber interface. If the advisory shaping rate is not configured on the underlying interface, then the actual port speed is used.
If you do not configure the transmit connect speed using the CLI interface, and if the advisory speed is also not available, then the actual port speed is used. For ge and xe interfaces, the speed value is set to 10,000,000 and for ae interfaces, the speed value is set to 0 and sent in both AVP 24 and AVP 38.
