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Traffic Rate Reporting and Adjustment by ANCP
The ANCP agent monitors the subscriber access lines and reports to AAA and CoS information about the lines that it receives from the access node.
Overview
ANCP reports two kinds of data rates:
- The net data rate is the portion of the total data rate that can be used to transmit user information. The net data rate is also called the unadjusted traffic rate.
- However, each DSL line type has a certain technology overhead; so the actual rate for user data is less than the net data rate. The adjusted or calculated rate is the net data rate reduced by the amount of technology overhead incurred by each DSL line type. The result is a closer approximation of the actual rate of subscriber data traffic. You can configure the ANCP agent to adjust the net data rate by a fixed percentage for each line type to generate the adjusted rate.
The ANCP agent reports traffic rates differently to AAA and CoS.
- The agent always reports both unadjusted and adjusted rates for both upstream and downstream traffic to AAA in response to a AAA request.
- The agent always reports only unadjusted downstream traffic rates to CoS in support of CoS traffic shaping. It never reports upstream traffic rates to CoS because CoS does not shape upstream traffic. It never reports adjusted traffic rates to CoS. In addition to the unadjusted downstream rate, the agent also reports to CoS the overhead mode and bytes for the access line; CoS can use this information when it subsequently shapes the traffic.
When you remove a shaping rate configuration that the ANCP agent previously applied, the traffic shaping rate reverts to the CoS session shaping as determined by the CoS traffic control profiles specified in the dynamic profile. If ANCP remains running but loses a connection to a particular neighbor whose subscriber traffic is adjusted as a result of ANCP, the adjusted rate remains in effect. The rate currently in effect changes only when the ANCP agent restores the connection and sends fresh updates to CoS, or when you remove the qos-adjust statement.
Traffic Rate Adjustment
When a DSLAM determines the data rate on the subscriber local loop, it ignores the additional headers on the DSL line that are associated with the overhead of the access mode (ATM or Ethernet) and the technology of the DSL line type. However, when the ANCP agent subsequently reports a net data rate, by default it includes this overhead and therefore reports a slightly higher value than the actual subscriber data rate seen by the DSLAM.
You can configure the ANCP agent to dynamically adjust the net data rate by a fixed percentage to account for the traffic overhead. To do so, include one or more of the qos-adjust-dsl-line-type statements at the [edit protocols ancp] hierarchy level. Each of these statements sets an adjustment factor for a particular DSL line type such as ADSL or VDS2. The adjustment factor is a percentage value that the ANCP agent applies to the traffic rates it receives from the DSLAM. The percentage accounts for the traffic overhead for that line type. That is, you configure the statements for all relevant line types, and the ANCP agent applies the appropriate adjustment when it identifies the line type for the interface. The adjustment factor applies globally for all subscribers of the particular DSL line type associated with the statement: ADSL, ADSL2, ADSL+, SDS1, VDS1, or VDS2. The ANCP agent subsequently reports the adjusted rate to AAA in addition to the unadjusted data rate.
The qos-adjust-dsl-line-type statements are enabled by default with an adjustment factor of 100 percent, meaning that by default the ANCP agent effectively makes no adjustment to the rates.
The ANCP agent reports traffic rates to CoS only when you have included the qos-adjust statement at the [edit protocols ancp] hierarchy level. However, the ANCP agent only reports net data rates to CoS; it never reports adjusted data rates to CoS. CoS attempts to avoid traffic drops in the access node by itself adjusting the traffic shaping rate that it applies to downstream traffic for a particular VLAN or set of VLANs. The discrepancy between the actual user data rate and the ANCP-reported net data rate reduces the accuracy of CoS traffic shaping.
Recommended Traffic Shaping Rates
To handle a situation where the router does not receive information from the access node about the downstream and upstream calculated traffic rates for an interface, you can specify recommended advisory values for shaping the traffic sent to the interface so that it matches the subscriber local loop speed.
The transmit speed is the recommended traffic value in bits per second used for downstream traffic for an ANCP interface, and is conveyed in the Juniper Networks VSA, Downstream-Calculated-Qos-Rate (IANA 4874, 26–141). The receive speed is the recommended traffic value in bits per second used for upstream traffic for an ANCP interface, and is conveyed in the Juniper Networks VSA, Upstream-Calculated-Qos-Rate VSA (IANA 4874, 26-142).
To set the recommended shaping rates that are used as the default values for these VSAs in static configurations, include the downstream-rate and upstream-rate statements at the [edit interfaces interface-name unit logical-unit-number advisory-options] hierarchy level.
To configure the recommended rates on dynamically created VLAN interfaces, include the upstream-rate or downstream-rate statements at the [edit dynamic-profiles profile-name interfaces $junos-interface-ifd-name unit $junos-interface-unit advisory-options] hierarchy level.
To configure the recommended rates on dynamically created ACI interface sets, include the upstream-rate or downstream-rate statements at the [edit dynamic-profiles profile-name interface-set $junos-interface-set-name interfaces $junos-interface-ifd-name advisory-options] hierarchy level.
ANCP Keepalives
ANCP sends a keepalive message to CoS at specific intervals. If CoS does not receive a keepalive in the expected time, it reverts the shaping rate changes it made in response to ANCP. You can adjust how long CoS waits for a keepalive message by including the maximum-helper-restart-time statement at the [edit protocols ancp] hierarchy level. The interval between keepalive messages is automatically set to one-third the value of the maximum helper restart time. For example, if you set the maximum helper restart time to 120 seconds, then ANCP sends keepalive messages every 40 seconds. In this example, if CoS does not receive a keepalive message within 120 seconds, then it reverts any ANCP-derived policy changes.
