Traffic Rate Reporting and Adjustment by the ANCP Agent

 

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. Starting in Junos OS Release 17.4R1, the ANCP agent can use access line information that it receives in the PPPoE intermediate agent (PPPoE-IA) tags. This information is carried in the Vendor-Specific-Tags TLV in subattribute DSL-Type (0x0091) in PADI or PADO packets. In earlier releases, the ANCP agent can use only access line information that it receives in ANCP messages. The access line information for both carriers is logically sourced from the same data on the access node; it represents a current, accurate snapshot of the values at the moment that the subscriber connection is initiated.

It is theoretically possible for ANCP and PPPoE subscribers to specify different data rates in the Vendor-Specific-Tags TLV when the connection is first established. This is an unlikely occurrence, but when the dynamic profile is configured to accept these values, the most recently received value takes precedence. The rates announced on the PPPoE connection are expected to be used only when ANCP is either not used or does not include rates. However, network dynamics make it impossible to guarantee the source from which the information arrives first. If the values conflict, a subsequent Port Up message from the access node forces the resolution to the ANCP values.

Overview

The ANCP agent 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.

  • Because each DSL line type has a certain technology overhead, 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.

The ANCP agent reports traffic rates differently to AAA and CoS:

  • The agent always reports unadjusted rates for both upstream and downstream traffic to AAA in response to a AAA request. When configured, the agent adjusts the traffic rates and reports the adjusted values in addition to the unadjusted rate.

  • The ANCP agent reports traffic rates to CoS only when you include the qos-adjust statement at the [edit protocols ancp] hierarchy level .The agent reports only 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. 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. However, if the ANCP agent remains running but loses a connection to a particular neighbor whose subscriber traffic has been adjusted as a result of ANCP agent action, 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.

Because CoS can perform traffic shaping only when a traffic-control profile has been applied to the interface or interface set, you might expect the ANCP agent to always influence traffic shaping when the ANCP subscriber interface or interface set has a traffic-control profile. This behavior does not always occur.

Consider a configuration where a subscriber logical interface is a member of an ACI-based VLAN (interface set); all members share the same ACI. The dynamic profile that instantiates the subscriber interface applies a traffic-control profile to the interface. The profile that instantiates the VLAN applies an interface-shared filter instead of a traffic-control profile.

The following sequence of events takes place when the subscriber logs in.

  1. The first packet creates the auto-sensed, underlying VLAN.

  2. The second packet creates the ACI-based subscriber VLAN

  3. The third packet creates the subscriber logical interface.

Because the VLAN comes up first, the ANCP agent attaches to the VLAN and not to the interface. Consequently, the agent reports to CoS the downstream data rate only for the VLAN, not for the logical interface. CoS has no information to adjust the shaping rate for the interface, so it shapes traffic for the interface only according to the interface’s traffic-control profile.

Although the agent does report the downstream rate for the VLAN, CoS cannot use that information to shape the VLAN traffic, because the VLAN does not have a traffic-control profile. Consequently, the VLAN rate does not affect the logical interface’s rate even though the logical interface is a member of that interface set.

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. When the ANCP agent subsequently reports a net data rate, by default it includes this overhead, reporting a slightly higher value than the actual subscriber data rate seen by the DSLAM.

You can configure the ANCP agent to additionally report an adjusted rate to account for the traffic overhead. The ANCP agent dynamically adjusts the net data rate by applying a fixed percentage value to the net data rate received from the DSLAM. The percentage adjustment factor applies globally for all subscribers of the particular DSL line type as follows:

  • The agent can adjust the rates it reports to AAA for all DSL types.

  • The agent can adjust the rates it reports to CoS for only frame-mode DSL types (SDSL, VDSL, VDSL2, and OTHER), It cannot adjust the rates reported to CoS for cell-mode DSL types (ADSL, ADSL2, and ADSL2+).

You can also configure the ANCP agent to adjust the number of overhead bytes that it reports to CoS per cell or frame. The agent can add or subtract the specified value from the actual number of overhead bytes for all DSL types. The agent does not report the number of overhead bytes (adjusted or unadjusted) to AAA.

Table 1 summarizes how adjusted rates and overheads are reported.

Table 1: Traffic Adjustment Reporting by Access Line Type

DSL Access Line Type

Upstream and Downstream Adjusted Rate Reported to AAA

Downstream-Only Adjusted Rate Reported to CoS

Adjusted Overhead Byte Count Reported to CoS

ADSL

ADSL2

ADSL2+

OTHER

SDSL

VDSL

VDSL2

The ANCP agent reports traffic rates to CoS only when you have included the qos-adjust statement at the [edit protocols ancp] hierarchy level. By default, these are unadjusted rates. 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 agent-reported net data rate reduces the accuracy of CoS traffic shaping. You increase the accuracy of CoS traffic shaping by configuring the ANCP agent to report adjusted rate and byte values to CoS.

If you are running Junos OS Release 17.3 or earlier, use the CLI configuration statements in Table 2 to make traffic adjustments. The CoS statements are at the [edit protocols ancp qos-adjust] hierarchy level. The AAA statements are at the [edit protocols ancp] hierarchy level.

Table 2: Statements for Adjusting Traffic Rate and Overhead by Access Line Type Through Junos OS Release 17.3

Access Line Type

Adjust Net Downstream and Upstream Rates for AAA

Adjust Net Downstream Rates for CoS

Adjust Overhead Bytes for CoS

ADSL

qos-adjust-adsl

adsl-bytes

ADSL2

qos-adjust-adsl2

adsl2-bytes

ADSL2+

qos-adjust-adsl2-plus

adsl2-plus-bytes

OTHER

qos-adjust-other

other-overhead-adjust

other-bytes

SDSL

qos-adjust-sdsl

sdsl-overhead-adjust

sdsl-bytes

VDSL

qos-adjust-vdsl

vdsl-overhead-adjust

vdsl-bytes

VDSL2

qos-adjust-vdsl2

vdsl2-overhead-adjust

vdsl2-bytes

If you are running Junos OS Release 17.4R1 or later, use the access-line configuration statement options in Table 3 to make traffic adjustments for CoS and AAA options. The access-line statement is at the [edit system] hierarchy level.

Table 3: Statements for Adjusting Traffic Rate and Overhead by Access Line Type Starting in Junos OS Release 17.4R1

Access Line Type

Adjust Net Downstream and Upstream Rates for AAA

Adjust Net Downstream Rates for CoS

Adjust Overhead Bytes for CoS

ADSL

adsl-total-adjust

adsl-overhead-bytes

ADSL2

adsl2-total-adjust

adsl2-overhead-bytes

ADSL2+

adsl2-plus-total-adjust

adsl2-plus-overhead-bytes

OTHER

other-total-adjust

other-overhead-adjust

other-overhead-bytes

SDSL

sdsl-total-adjust

sdsl-overhead-adjust

sdsl-overhead-bytes

VDSL

vdsl-total-adjust

vdsl-overhead-adjust

vdsl-overhead-bytes

VDSL2

vdsl-total-adjust

vdsl2-overhead-adjust

vdsl2-overhead-bytes

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 Agent Keepalives for CoS

The ANCP agent 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 the ANCP agent. 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 the ANCP agent sends keepalive messages every 40 seconds. In this example, if CoS does not receive a keepalive message within 120 seconds, then it reverts any policy changes derived from the ANCP agent.

Release History Table
Release
Description
Starting in Junos OS Release 17.4R1, the ANCP agent can use access line information that it receives in the PPPoE intermediate agent (PPPoE-IA) tags.