Configuring Access Node Control Protocol on Cisco ASR 9000 Series Routers
Information About Configuring ANCP on Cisco ASR 9000 Series Routers
QC-92
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
Rate Adjustment
ANCP can apply a correction factor to the DSL line rate reported in Port Up messages before publishing
the rate update to the system. This correction factor or rate adjustment is configurable in the global
configuration mode per DSL type and access encapsulation type (ATM or Ethernet). DSL type and
encapsulation type are provided in mandatory type, length, and value (TLV) data in the Port Up message.
Note To use the rate adjustment feature for non-default loop types (Ethernet), DSLAMs must support the
optional Access Loop Encapsulation sub-TLV.
ANCP rate-adaptive mode information is processed by the ANCP module to determine the maximum
bandwidth (shape rate) available for a given subscriber line. A fixed correction factor is then applied to
the ANCP bandwidth based on the DSL type to account for the overhead of different DSL technologies.
For example, a given subscriber’s ANCP bandwidth may be 15 Mbps, but due to the DSL technology
overhead, the effective bandwidth for that subscriber should be limited to 80 percent of 15 Mbps, which
is 12 Mbps. This corrected effective bandwidth is conveyed to QoS modules to limit the maximum rate
for the subscriber’s traffic.
Note The ANCP rate is used as a QoS shaping rate only if the ANCP rate is greater than the currently
configured QoS shaping rate. (The ANCP rate used by QoS is rounded down to the nearest 128 kbps.)
Prioritization of ANCP Traffic
In case of congestion, the Cisco ASR 9000 Series Router marks ANCP messages as high priority so that
the aggregation network between the Network Access Server (NAS) and the access node (AN) can
prioritize the ANCP messages ahead of other traffic.
Process Restart
During a process restart, TCP connections with ANCP neighbors normally drop. When the ANCP server
comes back, TCP connections and ANCP sessions are reestablished by the neighbors. Upon
reconnecting to the server, DSLAMs send Port Up messages for every active port. Any published rate
information received prior to restart is restored in the ANCP configuration. If the restart occurred due to
a crash, conflicts between published data and configuration data are detected and published data is
corrected.
ANCP and QoS Interaction
When the ANCP value is applied correctly, it overrides the configured QoS shaper value. For an example
of an ANCP value applied incorrectly and an example of the interaction with QoS when the ANCP value
is applied correctly, see
“ANCP and QoS Interaction: Example” section on page 111.
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