Ancp Messages; Port Mapping; Rate Adjustment - Cisco ASR 9000 Series Configuration Manual

Configuring Access Node Control Protocol
ANCP adjacency lifetime is governed by the adjacency protocol. If synchronization with the peer access node
is lost (for example, if the adjacency dead timer expires), the ANCP server removes the adjacency, and the
underlying TCP connection is closed.

ANCP Messages

Two ANCP message types are processed by the ANCP server: Port Up and Port Down. Port Up messages
contain DSL rate information; Port Down messages indicate that the corresponding access line is no longer
available. DSL rate updates from Port Up messages are made available to the QoS subsystem. Port Down
messages are used to internally track the ANCP port state.
These messages can only be received by the server after the ANCP adjacency is established. However, once
a Port Up message is received, the DSL rate information it contains is considered valid indefinitely, provided
AN-port-to-interface mapping is configured for that port. It is stored in the AN port database until it is
overwritten by another Port Up message for this port or is cleared manually. The removal of an adjacency or
the reception of a Port Down message is reflected in the database for display and troubleshooting purposes,
but DSL rate information is not invalidated.

Port Mapping

AN ports are statically mapped to VLAN subinterfaces, referred to as AN-port-to-interface mapping. This
implies that there is at least one VLAN subinterface configured per subscriber line. There is no limit to the
number of interfaces that can be mapped to an AN port.
VLAN subinterfaces mapped to an AN port can be created or removed. When mapping is configured, VLAN
subinterfaces are referenced in the ANCP module by name. This name is used for notifications of interface
creation and deletion and provides the information that is used in updating the DSL rate.
An AN port database is maintained for all ports learned from Port Up messages. This database also contains
the AN-port-to-interface mapping database. If a Port Up message for an AN port arrives but no interface is
mapped to that port, the rate information is stored in the AN port database but not published. When a mapping
for that port is configured, the AN port database is scanned to identify any ANCP messages that were received
on this port prior to the mapping configuration. If there were, the known rate is published.

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.
To use the rate adjustment feature for non-default loop types (Ethernet), DSLAMs must support the
Note
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
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release 6.1.x
ANCP Messages
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