The purpose of the ANCP WG is to standardize an IP-based Access Node Control Protocol (ANCP) for use in service provider Digital Subscriber Line (DSL) and Passive Optical Network (PON) access and aggregation networks. ANCP operates between an Access Node (AN) and Network Access Server (NAS).
Access Node (AN) - Network device, usually located at a service provider central office or street cabinet, that terminates access loop connections from Subscribers. In DSL, this is often referred to as a Digital Subscriber Line Access Multiplexer (DSLAM). In PON, this is usually comprised of an Optical Network Termination (ONT) / Optical Network Unit (ONU) and an Optical Line Termination (OLT).
Network Access Server (NAS) - Network device which aggregates multiplexed Subscriber traffic from a number of Access Nodes. The NAS plays a central role in per-subscriber policy enforcement and QoS. This is often referred to as a Broadband Network Gateway (BNG) or Broadband Remote Access Server (BRAS). A detailed definition of the NAS is given in RFC2881.
ANCP is intended to address the requirement for a bidirectional, IP- based, control protocol that operates across multiple types (i.e., Ethernet, ATM) of DSL and PON access and aggregation networks. The goal of an ANCP message exchange is to convey status and control information between one or more ANs and one or more NASs without going through intermediate element managers.
The ANCP WG will address the following four use-cases:
1. Dynamic Access Loop Attributes Various queuing and scheduling mechanisms are used in access networks to avoid congestion while dealing with multiple flows and distinct QoS profiles. Communicating the access-loop status, attributes and current DSL synchronization rate between the AN and Subscriber up to the NAS is desirable, particularly when the NAS is providing QoS for individual flows and subscribers. ANCP will provide a mechanism to communicate dynamic access-loop attributes from the AN to the NAS.
2. Access Loop Configuration In additional to reporting Access Loop characteristics from the AN to the NAS, ANCP will allow a NAS to send loop-specific configuration information to an AN based on the results of subscriber authentication and authorization (e.g., after AAA responses have been received at the NAS).
3. Remote Connectivity Test Traditional DSL access and aggregation networks employ point-to-point ATM circuits between the AN and NAS for each subscriber, allowing troubleshooting of the local loop from the NAS via ATM OAM tools. With the increasing deployment of Ethernet in the access and aggregation network, operators require consistent methods to test and troubleshoot connectivity for mixed Ethernet and ATM access networks (including the local loop). ANCP will allow a remote procedure for a local loop connectivity test to be triggered from the NAS with results communicated back to the NAS.
4. Multicast When multicast replication for subscriber-bound traffic is performed at the AN, it offloads the network between the AN and NAS. However, a subscriber's policy and configuration for multicast traffic may only be known at the NAS. ANCP will provide a mechanism to communicate the necessary information exchange between the AN and NAS so as to allow the AN to perform subscriber bound multicast group replication in line with the subscriber's policy and configuration, and also allow the NAS to follow each subscriber's multicast group membership.
ANCP is an IP-based protocol that operates between the AN and NAS. It will not address setup or configuration of circuits or connections in the access and aggregation network itself.
The focus of this WG is on one very specific application space. While the design of the protocol must be general as to not preclude other uses in the future should a need arise, it is not a goal of this WG to address specific requirements outside of service provider broadband (such as xDSL, xPON) access and aggregation networks.
The ANCP working group will provide a threat analysis and address the associated security aspects of the control protocol.
Resiliency and Scalability:
A graceful restart mechanism will be defined to enable the protocol to be resilient to network failures between the AN and NAS.
Scalability at the NAS is of primary concern, as it may be aggregating traffic from a large number of ANs, which in turn may be serving a large number of Subscribers. ANCP traffic should not become a denial of service attack on the NAS control plane. Format of messages, pacing, transport over UDP or TCP, etc. will be considered with this in mind.
For reasons of aggregation network scalability, some use cases require that aspects of NAS or AN functionality may be distributed in nodes in the aggregation network. In these cases, ANCP can run between these nodes.
The working group will define a basic framework and requirements document intended for Informational publication, focusing on the four use-cases outlined in this charter. This document will include a security threat analysis and associated requirements. The WG will then investigate and define a solution for an IP based control protocol meeting these requirements.
There are early interoperable implementations of an ANCP-like protocol which are based on an extended subset of the GSMPv3 protocol. This running code will be the the starting point for the working group solution, and will be abandoned only if the WG determines it is not adequate to meet requirements going forward.
Coordination with other Working Groups or Organizations:
The working group will coordinate with the ADSL MIB working group so the management framework and MIB modules are consistent for DSL access environments. The working group will re-use, as far as possible, standard MIB modules that have already been defined.
The remote connectivity test use case may require coordination with ITU-T Ethernet OAM and PON work and with IEEE 802.1ag.
Accept WG I-D for ANCP Framework and Requirements
Accept WG I-D for Access Node Control Protocol (ANCP)