RFC 6320
Protocol for Access Node Control Mechanism in Broadband Networks
Internet Engineering Task Force (IETF) S. Wadhwa Request for Comments: 6320 Alcatel-Lucent Category: Standards Track J. Moisand ISSN: 2070-1721 Juniper Networks T. Haag Deutsche Telekom N. Voigt Nokia Siemens Networks T. Taylor, Ed. Huawei Technologies October 2011 Protocol for Access Node Control Mechanism in Broadband NetworksAbstract
This document describes the Access Node Control Protocol (ANCP). ANCP operates between a Network Access Server (NAS) and an Access Node (e.g., a Digital Subscriber Line Access Multiplexer (DSLAM)) in a multi-service reference architecture in order to perform operations related to Quality of Service, service, and subscribers. Use cases for ANCP are documented in RFC 5851. As well as describing the base ANCP protocol, this document specifies capabilities for Digital Subscriber Line (DSL) topology discovery, line configuration, and remote line connectivity testing. The design of ANCP allows for protocol extensions in other documents if they are needed to support other use cases and other access technologies. ANCP is based on the General Switch Management Protocol version 3 (GSMPv3) described in RFC 3292, but with many modifications and extensions, to the point that the two protocols are not interoperable. For this reason, ANCP was assigned a separate version number to distinguish it. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6320.
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1. Introduction ....................................................5 1.1. Historical Note ............................................6 1.2. Requirements Language ......................................6 1.3. Terminology ................................................6 2. Broadband Access Aggregation ....................................8 2.1. ATM-Based Broadband Aggregation ............................8 2.2. Ethernet-Based Broadband Aggregation .......................9 3. Access Node Control Protocol -- General Aspects ................10 3.1. Protocol Version ..........................................10 3.2. ANCP Transport ............................................10 3.3. Encoding of Text Fields ...................................11 3.4. Treatment of Reserved and Unused Fields ...................12 3.5. The ANCP Adjacency Protocol ...............................12 3.5.1. ANCP Adjacency Message Format ......................12 3.5.2. ANCP Adjacency Procedures ..........................18 3.6. ANCP General Message Formats ..............................29 3.6.1. The ANCP Message Header ............................29 3.6.2. The ANCP Message Body ..............................36 3.7. General Principles for the Design of ANCP Messages ........37
4. Generally Useful ANCP Messages and TLVs ........................38 4.1. Provisioning Message ......................................38 4.2. Generic Response Message ..................................39 4.3. Target TLV ................................................41 4.4. Command TLV ...............................................41 4.5. Status-Info TLV ...........................................42 5. Introduction to ANCP Capabilities for Digital Subscriber Lines (DSLs) ........................................43 5.1. DSL Access Line Identification ............................44 5.1.1. Control Context (Informative) ......................44 5.1.2. TLVs for DSL Access Line Identification ............45 6. ANCP-Based DSL Topology Discovery ..............................48 6.1. Control Context (Informative) .............................48 6.2. Protocol Requirements .....................................50 6.2.1. Protocol Requirements on the AN Side ...............50 6.2.2. Protocol Requirements on the NAS Side ..............50 6.3. ANCP Port Up and Port Down Event Message Descriptions .....51 6.4. Procedures ................................................52 6.4.1. Procedures on the AN Side ..........................52 6.4.2. Procedures on the NAS Side .........................53 6.5. TLVs for DSL Line Attributes ..............................53 6.5.1. DSL-Line-Attributes TLV ............................53 6.5.2. DSL-Type TLV .......................................54 6.5.3. Actual-Net-Data-Rate-Upstream TLV ..................54 6.5.4. Actual-Net-Data-Rate-Downstream TLV ................54 6.5.5. Minimum-Net-Data-Rate-Upstream TLV .................55 6.5.6. Minimum-Net-Data-Rate-Downstream TLV ...............55 6.5.7. Attainable-Net-Data-Rate-Upstream TLV ..............55 6.5.8. Attainable-Net-Data-Rate-Downstream TLV ............55 6.5.9. Maximum-Net-Data-Rate-Upstream TLV .................56 6.5.10. Maximum-Net-Data-Rate-Downstream TLV ..............56 6.5.11. Minimum-Net-Low-Power-Data-Rate-Upstream TLV ......56 6.5.12. Minimum-Net-Low-Power-Data-Rate-Downstream TLV ....56 6.5.13. Maximum-Interleaving-Delay-Upstream TLV ...........57 6.5.14. Actual-Interleaving-Delay-Upstream TLV ............57 6.5.15. Maximum-Interleaving-Delay-Downstream TLV .........57 6.5.16. Actual-Interleaving-Delay-Downstream ..............57 6.5.17. DSL-Line-State TLV ................................58 6.5.18. Access-Loop-Encapsulation TLV .....................58 7. ANCP-Based DSL Line Configuration ..............................59 7.1. Control Context (Informative) .............................59 7.2. Protocol Requirements .....................................61 7.2.1. Protocol Requirements on the NAS Side ..............61 7.2.2. Protocol Requirements on the AN Side ...............61 7.3. ANCP Port Management (Line Configuration) Message Format ..62 7.4. Procedures ................................................64 7.4.1. Procedures on the NAS Side .........................64 7.4.2. Procedures on the AN Side ..........................64
7.5. TLVs for DSL Line Configuration ...........................64
7.5.1. Service-Profile-Name TLV ...........................65
8. ANCP-Based DSL Remote Line Connectivity Testing ................65
8.1. Control Context (Informative) .............................65
8.2. Protocol Requirements .....................................66
8.2.1. Protocol Requirements on the NAS Side ..............66
8.2.2. Protocol Requirements on the AN Side ...............66
8.3. Port Management (OAM) Message Format ......................67
8.4. Procedures ................................................68
8.4.1. NAS-Side Procedures ................................68
8.4.2. AN-Side Procedures .................................69
8.5. TLVs for the DSL Line Remote Connectivity Testing
Capability ................................................70
8.5.1. OAM-Loopback-Test-Parameters TLV ...................70
8.5.2. Opaque-Data TLV ....................................71
8.5.3. OAM-Loopback-Test-Response-String TLV ..............71
9. IANA Considerations ............................................71
10. IANA Actions ..................................................72
10.1. ANCP Message Type Registry ...............................72
10.2. ANCP Result Code Registry ................................73
10.3. ANCP Port Management Function Registry ...................74
10.4. ANCP Technology Type Registry ............................75
10.5. ANCP Command Code Registry ...............................75
10.6. ANCP TLV Type Registry ...................................75
10.7. ANCP Capability Type Registry ............................77
10.8. Joint GSMP / ANCP Version Registry .......................77
11. Security Considerations .......................................77
12. Contributors ..................................................79
13. Acknowledgements ..............................................79
14. References ....................................................79
14.1. Normative References .....................................79
14.2. Informative References ...................................80
1. Introduction
This document defines a new protocol, the Access Node Control Protocol (ANCP), to realize a control plane between a service- oriented layer 3 edge device (the Network Access Server, NAS) and a layer 2 Access Node (e.g., Digital Subscriber Line Access Multiplexer, DSLAM) in order to perform operations related to quality of service (QoS), services, and subscriptions. The requirements for ANCP and the context within which it operates are described in [RFC5851]. ANCP provides its services to control applications operating in the AN and NAS, respectively. This relationship is shown in Figure 1. Specification of the control applications is beyond the scope of this document, but informative partial descriptions are provided as necessary to give a context for the operation of the protocol. Access Node Network Access Server +--------------------+ +--------------------+ | +----------------+ | | +----------------+ | | | AN Control | | | | NAS Control | | | | Application | | | | Application | | | +----------------+ | | +----------------+ | | +----------------+ | | +----------------+ | | | ANCP Agent | | ANCP Messages | | ANCP Agent | | | | (AN side) |<----------------------->| (NAS side) | | | +----------------+ | | +----------------+ | +--------------------+ +--------------------+ Figure 1: Architectural Context for the Access Node Control Protocol At various points in this document, information flows between the control applications and ANCP are described. The purpose of such descriptions is to clarify the boundary between this specification and, for example, [TR-147]. There is no intention to place limits on the degree to which the control application and the protocol implementation are integrated. This specification specifies ANCP transport over TCP/IP. TCP encapsulation for ANCP is as defined in Section 3.2. The organization of this document is as follows: o Sections 1.2 and 1.3 introduce some terminology that will be useful in understanding the rest of the document. o Section 2 provides a description of the access networks within which ANCP will typically be deployed.
o Section 3 specifies generally applicable aspects of ANCP. o Section 4 specifies some messages and TLVs intended for use by multiple capabilities spanning multiple technologies. o Section 5 and the three following sections describe and specify the ANCP implementation of three capabilities applicable to the control of DSL access technology: topology discovery, line configuration, and remote line connectivity testing. o Section 9 is the IANA Considerations section. This section defines a number of new ANCP-specific registries as well as the joint GSMP/ANCP version registry mentioned below. o Section 11 addresses security considerations relating to ANCP, beginning with the requirements stated in [RFC5713].1.1. Historical Note
Initial implementations of the protocol that became ANCP were based on the General Switch Management Protocol version 3 (GSMPv3) [RFC3292]. The ANCP charter required the Working Group to develop its protocol based on these implementations. In the end, ANCP introduced so many extensions and modifications to GSMPv3 that the two protocols are not interoperable. Nevertheless, although this specification has no normative dependencies on [RFC3292], the mark of ANCP's origins can be seen in the various unused fields within the ANCP message header. Early in ANCP's development, the decision was made to use the same TCP port and encapsulation as GSMPv3, and by the time ANCP was finished, it was too late to reverse that decision because of existing implementations. As a result, it is necessary to have a way for an ANCP peer to quickly distinguish ANCP from GSMP during initial adjacency negotiations. This has been provided by a joint registry of GSMP and ANCP version numbers. GSMP has version numbers 1 through 3. ANCP has the initial version number 50.1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].1.3. Terminology
This section repeats some definitions from [RFC5851], but it also adds definitions for terms used only in this document.
Access Node (AN): [RFC5851] Network device, usually located at a service provider central office or street cabinet that terminates access (local) loop connections from subscribers. In case the access loop is a Digital Subscriber Line (DSL), the Access Node provides DSL signal termination and is referred to as a DSL Access Multiplexer (DSLAM). Network Access Server (NAS): [RFC5851] Network element that aggregates subscriber traffic from a number of Access Nodes. The NAS is an enforcement point for policy management and IP QoS in the access network. It is also referred to as a Broadband Network Gateway (BNG) or Broadband Remote Access Server (BRAS). Home Gateway (HGW): Network element that connects subscriber devices to the Access Node and the access network. In the case of DSL, the Home Gateway is a DSL network termination that may operate either as a layer 2 bridge or as a layer 3 router. In the latter case, such a device is also referred to as a Routing Gateway (RG). ANCP agent: A logical entity that implements ANCP in the Access Node (AN-side) or NAS (NAS-side). Access Node control adjacency: (modified from [RFC5851]) The relationship between the AN-side ANCP agent and the NAS-side ANCP agent for the purpose of exchanging Access Node Control Protocol messages. The adjacency may be either up or down, depending on the result of the Access Node Control adjacency protocol operation. ANCP capability: A specific set of ANCP messages, message content, and procedures required to implement a specific use case or set of use cases. Some ANCP capabilities are applicable to just one access technology while others are technology independent. The capabilities applicable to a given ANCP adjacency are negotiated during adjacency startup. Type-Length-Value (TLV): A data structure consisting of a 16-bit type field, a sixteen-bit length field, and a variable-length value field padded to the nearest 32-bit word boundary, as described in Section 3.6.2. The value field of a TLV can contain other TLVs. An IANA registry is maintained for values of the ANCP TLV Type field. Net data rate: [RFC5851] Defined by ITU-T G.993.2 [G.993.2], Section 3.39, i.e., the portion of the total data rate that can be used to transmit user information (e.g., ATM cells or Ethernet frames). It excludes overhead that pertains to the physical transmission mechanism (e.g., trellis coding in the case of DSL). It includes
TPS-TC (Transport Protocol Specific - Transmission Convergence)
encapsulation; this is zero for ATM encapsulation and non-zero for
64/65 encapsulation.
Line rate: [RFC5851] Defined by ITU-T G.993.2. It contains the
complete overhead including Reed-Solomon and trellis coding.
DSL multi-pair bonding: Method for bonding (or aggregating) multiple
xDSL access lines into a single bidirectional logical link,
henceforth referred to in this document as "DSL bonded circuit".
DSL "multi-pair" bonding allows an operator to combine the data
rates on two or more copper pairs, and deliver the aggregate data
rate to a single customer. ITU-T recommendations G.998.1
[G.998.1] and G.998.2 [G.998.2], respectively, describe ATM- and
Ethernet-based multi-pair bonding.
2. Broadband Access Aggregation
2.1. ATM-Based Broadband Aggregation
The end-to-end DSL network consists of network service provider (NSP)
and application service provider (ASP) networks, regional/access
network, and customer premises network. Figure 2 shows ATM broadband
access network components.
The regional/access network consists of the regional network, Network
Access Server (NAS), and the access network as shown in Figure 2.
Its primary function is to provide end-to-end transport between the
customer premises and the NSP or ASP.
The Access Node terminates the DSL signal. It may be in the form of
a DSLAM in the central office, a remote DSLAM, or a Remote Access
Multiplexer (RAM). The Access Node is the first point in the network
where traffic on multiple DSL access lines will be aggregated onto a
single network.
The NAS performs multiple functions in the network. The NAS is the
aggregation point for subscriber traffic. It provides aggregation
capabilities (e.g., IP, PPP, ATM) between the Regional/Access Network
and the NSP or ASP. These include traditional ATM-based offerings
and newer, more native IP-based services. This includes support for
Point-to-Point Protocol over ATM (PPPoA) and PPP over Ethernet
(PPPoE), as well as direct IP services encapsulated over an
appropriate layer 2 transport.
Beyond aggregation, the NAS is also the enforcement point for policy
management and IP QoS in the regional/access networks. To allow IP
QoS support over an existing non-IP-aware layer 2 access network
without using multiple layer 2 QoS classes, a mechanism based on hierarchical scheduling is used. This mechanism, defined in [TR-059], preserves IP QoS over the ATM network between the NAS and the Routing Gateway (RG) at the edge of the subscriber network, by carefully controlling downstream traffic in the NAS, so that significant queuing and congestion do not occur farther down the ATM network. This is achieved by using a Diffserv-aware hierarchical scheduler in the NAS that will account for downstream trunk bandwidths and DSL synchronization rates. [RFC5851] provides detailed definitions of the functions of each network element in the broadband reference architecture. Access Customer <--- Aggregation --> <------- Premises -------> Network Network +------------------+ +--------------------------+ +---------+ +---+ | +-----+ +------+ | |+-----+ +---+ +---------+ | NSP| | +-|NAS|-| |ATM |-|Access| --||DSL |-|HGW|-|Subscriber|| ---+ Regional| | +---+ | +-----+ | Node | | ||Modem| +---+ |Devices || |Broadband| | +---+ | +------+ | |+-----+ +----------+| ASP|Network |-+-|NAS| +--------------|---+ +--------------------------+ ---+ | | +---+ | +--------------------------+ | | | +---+ | |+-----+ +---+ +----------+| +---------+ +-|NAS| +-----|| DSL |-|HGW|-|Subscriber|| +---+ ||Modem| +---+ |Devices || |+-----+ +----------+| +--------------------------+ HGW: Home Gateway NAS: Network Access Server Figure 2: ATM Broadband Aggregation Topology2.2. Ethernet-Based Broadband Aggregation
The Ethernet aggregation network architecture builds on the Ethernet bridging/switching concepts defined in IEEE 802. The Ethernet aggregation network provides traffic aggregation, class of service distinction, and customer separation and traceability. VLAN tagging, defined in [IEEE802.1Q] and enhanced by [IEEE802.1ad], is used as the standard virtualization mechanism in the Ethernet aggregation network. The aggregation devices are "provider edge bridges" defined in [IEEE802.1ad]. Stacked VLAN tags provide one possible way to create an equivalent of "virtual paths" and "virtual circuits" in the aggregation network. The "outer" VLAN can be used to create a form of "virtual path"
between a given DSLAM and a given NAS. "Inner" VLAN tags create a form of "virtual circuit" on a per-DSL-line basis. This is the 1:1 VLAN allocation model. An alternative model is to bridge sessions from multiple subscribers behind a DSLAM into a single VLAN in the aggregation network. This is the N:1 VLAN allocation model. Section 1.6 of [TR-101] provides brief definitions of these two models, while Section 2.5.1 describes them in more detail.
(page 10 continued on part 2)
