Framework and Requirements for an Access Node Control Mechanism

in Broadband Multi-Service Networks

Abstract

The purpose of this document is to define a framework for an Access Node Control Mechanism 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 service, quality of service, and subscribers. The Access Node Control Mechanism will ensure that the transmission of the information does not need to go through distinct element managers but rather uses a direct device-device communication. This allows for performing access-link-related operations within those network elements, while avoiding impact on the existing Operational Support Systems.

This document first identifies a number of use cases for which the Access Node Control Mechanism may be appropriate. It then presents the requirements for the Access Node Control Protocol (ANCP) that must be taken into account during protocol design. Finally, it describes requirements for the network elements that need to support ANCP and the described use cases. These requirements should be seen as guidelines rather than as absolute requirements. RFC 2119 therefore does not apply to the nodal requirements.

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see 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/rfc5851.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  5
     1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  General Architecture Aspects . . . . . . . . . . . . . . . . .  7
     2.1.  Concept of an Access Node Control Mechanism  . . . . . . .  7
     2.2.  Reference Architecture . . . . . . . . . . . . . . . . . .  8
       2.2.1.  Home Gateway . . . . . . . . . . . . . . . . . . . . .  9
       2.2.2.  Access Loop  . . . . . . . . . . . . . . . . . . . . .  9
       2.2.3.  Access Node  . . . . . . . . . . . . . . . . . . . . .  9
       2.2.4.  Access Node Uplink . . . . . . . . . . . . . . . . . . 10
       2.2.5.  Aggregation Network  . . . . . . . . . . . . . . . . . 10
       2.2.6.  Network Access Server  . . . . . . . . . . . . . . . . 10
       2.2.7.  Regional Network . . . . . . . . . . . . . . . . . . . 10
     2.3.  Prioritizing Access Node Control Traffic . . . . . . . . . 11
     2.4.  Interaction with Management Systems  . . . . . . . . . . . 12
     2.5.  Circuit Addressing Scheme  . . . . . . . . . . . . . . . . 12
   3.  Use Cases for Access Node Control Mechanism  . . . . . . . . . 13
     3.1.  Access Topology Discovery  . . . . . . . . . . . . . . . . 13
     3.2.  Access-Loop Configuration  . . . . . . . . . . . . . . . . 15
     3.3.  Remote Connectivity Test . . . . . . . . . . . . . . . . . 16
     3.4.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 17
       3.4.1.  Multicast Conditional Access . . . . . . . . . . . . . 18
       3.4.2.  Multicast Admission Control  . . . . . . . . . . . . . 21
       3.4.3.  Multicast Accounting and Reporting . . . . . . . . . . 26
       3.4.4.  Spontaneous Admission Response . . . . . . . . . . . . 27
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 28
     4.1.  ANCP Functional Requirements . . . . . . . . . . . . . . . 28
     4.2.  ANCP Multicast Requirements  . . . . . . . . . . . . . . . 29
     4.3.  Protocol Design Requirements . . . . . . . . . . . . . . . 30
     4.4.  Access Node Control Adjacency Requirements . . . . . . . . 31
     4.5.  ANCP Transport Requirements  . . . . . . . . . . . . . . . 31
     4.6.  Access Node Requirements . . . . . . . . . . . . . . . . . 32
       4.6.1.  General Architecture . . . . . . . . . . . . . . . . . 32
       4.6.2.  Control Channel Attributes . . . . . . . . . . . . . . 33
       4.6.3.  Capability Negotiation Failure . . . . . . . . . . . . 33
       4.6.4.  Adjacency Status Reporting . . . . . . . . . . . . . . 33
       4.6.5.  Identification . . . . . . . . . . . . . . . . . . . . 34
       4.6.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . . 34
       4.6.7.  Message Handling . . . . . . . . . . . . . . . . . . . 36
       4.6.8.  Parameter Control  . . . . . . . . . . . . . . . . . . 37
     4.7.  Network Access Server Requirements . . . . . . . . . . . . 37
       4.7.1.  General Architecture . . . . . . . . . . . . . . . . . 37
       4.7.2.  Control Channel Attributes . . . . . . . . . . . . . . 39
       4.7.3.  Capability Negotiation Failure . . . . . . . . . . . . 39
       4.7.4.  Adjacency Status Reporting . . . . . . . . . . . . . . 40
       4.7.5.  Identification . . . . . . . . . . . . . . . . . . . . 40
   
       4.7.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . . 40
       4.7.7.  Message Handling . . . . . . . . . . . . . . . . . . . 42
       4.7.8.  Wholesale Model  . . . . . . . . . . . . . . . . . . . 42
   5.  Management-Related Requirements  . . . . . . . . . . . . . . . 43
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 44
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 45
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 45

1. Introduction

Digital Subscriber Line (DSL) technology is widely deployed for Broadband Access for Next Generation Networks. Several documents like Broadband Forum TR-058 [TR-058], Broadband Forum TR-059 [TR-059], and Broadband Forum TR-101 [TR-101] describe possible architectures for these access networks. The scope of these specifications consists of the delivery of voice, video, and data services. The framework defined by this document is targeted at DSL- based access (either by means of ATM/DSL or as Ethernet/DSL). The framework shall be open to other access technologies, such as Passive Optical Networks using DSL technology at the Optical Network Unit (ONU), or wireless technologies like IEEE 802.16. Several use cases such as Access Topology Discovery, Remote Connectivity Test, and Multicast may be applied to these access technologies, but the details of this are outside the scope of this document.

Traditional architectures require Permanent Virtual Circuit(s) per subscriber. Such a virtual circuit is configured on layer 2 and terminated at the first layer 3 device (e.g., Broadband Remote Access Server (BRAS)). Beside the data plane, the models define the architectures for element, network, and service management. Interworking at the management plane is not always possible because of the organizational boundaries between departments operating the local loop, departments operating the ATM network, and departments operating the IP network. Besides, management networks are usually not designed to transmit management data between the different entities in real time.

When deploying value-added services across DSL access networks, special attention regarding quality of service and service control is required, which implies a tighter coordination between Network Nodes (e.g., Access Nodes and Network Access Server (NAS)), without burdening the Operational Support System (OSS) with unpractical expectations.

Therefore, there is a need for an Access Node Control Mechanism between a 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 service, quality of service, and subscribers. The Access Node Control Mechanism will ensure that the transmission of the information does not need to go through distinct element managers but rather using a direct device- device communication. This allows for performing access-link-related operations within those network elements, while avoiding impact on the existing OSSes.

This document provides a framework for such an Access Node Control Mechanism and identifies a number of use cases for which this mechanism can be justified. Next, it presents a number of requirements for the Access Node Control Protocol (ANCP) and the network elements that need to support it.

The requirements spelled out in this document are based on the work that is performed by the Broadband Forum [TR-147].

1.1. Requirements Notation

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].

1.2. Definitions

• Access Node (AN): network device, usually located at a service provider central office or street cabinet, that terminates access- loop connections from subscribers. In case the access loop is a Digital Subscriber Line (DSL), this is often referred to as a DSL Access Multiplexer (DSLAM).

• Network Access Server (NAS): network device that aggregates multiplexed subscriber traffic from a number of Access Nodes. The NAS plays a central role in per-subscriber policy enforcement and quality of service (QoS). 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].

   o  "Net Data Rate": 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": defined by ITU-T G.993.2. It contains the complete overhead including Reed-Solomon and Trellis coding.

• Access Node Control Mechanism: a method for multiple network scenarios with an extensible communication scheme that conveys status and control information between one or more ANs and one or more NASes without using intermediate element managers.

• Control Channel: a bidirectional IP communication interface between the controller function (in the NAS) and the reporting/ enforcement function (in the AN). It is assumed that this interface is configured (rather than discovered) on the AN and the NAS.

• Access Node Control Adjacency: the relationship between an Access Node and a NAS for the purpose of exchanging Access Node Control Protocol messages. The adjacency may either be up or down, depending on the result of the Access Node Control Adjacency protocol operation.

• Multicast Flow: designates datagrams sent to a group from a set of sources for which multicast reception is desired. A distinction can be made between Any Source Multicast (ASM) and Source-Specific Multicast (SSM).

• Join: signaling from the user equipment that it wishes to start receiving a new multicast flow. In ASM, it is referred to as a "Join". In SSM [RFC4607], it is referred to as a "subscribe". In IGMPv2, "joins" are indicated through an "IGMPv2 membership report". In IGMPv3 [RFC3376], "join" is indicated through "membership report" using different Filter-Mode-Change (ASM) and Source-List-Change Records.

• Leave: signaling from the user equipment that it wishes to stop receiving a multicast flow. With IGMPv2, this is conveyed inside the "Leave Group" message, while in IGMPv3, "leave" is indicated through the "IGMPv3 membership report" message using different Filter-Mode-Change (ASM) and Source-List-Change Records.

2. General Architecture Aspects

This section introduces the basic concept of the Access Node Control Mechanism and describes the reference architecture where it is being applied. Based on the reference architecture, the section then describes how Access Node Control messages are to be prioritized over other data traffic, and the interaction between ANCP and the network management system. Finally, the addressing schemes are described that allow identifying an Access Port in Access Node Control messages.

2.1. Concept of an Access Node Control Mechanism

The high-level communication framework for an Access Node Control Mechanism is defined in Figure 1. The Access Node Control Mechanism defines a quasi-real-time, general-purpose method for multiple network scenarios with an extensible communication scheme, addressing the different use cases that are described throughout this document.

                                                 +--------+
                                                 | Policy |
                                                 | Server |
                                                 +--------+
                                                      |
                                                      |
  +-----+  +-----+  +--------+                     +-----+  +----------+
  | CPE |--| HGW |--|        |                     |     |  |          |
  +-----+  +-----+  | Access |   +-------------+   |     |  | Regional |
                    |  Node  |---| Aggregation |---| NAS |--| Network  |
  +-----+  +-----+  |        |   |   Network   |   |     |  |          |
  | CPE |--| HGW |--|        |   +-------------+   |     |  |          |
  +-----+  +-----+  +--------+                     +-----+  +----------+
                     Information Report / Admission Request
                         ------------------------------>
                      Admission Response / Control Request
                         <------------------------------
                               Control Response
                         ------------------------------>
  
                          Access Node Control Mechanism
                         <----------------------------->
                                 PPP, DHCP, IP
    <---------><----------------------------------------->

CPE: Customer Premises Equipment
HGW: Home Gateway

Figure 1: Access Network Architecture

A number of functions can be identified:

• A controller function: this function is used either to send out requests for information to be used by the network element where the controller function resides, or to trigger a certain behavior in the network element where the reporting and/or enforcement function resides.

• A reporting function: this function is used to convey status information to the controller function. An example of this is the transmission of the access-loop data rate from an Access Node to a Network Access Server (NAS) tasked with shaping traffic to that rate.

• An enforcement function: this function is contacted by the controller function to trigger a remote action on the Access Node. An example is the initiation of a port-testing mechanism on an Access Node. Another example is enforcing whether a multicast join is to be honored or denied.

The messages shown in Figure 1 show the conceptual message flow. The actual use of these flows, and the times or frequencies when these messages are generated depends on the actual use cases, which are described in Section 3.

The use cases in this document are described in an abstract way, independent from any actual protocol mapping. The actual protocol specification is out of scope of this document, but there are certain characteristics of the protocol that are required to simplify specification, implementation, debugging and troubleshooting, and to extend support for additional use cases.

2.2. Reference Architecture

The reference architecture used in this document can be based on ATM or Ethernet access/aggregation. Specifically:

• In case of a legacy ATM aggregation network that is to be used for the introduction of new QoS-enabled IP services, the architecture builds on the reference architecture specified in the Broadband Forum [TR-059];

• In case of an Ethernet aggregation network that supports new QoS- enabled IP services (including Ethernet multicast replication), the architecture builds on the reference architecture specified in the Broadband Forum [TR-101].

Given the industry's move towards Ethernet as the new access and aggregation technology for triple-play services, the primary focus throughout this document is on a TR-101 architecture. However the concepts are equally applicable to an ATM architecture based on TR- 059.

2.2.1. Home Gateway

The Home Gateway (HGW) connects the different Customer Premises Equipment (CPE) to the Access Node and the access network. In case of DSL, the HGW is a DSL Network Termination (NT) that could either operate 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).

2.2.2. Access Loop

The access loop ensures physical connectivity between the HGW at the customer premises and the Access Node. In case of DSL, the access- loop physical layer could be, e.g., ADSL, ADSL2+, VDSL, VDSL2, or SHDSL. In order to increase bandwidth, it is also possible that multiple DSL links are grouped together to form a single virtual link; this process is called "DSL bonding". The protocol encapsulation on the access loop could be based on multi-protocol encapsulation over ATM Adaption Layer 5 (AAL5) defined in [RFC2684]. This covers PPP over Ethernet (PPPoE, defined in [RFC2516]), bridged IP (IP over Ethernet (IPoE), defined in [RFC894]) and routed IP (IP over ATM (IPoA), defined in [RFC2225]). Next to this, PPP over AAL5 (PPPoA) as defined in [RFC2364] can be used. Future scenarios include cases where the access loop supports direct Ethernet encapsulation (e.g., when using VDSL or VDSL2).

2.2.3. Access Node

The Access Node (AN) may support one or more access-loop technologies and allow them to interwork with a common aggregation network technology. Besides the access-loop termination, the AN can also aggregate traffic from other Access Nodes using ATM or Ethernet.

The framework defined by this document is targeted at DSL-based access (either by means of ATM/DSL or as Ethernet/DSL). The framework shall be open to non-DSL technologies, like Passive Optical Networks (PONs) and IEEE 802.16 (WiMAX), but the details of this are outside the scope of this document.

The reporting and/or enforcement function defined in Section 2.1 typically resides in an Access Node.

2.2.4. Access Node Uplink

The fundamental requirements for the Access Node uplink are to provide traffic aggregation, Class of Service (CoS) distinction, and customer separation and traceability. This can be achieved using an ATM- or Ethernet-based technology.

2.2.5. Aggregation Network

The aggregation network provides traffic aggregation towards the NAS. The aggregation technology can be based on ATM (in case of a TR-059 architecture) or Ethernet (in case of a TR-101 architecture).

2.2.6. Network Access Server

The Network Access Server (NAS) interfaces to the aggregation network by means of standard ATM or Ethernet interfaces, and towards the Regional Network by means of transport interfaces for Ethernet frames (e.g., Gigabit Ethernet (GigE), Ethernet over Synchronous Optical Network (SONET)). The NAS functionality corresponds to the BNG functionality described in Broadband Forum TR-101. In addition to this, the NAS supports the Access Node Control functionality defined for the respective use cases throughout this document.

The controller function defined in Section 2.1 typically resides in a NAS.

2.2.7. Regional Network

The Regional Network connects one or more NAS and associated Access Networks to Network Service Providers (NSPs) and Application Service Providers (ASPs). The NSP authenticates access and provides and manages the IP address to subscribers. It is responsible for overall service assurance and includes Internet Service Providers (ISPs). The ASP provides application services to the application subscriber (gaming, video, content on demand, IP telephony, etc.).

The Regional Network supports aggregation of traffic from multiple Access Networks and hands off larger geographic locations to NSPs and ASPs -- relieving a potential requirement for them to build infrastructure to attach more directly to the various Access Networks.

2.3. Prioritizing Access Node Control Traffic

When sending Access Node Control messages across the aggregation network, care is needed that messages won't get lost. The connectivity between the Access Node and the NAS may differ depending on the actual layer 2 technology used (ATM or Ethernet). This section briefly outlines how network connectivity can be established.

In case of an ATM access/aggregation network, a typical practice is to send the Access Node Control Protocol messages over a dedicated Permanent Virtual Circuit (PVC) configured between the AN and the NAS. These ATM PVCs would then be given a high priority so that at times of network congestion, loss of the ATM cells carrying the Access Node Control Protocol is avoided or minimized. It is discouraged to route the Access Node Control Protocol messages within the Virtual Path (VP) that also carries the customer connections, if that VP is configured with a best-effort QoS class (e.g., Unspecified Bitrate (UBR)). The PVCs of multiple Access Node Control Adjacencies can be aggregated into a VP that is given a high priority and runs across the aggregation network. This requires the presence of a VC cross-connect in the aggregation node that terminates the VP.

In case of an Ethernet access/aggregation network, a typical practice is to send the Access Node Control Protocol messages over a dedicated Ethernet Virtual LAN (VLAN) using a separate VLAN identifier (VLAN ID). This can be achieved using a different VLAN ID for each Access Node, or, in networks with many Access Nodes and a high degree of aggregation, one Customer VLAN (C-VLAN) per Access Node and one Service VLAN (S-VLAN) for the Access Node Control Adjacencies of all Access Nodes. The traffic should be given a high priority (e.g., by using a high CoS value) so that the frame loss of Ethernet frames carrying the Access Node Control Protocol messages is minimized in the event of network congestion.

In both cases, the Control Channel between NAS and Access Node could use the same physical network and routing resources as the subscriber traffic. This means that the connection is an inband connection between the involved network elements. Therefore, there is no need for an additional physical interface to establish the Control Channel.

Note that these methods for transporting Access Node Control Protocol messages are typical examples; they do not rule out other methods that achieve the same behavior.

The Access Node Control Adjacency interactions must be reliable. In addition to this, some of the use cases described in Section 3 require the interactions to be performed in a transactional fashion, i.e., using a "request/response" mechanism. This is required so that the network elements always remain in a known state, irrespective of whether or not the transaction is successful.

2.4. Interaction with Management Systems

When introducing an Access Node Control Mechanism, care is needed to ensure that the existing management mechanisms remain operational as before.

Specifically, when using the Access Node Control Mechanism for performing a configuration action on a network element, one gets confronted with the challenge of supporting multiple managers for the same network element: both the Element Manager as well as the Access Node Control Mechanism may now perform configuration actions on the same network element. Therefore, conflicts need to be avoided.

Using the Access Node Control Mechanism, the NAS retrieves and controls a number of subscriber-related parameters. The NAS may decide to communicate this information to a central Policy or AAA Server so that it can keep track of the parameters and apply policies on them. The Server can then enforce those policies on the NAS. For instance, in case a subscriber is connected to more than one NAS, the policy server could be used to coordinate the bandwidth available on a given Access Port for use amongst the different NAS devices.

Guidelines related to management will be addressed in Section 5.

2.5. Circuit Addressing Scheme

In order to associate subscriber parameters to a particular Access Port, the NAS needs to be able to uniquely identify the Access Port (or a specific circuit on an Access Port) using an addressing scheme.

In deployments using an ATM aggregation network, the ATM PVC on an access loop connects the subscriber to a NAS. Based on this property, the NAS typically includes a NAS-Port-Id, NAS-Port, or Calling-Station-Id attribute in RADIUS authentication and accounting packets sent to the RADIUS server(s). Such attribute includes the identification of the ATM VC for this subscriber, which allows in turn identifying the access loop.

In an Ethernet-based aggregation network, a new addressing scheme is defined in [TR-101]. Two mechanisms can be used:

• A first approach is to use a one-to-one VLAN assignment model for all Access Ports (e.g., a DSL port) and circuits on an Access Port (e.g., an ATM PVC on an ADSL port). This enables directly deriving the port and circuit identification from the VLAN tagging information, i.e., S-VLAN ID or <S-VLAN ID, C-VLAN ID> pair.

• A second approach is to use a many-to-one VLAN assignment model and to encode the Access Port and circuit identification in the "Agent Circuit ID" sub-option to be added to a DHCP or PPPoE message. The details of this approach are specified in [TR-101].

This document reuses the addressing scheme specified in TR-101. It should be noted however that the use of such a scheme does not imply the actual existence of a PPPoE or DHCP session, nor the presence of the specific interworking function in the Access Node. In some cases, no PPPoE or DHCP session may be present, while port and circuit addressing would still be desirable.

3. Use Cases for Access Node Control Mechanism

3.1. Access Topology Discovery

[TR-059] and [TR-101] discuss various queuing/scheduling mechanisms to avoid congestion in the access network while dealing with multiple flows with distinct QoS requirements. One technique that can be used on a NAS is known as "Hierarchical Scheduling" (HS). This option is applicable in a single NAS scenario (in which case the NAS manages all the bandwidth available on the access loop) or in a dual NAS scenario (in which case the NAS manages some fraction of the access loop's bandwidth). The HS must, at a minimum, support 3 levels modeling the NAS port, Access Node uplink, and access-loop sync rate. The rationale for the support of HS is as follows:

• Provide fairness of network resources within a class.

• Allow for a better utilization of network resources. Drop traffic early at the NAS rather than letting it traverse the aggregation network just to be dropped at the Access Node.

• Enable more flexible CoS behaviors than only strict priority.

• The HS system could be augmented to provide per-application admission control.

• Allow fully dynamic bandwidth partitioning between the various applications (as opposed to static bandwidth partitioning).

• Support "per-user weighted scheduling" to allow differentiated Service Level Agreements (e.g., business services) within a given traffic class.

Such mechanisms require that the NAS gains knowledge about the topology of the access network, the various links being used, and their respective rates. Some of the information required is somewhat dynamic in nature (e.g., DSL line rate -- thus also the net data rate); hence, it cannot come from a provisioning and/or inventory management OSS system. Some of the information varies less frequently (e.g., capacity of a DSLAM uplink), but nevertheless needs to be kept strictly in sync between the actual capacity of the uplink and the image the BRAS has of it.

OSS systems are typically not designed to enforce the consistency of such data in a reliable and scalable manner across organizational boundaries. The Access Topology Discovery function is intended to allow the NAS to perform these functions without having to rely on an integration with an OSS system.

Communicating access-loop attributes is specifically important in case the rate of the access loop changes overtime. The DSL actual data rate may be different every time the DSL NT is turned on. In this case, the Access Node sends an Information Report message to the NAS after the DSL line has resynchronized.

Additionally, during the time the DSL NT is active, data rate changes can occur due to environmental conditions (the DSL access loop can get "out of sync" and can retrain to a lower value, or the DSL access loop could use Seamless Rate Adaptation making the actual data rate fluctuate while the line is active). In this case, the Access Node sends an additional Information Report to the NAS each time the access-loop attributes change above a threshold value.

The hierarchy and the rates of the various links to enable the NAS hierarchical scheduling and policing mechanisms are the following:

• The identification and speed (data rate) of the DSL access loop (i.e., the net data rate)

• The identification and speed (data rate) of the Remote Terminal (RT) / Access Node uplink (when relevant)

The NAS can adjust downstream shaping to the Access Loop's current actual data rate, and more generally reconfigure the appropriate nodes of its hierarchical scheduler (support of advanced capabilities according to TR-101).

This use case may actually include more information than link identification and corresponding data rates. In case of DSL access loops, the following access-loop characteristics can be sent to the NAS (cf. ITU-T Recommendation G.997.1 [G.997.1]):

   o  DSL Type (e.g., ADSL1, ADSL2, SDSL, ADSL2+, VDSL, VDSL2)
   
   o  Framing mode (e.g., ATM, ITU-T Packet Transfer Mode (PTM), IEEE
      802.3 Ethernet in the First Mile (EFM))
   
   o  DSL port state (e.g., synchronized/showtime, low power, no power/
      idle)

• Actual net data rate (upstream/downstream)

   o  Maximum achievable/attainable net data rate (upstream/downstream)

• Minimum net data rate configured for the access loop (upstream/ downstream)

• Maximum net data rate configured for the access loop (upstream/ downstream)

• Minimum net data rate in low power state configured for the access loop (upstream/downstream)

• Maximum achievable interleaving delay (upstream/downstream)

   o  Actual interleaving delay (upstream/downstream)

The NAS MUST be able to receive access-loop characteristics information, and share such information with AAA/policy servers.

3.2. Access-Loop Configuration

access-loop rates are typically configured in a static way. When a subscriber wants to change its access-loop rate, the network operator needs to reconfigure the Access Port configuration, possibly implying a business-to-business transaction between an Internet Service Provider (ISP) and an Access Provider. From an Operating Expenditures (OPEX) perspective this is a costly operation.

Using the Access Node Control Mechanism to change the access-loop rate from the NAS avoids those cross-organization business-to- business interactions and allows to centralize subscriber-related service data in e.g., a policy server. More generally, several access-loop parameters (e.g., minimum data rate, interleaving delay) could be changed by means of the Access Node Control Mechanism.

Triggered by the communication of the access-loop attributes described in Section 3.1, the NAS could query a Policy or AAA Server to retrieve access-loop configuration data. The best way to change access-loop parameters is by using profiles. These profiles (e.g., DSL profiles for different services) are pre-configured by the Element Manager managing the Access Nodes. The NAS may then use the Configure Request message to send a reference to the right profile to the Access Node. The NAS may also update the access-loop configuration due to a subscriber service change (e.g., triggered by the policy server).

The access-loop configuration mechanism may also be useful for configuration of parameters that are not specific to the access-loop technology. Examples include the QoS profile to be used for an access loop, or the per-subscriber multicast channel entitlement information, used for IPTV applications where the Access Node is performing IGMP snooping or IGMP proxy function. The latter is also discussed in Section 3.4.

It may be possible that a subscriber wants to change its access-loop rate, and that the operator wants to enforce this updated access-loop rate on the Access Node using ANCP, but that the Access Node Control Adjacency is down. In such a case, the NAS will not be able to request the configuration change on the Access Node. The NAS should then report this failure to the external management system, which could use application-specific signaling to notify the subscriber of the fact that the change could not be performed at this time.

3.3. Remote Connectivity Test

Traditionally, ATM circuits are point-to-point connections between the BRAS and the DSLAM or DSL NT. In order to test the connectivity on layer 2, appropriate Operations, Administration, and Maintenance (OAM) functionality is used for operation and troubleshooting. An end-to-end OAM loopback is performed between the edge devices (NAS and HGW) of the broadband access network.

When migrating to an Ethernet-based aggregation network (as defined by TR-101), end-to-end ATM OAM functionality is no longer applicable. Ideally in an Ethernet aggregation network, end-to-end Ethernet OAM (as specified in IEEE 802.1ag and ITU-T Recommendation Y.1730/1731) can provide access-loop connectivity testing and fault isolation. However, most HGWs do not yet support these standard Ethernet OAM procedures. Also, various access technologies exist such as ATM/DSL, Ethernet in the First Mile (EFM), etc. Each of these access technologies have their own link-based OAM mechanisms that have been or are being standardized in different standard bodies.

In a mixed Ethernet and ATM access network (including the local loop), it is desirable to keep the same ways to test and troubleshoot connectivity as those used in an ATM-based architecture. To reach consistency with the ATM-based approach, an Access Node Control Mechanism between NAS and Access Node can be used until end-to-end Ethernet OAM mechanisms are more widely available.

Triggered by a local management interface, the NAS can use the Access Node Control Mechanism to initiate an access-loop test between Access Node and HGW. In case of an ATM-based access loop, the Access Node Control Mechanism can trigger the Access Node to generate ATM (F4/F5) loopback cells on the access loop. In case of Ethernet, the Access Node can perform a port synchronization and administrative test for the access loop. The Access Node can send the result of the test to the NAS via a Control Response message. The NAS may then send the result via a local management interface. Thus, the connectivity between the NAS and the HGW can be monitored by a single trigger event.

3.4. Multicast

With the rise of supporting IPTV services in a resource efficient way, multicast services are getting increasingly important.

In case of an ATM access/aggregation network, such as the reference architecture specified in Broadband Forum [TR-059], multicast traffic replication is performed in the NAS. In this model, typically IGMP is used to control the multicast replication process towards the subscribers. The NAS terminates and processes IGMP signaling messages sent by the subscribers; towards the Regional Network, the NAS typically uses a multicast routing protocol such as Protocol Independent Multicast (PIM). The ATM Access Nodes and aggregation switches don't perform IGMP processing, nor do they perform multicast traffic replication. As a result, network resources are wasted within the access/aggregation network.

To overcome this resource inefficiency, the Access Node, aggregation node(s), and the NAS must all be involved in the multicast replication process. This prevents several copies of the same stream from being sent within the access/aggregation network. In case of an Ethernet-based access/aggregation network, this may, for example, be achieved by means of IGMP snooping or IGMP proxy in the Access Node and aggregation node(s).

By introducing IGMP processing in the access/aggregation nodes, the multicast replication process is now divided between the NAS, the aggregation node(s), and Access Nodes. In order to ensure backward compatibility with the ATM-based model, the NAS, aggregation node, and Access Node need to behave as a single logical device. This logical device must have exactly the same functionality as the NAS in the ATM access/aggregation network. The Access Node Control Mechanism can be used to make sure that this logical/functional equivalence is achieved by exchanging the necessary information between the Access Node and the NAS.

Another option is for the subscriber to communicate the "join/leave" information with the NAS. This can for instance be done by terminating all subscriber IGMP signaling on the NAS. Another example could be a subscriber using some form of application-level signaling, which is redirected to the NAS. In any case, this option is transparent to the access and aggregation network. In this scenario, the NAS can use ANCP to create replication state in the AN for efficient multicast replication. The NAS sends a single copy of the multicast stream towards the AN. The NAS can perform conditional access and multicast admission control on multicast joins, and create replication state in the AN if the flow is admitted by the NAS.

The following subsections describe the different use cases related to multicast.

3.4.1. Multicast Conditional Access

In a DSL broadband access scenario, service providers may want to dynamically control, at the network level, access to some multicast flows on a per-user basis. This may be used in order to differentiate among multiple Service Offers or to realize/reinforce conditional access for sensitive content. Note that, in some environments, application-layer conditional access by means of Digital Rights Management (DRM) may provide sufficient control, so that Multicast Conditional Access may not be needed.

Where Multicast Conditional Access is required, it is possible, in some cases, to provision the necessary conditional access information into the AN so the AN can then perform the conditional access decisions autonomously. For these cases, the NAS can use ANCP to provision the necessary information in the AN so that the AN can decide locally to honor a join or to not honor a join. This can be done with the Control Request and Control Response messages.

Provisioning the conditional access information on the AN can be done using a "white list", "grey list", and/or a "black list". A white list associated with an Access Port identifies the multicast flows that are allowed to be replicated to that port. A black list associated with an Access Port identifies the multicast flows that are not allowed to be replicated to that port. A grey list associated with an Access Port identifies the multicast flows for which the AN on receiving a join message, before starting traffic replication queries the NAS for further authorization. Each list contains zero, one, or multiple entries, and each entry may specify a single flow or contain ranges (i.e., mask on Group address and/or mask on Source address).

Upon receiving a join message on an Access Port, the Access Node will first check if the requested multicast flow is part of a white, grey, or a black list associated with that Access Port. If it is part of a white list, the AN autonomously starts replicating multicast traffic. If it is part of a black list, the AN autonomously discards the message because the request is not authorized, and may thus inform the NAS and log the request accordingly. If it is part of a grey list the AN uses ANCP to query the NAS, that in turn will respond to the AN indicating whether the join is to be honored (and hence replication performed by the AN) or denied (and hence replication not performed by the AN).

If the requested multicast flow is part of multiple lists associated with the Access Port, then the most specific match will be used. If the most specific match occurs in multiple lists, the black list entry takes precedence over the grey list, which takes precedence over the white list.

If the requested multicast flow is not part of any list, the message should be discarded. This default behavior can easily be changed by means of a "catch-all" statement in either the white list or the grey list. For instance, adding (<S=*,G=*>) in the white list would make the default behavior to accept join messages for a multicast flow that has no other match on any list. Similarly, if the default behavior should be to send a request to the NAS, then adding (<S=*,G=*>) in the grey list accomplishes that.

The white list, black list, and grey list can contain entries allowing:

   o  an exact match for a (*,G) ASM group (e.g., <G=g.h.i.l>);

• an exact match for a (S,G) SSM channel (e.g., <S=s.t.u.v,G=g.h.i.l>);

   o  a mask-based range match for a (*,G) ASM group (e.g., <G=g.h.i.l/
      Mask>);
   
   o  a mask-based range match for a (S,G) SSM channel (e.g.,
      <S=s.t.u.v/Mask,G=g.h.i.l/Mask>);

The following are some example configurations:

• Scenario 1: reject all messages

      *  black list = {<S=*,G=*>}
   
   o  Scenario 2: reject all messages, except Join (S=*,G=Gi) (1<=i<=n)
   
      *  white list = { <S=*,G=G1> , <S=*,G=G2>, ... <S=*,G=Gn>}
   
      *  black list = {<S=*,G=*>}

• Scenario 3: AN performs autonomous decisions for some channels, and asks the NAS for other channels

      *  white list = { <S=*,G=G1> , <S=*,G=G2>, ... <S=*,G=Gn>}
      
      *  grey list = { <S=s,G=Gm>} for m>n
      
      *  black list = {<S=*,G=*>}
      
      *  ==> Join (S=*,G=Gi) gets honored by AN (1<=i<=n)

• ==> Join (S=s,G=Gm) triggers ANCP Admission Request to NAS

• ==> everything else gets rejected by AN

The use of a white list and black list may be applicable, for instance, to regular IPTV services (i.e., broadcast TV) offered by an Access Provider to broadband (e.g., DSL) subscribers. For this application, the IPTV subscription is typically bound to a specific DSL line, and the multicast flows that are part of the subscription are well-known beforehand. Furthermore, changes to the conditional access information are infrequent, since they are bound to the subscription. Hence, the Access Node can be provisioned with the conditional access information related to the IPTV service.

In some other cases, it may be desirable to have the conditional access decision being taken by the NAS or a Policy Server. This may be the case when conditional access information changes frequently, or when the multicast groups are not known to a client application in advance. The conditional access control could be tied to a more complex policy/authorization mechanism, e.g., time-of-day access, location-based access, or to invoke a remote authorization server. For these cases, the AN can use ANCP to query the NAS that in turn will respond to the AN indicating whether the join is to be denied or honored (and hence replication performed by the AN). This can be done with the Admission Request and Admission Response messages.

Some examples of using NAS querying are the following:

• Roaming users: a subscriber that logs in on different wireless hotspots and would like to receive multicast content he is entitled to receive;

• Mobility or seamless handover (a related example): in both cases, the burden of (re)configuring access nodes with white lists or black lists may be too high;

• "Over-the-top video partnerships": service providers may choose to partner with Internet video providers to provide video content. In this case, the multicast group mappings may not be known in advance, or may be reused for different content in succession.

• "Pay Per View": a subscriber chooses a specific IPTV channel which is made available for a given amount of time.

3.4.2. Multicast Admission Control

The successful delivery of triple-play broadband services is quickly becoming a big capacity planning challenge for most of the Service Providers nowadays. Solely increasing available bandwidth is not always practical, cost-economical, and/or sufficient to satisfy end- user experience given not only the strict requirements of unicast delay sensitive applications like VoIP and video, but also the fast growth of multicast interactive applications such as videoconferencing, digital TV, digital audio, online movies, and networked gaming. These applications are typically characterized by a delay-sensitive nature, an extremely loss-sensitive nature, and intensive bandwidth requirements. They are also typically "non- elastic", which means that they operate at a fixed bandwidth that cannot be dynamically adjusted to the currently available bandwidth.

Therefore, a Connection Admission Control (CAC) mechanism covering admission of video traffic over the DSL broadband access is required, in order to avoid oversubscribing the available bandwidth and negatively impacting the end-user experience.

Considering specifically admission control over the access line, before honoring a user request to join a new multicast flow, the combination of AN and NAS must ensure admission control is performed to validate that there is sufficient bandwidth remaining on the access line to carry the new video stream (in addition to all other multicast and unicast video streams sent over the access line). The solution needs to cope with multiple flows per access line and needs to allow access-line bandwidth to be dynamically shared across multicast and unicast traffic (the unicast CAC is performed either by the NAS or by some off-path policy server).

Thus, supporting CAC for the access line requires some form of synchronization between the entity performing multicast CAC (e.g., the NAS or the AN), the entity performing unicast CAC (e.g., the policy server), and the entity actually enforcing the multicast replication (i.e., the AN). This synchronization can be achieved in a number of ways:

• One approach is for the AN to query the NAS so that Admission Control for the access line is performed by the NAS, or by the policy server which interacts with the AN via NAS. The AN can use ANCP to query the NAS that in turn performs a multicast Admission Control check for the new multicast flow and responds to the AN indicating whether the join is to be denied or honored (and hence replication performed by the AN). The NAS may locally keep track of the portion of the access-loop net data rate that is available for (unicast or multicast) video flows and perform video bandwidth accounting for the access loop. Upon receiving an Admission Request from the AN, the NAS can check available access-loop bandwidth before admitting or denying the multicast flow. In the process, the NAS may communicate with the policy server. For unicast video services such as Video on Demand (VoD), the NAS may also be queried (by a policy server or via on-path CAC signaling), so that it can perform admission control for the unicast flow and update the remaining available access-loop bandwidth. The ANCP requirements to support this approach are specified in this document.

• The above model could be enhanced with the notion of "Delegation of Authorization". In such a model, the NAS or the policy server delegates authority to the Access Node to perform multicast Admission Control on the access loop. This is sometimes referred to as "Bandwidth Delegation", referring to the portion of the total access-loop bandwidth that can be used by the Access Node for multicast Admission Control. In this model, the NAS or the policy server manages the total access-line bandwidth, performs unicast admission control, and uses ANCP to authorize the Access Node to perform multicast Admission Control within the bounds of the "delegated bandwidth". Upon receiving a request for a multicast flow replication that matches an entry in the white or grey list, the AN performs the necessary bandwidth admission control check for the new multicast flow, before starting the multicast flow replication. At this point, there is typically no need for the Access Node to communicate with the NAS or the policy server via the NAS. The ANCP requirements to support this approach are also specified in this document.

• In case the subscriber communicates the "join/leave" information with the NAS (e.g., by terminating all subscriber IGMP signaling on the NAS or by using some form of application-level signaling), the approach is very similar. In this case, the NAS may locally keep track of the portion of the access-loop bandwidth that is available for video flows, perform CAC for unicast and multicast flows, and perform video bandwidth management. The NAS can set the replication state on the AN using ANCP if the flow is admitted. For unicast video services, the NAS may be queried (by a policy server or via on-path CAC signaling) to perform admission control for the unicast flow, and update the remaining available access-loop bandwidth. The ANCP requirements to support this approach are specified in this document.

• In the last approach, the policy server queries the AN directly or indirectly via the NAS, so that both unicast and multicast CAC for the access line are performed by the AN. In this case, a subscriber request for a unicast flow (e.g., a Video on Demand session) will trigger a resource request message towards a policy server; the latter will then query the AN (possibly via the NAS), that in turn will perform unicast CAC for the access line and respond, indicating whether the unicast request is to be honored or denied. The above model could also be enhanced with the notion of "Delegation of Authorization". In such a model, the policy server delegates authority to the Access Node to perform multicast Admission Control on the access loop. In the case when the policy server queries the AN directly, the approach doesn't require the use of ANCP. It is therefore beyond the scope of this document. In the case when the policy server queries the AN indirectly via the NAS, the approach requires the use of ANCP and is therefore in the scope of this document.

3.4.2.1. Delegation of Authority - Bandwidth Delegation

The NAS uses ANCP to indicate to the AN whether or not Admission Control is required for a particular multicast flow on a given Access Port. In case Admission Control is required, the Access Node needs to know whether or not it is authorized to perform Admission Control itself and, if so, within which bounds it is authorized to do so (i.e., how much bandwidth is "delegated" by the NAS or the policy server). Depending on the type of multicast flow, Admission Control may or may not by done by the AN:

• Multicast flows that require a Conditional Access operation to be performed by the Access Node are put in the black or white list. In addition, the Access Node performs Admission Control for those flows in the white list for which it is authorized to do so.

• Multicast flows that require a Conditional Access operation to be performed by the NAS or the policy server, are put in the grey list. In addition, for those flows in the grey list for which the Access Node should perform Admission Control, the NAS or the policy server will delegate authority to the AN.

In some cases, the bandwidth that the NAS or the policy server initially delegated to the AN may not be enough to satisfy a multicast request for a new flow. In this scenario, the AN can use ANCP to query the NAS in order to request additional delegated multicast bandwidth. This is a form of extending the AN authorization to perform Admission Control. The NAS or the policy server decides if the request for more bandwidth can be satisfied and uses ANCP to send a response to the AN indicating the updated delegated multicast bandwidth. It is worth noting that in this case, the time taken to complete the procedure is an increment to the zapping delay. In order to minimize the zapping delay for future join requests, the AN can insert in the request message two values: the minimum amount of additional multicast bandwidth requested and the preferred additional amount. The first value is the amount that allows the present join request to be satisfied, the second value an amount that anticipates further join requests.

In some cases, the NAS or the policy server may not have enough unicast bandwidth to satisfy a new incoming video request: in these scenarios, the NAS can use ANCP to query (or instruct) the AN in order to decrease the amount of multicast bandwidth previously delegated on a given Access Port. This is a form of limiting/ withdrawing AN authorization to perform Admission Control. The NAS can use ANCP to send a response to AN indicating the updated delegated multicast bandwidth. Based on considerations similar to those of the previous paragraph, it indicates the minimum amount of multicast bandwidth that it needs released and a preferred amount, which may be larger.

Note: in order to avoid impacting existing multicast traffic, the NAS must not decrease the amount of delegated multicast bandwidth to a value lower than the bandwidth that is currently in use. This requires the NAS to be aware of this information (e.g., by means of a separate query action).

In addition, in some cases, upon receiving a leave for a specific multicast flow, the AN may decide that it has an excess of delegated but uncommitted bandwidth. In such case, the AN can use ANCP to send a message to the NAS to release all of part of the unused multicast bandwidth that was previously delegated. In this process, the Access Node may decide to retain a minimum amount of bandwidth for multicast services.

3.4.2.2. When Not to Perform Admission Control for a Subset of Flows

In general, the Access Node and NAS may not be aware of all possible multicast groups that will be streamed in the access network. For instance, it is likely that there will be multicast streams offered across the Internet. For these unknown streams, performing bandwidth Admission Control may be challenging.

To solve this, these requests could be accepted without performing Admission Control. This solution works, provided that the network handles the streams as best effort, so that other streams (that are subject to Admission Control) are not impacted at times of congestion.

Disabling Admission Control for an unknown stream can be achieved by adding a "catch-all statement" in the Access Node white list or grey list. In case the Access Node queries the NAS, the NAS on his turn will have to accept the request. That way, the unknown streams are not blocked by default.

Next, in order to ensure that the streams are handled as best effort, the flow must be marked as such when entering the service provider network. This way, whenever congestion occurs somewhere in the access/aggregation network, this stream will be kicked out before the access provider's own premium content.

The above concept is applicable beyond the notion of "Internet streams" or other unknown streams; it can be applied to known multicast streams as well. In this case, the Access Node or NAS will accept the stream even when bandwidth may not be sufficient to support the stream. This again requires that the stream be marked as best-effort traffic before entering the access/aggregation network.

3.4.2.3. Multicast Admission Control and White Lists

As mentioned in Section 3.4.1, conditional access to popular IPTV channels can be achieved by means of a white and black list configured on the Access Node. This method allows the Access Node to autonomously decide whether or not access can be granted to a multicast flow.

IPTV is an example of a service that will not be offered as best effort, but requires some level of guaranteed quality of service. This requires the use of Multicast Admission Control. Hence, if the Access Node wants to autonomously perform the admission process, it must be aware of the bandwidth characteristics of multicast flows. Otherwise, the Access Node would have to query the NAS for Multicast Admission Control (per the grey list behavior); this would defeat the purpose of using a white and black list.

Some network deployments may combine the use of white list, black list, and grey list. The implications of such a model to the overall Multicast Admission Control model are not fully explored in this document.

3.4.3. Multicast Accounting and Reporting

It may be desirable to perform time- and/or volume-based accounting for certain multicast flows sent on particular Access Ports. In case the AN is performing the traffic replication process, it knows when replication of a multicast flow to a particular Access Port or user start and stops. Multicast accounting can be addressed in two ways:

• The AN keeps track of when replication for a given multicast flow starts or ends on a specified Access Port, and generates time- and/or volume-based accounting information per Access Port and per multicast flow, before sending it to a central accounting system for logging. Given that the AN communicates with the accounting system directly, the approach doesn't require the use of ANCP. It is therefore beyond the scope of this document;

• The AN keeps track of when replication for a given multicast flow starts or ends on a specified Access Port, and reports this information to the NAS for further processing. In this case, ANCP can be used to send the information from the AN to the NAS. This will be discussed in the remainder of this document.

The Access Node can send multicast accounting information to the NAS using the Information Report message. A distinction can be made between two cases:

• Basic accounting information: the Access Node informs the NAS whenever replication starts or ends for a given multicast flow on a particular Access Port;

• Detailed accounting information: the Access Node not only informs the NAS when replication starts or ends, but also informs the NAS about the multicast traffic volume replicated on the Access Port for that multicast flow. This is done by adding a byte count in the Information Report message that is sent to the NAS when replication ends.

Upon receiving the Information Report messages, the NAS generates the appropriate time- and/or volume-based accounting records per access loop and per multicast flow to be sent to the accounting system.

The NAS should inform the Access Node about the type of accounting needed for a given multicast flow on a particular Access Port:

• No reporting messages need to be sent to the NAS.

• Basic accounting is required.

• Detailed accounting is required.

Note that in case of very fast channel changes, the amount of Information Report messages to be sent to the NAS could become high.

The ANCP requirements to support this use case are specified below in this document.

It may also be desirable for the NAS to have the capability to asynchronously query the AN to obtain an instantaneous status report related to multicast flows currently replicated by the AN. Such a reporting functionality could be useful for troubleshooting and monitoring purposes. The NAS can query the AN to know the following:

• Which flows are currently being sent on a specific Access Port (i.e., a report for one Access Port)

• On which Access Ports a specified multicast flow is currently being sent (i.e., a report for one multicast flow)

• Which multicast flows are currently being sent on each of the Access Ports (i.e., a global report for one Access Node)

3.4.4. Spontaneous Admission Response

The capability to dynamically stop the replication of a multicast flow can be useful in different scenarios: for example in case of prepaid service, when available credit expires, the Service Provider may want to be able to stop multicast replication on a specified Access Port for a particular user. Another example of applicability for this functionality is a scenario where a Service Provider would like to show a "Content Preview": in this case, a multicast content will be delivered just for a fixed amount of time.

In both cases, an external entity (for example, a policy server or an external application entity) can instruct the NAS to interrupt the multicast replication of a specified multicast flow to a specified Access Port or user. The NAS can then use ANCP to communicate this decision to the Access Node. This can be done with the Admission Response message.

In some deployment scenarios, the NAS may be made aware of end-users' requests to join/leave a multicast flow by other means than ANCP Admission Requests sent by the AN. One possible deployment scenario where this model applies is the case where the Access Node doesn't process the IGMP join/leave messages from the end-user (e.g., because they are tunneled), but forwards them to the NAS. In such environments, the NAS can control multicast replication on the AN via ANCP through the use of Spontaneous Admission Responses (i.e., sent by the NAS without prior receipt of a corresponding Admission Request).

4. Requirements

4.1. ANCP Functional Requirements

   R-1  The ANCP MUST be easily extensible through the definition of new
        message types or TLVs to support use cases beyond those
        currently addressed in this document (this includes the use of
        Access Nodes different from a DSLAM, e.g., a PON Access Node).
   
   R-2  The ANCP MUST be flexible enough to accommodate the various
        technologies that can be used in an access network and in the
        Access Node; this includes both ATM and Ethernet.
   
   R-3  The Access Node Control interactions MUST be reliable (using
        either a reliable transport protocol (e.g., TCP) for the Access
        Node Control Protocol messages, or by designing ANCP to be
        reliable).
   
   R-4  The ANCP MUST support "request/response" transaction-based
        interactions for the NAS to communicate control decisions to the
        Access Node, or for the NAS to request information from the
        Access Node.  Transactions MUST be atomic, i.e., they are either
        fully completed, or rolled back to the previous state.  This is
        required so that the network elements always remain in a known
        state, irrespective of whether or not the transaction is
        successful.

In case the NAS wants to communicate a bulk of independent control decisions to the Access Node, the transaction (and notion of atomicity) applies to the individual control decisions. This avoids having to roll back all control decisions. Similarly, if the NAS wants to request a bulk of independent information elements from the Access Node, the notion of transaction applies to the individual information elements.

   R-5  The ANCP MUST be scalable enough to allow a given NAS to control
        at least 5000 Access Nodes.
   
   R-6  The operation of the ANCP in the NAS and Access Nodes MUST be
        controllable via a management station (e.g., via SNMP).  This
        MUST allow a management station to retrieve statistics and
        alarms related to the operation of the ANCP, as well as to allow
        it to initiate OAM operations and retrieve corresponding
        results.

4.2. ANCP Multicast Requirements

   R-7   The ANCP MUST support providing multicast conditional access
         information to Access Ports on an Access Node, using black,
         grey, and white lists.
   
   R-8   The ANCP MUST support binding a particular black, grey, and
         white List to a given Access Port.
   
   R-9   Upon receiving a join to a multicast flow that matches the grey
         list, the ANCP MUST allow the AN to query the NAS to request an
         admission decision for replicating that multicast flow to a
         particular Access Port.
   
   R-10  The ANCP MUST allow the NAS to send an admission decision to
         the AN indicating whether or not a multicast flow may be
         replicated to a particular Access Port.
   
   R-11  The ANCP MUST allow the NAS to indicate to the AN whether or
         not Admission Control is needed for some multicast flows on a
         given Access Port, and (where needed) whether or not the Access
         Node is authorized to perform Admission Control itself (i.e.,
         whether or not AN Bandwidth Delegation applies).
   
   R-12  In case of Admission Control without AN Bandwidth Delegation,
         the ANCP MUST allow the NAS to reply to a query from the AN
         indicating whether or not a multicast flow is allowed to be
         replicated to a particular Access Port.
   
   R-13  In case of Admission Control with AN Bandwidth Delegation, the
         ANCP MUST allow the NAS to delegate a certain amount of
         bandwidth to the AN for a given Access Port for multicast
         services only.
   
   R-14  In case of Admission Control with AN Bandwidth Delegation, the
         ANCP MUST allow the AN to query the NAS to request additional
         multicast bandwidth on a given Access Port.
   
   R-15  In case of Admission Control with AN Bandwidth Delegation, the
         ANCP MUST allow the NAS to query (or to instruct) the AN to
         reduce the amount of bandwidth previously delegated on a given
         Access Port.
   
   R-16  In case of Admission Control with AN Bandwidth Delegation, the
         ANCP MUST allow the AN to inform the NAS if it autonomously
         releases redundant multicast bandwidth on a given Access Port.
   
   R-17  The ANCP MUST allow the AN to send an Information Report
         message to the NAS whenever replication of a multicast flow on
         a particular Access Port starts or ends.
   
   R-18  The ANCP MUST allow the AN to send an Information Report
         message to the NAS indicating the multicast traffic volume that
         has been replicated on that port.
   
   R-19  The ANCP MUST allow the NAS to indicate to the AN whether or
         not multicast accounting is needed for a multicast flow on a
         particular Access Port.
   
   R-20  In case multicast accounting is needed for a multicast flow on
         a particular Access Port, the ANCP MUST allow the NAS to
         indicate to the AN whether or not additional volume accounting
         information is required.
   
   R-21  The ANCP MUST allow the NAS to revoke a decision to replicate a
         multicast flow to a particular Access Port, which had been
         conveyed earlier to an AN.
   
   R-22  The ANCP MUST support partial updates of the white, grey, and
         black lists.
   
   R-23  The ANCP MUST allow the NAS to query the AN to obtain
         information on what multicast flows are currently being
         replicated on a given Access Port, what Access Ports are
         currently receiving a given multicast flow, or what multicast
         flows are currently replicated on each Access Port.

4.3. Protocol Design Requirements

   R-24  The ANCP SHOULD provide a "shutdown" sequence allowing the
         protocol to inform the peer that the system is gracefully
         shutting down.
   
   R-25  The ANCP SHOULD include a "report" model for the Access Node to
         spontaneously communicate to the NAS changes of states.
   
   R-26  The ANCP SHOULD support a graceful restart mechanism to enable
         it to be resilient to network failures between the AN and NAS.
   
   R-27  The ANCP MUST provide a means for the AN and the NAS to inform
         each peer about the supported use cases (either use cases
         defined in this document or future use cases yet to be
         defined), and to negotiate a common subset.

4.4. Access Node Control Adjacency Requirements

The notion of an Access Node Control Adjacency is defined in Section 1.2.

   R-28  The ANCP MUST support an adjacency protocol in order to
         automatically synchronize its operational state between its
         peers, to agree on which version of the protocol to use, to
         discover the identity of its peers, and to detect when they
         change.
   
   R-29  The ANCP MUST include a mechanism to automatically detect
         adjacency loss.
   
   R-30  A loss of the Access Node Control Adjacency MUST NOT affect
         subscriber connectivity.
   
   R-31  If the Access Node Control Adjacency is lost, it MUST leave the
         network elements in a known state, irrespective of whether or
         not the ongoing transaction was successful.
   
   R-32  The ANCP MUST support a mechanism to synchronize access port
         configuration and status information between ANCP peers as part
         of establishing or recovering the Access Node Control
         Adjacency.

4.5. ANCP Transport Requirements

   R-33  The Access Node Control Mechanism MUST be defined in a way that
         is independent of the underlying layer 2 transport technology.
         Specifically, the Access Node Control Mechanism MUST support
         transmission over an ATM as well as over an Ethernet
         aggregation network.
   
   R-34  The ANCP MUST use the IP protocol stack.
   R-35  If the layer 2 transport technology is based on ATM, then the
         ANCP peers must use the encapsulation according to [RFC2684]
         (IPoA).
   
   R-36  If the layer 2 transport technology is based on Ethernet, then
         the ANCP peers must use the encapsulation according to [RFC894]
         (IPoE).

4.6. Access Node Requirements

This section lists the requirements for an AN that supports the use cases defined in this document. Note that this document does not intend to impose absolute requirements on network elements. Therefore, the words "must" and "should" used in this section are not capitalized.

4.6.1. General Architecture

The Access Node Control Mechanism is defined to operate between an Access Node (AN) and a NAS. In some cases, one AN can be connected to more than one physical NAS device (e.g., in case different wholesale service providers have different NAS devices). In such a model, the physical AN needs to be split in virtual ANs, each having its own Access Node Control reporting and/or enforcement function.

   R-37  An Access Node as physical device can be split in logical
         partitions.  Each partition may have its independent NAS.
         Therefore, the Access Node must support at least 2 partitions.
         The Access Node should support 8 partitions.
   
   R-38  One partition is grouped of several Access Ports.  Each Access
         Port on an Access Node must be assigned uniquely to one
         partition.

It is assumed that all circuits (i.e., ATM PVCs or Ethernet VLANs) on top of the same physical Access Port are associated with the same partition. In other words, partitioning is performed at the level of the physical Access Port only.

   R-39  Each AN partition must have a separate Access Node Control
         Adjacency to a NAS.
   
   R-40  Each AN partition must be able to enforce access of the
         controllers to their designated partitions.
   
   R-41  The Access Node should be able to establish and maintain ANCP
         Adjacencies to redundant controllers.

4.6.2. Control Channel Attributes

The Control Channel is a bidirectional IP communication interface between the controller function (in the NAS) and the reporting/ enforcement function (in the AN). It is assumed that this interface is configured (rather than discovered) on the AN and the NAS.

Depending on the network topology, the Access Node can be located in a street cabinet or in a central office. If an Access Node in a street cabinet is connected to a NAS, all user traffic and Access Node Control data can use the same physical link.

   R-42  The Control Channel should use the same facilities as the ones
         used for the data traffic.  Note that this is actually a
         deployment consideration, which has no impact on the actual
         protocol design.
   
   R-43  The Access Node must process control transactions in real-time
         (i.e., with a specific response latency).
   
   R-44  The Access Node should mark Access Node Control Protocol
         messages with a high priority (e.g., Variable Bit Rate - Real
         Time (VBR-RT) for ATM cells, p-bit 6 or 7 for Ethernet packets)
         in order to avoid or reduce the likelihood of dropping packets
         in case of network congestion.
   
   R-45  If ATM interfaces are used, then any Virtual Path Identifier
         (VPI) and Virtual Circuit Identifier (VCI) value must be able
         to be used for the purpose of supporting the Access Node
         Control Channel.
   
   R-46  If Ethernet interfaces are used then any C-VID and S-VID must
         be able to be used for the purpose of supporting the Access
         Node Control Channel.

4.6.3. Capability Negotiation Failure

   R-47  In case the Access Node and NAS cannot agree on a common set of
         capabilities, as part of the ANCP capability negotiation
         procedure, the Access Node must report this to network
         management.

4.6.4. Adjacency Status Reporting

   R-48  The Access Node should support generating an alarm to a
         management station upon loss or malfunctioning of the Access
         Node Control Adjacency with the NAS.

4.6.5. Identification

   R-49  To identify the Access Node and Access Port within a control
         domain, a unique identifier is required.  This identifier must
         be in line with the addressing scheme principles specified in
         Section 3.9.3 of TR-101.
   
   R-50  In a Broadband Forum TR-101 network architecture, an Access
         Circuit Identifier (ACI) identifying an AN and Access Port is
         added to DHCP and PPPoE messages.  The NAS must use the same
         ACI format in ANCP messages in order to allow the NAS to
         correlate this information with the information present in DHCP
         and PPPoE messages.

4.6.6. Multicast

   R-51  The AN must deny any join to a multicast flow matching the
         black list for the relevant Access Port.
   
   R-52  The AN must accept any join to a multicast flow matching the
         white list and for which no Bandwidth Delegation is used.
   
   R-53  Upon receiving a join to a multicast flow that matches the
         white list and for which Bandwidth Delegation is used, the AN
         must perform the necessary bandwidth admission control check
         for the new flow before starting the multicast flow
         replication.  This may involve a decision made locally, or
         querying the NAS or external system such as a policy server, to
         request additional delegated multicast bandwidth on a given
         Access Port.
   
   R-54  Upon receiving a join to a multicast flow which matches the
         grey list and for which no Bandwidth Delegation is used, the AN
         must support using ANCP to query the NAS to receive a response
         indicating whether that join is to be honored or denied.  In
         this case, the NAS will perform both the necessary conditional
         access and the admission control checks for the new flow.
   
   R-55  Upon receiving a join to a multicast flow that matches the grey
         list and for which Bandwidth Delegation is used, the AN must
         first perform the necessary bandwidth admission control check
         for the new flow.  If successful, the AN must support using
         ANCP to query the NAS to receive a response indicating whether
         that join is to be honored or denied.
   
   R-56  In case of Admission Control with AN Bandwidth Delegation, the
         AN must support using ANCP to notify the NAS when the user
         leaves the multicast flow.
   
   R-57  In case of Admission Control with AN Bandwidth Delegation, the
         AN must support using ANCP to query the NAS to request
         additional delegated multicast bandwidth on a given Access
         Port; the AN should be able to specify both the minimum and the
         preferred amount of additional multicast bandwidth requested.
   
   R-58  In case of Admission Control with AN Bandwidth Delegation, upon
         receiving a Bandwidth Delegation Request from the NAS querying
         the AN for the delegated multicast bandwidth on a given Access
         Port, the AN must support using ANCP to send a Bandwidth
         Delegation Response, indicating the currently delegated
         multicast bandwidth.
   
   R-59  In case of Admission Control with AN Bandwidth Delegation, it
         may happen that the NAS wants to "revoke" all or part of the
         delegated bandwidth.  Part of the previously delegated
         bandwidth may however be in use by multicast services.
         Therefore, upon receiving a Bandwidth Delegation Request from
         the NAS instructing to decrease the delegated multicast
         bandwidth on a given Access Port, the AN must support using
         ANCP to send a Bandwidth Delegation Response, indicating the
         delegated multicast bandwidth after the decrease (indicating
         how much of the delegated bandwidth can be returned to the NAS
         without impacting multicast services that are currently
         running).
   
   R-60  In case of Admission Control with AN Bandwidth Delegation, the
         AN must support using ANCP to send a Bandwidth Release message
         to the NAS in order to release unused delegated multicast
         bandwidth on a given Access Port.
   
   R-61  If the requested multicast flow is not part of any list
         associated with the Access Port, the AN must discard the
         message.
   
   R-62  If the requested multicast flow is part of multiple lists
         associated with the Access Port, the AN must use the most
         specific match.
   
   R-63  If the requested multicast flow has the same most specific
         match in multiple lists, the AN must give precedence to the
         black list, followed by the grey list, and then the white list.
   
   R-64  The AN must support configuring a "catch-all" statement in the
         black, white, or grey list in order to enforce a default
         behavior for a join to a multicast flow which doesn't match any
         other entry in a list for the relevant Access Port.
   
   R-65  Upon querying the NAS, the AN must not propagate the join
         message before the successful authorization from the NAS is
         received.
   
   R-66  Upon receiving a leave for a multicast flow that matches the
         grey list, the AN should be able to autonomously stop
         replication and advertise this event to the NAS.
   
   R-67  The AN must support using ANCP to send an Information Report
         message to the NAS whenever replication starts or ends.
   
   R-68  The AN should support using ANCP to send an Information Report
         message to the NAS indicating the multicast traffic volume that
         has been replicated on that port.
   
   R-69  Upon request by the NAS, the AN must support using ANCP to send
         an Information Report message to the NAS, indicating what
         multicast flows are currently being replicated on a given
         Access Port.
   
   R-70  Upon request by the NAS, the AN must support using ANCP to send
         an Information Report message to the NAS, indicating what
         Access Ports are currently receiving a given multicast flow.
   
   R-71  Upon request by the NAS, the AN must support using ANCP to send
         an Information Report message to the NAS, indicating what
         multicast flows are currently being replicated on each Access
         Port.
   
   R-72  Upon receiving an Admission Response from the NAS, indicating
         that replication of a multicast flow is to start or stop on a
         given access port of the AN, the AN must enforce this decision.
         This decision must be taken irrespective of whether or not a
         corresponding Admission Request was issued by the AN earlier.

4.6.7. Message Handling

   R-73  The Access Node must be designed to allow fast completion of
         ANCP operations, in the order of magnitude of tens of
         milliseconds.
   
   R-74  The Access Node should avoid sending bursts of ANCP messages
         related to notification of line attributes or line state, by
         spreading message transmission over time.

4.6.8. Parameter Control

Naturally, the Access Node Control Mechanism is not designed to replace an Element Manager managing the Access Node. There are parameters in the Access Node, such as the DSL noise margin and DSL Power Spectral Density (PSD), which are not allowed to be changed via ANCP or any other control session, but only via the Element Manager. This has to be ensured and protected by the Access Node.

When using ANCP for access-loop configuration, the EMS needs to configure on the Access Node which parameters may or may not be modified using the Access Node Control Mechanism. Furthermore, for those parameters that may be modified using ANCP, the EMS needs to specify the default values to be used when an Access Node comes up after recovery.

   R-75  When access-loop configuration via ANCP is required, the EMS
         must configure on the Access Node which parameter set(s) may be
         changed/controlled using ANCP.
   
   R-76  Upon receiving an Access Node Control Request message, the
         Access Node must not apply changes to the parameter set(s) that
         have not been enabled by the EMS.

4.7. Network Access Server Requirements

This section lists the requirements for a NAS that supports the use cases defined in this document. Note that this document does not intend to impose absolute requirements on network elements. Therefore, the words "must" and "should" used in this section are not capitalized.

4.7.1. General Architecture

   R-77  The NAS must establish ANCP Adjacencies only with authorized
         ANCP peers.
   
   R-78  The NAS must support the capability to simultaneously run ANCP
         with multiple ANs in a network.
   
   R-79  The NAS must be able to establish an Access Node Control
         Adjacency to a particular partition on an AN and control the
         access loops belonging to such a partition.
   
   R-80  The NAS must support obtaining access-loop information (e.g.,
         net data rate), from its peer Access Node partitions via the
         Access Node Control Mechanism.
   
   R-81  The NAS must support shaping traffic directed towards a
         particular access loop to not exceed the net data rate learned
         from the AN via the Access Node Control Mechanism.
   
   R-82  The NAS should support reducing or disabling the shaping limit
         used in the Hierarchical Scheduling process, according to per-
         subscriber authorization data retrieved from a AAA or policy
         server.
   
   R-83  The NAS must support reporting of access-loop attributes
         learned via the Access Node Control Mechanism to a Policy or
         AAA Server using RADIUS Vendor-Specific Attributes (VSAs).
   
   R-84  In a TR-059/TR-101 network architecture, the NAS shapes traffic
         sent to a particular Access Port according to the bitrate
         available on that port.  The NAS should take into account the
         layer 1 and layer 2 encapsulation overhead on the Access Port,
         retrieved from the AN via the Access Node Control Mechanism.
   
   R-85  The NAS should support dynamically configuring and
         reconfiguring discrete service parameters for access loops that
         are controlled by the NAS.  The configurable service parameters
         for access loops could be driven by local configuration on the
         NAS or by a policy server.
   
   R-86  The NAS should support triggering an AN via the Access Node
         Control Mechanism to execute local OAM procedures on an access
         loop that is controlled by the NAS.  If the NAS supports this
         capability, then the following applies:

• The NAS must identify the access loop on which OAM procedures need to be executed by specifying an Access Circuit Identifier (ACI) in the request message to the AN.

• The NAS should support processing and reporting of the remote OAM results learned via the Access Node Control Mechanism.

• As part of the parameters conveyed within the OAM message to the AN, the NAS should send the list of test parameters pertinent to the OAM procedure. The AN will then execute the OAM procedure on the specified access loop according to the specified parameters. In case no test parameters are conveyed, the AN and NAS must use default and/or appropriately computed values.

• After issuing an OAM request, the NAS will consider the request to have failed if no response is received after a certain period of time. The timeout value should be either the one sent within the OAM message to the AN, or the computed timeout value when no parameter was sent.

The exact set of test parameters mentioned above depends on the particular OAM procedure executed on the access loop. An example of a set of test parameters is the number of loopbacks to be performed on the access loop and the timeout value for the overall test. In this case, and assuming an ATM-based access loop, the default value for the timeout parameter would be equal to the number of F5 loopbacks to be performed, multiplied by the F5 loopback timeout (i.e., 5 seconds per the ITU-T I.610 standard).

   R-87  The NAS must treat PPP or DHCP session state independently from
         any Access Node Control Adjacency state.  The NAS must not
         bring down the PPP or DHCP sessions just because the Access
         Node Control Adjacency goes down.
   
   R-88  The NAS should internally treat Access Node Control traffic in
         a timely and scalable fashion.
   
   R-89  The NAS should support protection of Access Node Control
         communication to an Access Node in case of line card failure.

4.7.2. Control Channel Attributes

   R-90  The NAS must mark Access Node Control Protocol messages as high
         priority (e.g., appropriately set Diffserv Code Point (DSCP),
         Ethernet priority bits, or ATM Cell Loss Priority (CLP) bit)
         such that the aggregation network between the NAS and the AN
         can prioritize the Access Node Control Protocol messages over
         user traffic in case of congestion.

4.7.3. Capability Negotiation Failure

   R-91  In case the NAS and Access Node cannot agree on a common set of
         capabilities, as part of the ANCP capability negotiation
         procedure, the NAS must report this to network management.
   
   R-92  The NAS must only commence Access Node Control information
         exchange and state synchronization with the AN when there is a
         non-empty common set of capabilities with that AN.

4.7.4. Adjacency Status Reporting

   R-93  The NAS must support generating an alarm to a management
         station upon loss or malfunctioning of the Access Node Control
         Adjacency with the Access Node.

4.7.5. Identification

   R-94  The NAS must support correlating Access Node Control Protocol
         messages pertaining to a given access loop with subscriber
         session(s) over that access loop.  This correlation must be
         achieved by either:

• Matching an Access Circuit Identifier (ACI) inserted by the AN in Access Node Control Protocol messages with the corresponding ACI value received in subscriber signaling (e.g., PPPoE and DHCP) messages as inserted by the AN. The format of ACI is defined in [TR-101]; or

• Matching an ACI inserted by the AN in Access Node Control Protocol messages with an ACI value locally configured for a static subscriber on the NAS.

4.7.6. Multicast

   R-95   The NAS must support using ANCP to configure multicast
          conditional access information to Access Ports on an Access
          Node, using black lists, grey lists, and white lists.
   
   R-96   The NAS must support using ANCP to indicate to the AN whether
          or not Admission Control is needed for some multicast flows on
          a given Access Port and where needed whether or not the Access
          Node is authorized to perform Admission Control itself (i.e.,
          whether or not AN Bandwidth Delegation applies).
   
   R-97   Upon receiving a query from the AN for a request to replicate
          a multicast flow to a particular Access Port, and no AN
          Bandwidth Delegation is used for that flow, the NAS must be
          able to perform the necessary checks (conditional access
          and/or admission control) for the new flow.  The NAS must
          support using ANCP to reply to the AN indicating whether the
          request is to be honored or denied.  This may involve a
          decision made locally or querying an external system such as a
          policy server.
   
   R-98   Upon receiving a query from the AN for a request to replicate
          a multicast flow to a particular Access Port, and Admission
          Control with AN Bandwidth Delegation is used for that flow,
          the NAS must be able to perform the conditional access checks
          (if needed), and must support using ANCP to delegate a certain
          amount of bandwidth to the AN for a given Access Port.
   
   R-99   In case of Admission Control with AN Bandwidth Delegation,
          upon receiving a Bandwidth Delegation Request from the AN
          requesting to increase the delegated multicast bandwidth on a
          given Access Port, the NAS must support using ANCP to send a
          Bandwidth Delegation Response indicating the new delegating
          multicast bandwidth.
   
   R-100  In case of Admission Control with AN Bandwidth Delegation, the
          NAS must support using ANCP to send a request to the AN to
          decrease the amount of multicast bandwidth previously
          delegated on a given Access Port; the NAS should be able to
          specify both the minimum and the preferred amount of decrement
          of multicast bandwidth requested.
   
   R-101  In case of Admission Control with AN Bandwidth Delegation,
          upon receiving an ANCP Bandwidth Release message, the NAS must
          be able to update accordingly its view of the multicast
          bandwidth delegated to the AN.
   
   R-102  The NAS must support using ANCP to configure the Access Node
          with the "maximum number of multicast streams" allowed to be
          received concurrently per Access Port.
   
   R-103  The NAS must support using ANCP to incrementally add, remove,
          and modify individual entries in white, black, and grey lists.
   
   R-104  The NAS must support using ANCP to indicate to the AN whether
          or not multicast accounting is needed for a multicast flow on
          a particular Access Port.
   
   R-105  In case multicast accounting is needed for a multicast flow on
          a particular Access Port, the NAS should support using ANCP to
          indicate to the AN whether or not additional volume accounting
          information is required.
   
   R-106  The NAS must support using ANCP to query the AN to obtain
          information on what multicast flows are currently replicated
          on a given Access Port.
   
   R-107  The NAS must support using ANCP to query the AN to obtain
          information on what Access Ports are currently receiving a
          given multicast flow.
   
   R-108  The NAS must support using ANCP to query the AN to obtain
          information on what multicast flows are currently replicated
          on each Access Port.
   
   R-109  When Multicast replication occurs on the AN, the NAS must
          support using ANCP to revoke the authorization to replicate a
          multicast flow to a particular Access Port.
   
   R-110  The NAS should support using ANCP to indicate to the AN that
          replication of a multicast flow is to start or stop on a given
          access port of the AN, without having received a corresponding
          Admission Request from the AN earlier on.

4.7.7. Message Handling

   R-111  The NAS must be designed to allow fast completion of ANCP
          operations, in the order of magnitude of tens of milliseconds.
   
   R-112  The NAS should protect its resources from misbehaving Access
          Node Control peers by providing a mechanism to dampen
          information related to an Access Node partition.

4.7.8. Wholesale Model

Broadband Forum TR-058 [TR-058], Broadband Forum TR-059 [TR-059], and Broadband Forum TR-101 [TR-101] describe a DSL broadband access architecture and how it enables wholesaling. In such a model, the broadband access provider has a wholesale agreement with one or more service providers. The access provider owns the broadband access network and manages connectivity to the service providers. This allows service providers to provide broadband services to retail customers without having to own the access network infrastructure itself.

When applying the Access Node Control Mechanism to a wholesale network architecture, a number of additional requirements apply.

   R-113  In case of wholesale access, the network provider's NAS should
          support reporting of access-loop attributes learned from the
          AN via the Access Node Control Mechanism (or values derived
          from such attributes), to a retail provider's network gateway
          owning the corresponding subscriber(s).
   
   R-114  In case of Layer 2 Tunneling Protocol (L2TP) wholesale, the
          NAS must support a proxy architecture that gives different
          providers conditional access to dedicated Access Node Control
          resources on an Access Node.
   
   R-115  The NAS when acting as an L2TP Access Concentrator (LAC) must
          communicate generic access-line-related information to the
          L2TP Network Server (LNS) in a timely fashion.
   
   R-116  The NAS when acting as a LAC may asynchronously notify the LNS
          of updates to generic access-line-related information.

5. Management-Related Requirements

This section lists the management-related requirements for the AN and NAS. Note that this document does not intend to impose absolute requirements on network elements. Therefore, the words "must" and "should" used in this section are not capitalized.

   R-117  It must be possible to configure the following parameters on
          the Access Node and the NAS:

• Parameters related to the Control Channel transport method: these include the VPI/VCI and transport characteristics (e.g., VBR-RT or Constant Bitrate (CBR)) for ATM networks, or the C-VLAN ID, S-VLAN ID, and p-bit marking for Ethernet networks;

• Parameters related to the Control Channel itself: these include the IP address of the IP interface on the Access Node and the NAS.

   R-118  When the operational status of the Control Channel is changed
          (up>down, down>up) a linkdown/linkup trap should be sent
          towards the EMS.  This requirement applies to both the AN and
          the NAS.
   
   R-119  The Access Node must provide the possibility using SNMP to
          associate individual DSL lines with specific Access Node
          Control Adjacencies.
   
   R-120  The Access Node must notify the EMS of configuration changes
          made by the NAS on the AN using ANCP, in a timely manner.
   
   R-121  The Access Node must provide a mechanism that allows the
          concurrent access on the same resource from several managers
          (EMS via SNMP, NAS via ANCP).  Only one manager may perform a
          change at a certain time.
   
   R-122  The ANCP may provide a notification mechanism to inform the
          NAS about configuration changes done by an EMS, in a timely
          manner.  This applies only to changes of parameters that are
          part of the use case "Access-Loop Configuration"
          (Section 3.2).

6. Security Considerations

[RFC5713] lists the ANCP-related security threats that could be encountered on the Access Node and the NAS. It develops a threat model and identifies requirements for ANCP security, aiming to decide which security functions are required at the ANCP level.

With multicast handling as described in this document, ANCP protocol activity between the AN and the NAS is triggered by join/leave requests coming from the end-user equipment. This could potentially be used for denial-of-service attacks against the AN and/or the NAS.

This is not a new class of risk over already possible IGMP messages sent from subscribers to the NAS when the AN uses no IGMP snooping, and thus is transparent as long as processing of ANCP messages on the NAS/AN is comparably efficient and protected against congestion.

To mitigate this risk, the AN MAY implement control-plane protection mechanisms such as limiting the number of multicast flows a given user can simultaneously join, or limiting the maximum rate of join/ leave from a given user.

We also observe that an operator can easily deploy some protection against attacks using invalid multicast flows by taking advantage of the mask-based match in the black list. This way, joins for invalid multicast flows can be denied at the AN level without any ANCP protocol interactions and without NAS involvement.

   R-123  The ANCP MUST comply with the security requirements spelled
          out in RFC 5713.
   
   R-124  The Access Node MUST NOT allow the sending of Access Node
          Control Messages towards the customer premises.

7. Acknowledgements

The authors would like to thank everyone that has provided comments or input to this document. In particular, the authors acknowledge the work done by the contributors to the activities related to the Broadband Forum: Jerome Moisand, Wojciech Dec, Peter Arberg, and Ole Helleberg Andersen. The authors also acknowledge the inputs provided by Roberta Maglione, Angelo Garofalo, Francois Le Faucheur, and

Toerless Eckert regarding multicast. Finally, the authors thank Bharat Joshi, Stefaan De Cnodder, Kirubaharan Dorairaj, Markus Freudenberger, Fortune Huang, and Lothar Reith for providing comments.

8. References

8.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
   
   [RFC2684]  Grossman, D. and J. Heinanen, "Multiprotocol Encapsulation
              over ATM Adaptation Layer 5", RFC 2684, September 1999.
   
   [RFC5713]  Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security
              Threats and Security Requirements for the Access Node
              Control Protocol (ANCP)", RFC 5713, January 2010.
   
   [RFC894]   Hornig, C., "A Standard for the Transmission of IP
              Datagrams over Ethernet Networks", STD 41, RFC 894,
              April 1984.
   
   [TR-101]   Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL
              Aggregation", Broadband Forum TR-101, May 2006.

8.2. Informative References

   [G.993.2]  ITU-T, "Very high speed digital subscriber line
              transceivers 2 (VDSL2)", ITU-T Rec. G.993.2, Feb 2006.
   
   [G.997.1]  ITU-T, "Physical layer management for digital subscriber
              line (DSL) transceivers", ITU-T Rec. G.997.1, Sep 2005.
   
   [RFC2225]  Laubach, M. and J. Halpern, "Classical IP and ARP over
              ATM", RFC 2225, April 1998.
   
   [RFC2364]  Gross, G., Kaycee, M., Lin, A., Malis, A., and J.
              Stephens, "PPP Over AAL5", RFC 2364, July 1998.
   
   [RFC2516]  Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
              and R. Wheeler, "A Method for Transmitting PPP Over
              Ethernet (PPPoE)", RFC 2516, February 1999.
   
   [RFC2881]  Mitton, D. and M. Beadles, "Network Access Server
              Requirements Next Generation (NASREQNG) NAS Model",
              RFC 2881, July 2000.
   
   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.
   
   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.
   
   [TR-058]   Elias, M. and S. Ooghe, "Multi-Service Architecture &
              Framework Requirements", Broadband Forum TR-058,
              September 2003.
   
   [TR-059]   Anschutz, T., "DSL Evolution - Architecture Requirements
              for the Support of QoS-Enabled IP Services", Broadband
              Forum TR-059, September 2003.
   
   [TR-147]   Voigt, N., Ooghe, S., and M. Platnic, "Layer 2 Control
              Mechanism For Broadband Multi-Service Architectures",
              Broadband Forum TR-147, November 2008.

Authors' Addresses

Sven Ooghe
Alcatel-Lucent
Copernicuslaan 50
B-2018 Antwerpen
Belgium

   Phone: +32 3 240 42 26
   EMail: sven.ooghe@alcatel-lucent.com

Norbert Voigt
Nokia Siemens Networks
Siemensallee 1
17489 Greifswald
Germany

   Phone: +49 3834 555 771
   EMail: norbert.voigt@nsn.com

Michel Platnic
ECI Telecom
30 Hasivim Street
49517 Petakh Tikva
Israel

   Phone: + 972 54 33 81 567
   EMail: mplatnic@gmail.com

Thomas Haag
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
64295 Darmstadt
Germany

   Phone: +49 6151 628 2088
   EMail: haagt@telekom.de

Sanjay Wadhwa
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US

   Phone:
   EMail: swadhwa@juniper.net