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Versions: (draft-ooghe-ancp-framework) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 5851

Network Working Group                                           S. Ooghe
Internet-Draft                                            Alcatel-Lucent
Intended status: Informational                                  N. Voigt
Expires: August 8, 2009                           Nokia Siemens Networks
                                                              M. Platnic
                                                             ECI Telecom
                                                                 T. Haag
                                                        Deutsche Telekom
                                                               S. Wadhwa
                                                        Juniper Networks
                                                        February 4, 2009


   Framework and Requirements for an Access Node Control Mechanism in
                    Broadband Multi-Service Networks
                    draft-ietf-ancp-framework-08.txt

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.
















































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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 QoS-related, service-related and Subscriber-related
   operations.  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 OSS systems.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  6
     1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  General Architecture Aspects . . . . . . . . . . . . . . . . .  8
     2.1.  Concept of an Access Node Control Mechanism  . . . . . . .  8
     2.2.  Reference Architecture . . . . . . . . . . . . . . . . . .  9
       2.2.1.  Home Gateway . . . . . . . . . . . . . . . . . . . . . 10
       2.2.2.  Access Loop  . . . . . . . . . . . . . . . . . . . . . 10
       2.2.3.  Access Node  . . . . . . . . . . . . . . . . . . . . . 10
       2.2.4.  Access Node Uplink . . . . . . . . . . . . . . . . . . 11
       2.2.5.  Aggregation Network  . . . . . . . . . . . . . . . . . 11
       2.2.6.  Network Access Server  . . . . . . . . . . . . . . . . 11
       2.2.7.  Regional Network . . . . . . . . . . . . . . . . . . . 11
     2.3.  Access Node Control Mechanism Transport Methods  . . . . . 12
     2.4.  Operation and Management . . . . . . . . . . . . . . . . . 13
       2.4.1.  Circuit Addressing Scheme  . . . . . . . . . . . . . . 13
   3.  Use Cases for Access Node Control Mechanism  . . . . . . . . . 15
     3.1.  Access Topology Discovery  . . . . . . . . . . . . . . . . 15
     3.2.  Access Loop Configuration  . . . . . . . . . . . . . . . . 17
     3.3.  Remote Connectivity Test . . . . . . . . . . . . . . . . . 18
     3.4.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 19
       3.4.1.  Multicast Conditional Access . . . . . . . . . . . . . 20
       3.4.2.  Multicast Admission Control  . . . . . . . . . . . . . 23
       3.4.3.  Multicast Accounting and Reporting . . . . . . . . . . 27
       3.4.4.  Spontaneous Admission Response . . . . . . . . . . . . 29
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 30
     4.1.  ANCP Functional Requirements . . . . . . . . . . . . . . . 30
     4.2.  ANCP Multicast Requirements  . . . . . . . . . . . . . . . 31
     4.3.  Protocol Design Requirements . . . . . . . . . . . . . . . 32
     4.4.  Access Node Control Adjacency Requirements . . . . . . . . 33
     4.5.  ANCP Transport Requirements  . . . . . . . . . . . . . . . 33



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     4.6.  Access Node Requirements . . . . . . . . . . . . . . . . . 33
       4.6.1.  General Architecture . . . . . . . . . . . . . . . . . 33
       4.6.2.  Control Channel Attributes . . . . . . . . . . . . . . 34
       4.6.3.  Capability Negotiation Failure . . . . . . . . . . . . 35
       4.6.4.  Adjacency Status Reporting . . . . . . . . . . . . . . 35
       4.6.5.  Identification . . . . . . . . . . . . . . . . . . . . 35
       4.6.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . . 35
       4.6.7.  Message Handling . . . . . . . . . . . . . . . . . . . 38
       4.6.8.  Parameter Control  . . . . . . . . . . . . . . . . . . 38
     4.7.  Network Access Server Requirements . . . . . . . . . . . . 38
       4.7.1.  General Architecture . . . . . . . . . . . . . . . . . 38
       4.7.2.  Control Channel Attributes . . . . . . . . . . . . . . 40
       4.7.3.  Capability Negotiation Failure . . . . . . . . . . . . 40
       4.7.4.  Adjacency Status Reporting . . . . . . . . . . . . . . 41
       4.7.5.  Identification . . . . . . . . . . . . . . . . . . . . 41
       4.7.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . . 41
       4.7.7.  Message Handling . . . . . . . . . . . . . . . . . . . 43
       4.7.8.  Wholesale Model  . . . . . . . . . . . . . . . . . . . 43
   5.  Policy Server Interaction  . . . . . . . . . . . . . . . . . . 44
   6.  Management Related Requirements  . . . . . . . . . . . . . . . 45
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 46
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 47
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 48
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 48
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50

























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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).

   Traditional architectures require Permanent Virtual Circuit(s) per
   Subscriber.  Such 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 NAS), without burdening the OSS layer with
   unpractical expectations.

   Therefore, there is a need 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 QoS-related,
   service-related and Subscriber-related operations.  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 OSS systems.

   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]).



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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

   o  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).

   o  Network Access Server (NAS): Network device which aggregates
      multiplexed Subscriber traffic from a number of Access Nodes.  The
      NAS plays a central role in per-subscriber policy enforcement and
      QoS.  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, 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 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.

   o  Line Rate: defined by ITU-T G.993.2.  It contains the complete
      overhead including RS and trellis coding.

   o  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 NASs without using intermediate element managers.

   o  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.

   o  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



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      protocol operation.

   o  Multicast Flow: multicast Any Source Multicast (ASM) group or
      multicast Source Specific Multicast (SSM) (S,G) channel.  An
      application channel (such as a TV channel) is mapped onto a
      Multicast Flow.

   o  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" are indicated through
      "membership report" using different Filter-Mode-Change (ASM) and
      Source-List-Change Records.

   o  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 "IGMPv3 membership report" message using different Filter-
      Mode-Change (ASM) and Source-List-Change Records.































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2.  General Architecture Aspects

   In this section first the concept of the Access Node Control
   Mechanism is described.  Then, the reference architecture is
   described where the Access Node Control Mechanism is introduced.

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-realtime, 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  |---| Aggreg. |---| NAS |---| Network  |
   +-----+   +-----+   |        |   |  Node   |   |     |   |          |
   | CPE |---| HGW |---|        |   +---------+   |     |   |          |
   +-----+   +-----+   +--------+                 +-----+   +----------+
                      Information Report / Admission Request
                            -------------------------->
                       Admission Response / Control Request
                            <--------------------------
                                Control Response
                            -------------------------->

                           Access Node Control Mechanism
                            <------------------------->
                                  PPP, DHCP, IP
     <---------><------------------------------------->

                                 Figure 1

   A number of functions can be identified:

   o  A controller function: this function is used to either 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.



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   o  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.

   o  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 case, 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 required such as to simplify
   specification, implementation, debugging & troubleshooting, but also
   to be easily extensible in order to support additional use cases.

2.2.  Reference Architecture

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

   o  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 Broadband Forum
      [TR-059];

   o  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
      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.







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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 AAL5, defined in [RFC2684].  This covers PPP over
   Ethernet (PPPoE, defined in [RFC2516]), bridged IP (IPoE, defined in
   [RFC894]) and routed IP (IPoA, defined in [RFC2225]).  Next to this,
   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) is a 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).  The AN may support one or more Access
   Loop technologies and allow them to inter-work 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 (PON) 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.






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2.2.4.  Access Node Uplink

   The fundamental requirements for the Access Node uplink are to
   provide traffic aggregation, Class of Service distinction and
   customer separation and traceability.  This can be achieved using an
   ATM or an 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 NAS is a network device which aggregates multiplexed Subscriber
   traffic from a number of Access Nodes.  The NAS plays a central role
   in per-subscriber policy enforcement and QoS.  It is often referred
   to as a Broadband Network Gateway (BNG) or Broadband Remote Access
   Server (BRAS).  A detailed definition of the NAS is given in
   [RFC2881].

   The 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.  GigE, Ethernet
   over SONET).  The NAS functionality correpsonds 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.



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2.3.  Access Node Control Mechanism Transport Methods

   The connectivity between the Access Node and the NAS may differ
   depending on the actual layer 2 technology used (ATM or Ethernet).
   Therefore the identification of unicast & multicast flows/channels
   will also differ (see also Section 2.4.1).

   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 the
   ATM cells carrying the Access Node Control Protocol messages are not
   lost in the event of congestion.  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 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 Class of Service (COS) value) so that the Ethernet
   frames carrying the Access Node Control Protocol messages are not
   lost in the event of 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.  In case the response is



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   negative, the state of the peer must then be rolled back to the state
   prior to the transaction.

2.4.  Operation and Management

   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.  Conflicts therefore need to be avoided.  A
   Policy Server may also be used to coordinate network management
   actions.

   Also, there is a possibility to integrate this with a Policy Server
   such as a AAA/RADIUS server that keeps track of the different
   Subscriber related parameters.  In case a subscriber is connected to
   more than one NAS, a Policy Server can be used to coordinate the
   bandwidth allocated to a given Access Port.

2.4.1.  Circuit 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 & 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:

   o  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;

   o  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.




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   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 on the specific
   interworking function present in the Access Node.  In some cases, no
   PPPoE or DHCP session may be present, while port and circuit
   addressing would still be desirable.













































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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 "Hierarchal 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
   modelling the NAS port, Access Node uplink, and Access Loop sync
   rate.  The rationale for the support of HS is as follows:

   o  Provide fairness of network resources within a class.

   o  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.

   o  Enable more flexible Class of Service (CoS) behaviors other than
      only strict priority.

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

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

   o  Support "per user weighted scheduling" to allow differentiated
      SLAs (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 - hence also the net data
   rate), hence 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 rarely able to enforce in a reliable and scalable
   manner the consistency of such data, notably across organizational
   boundaries.  The Access Topology Discovery function allows the NAS to
   perform these advanced functions without having to depend on an
   error-prone & possibly complex integration with an OSS system.



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   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:

   o  The identification and speed (data rate) of the DSL Access Loop
      (i.e. the net data rate)

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

   The NAS can adjust downstream shaping to current Access Loop actual
   data rate, and more generally re-configure 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)

   o  Actual net data rate (upstream/downstream)

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

   o  Minimum net data rate configured for the Access Loop (upstream/
      downstream)




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   o  Maximum net data rate configured for the Access Loop (upstream/
      downstream)

   o  Minimum net data rate in low power state configured for the Access
      Loop (upstream/downstream)

   o  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.  If a
   Subscriber wants to change its Access Loop rate, this requires an
   OPEX intensive reconfiguration of the Access Port configuration via
   the network operator, possibly implying a business-to-business
   transaction between an Internet Service Provider (ISP) and an Access
   Provider.

   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 Server such as
   a AAA/RADIUS 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.




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   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 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.





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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 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 avoids that several copies of the same stream are 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



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   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



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   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>);

   o  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>);

   Following are some example configurations:

   o  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=*>}

   o  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=*>}




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      *  ==> 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, or
   location based access or to invoke a remote authorisation 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 honored
   (and hence replication performed by the AN) or denied.  This can be
   done with the Admission Request and Admission Response messages.

   Some examples of using NAS querying are the following:

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

   o  A related example is that of mobility or seamless handover; in
      both cases the burden of (re)configuring access nodes with White
      lists or Black lists may be too high;

   o  "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.

   o  "Pay Per View": This is the case when a subscriber chooses a
      specific IPTV channel which is made available for a given amount
      of time.





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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:

   o  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 multicast Admission
      Control check for the new multicast flow and responds to the AN
      indicating whether the join is to be honored (and hence
      replication performed by the AN) or denied.  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



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      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.

   o  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 which 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 which 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.

   o  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;

   o  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



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      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:

   o  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.

   o  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



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   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 (part of the) unused multicast
   bandwidth 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



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   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 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 is 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 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 (as 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:

   o  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



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      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;

   o  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:

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

   o  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 which 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:

   o  No reporting messages need to be sent to the NAS

   o  Basic accounting is required

   o  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



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   reporting functionality could be useful for troubleshooting and
   monitoring purposes.  The NAS can query the AN to know the following:

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

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

   o  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).












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4.  Requirements

4.1.  ANCP Functional Requirements

   o  The ANCP MUST address all use cases described in this document,
      and be general-purpose and extensible enough to foresee additional
      use cases (including the use of other Access Nodes than a DSLAM,
      e.g. a PON Access Node).

   o  The ANCP MUST be flexible enough to accommodate the various
      technologies that can be used in an access network and in the
      Access Node.

   o  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).

   o  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.

   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.

   o  The ANCP MUST allow fast-paced transactions, in order to provide
      real time transactions between a NAS and a fully populated Access
      Node.

   o  The ANCP MUST allow fast completion of a given operation, in the
      order of magnitude of tens of milliseconds.

   o  The ANCP MUST be scalable enough to allow a given NAS to control
      at least 5000 Access Nodes.

   o  The implementation of the ANCP in the NAS and Access Nodes MUST be
      manageable via an element management interface.  This MUST allow
      to retrieve statistics and alarms (e.g. via SNMP) about the
      operation of the ANCP, as well as initiate OAM operations and
      retrieve corresponding results.




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   o  The ANCP SHOULD support a means to handle sending/receiving a
      large burst of messages efficiently.

4.2.  ANCP Multicast Requirements

   o  The ANCP MUST support providing multicast conditional access
      information to Access Ports on an Access Node, using Black, Grey
      and White lists.

   o  The ANCP MUST support binding a particular Black, Grey and White
      List to a given Access Port.

   o  Upon receiving a join to a multicast flow which 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.

   o  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.

   o  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).

   o  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 may be replicated to a particular
      Access Port.

   o  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.

   o  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.

   o  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.

   o  In case of Admission Control with AN Bandwidth Delegation, the
      ANCP must allow the AN to autonomous release redundant multicast
      bandwidth on a given Access Port.



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   o  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 start or ends.

   o  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.

   o  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.

   o  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.

   o  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.

   o  The ANCP MUST support partial updates of the White, Grey and Black
      lists.

   o  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

   o  The ANCP MUST be simple and lightweight enough to allow an
      implementation on Access Nodes with limited control plane
      resources (e.g.  CPU and memory).

   o  The ANCP SHOULD provide a "shutdown" sequence allowing to inform
      the peer that the system is gracefully shutting down.

   o  The ANCP SHOULD include a "report" model for the Access Node to
      spontaneously communicate to the NAS changes of states.

   o  The ANCP SHOULD support a graceful restart mechanism to enable it
      to be resilient to network failures between the AN and NAS.

   o  The ANCP MUST provide a means for the AN and the NAS to perform
      capability negotiation and negotiate a common subset.




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4.4.  Access Node Control Adjacency Requirements

   o  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 detect when they change.

   o  The ANCP MUST include a mechanism to automatically detect
      adjacency loss.

   o  A loss of the Access Node Control Adjacency MUST NOT affect
      subscriber connectivity.

   o  If the Access Node Control Adjacency is lost, it MUST result in
      deterministic behavior on all network elements involved.

   o  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

   o  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.

   o  The ANCP MUST be mapped on top of the IP network layer.

   o  If the layer 2 transport technology is based on ATM, then the
      encapsulation MUST be according to [RFC2684] routed (IPoA).

   o  If the layer 2 transport technology is based on Ethernet, then the
      encapsulation MUST be 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.

4.6.1.  General Architecture

   The Access Node Control Mechanism is defined by a dedicated relation
   between the Access Node (AN) and the NAS.  If one service provider
   has multiple physical NAS devices which represent one logical device
   (single edge architecture), then one AN can be connected to more than
   one NAS.  Therefore the physical AN needs to be split in virtual ANs



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   each having its own Access Node Control reporting and/or enforcement
   function.

   o  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.

   o  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.

   o  Each AN partition must have a separate Access Node Control
      Adjacency to a NAS.

   o  Each AN partition must be able to enforce access of the
      controllers to their designated partitions.

   o  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.

   o  The Control Channel SHOULD use the same facilities as the ones
      used for the data traffic.

   o  The Control Channel MUST be terminated at the Access Node.

   o  The Access Node should process control transactions in a timely
      fashion.

   o  The Access Node should mark Access Node Control Protocol messages
      with a high priority (e.g.  VBR-rt for ATM cells, p-bit 6 or 7 for
      Ethernet packets) in order for the packets not to be dropped in



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      case of congestion.

   o  If ATM interfaces are used then any VPI and VCI value must be able
      to be used for the purpose of supporting the Access Node Control
      Channel.

   o  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

   o  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

   o  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

   o  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.

   o  To allow for correlation in the NAS, the AN must use the same
      Access Circuit Identifier (ACI) format for identifying the AN and
      Access Port in Access Node Control Protocol messages, PPPoE and
      DHCP messages.

4.6.6.  Multicast

   o  The AN must deny any join to a multicast flow matching the Black
      List for the relevant Access Port.

   o  The AN must accept any join to a multicast flow matching the White
      List and for which no Bandwidth Delegation is used.

   o  Upon receiving a join to a multicast flow which 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 taken locally, or querying the NAS or external
      system such as a Policy Server, to request additional delegated



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      multicast bandwidth on a given Access Port.

   o  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.

   o  Upon receiving a join to a multicast flow which 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.

   o  In case of Admission Control with AN Bandwidth Delegation, the AN
      must support using ANCP to notify the NAS when the the user leaves
      the multicast flow.

   o  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.

   o  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.

   o  In case of Admission Control with AN Bandwidth Delegation, it may
      happen that the NAS wants to "revoke" (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).

   o  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.



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   o  If the requested multicast flow is not part of any list associated
      with the Access Port, the AN must discard the message.

   o  If the requested multicast flow is part of multiple lists
      associated with the Access Port, the AN must use the most specific
      match.

   o  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.

   o  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.

   o  Upon querying the NAS, the AN must not propagate the join message
      before the successful authorization from the NAS is received.

   o  Upon receiving a leave for a multicast flow which matches the Grey
      List, the AN should be able to autonomously stop replication and
      advertise this event to the NAS.

   o  The AN must support using ANCP to send an Information Report
      message to the NAS whenever replication starts or ends.

   o  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.

   o  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.

   o  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.

   o  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.

   o  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 on.




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4.6.7.  Message Handling

   o  The Access Node should dampen notifications related to line
      attributes or line state.

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 Densities (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.

   o  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.

   o  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.

4.7.1.  General Architecture

   o  The NAS must establish ANCP Adjacencies only with authorized ANCP
      peers.

   o  The NAS must support the capability to simultaneously run ANCP
      with multiple ANs in a network.

   o  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.

   o  The NAS must support learning of access loop attributes (e.g. net
      data rate), from its peer Access Node partitions via the Access



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      Node Control Mechanism.

   o  The NAS must support shaping traffic directed towards a particular
      access loop to not exceed the net data rate learnt from the AN via
      the Access Node Control Mechanism.

   o  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.

   o  The NAS must support reporting of access loop attributes learned
      via the Access Node Control Mechanism to a Radius server or Policy
      Server using RADIUS VSAs.

   o  The NAS must correlate Access Node Control information with the
      RADIUS authorization process and related subscriber data.

   o  The NAS should support shaping traffic directed towards a
      particular access loop to include layer-1 and layer-2
      encapsulation overhead information received for a specific access
      loop from the AN via the Access Node Control Mechanism.

   o  The NAS should support dynamically configuring and re-configuring
      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.

   o  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.



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      *  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).

   o  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.

   o  The NAS should internally treat Access Node Control traffic in a
      timely and scalable fashion.

   o  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

   o  The NAS must mark Access Node Control Protocol messages as high
      priority (e.g. appropriately set DSCP, Ethernet priority bits or
      ATM 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

   o  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.

   o  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.








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4.7.4.  Adjacency Status Reporting

   o  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

   o  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 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];

      *  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

   o  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.

   o  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).

   o  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 taken locally or querying an external
      system such as a Policy Server.

   o  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



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      must support using ANCP to delegate a certain amount of bandwidth
      to the AN for a given Access Port.

   o  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.

   o  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 decrement of multicast bandwidth
      requested.

   o  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.

   o  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.

   o  The NAS must support using ANCP to incrementally add, remove and
      modify individual entries in White, Black and Grey lists.

   o  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.

   o  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.

   o  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.

   o  The NAS must support using ANCP to query the AN to obtain
      information on what Access Ports are currently receiving a given
      multicast flow.

   o  The NAS must support using ANCP to query the AN to obtain
      information on what multicast flows are currently replicated on
      each Access Port.



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   o  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.

   o  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

   o  The NAS should protect its resources from misbehaved Access Node
      Control peers by providing a mechanism to dampen information
      related to an Access Node partition.

4.7.8.  Wholesale Model

   o  In case of wholesale access, the network provider's NAS should
      support reporting of access loop attributes learned from 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).

   o  In case of 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.

   o  The NAS when acting as a LAC must communicate generic access line
      related information to the LNS in a timely fashion.

   o  The NAS when acting as a LAC may asynchronously notify the LNS of
      updates to generic access line related information.



















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5.  Policy Server Interaction

   This document does not consider the specific details of the
   communication with a Policy Server.















































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6.  Management Related Requirements

   o  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 CBR) for ATM networks or the C-VLAN ID and 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

   o  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.

   o  The Access Node must provide the possibility using SNMP to
      associate individual DSL lines with specific Access Node Control
      Adjacencies.

   o  The Access Node must notify the EMS of configuration changes made
      by the NAS on the AN using ANCP, in a timely manner.

   o  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.

   o  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 which are part of the
      Use Case Access Loop Configuration.

















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7.  Security Considerations

   [draft-ietf-ancp-security-threats] lists the ANCP related security
   threats that could be encountered on the Access Node and the NAS.  It
   develops a threat model 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 attack 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 comparable 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.

   o  The Access Node MUST NOT allow the sending of Access Node Control
      Messages towards the customer premises.





















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8.  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 Broadband Forum related
   activities: 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.








































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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC2225]  Laubach, M. and J. Halpern, "Source-Specific Multicast for
              IP", 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.

   [RFC2684]  Grossman, D. and J. Heinanen, "Multiprotocol Encapsulation
              over ATM Adaptation Layer 5", RFC 2684, September 1999.

   [RFC2881]  Mitton, D. and M. Beadles, "Network Access Server
              Requirements Next Generation (NASREQNG) NAS Model",
              RFC 2881, Jul 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.

   [RFC894]   Hornig, C., "A Standard for the Transmission of IP
              Datagrams over Ethernet Networks", RFC 894, April 1984.

9.2.  Informative References

   [G.997.1]  ITU-T, "Physical layer management for digital subscriber
              line (DSL) transceivers", ITU-T Rec. G.997.1, Sep 2005.

   [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-101]   Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL



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              Aggregation", Broadband Forum TR-101, May 2006.

   [TR-147]   Voigt, N., Ooghe, S., and M. Platnic, "Layer 2 Control
              Mechanism For Broadband Multi-Service Architectures",
              Broadband Forum TR-147, November 2008.

   [draft-ietf-ancp-security-threats]
              Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security
              Threats and Security Requirements for the Access Node
              Control Protocol (ANCP)",
              IETF draft-ietf-ancp-security-threats-06.txt,
              October 2008.







































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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 3 926 85 35
   Email: michel.platnic@ecitele.com


   Thomas Haag
   Deutsche Telekom
   Deutsche Telekom Allee 7
   64295 Darmstadt
   Germany

   Phone: +49 6151 937 5347
   Email: haagt@telekom.de











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

   Phone:
   Email: swadhwa@juniper.net











































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