RFC5851: Framework and Requirements for an Access Node Control Mechanism in Broadband Multi-Service Networks
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Related keywords:
(Access Node)
(Access Node Control Protocol)
(Loop Configuration)
(multicast)
(network access server)
(Remote Connectivity Test)
(Topology Discovery)
Internet Engineering Task Force (IETF) S. Ooghe
Request for Comments: 5851 Alcatel-Lucent
Category: Informational N. Voigt
ISSN: 2070-1721 Nokia Siemens Networks
M. Platnic
ECI Telecom
T. Haag
Deutsche Telekom
S. Wadhwa
Juniper Networks
May 2010
Framework and Requirements for an Access Node Control Mechanism
in Broadband Multi-Service Networks
Abstract
The purpose of this document is to define a framework for an Access
Node Control Mechanism between a Network Access Server (NAS) and an
Access Node (e.g., a Digital Subscriber Line Access Multiplexer
(DSLAM)) in a multi-service reference architecture in order to
perform operations related to service, quality of service, and
subscribers. The Access Node Control Mechanism will ensure that the
transmission of the information does not need to go through distinct
element managers but rather uses a direct device-device
communication. This allows for performing access-link-related
operations within those network elements, while avoiding impact on
the existing Operational Support Systems.
This document first identifies a number of use cases for which the
Access Node Control Mechanism may be appropriate. It then presents
the requirements for the Access Node Control Protocol (ANCP) that
must be taken into account during protocol design. Finally, it
describes requirements for the network elements that need to support
ANCP and the described use cases. These requirements should be seen
as guidelines rather than as absolute requirements. RFC 2119
therefore does not apply to the nodal requirements.
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Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5851.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2. General Architecture Aspects . . . . . . . . . . . . . . . . . 7
2.1. Concept of an Access Node Control Mechanism . . . . . . . 7
2.2. Reference Architecture . . . . . . . . . . . . . . . . . . 8
2.2.1. Home Gateway . . . . . . . . . . . . . . . . . . . . . 9
2.2.2. Access Loop . . . . . . . . . . . . . . . . . . . . . 9
2.2.3. Access Node . . . . . . . . . . . . . . . . . . . . . 9
2.2.4. Access Node Uplink . . . . . . . . . . . . . . . . . . 10
2.2.5. Aggregation Network . . . . . . . . . . . . . . . . . 10
2.2.6. Network Access Server . . . . . . . . . . . . . . . . 10
2.2.7. Regional Network . . . . . . . . . . . . . . . . . . . 10
2.3. Prioritizing Access Node Control Traffic . . . . . . . . . 11
2.4. Interaction with Management Systems . . . . . . . . . . . 12
2.5. Circuit Addressing Scheme . . . . . . . . . . . . . . . . 12
3. Use Cases for Access Node Control Mechanism . . . . . . . . . 13
3.1. Access Topology Discovery . . . . . . . . . . . . . . . . 13
3.2. Access-Loop Configuration . . . . . . . . . . . . . . . . 15
3.3. Remote Connectivity Test . . . . . . . . . . . . . . . . . 16
3.4. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 17
3.4.1. Multicast Conditional Access . . . . . . . . . . . . . 18
3.4.2. Multicast Admission Control . . . . . . . . . . . . . 21
3.4.3. Multicast Accounting and Reporting . . . . . . . . . . 26
3.4.4. Spontaneous Admission Response . . . . . . . . . . . . 27
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1. ANCP Functional Requirements . . . . . . . . . . . . . . . 28
4.2. ANCP Multicast Requirements . . . . . . . . . . . . . . . 29
4.3. Protocol Design Requirements . . . . . . . . . . . . . . . 30
4.4. Access Node Control Adjacency Requirements . . . . . . . . 31
4.5. ANCP Transport Requirements . . . . . . . . . . . . . . . 31
4.6. Access Node Requirements . . . . . . . . . . . . . . . . . 32
4.6.1. General Architecture . . . . . . . . . . . . . . . . . 32
4.6.2. Control Channel Attributes . . . . . . . . . . . . . . 33
4.6.3. Capability Negotiation Failure . . . . . . . . . . . . 33
4.6.4. Adjacency Status Reporting . . . . . . . . . . . . . . 33
4.6.5. Identification . . . . . . . . . . . . . . . . . . . . 34
4.6.6. Multicast . . . . . . . . . . . . . . . . . . . . . . 34
4.6.7. Message Handling . . . . . . . . . . . . . . . . . . . 36
4.6.8. Parameter Control . . . . . . . . . . . . . . . . . . 37
4.7. Network Access Server Requirements . . . . . . . . . . . . 37
4.7.1. General Architecture . . . . . . . . . . . . . . . . . 37
4.7.2. Control Channel Attributes . . . . . . . . . . . . . . 39
4.7.3. Capability Negotiation Failure . . . . . . . . . . . . 39
4.7.4. Adjacency Status Reporting . . . . . . . . . . . . . . 40
4.7.5. Identification . . . . . . . . . . . . . . . . . . . . 40
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4.7.6. Multicast . . . . . . . . . . . . . . . . . . . . . . 40
4.7.7. Message Handling . . . . . . . . . . . . . . . . . . . 42
4.7.8. Wholesale Model . . . . . . . . . . . . . . . . . . . 42
5. Management-Related Requirements . . . . . . . . . . . . . . . 43
6. Security Considerations . . . . . . . . . . . . . . . . . . . 44
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.1. Normative References . . . . . . . . . . . . . . . . . . . 45
8.2. Informative References . . . . . . . . . . . . . . . . . . 45
1. Introduction
Digital Subscriber Line (DSL) technology is widely deployed for
Broadband Access for Next Generation Networks. Several documents
like Broadband Forum TR-058 [TR-058], Broadband Forum TR-059
[TR-059], and Broadband Forum TR-101 [TR-101] describe possible
architectures for these access networks. The scope of these
specifications consists of the delivery of voice, video, and data
services. The framework defined by this document is targeted at DSL-
based access (either by means of ATM/DSL or as Ethernet/DSL). The
framework shall be open to other access technologies, such as Passive
Optical Networks using DSL technology at the Optical Network Unit
(ONU), or wireless technologies like IEEE 802.16. Several use cases
such as Access Topology Discovery, Remote Connectivity Test, and
Multicast may be applied to these access technologies, but the
details of this are outside the scope of this document.
Traditional architectures require Permanent Virtual Circuit(s) per
subscriber. Such a virtual circuit is configured on layer 2 and
terminated at the first layer 3 device (e.g., Broadband Remote Access
Server (BRAS)). Beside the data plane, the models define the
architectures for element, network, and service management.
Interworking at the management plane is not always possible because
of the organizational boundaries between departments operating the
local loop, departments operating the ATM network, and departments
operating the IP network. Besides, management networks are usually
not designed to transmit management data between the different
entities in real time.
When deploying value-added services across DSL access networks,
special attention regarding quality of service and service control is
required, which implies a tighter coordination between Network Nodes
(e.g., Access Nodes and Network Access Server (NAS)), without
burdening the Operational Support System (OSS) with unpractical
expectations.
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Therefore, there is a need for an Access Node Control Mechanism
between a NAS and an Access Node (e.g., a Digital Subscriber Line
Access Multiplexer (DSLAM)) in a multi-service reference architecture
in order to perform operations related to service, quality of
service, and subscribers. The Access Node Control Mechanism will
ensure that the transmission of the information does not need to go
through distinct element managers but rather using a direct device-
device communication. This allows for performing access-link-related
operations within those network elements, while avoiding impact on
the existing OSSes.
This document provides a framework for such an Access Node Control
Mechanism and identifies a number of use cases for which this
mechanism can be justified. Next, it presents a number of
requirements for the Access Node Control Protocol (ANCP) and the
network elements that need to support it.
The requirements spelled out in this document are based on the work
that is performed by the Broadband Forum [TR-147].
1.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Definitions
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 that aggregates
multiplexed subscriber traffic from a number of Access Nodes. The
NAS plays a central role in per-subscriber policy enforcement and
quality of service (QoS). Often referred to as a Broadband
Network Gateway (BNG) or Broadband Remote Access Server (BRAS). A
detailed definition of the NAS is given in [RFC2881].
o "Net Data Rate": defined by ITU-T G.993.2 [G.993.2], section 3.39,
i.e., the portion of the total data rate that can be used to
transmit user information (e.g., ATM cells or Ethernet frames).
It excludes overhead that pertains to the physical transmission
mechanism (e.g., trellis coding in the case of DSL). It includes
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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 Reed-Solomon 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 NASes 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
protocol operation.
o Multicast Flow: designates datagrams sent to a group from a set of
sources for which multicast reception is desired. A distinction
can be made between Any Source Multicast (ASM) and Source-Specific
Multicast (SSM).
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" is 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 the "IGMPv3 membership report" message using different
Filter-Mode-Change (ASM) and Source-List-Change Records.
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2. General Architecture Aspects
This section introduces the basic concept of the Access Node Control
Mechanism and describes the reference architecture where it is being
applied. Based on the reference architecture, the section then
describes how Access Node Control messages are to be prioritized over
other data traffic, and the interaction between ANCP and the network
management system. Finally, the addressing schemes are described
that allow identifying an Access Port in Access Node Control
messages.
2.1. Concept of an Access Node Control Mechanism
The high-level communication framework for an Access Node Control
Mechanism is defined in Figure 1. The Access Node Control Mechanism
defines a quasi-real-time, general-purpose method for multiple
network scenarios with an extensible communication scheme, addressing
the different use cases that are described throughout this document.
+--------+
| Policy |
| Server |
+--------+
|
|
+-----+ +-----+ +--------+ +-----+ +----------+
| CPE |--| HGW |--| | | | | |
+-----+ +-----+ | Access | +-------------+ | | | Regional |
| Node |---| Aggregation |---| NAS |--| Network |
+-----+ +-----+ | | | Network | | | | |
| CPE |--| HGW |--| | +-------------+ | | | |
+-----+ +-----+ +--------+ +-----+ +----------+
Information Report / Admission Request
------------------------------>
Admission Response / Control Request
<------------------------------
Control Response
------------------------------>
Access Node Control Mechanism
<----------------------------->
PPP, DHCP, IP
<---------><----------------------------------------->
CPE: Customer Premises Equipment
HGW: Home Gateway
Figure 1: Access Network Architecture
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A number of functions can be identified:
o A controller function: this function is used either to send out
requests for information to be used by the network element where
the controller function resides, or to trigger a certain behavior
in the network element where the reporting and/or enforcement
function resides.
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 cases, which are
described in Section 3.
The use cases in this document are described in an abstract way,
independent from any actual protocol mapping. The actual protocol
specification is out of scope of this document, but there are certain
characteristics of the protocol that are required to simplify
specification, implementation, debugging and troubleshooting, and to
extend support for additional use cases.
2.2. Reference Architecture
The reference architecture used in this document can be based on ATM
or Ethernet access/aggregation. Specifically:
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 the 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
the Broadband Forum [TR-101].
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Given the industry's move towards Ethernet as the new access and
aggregation technology for triple-play services, the primary focus
throughout this document is on a TR-101 architecture. However the
concepts are equally applicable to an ATM architecture based on TR-
059.
2.2.1. Home Gateway
The Home Gateway (HGW) connects the different Customer Premises
Equipment (CPE) to the Access Node and the access network. In case
of DSL, the HGW is a DSL Network Termination (NT) that could either
operate as a layer 2 bridge or as a layer 3 router. In the latter
case, such a device is also referred to as a Routing Gateway (RG).
2.2.2. Access Loop
The access loop ensures physical connectivity between the HGW at the
customer premises and the Access Node. In case of DSL, the access-
loop physical layer could be, e.g., ADSL, ADSL2+, VDSL, VDSL2, or
SHDSL. In order to increase bandwidth, it is also possible that
multiple DSL links are grouped together to form a single virtual
link; this process is called "DSL bonding". The protocol
encapsulation on the access loop could be based on multi-protocol
encapsulation over ATM Adaption Layer 5 (AAL5) defined in [RFC2684].
This covers PPP over Ethernet (PPPoE, defined in [RFC2516]), bridged
IP (IP over Ethernet (IPoE), defined in [RFC894]) and routed IP (IP
over ATM (IPoA), defined in [RFC2225]). Next to this, PPP over AAL5
(PPPoA) as defined in [RFC2364] can be used. Future scenarios
include cases where the access loop supports direct Ethernet
encapsulation (e.g., when using VDSL or VDSL2).
2.2.3. Access Node
The Access Node (AN) may support one or more access-loop technologies
and allow them to interwork with a common aggregation network
technology. Besides the access-loop termination, the AN can also
aggregate traffic from other Access Nodes using ATM or Ethernet.
The framework defined by this document is targeted at DSL-based
access (either by means of ATM/DSL or as Ethernet/DSL). The
framework shall be open to non-DSL technologies, like Passive Optical
Networks (PONs) and IEEE 802.16 (WiMAX), but the details of this are
outside the scope of this document.
The reporting and/or enforcement function defined in Section 2.1
typically resides in an Access Node.
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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 (CoS) distinction, and
customer separation and traceability. This can be achieved using an
ATM- or Ethernet-based technology.
2.2.5. Aggregation Network
The aggregation network provides traffic aggregation towards the NAS.
The aggregation technology can be based on ATM (in case of a TR-059
architecture) or Ethernet (in case of a TR-101 architecture).
2.2.6. Network Access Server
The Network Access Server (NAS) interfaces to the aggregation network
by means of standard ATM or Ethernet interfaces, and towards the
Regional Network by means of transport interfaces for Ethernet frames
(e.g., Gigabit Ethernet (GigE), Ethernet over Synchronous Optical
Network (SONET)). The NAS functionality corresponds to the BNG
functionality described in Broadband Forum TR-101. In addition to
this, the NAS supports the Access Node Control functionality defined
for the respective use cases throughout this document.
The controller function defined in Section 2.1 typically resides in a
NAS.
2.2.7. Regional Network
The Regional Network connects one or more NAS and associated Access
Networks to Network Service Providers (NSPs) and Application Service
Providers (ASPs). The NSP authenticates access and provides and
manages the IP address to subscribers. It is responsible for overall
service assurance and includes Internet Service Providers (ISPs).
The ASP provides application services to the application subscriber
(gaming, video, content on demand, IP telephony, etc.).
The Regional Network supports aggregation of traffic from multiple
Access Networks and hands off larger geographic locations to NSPs and
ASPs -- relieving a potential requirement for them to build
infrastructure to attach more directly to the various Access
Networks.
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2.3. Prioritizing Access Node Control Traffic
When sending Access Node Control messages across the aggregation
network, care is needed that messages won't get lost. The
connectivity between the Access Node and the NAS may differ depending
on the actual layer 2 technology used (ATM or Ethernet). This
section briefly outlines how network connectivity can be established.
In case of an ATM access/aggregation network, a typical practice is
to send the Access Node Control Protocol messages over a dedicated
Permanent Virtual Circuit (PVC) configured between the AN and the
NAS. These ATM PVCs would then be given a high priority so that at
times of network congestion, loss of the ATM cells carrying the
Access Node Control Protocol is avoided or minimized. It is
discouraged to route the Access Node Control Protocol messages within
the Virtual Path (VP) that also carries the customer connections, if
that VP is configured with a best-effort QoS class (e.g., Unspecified
Bitrate (UBR)). The PVCs of multiple Access Node Control Adjacencies
can be aggregated into a VP that is given a high priority and runs
across the aggregation network. This requires the presence of a VC
cross-connect in the aggregation node that terminates the VP.
In case of an Ethernet access/aggregation network, a typical practice
is to send the Access Node Control Protocol messages over a dedicated
Ethernet Virtual LAN (VLAN) using a separate VLAN identifier (VLAN
ID). This can be achieved using a different VLAN ID for each Access
Node, or, in networks with many Access Nodes and a high degree of
aggregation, one Customer VLAN (C-VLAN) per Access Node and one
Service VLAN (S-VLAN) for the Access Node Control Adjacencies of all
Access Nodes. The traffic should be given a high priority (e.g., by
using a high CoS value) so that the frame loss of Ethernet frames
carrying the Access Node Control Protocol messages is minimized in
the event of network congestion.
In both cases, the Control Channel between NAS and Access Node could
use the same physical network and routing resources as the subscriber
traffic. This means that the connection is an inband connection
between the involved network elements. Therefore, there is no need
for an additional physical interface to establish the Control
Channel.
Note that these methods for transporting Access Node Control Protocol
messages are typical examples; they do not rule out other methods
that achieve the same behavior.
The Access Node Control Adjacency interactions must be reliable. In
addition to this, some of the use cases described in Section 3
require the interactions to be performed in a transactional fashion,
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i.e., using a "request/response" mechanism. This is required so that
the network elements always remain in a known state, irrespective of
whether or not the transaction is successful.
2.4. Interaction with Management Systems
When introducing an Access Node Control Mechanism, care is needed to
ensure that the existing management mechanisms remain operational as
before.
Specifically, when using the Access Node Control Mechanism for
performing a configuration action on a network element, one gets
confronted with the challenge of supporting multiple managers for the
same network element: both the Element Manager as well as the Access
Node Control Mechanism may now perform configuration actions on the
same network element. Therefore, conflicts need to be avoided.
Using the Access Node Control Mechanism, the NAS retrieves and
controls a number of subscriber-related parameters. The NAS may
decide to communicate this information to a central Policy or AAA
Server so that it can keep track of the parameters and apply policies
on them. The Server can then enforce those policies on the NAS. For
instance, in case a subscriber is connected to more than one NAS, the
policy server could be used to coordinate the bandwidth available on
a given Access Port for use amongst the different NAS devices.
Guidelines related to management will be addressed in Section 5.
2.5. Circuit Addressing Scheme
In order to associate subscriber parameters to a particular Access
Port, the NAS needs to be able to uniquely identify the Access Port
(or a specific circuit on an Access Port) using an addressing scheme.
In deployments using an ATM aggregation network, the ATM PVC on an
access loop connects the subscriber to a NAS. Based on this
property, the NAS typically includes a NAS-Port-Id, NAS-Port, or
Calling-Station-Id attribute in RADIUS authentication and accounting
packets sent to the RADIUS server(s). Such attribute includes the
identification of the ATM VC for this subscriber, which allows in
turn identifying the access loop.
In an Ethernet-based aggregation network, a new addressing scheme is
defined in [TR-101]. Two mechanisms can be used:
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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].
This document reuses the addressing scheme specified in TR-101. It
should be noted however that the use of such a scheme does not imply
the actual existence of a PPPoE or DHCP session, nor the presence of
the specific interworking function in the Access Node. In some
cases, no PPPoE or DHCP session may be present, while port and
circuit addressing would still be desirable.
3. Use Cases for Access Node Control Mechanism
3.1. Access Topology Discovery
[TR-059] and [TR-101] discuss various queuing/scheduling mechanisms
to avoid congestion in the access network while dealing with multiple
flows with distinct QoS requirements. One technique that can be used
on a NAS is known as "Hierarchical Scheduling" (HS). This option is
applicable in a single NAS scenario (in which case the NAS manages
all the bandwidth available on the access loop) or in a dual NAS
scenario (in which case the NAS manages some fraction of the access
loop's bandwidth). The HS must, at a minimum, support 3 levels
modeling the NAS port, Access Node uplink, and access-loop sync rate.
The rationale for the support of HS is as follows:
o Provide fairness of network resources within a class.
o Allow for a better utilization of network resources. Drop traffic
early at the NAS rather than letting it traverse the aggregation
network just to be dropped at the Access Node.
o Enable more flexible CoS behaviors 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).
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o Support "per-user weighted scheduling" to allow differentiated
Service Level Agreements (e.g., business services) within a given
traffic class.
Such mechanisms require that the NAS gains knowledge about the
topology of the access network, the various links being used, and
their respective rates. Some of the information required is somewhat
dynamic in nature (e.g., DSL line rate -- thus also the net data
rate); hence, it cannot come from a provisioning and/or inventory
management OSS system. Some of the information varies less
frequently (e.g., capacity of a DSLAM uplink), but nevertheless needs
to be kept strictly in sync between the actual capacity of the uplink
and the image the BRAS has of it.
OSS systems are typically not designed to enforce the consistency of
such data in a reliable and scalable manner across organizational
boundaries. The Access Topology Discovery function is intended to
allow the NAS to perform these functions without having to rely on an
integration with an OSS system.
Communicating access-loop attributes is specifically important in
case the rate of the access loop changes overtime. The DSL actual
data rate may be different every time the DSL NT is turned on. In
this case, the Access Node sends an Information Report message to the
NAS after the DSL line has resynchronized.
Additionally, during the time the DSL NT is active, data rate changes
can occur due to environmental conditions (the DSL access loop can
get "out of sync" and can retrain to a lower value, or the DSL access
loop could use Seamless Rate Adaptation making the actual data rate
fluctuate while the line is active). In this case, the Access Node
sends an additional Information Report to the NAS each time the
access-loop attributes change above a threshold value.
The hierarchy and the rates of the various links to enable the NAS
hierarchical scheduling and policing mechanisms are the following:
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 the Access Loop's current
actual data rate, and more generally reconfigure the appropriate
nodes of its hierarchical scheduler (support of advanced capabilities
according to TR-101).
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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)
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. When a
subscriber wants to change its access-loop rate, the network operator
needs to reconfigure the Access Port configuration, possibly implying
a business-to-business transaction between an Internet Service
Provider (ISP) and an Access Provider. From an Operating
Expenditures (OPEX) perspective this is a costly operation.
Using the Access Node Control Mechanism to change the access-loop
rate from the NAS avoids those cross-organization business-to-
business interactions and allows to centralize subscriber-related
service data in e.g., a policy server. More generally, several
access-loop parameters (e.g., minimum data rate, interleaving delay)
could be changed by means of the Access Node Control Mechanism.
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Triggered by the communication of the access-loop attributes
described in Section 3.1, the NAS could query a Policy or AAA Server
to retrieve access-loop configuration data. The best way to change
access-loop parameters is by using profiles. These profiles (e.g.,
DSL profiles for different services) are pre-configured by the
Element Manager managing the Access Nodes. The NAS may then use the
Configure Request message to send a reference to the right profile to
the Access Node. The NAS may also update the access-loop
configuration due to a subscriber service change (e.g., triggered by
the policy server).
The access-loop configuration mechanism may also be useful for
configuration of parameters that are not specific to the access-loop
technology. Examples include the QoS profile to be used for an
access loop, or the per-subscriber multicast channel entitlement
information, used for IPTV applications where the Access Node is
performing IGMP snooping or IGMP proxy function. The latter is also
discussed in Section 3.4.
It may be possible that a subscriber wants to change its access-loop
rate, and that the operator wants to enforce this updated access-loop
rate on the Access Node using ANCP, but that the Access Node Control
Adjacency is down. In such a case, the NAS will not be able to
request the configuration change on the Access Node. The NAS should
then report this failure to the external management system, which
could use application-specific signaling to notify the subscriber of
the fact that the change could not be performed at this time.
3.3. Remote Connectivity Test
Traditionally, ATM circuits are point-to-point connections between
the BRAS and the DSLAM or DSL NT. In order to test the connectivity
on layer 2, appropriate Operations, Administration, and Maintenance
(OAM) functionality is used for operation and troubleshooting. An
end-to-end OAM loopback is performed between the edge devices (NAS
and HGW) of the broadband access network.
When migrating to an Ethernet-based aggregation network (as defined
by TR-101), end-to-end ATM OAM functionality is no longer applicable.
Ideally in an Ethernet aggregation network, end-to-end Ethernet OAM
(as specified in IEEE 802.1ag and ITU-T Recommendation Y.1730/1731)
can provide access-loop connectivity testing and fault isolation.
However, most HGWs do not yet support these standard Ethernet OAM
procedures. Also, various access technologies exist such as ATM/DSL,
Ethernet in the First Mile (EFM), etc. Each of these access
technologies have their own link-based OAM mechanisms that have been
or are being standardized in different standard bodies.
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In a mixed Ethernet and ATM access network (including the local
loop), it is desirable to keep the same ways to test and troubleshoot
connectivity as those used in an ATM-based architecture. To reach
consistency with the ATM-based approach, an Access Node Control
Mechanism between NAS and Access Node can be used until end-to-end
Ethernet OAM mechanisms are more widely available.
Triggered by a local management interface, the NAS can use the Access
Node Control Mechanism to initiate an access-loop test between Access
Node and HGW. In case of an ATM-based access loop, the Access Node
Control Mechanism can trigger the Access Node to generate ATM (F4/F5)
loopback cells on the access loop. In case of Ethernet, the Access
Node can perform a port synchronization and administrative test for
the access loop. The Access Node can send the result of the test to
the NAS via a Control Response message. The NAS may then send the
result via a local management interface. Thus, the connectivity
between the NAS and the HGW can be monitored by a single trigger
event.
3.4. Multicast
With the rise of supporting IPTV services in a resource efficient
way, multicast services are getting increasingly important.
In case of an ATM access/aggregation network, such as the reference
architecture specified in Broadband Forum [TR-059], multicast traffic
replication is performed in the NAS. In this model, typically IGMP
is used to control the multicast replication process towards the
subscribers. The NAS terminates and processes IGMP signaling
messages sent by the subscribers; towards the Regional Network, the
NAS typically uses a multicast routing protocol such as Protocol
Independent Multicast (PIM). The ATM Access Nodes and aggregation
switches don't perform IGMP processing, nor do they perform multicast
traffic replication. As a result, network resources are wasted
within the access/aggregation network.
To overcome this resource inefficiency, the Access Node, aggregation
node(s), and the NAS must all be involved in the multicast
replication process. This prevents several copies of the same stream
from being sent within the access/aggregation network. In case of an
Ethernet-based access/aggregation network, this may, for example, be
achieved by means of IGMP snooping or IGMP proxy in the Access Node
and aggregation node(s).
By introducing IGMP processing in the access/aggregation nodes, the
multicast replication process is now divided between the NAS, the
aggregation node(s), and Access Nodes. In order to ensure backward
compatibility with the ATM-based model, the NAS, aggregation node,
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and Access Node need to behave as a single logical device. This
logical device must have exactly the same functionality as the NAS in
the ATM access/aggregation network. The Access Node Control
Mechanism can be used to make sure that this logical/functional
equivalence is achieved by exchanging the necessary information
between the Access Node and the NAS.
Another option is for the subscriber to communicate the "join/leave"
information with the NAS. This can for instance be done by
terminating all subscriber IGMP signaling on the NAS. Another
example could be a subscriber using some form of application-level
signaling, which is redirected to the NAS. In any case, this option
is transparent to the access and aggregation network. In this
scenario, the NAS can use ANCP to create replication state in the AN
for efficient multicast replication. The NAS sends a single copy of
the multicast stream towards the AN. The NAS can perform conditional
access and multicast admission control on multicast joins, and create
replication state in the AN if the flow is admitted by the NAS.
The following subsections describe the different use cases related to
multicast.
3.4.1. Multicast Conditional Access
In a DSL broadband access scenario, service providers may want to
dynamically control, at the network level, access to some multicast
flows on a per-user basis. This may be used in order to
differentiate among multiple Service Offers or to realize/reinforce
conditional access for sensitive content. Note that, in some
environments, application-layer conditional access by means of
Digital Rights Management (DRM) may provide sufficient control, so
that Multicast Conditional Access may not be needed.
Where Multicast Conditional Access is required, it is possible, in
some cases, to provision the necessary conditional access information
into the AN so the AN can then perform the conditional access
decisions autonomously. For these cases, the NAS can use ANCP to
provision the necessary information in the AN so that the AN can
decide locally to honor a join or to not honor a join. This can be
done with the Control Request and Control Response messages.
Provisioning the conditional access information on the AN can be done
using a "white list", "grey list", and/or a "black list". A white
list associated with an Access Port identifies the multicast flows
that are allowed to be replicated to that port. A black list
associated with an Access Port identifies the multicast flows that
are not allowed to be replicated to that port. A grey list
associated with an Access Port identifies the multicast flows for
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which the AN on receiving a join message, before starting traffic
replication queries the NAS for further authorization. Each list
contains zero, one, or multiple entries, and each entry may specify a
single flow or contain ranges (i.e., mask on Group address and/or
mask on Source address).
Upon receiving a join message on an Access Port, the Access Node will
first check if the requested multicast flow is part of a white, grey,
or a black list associated with that Access Port. If it is part of a
white list, the AN autonomously starts replicating multicast traffic.
If it is part of a black list, the AN autonomously discards the
message because the request is not authorized, and may thus inform
the NAS and log the request accordingly. If it is part of a grey
list the AN uses ANCP to query the NAS, that in turn will respond to
the AN indicating whether the join is to be honored (and hence
replication performed by the AN) or denied (and hence replication not
performed by the AN).
If the requested multicast flow is part of multiple lists associated
with the Access Port, then the most specific match will be used. If
the most specific match occurs in multiple lists, the black list
entry takes precedence over the grey list, which takes precedence
over the white list.
If the requested multicast flow is not part of any list, the message
should be discarded. This default behavior can easily be changed by
means of a "catch-all" statement in either the white list or the grey
list. For instance, adding (<S=*,G=*>) in the white list would make
the default behavior to accept join messages for a multicast flow
that has no other match on any list. Similarly, if the default
behavior should be to send a request to the NAS, then adding
(<S=*,G=*>) in the grey list accomplishes that.
The white list, black list, and grey list can contain entries
allowing:
o an exact match for a (*,G) ASM group (e.g., <G=g.h.i.l>);
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>);
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The 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=*>}
* ==> Join (S=*,G=Gi) gets honored by AN (1<=i<=n)
* ==> Join (S=s,G=Gm) triggers ANCP Admission Request to NAS
* ==> everything else gets rejected by AN
The use of a white list and black list may be applicable, for
instance, to regular IPTV services (i.e., broadcast TV) offered by an
Access Provider to broadband (e.g., DSL) subscribers. For this
application, the IPTV subscription is typically bound to a specific
DSL line, and the multicast flows that are part of the subscription
are well-known beforehand. Furthermore, changes to the conditional
access information are infrequent, since they are bound to the
subscription. Hence, the Access Node can be provisioned with the
conditional access information related to the IPTV service.
In some other cases, it may be desirable to have the conditional
access decision being taken by the NAS or a Policy Server. This may
be the case when conditional access information changes frequently,
or when the multicast groups are not known to a client application in
advance. The conditional access control could be tied to a more
complex policy/authorization mechanism, e.g., time-of-day access,
location-based access, or to invoke a remote authorization server.
For these cases, the AN can use ANCP to query the NAS that in turn
will respond to the AN indicating whether the join is to be denied or
honored (and hence replication performed by the AN). This can be
done with the Admission Request and Admission Response messages.
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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 Mobility or seamless handover (a related example): in both cases,
the burden of (re)configuring access nodes with white lists or
black lists may be too high;
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": a subscriber chooses a specific IPTV channel which
is made available for a given amount of time.
3.4.2. Multicast Admission Control
The successful delivery of triple-play broadband services is quickly
becoming a big capacity planning challenge for most of the Service
Providers nowadays. Solely increasing available bandwidth is not
always practical, cost-economical, and/or sufficient to satisfy end-
user experience given not only the strict requirements of unicast
delay sensitive applications like VoIP and video, but also the fast
growth of multicast interactive applications such as
videoconferencing, digital TV, digital audio, online movies, and
networked gaming. These applications are typically characterized by
a delay-sensitive nature, an extremely loss-sensitive nature, and
intensive bandwidth requirements. They are also typically "non-
elastic", which means that they operate at a fixed bandwidth that
cannot be dynamically adjusted to the currently available bandwidth.
Therefore, a Connection Admission Control (CAC) mechanism covering
admission of video traffic over the DSL broadband access is required,
in order to avoid oversubscribing the available bandwidth and
negatively impacting the end-user experience.
Considering specifically admission control over the access line,
before honoring a user request to join a new multicast flow, the
combination of AN and NAS must ensure admission control is performed
to validate that there is sufficient bandwidth remaining on the
access line to carry the new video stream (in addition to all other
multicast and unicast video streams sent over the access line). The
solution needs to cope with multiple flows per access line and needs
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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 a multicast Admission
Control check for the new multicast flow and responds to the AN
indicating whether the join is to be denied or honored (and hence
replication performed by the AN). The NAS may locally keep track
of the portion of the access-loop net data rate that is available
for (unicast or multicast) video flows and perform video bandwidth
accounting for the access loop. Upon receiving an Admission
Request from the AN, the NAS can check available access-loop
bandwidth before admitting or denying the multicast flow. In the
process, the NAS may communicate with the policy server. For
unicast video services such as Video on Demand (VoD), the NAS may
also be queried (by a policy server or via on-path CAC signaling),
so that it can perform admission control for the unicast flow and
update the remaining available access-loop bandwidth. The ANCP
requirements to support this approach are specified in this
document.
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 that can be used by the Access Node
for multicast Admission Control. In this model, the NAS or the
policy server manages the total access-line bandwidth, performs
unicast admission control, and uses ANCP to authorize the Access
Node to perform multicast Admission Control within the bounds of
the "delegated bandwidth". Upon receiving a request for a
multicast flow replication that matches an entry in the white or
grey list, the AN performs the necessary bandwidth admission
control check for the new multicast flow, before starting the
multicast flow replication. At this point, there is typically no
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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
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:
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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 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).
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In addition, in some cases, upon receiving a leave for a specific
multicast flow, the AN may decide that it has an excess of delegated
but uncommitted bandwidth. In such case, the AN can use ANCP to send
a message to the NAS to release all of part of the unused multicast
bandwidth that was previously delegated. In this process, the Access
Node may decide to retain a minimum amount of bandwidth for multicast
services.
3.4.2.2. When Not to Perform Admission Control for a Subset of Flows
In general, the Access Node and NAS may not be aware of all possible
multicast groups that will be streamed in the access network. For
instance, it is likely that there will be multicast streams offered
across the Internet. For these unknown streams, performing bandwidth
Admission Control may be challenging.
To solve this, these requests could be accepted without performing
Admission Control. This solution works, provided that the network
handles the streams as best effort, so that other streams (that are
subject to Admission Control) are not impacted at times of
congestion.
Disabling Admission Control for an unknown stream can be achieved by
adding a "catch-all statement" in the Access Node white list or grey
list. In case the Access Node queries the NAS, the NAS on his turn
will have to accept the request. That way, the unknown streams are
not blocked by default.
Next, in order to ensure that the streams are handled as best effort,
the flow must be marked as such when entering the service provider
network. This way, whenever congestion occurs somewhere in the
access/aggregation network, this stream will be kicked out before the
access provider's own premium content.
The above concept is applicable beyond the notion of "Internet
streams" or other unknown streams; it can be applied to known
multicast streams as well. In this case, the Access Node or NAS will
accept the stream even when bandwidth may not be sufficient to
support the stream. This again requires that the stream be marked as
best-effort traffic before entering the access/aggregation network.
3.4.2.3. Multicast Admission Control and White Lists
As mentioned in Section 3.4.1, conditional access to popular IPTV
channels can be achieved by means of a white and black list
configured on the Access Node. This method allows the Access Node to
autonomously decide whether or not access can be granted to a
multicast flow.
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IPTV is an example of a service that will not be offered as best
effort, but requires some level of guaranteed quality of service.
This requires the use of Multicast Admission Control. Hence, if the
Access Node wants to autonomously perform the admission process, it
must be aware of the bandwidth characteristics of multicast flows.
Otherwise, the Access Node would have to query the NAS for Multicast
Admission Control (per the grey list behavior); this would defeat the
purpose of using a white and black list.
Some network deployments may combine the use of white list, black
list, and grey list. The implications of such a model to the overall
Multicast Admission Control model are not fully explored in this
document.
3.4.3. Multicast Accounting and Reporting
It may be desirable to perform time- and/or volume-based accounting
for certain multicast flows sent on particular Access Ports. In case
the AN is performing the traffic replication process, it knows when
replication of a multicast flow to a particular Access Port or user
start and stops. Multicast accounting can be addressed in two ways:
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
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
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for that multicast flow. This is done by adding a byte count in
the Information Report message that is sent to the NAS when
replication ends.
Upon receiving the Information Report messages, the NAS generates the
appropriate time- and/or volume-based accounting records per access
loop and per multicast flow to be sent to the accounting system.
The NAS should inform the Access Node about the type of accounting
needed for a given multicast flow on a particular Access Port:
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
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 a specified multicast flow is 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.
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In both cases, an external entity (for example, a policy server or an
external application entity) can instruct the NAS to interrupt the
multicast replication of a specified multicast flow to a specified
Access Port or user. The NAS can then use ANCP to communicate this
decision to the Access Node. This can be done with the Admission
Response message.
In some deployment scenarios, the NAS may be made aware of end-users'
requests to join/leave a multicast flow by other means than ANCP
Admission Requests sent by the AN. One possible deployment scenario
where this model applies is the case where the Access Node doesn't
process the IGMP join/leave messages from the end-user (e.g., because
they are tunneled), but forwards them to the NAS. In such
environments, the NAS can control multicast replication on the AN via
ANCP through the use of Spontaneous Admission Responses (i.e., sent
by the NAS without prior receipt of a corresponding Admission
Request).
4. Requirements
4.1. ANCP Functional Requirements
R-1 The ANCP MUST be easily extensible through the definition of new
message types or TLVs to support use cases beyond those
currently addressed in this document (this includes the use of
Access Nodes different from a DSLAM, e.g., a PON Access Node).
R-2 The ANCP MUST be flexible enough to accommodate the various
technologies that can be used in an access network and in the
Access Node; this includes both ATM and Ethernet.
R-3 The Access Node Control interactions MUST be reliable (using
either a reliable transport protocol (e.g., TCP) for the Access
Node Control Protocol messages, or by designing ANCP to be
reliable).
R-4 The ANCP MUST support "request/response" transaction-based
interactions for the NAS to communicate control decisions to the
Access Node, or for the NAS to request information from the
Access Node. Transactions MUST be atomic, i.e., they are either
fully completed, or rolled back to the previous state. This is
required so that the network elements always remain in a known
state, irrespective of whether or not the transaction is
successful.
In case the NAS wants to communicate a bulk of independent control
decisions to the Access Node, the transaction (and notion of
atomicity) applies to the individual control decisions. This avoids
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having to roll back all control decisions. Similarly, if the NAS
wants to request a bulk of independent information elements from the
Access Node, the notion of transaction applies to the individual
information elements.
R-5 The ANCP MUST be scalable enough to allow a given NAS to control
at least 5000 Access Nodes.
R-6 The operation of the ANCP in the NAS and Access Nodes MUST be
controllable via a management station (e.g., via SNMP). This
MUST allow a management station to retrieve statistics and
alarms related to the operation of the ANCP, as well as to allow
it to initiate OAM operations and retrieve corresponding
results.
4.2. ANCP Multicast Requirements
R-7 The ANCP MUST support providing multicast conditional access
information to Access Ports on an Access Node, using black,
grey, and white lists.
R-8 The ANCP MUST support binding a particular black, grey, and
white List to a given Access Port.
R-9 Upon receiving a join to a multicast flow that matches the grey
list, the ANCP MUST allow the AN to query the NAS to request an
admission decision for replicating that multicast flow to a
particular Access Port.
R-10 The ANCP MUST allow the NAS to send an admission decision to
the AN indicating whether or not a multicast flow may be
replicated to a particular Access Port.
R-11 The ANCP MUST allow the NAS to indicate to the AN whether or
not Admission Control is needed for some multicast flows on a
given Access Port, and (where needed) whether or not the Access
Node is authorized to perform Admission Control itself (i.e.,
whether or not AN Bandwidth Delegation applies).
R-12 In case of Admission Control without AN Bandwidth Delegation,
the ANCP MUST allow the NAS to reply to a query from the AN
indicating whether or not a multicast flow is allowed to be
replicated to a particular Access Port.
R-13 In case of Admission Control with AN Bandwidth Delegation, the
ANCP MUST allow the NAS to delegate a certain amount of
bandwidth to the AN for a given Access Port for multicast
services only.
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R-14 In case of Admission Control with AN Bandwidth Delegation, the
ANCP MUST allow the AN to query the NAS to request additional
multicast bandwidth on a given Access Port.
R-15 In case of Admission Control with AN Bandwidth Delegation, the
ANCP MUST allow the NAS to query (or to instruct) the AN to
reduce the amount of bandwidth previously delegated on a given
Access Port.
R-16 In case of Admission Control with AN Bandwidth Delegation, the
ANCP MUST allow the AN to inform the NAS if it autonomously
releases redundant multicast bandwidth on a given Access Port.
R-17 The ANCP MUST allow the AN to send an Information Report
message to the NAS whenever replication of a multicast flow on
a particular Access Port starts or ends.
R-18 The ANCP MUST allow the AN to send an Information Report
message to the NAS indicating the multicast traffic volume that
has been replicated on that port.
R-19 The ANCP MUST allow the NAS to indicate to the AN whether or
not multicast accounting is needed for a multicast flow on a
particular Access Port.
R-20 In case multicast accounting is needed for a multicast flow on
a particular Access Port, the ANCP MUST allow the NAS to
indicate to the AN whether or not additional volume accounting
information is required.
R-21 The ANCP MUST allow the NAS to revoke a decision to replicate a
multicast flow to a particular Access Port, which had been
conveyed earlier to an AN.
R-22 The ANCP MUST support partial updates of the white, grey, and
black lists.
R-23 The ANCP MUST allow the NAS to query the AN to obtain
information on what multicast flows are currently being
replicated on a given Access Port, what Access Ports are
currently receiving a given multicast flow, or what multicast
flows are currently replicated on each Access Port.
4.3. Protocol Design Requirements
R-24 The ANCP SHOULD provide a "shutdown" sequence allowing the
protocol to inform the peer that the system is gracefully
shutting down.
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R-25 The ANCP SHOULD include a "report" model for the Access Node to
spontaneously communicate to the NAS changes of states.
R-26 The ANCP SHOULD support a graceful restart mechanism to enable
it to be resilient to network failures between the AN and NAS.
R-27 The ANCP MUST provide a means for the AN and the NAS to inform
each peer about the supported use cases (either use cases
defined in this document or future use cases yet to be
defined), and to negotiate a common subset.
4.4. Access Node Control Adjacency Requirements
The notion of an Access Node Control Adjacency is defined in
Section 1.2.
R-28 The ANCP MUST support an adjacency protocol in order to
automatically synchronize its operational state between its
peers, to agree on which version of the protocol to use, to
discover the identity of its peers, and to detect when they
change.
R-29 The ANCP MUST include a mechanism to automatically detect
adjacency loss.
R-30 A loss of the Access Node Control Adjacency MUST NOT affect
subscriber connectivity.
R-31 If the Access Node Control Adjacency is lost, it MUST leave the
network elements in a known state, irrespective of whether or
not the ongoing transaction was successful.
R-32 The ANCP MUST support a mechanism to synchronize access port
configuration and status information between ANCP peers as part
of establishing or recovering the Access Node Control
Adjacency.
4.5. ANCP Transport Requirements
R-33 The Access Node Control Mechanism MUST be defined in a way that
is independent of the underlying layer 2 transport technology.
Specifically, the Access Node Control Mechanism MUST support
transmission over an ATM as well as over an Ethernet
aggregation network.
R-34 The ANCP MUST use the IP protocol stack.
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R-35 If the layer 2 transport technology is based on ATM, then the
ANCP peers must use the encapsulation according to [RFC2684]
(IPoA).
R-36 If the layer 2 transport technology is based on Ethernet, then
the ANCP peers must use the encapsulation according to [RFC894]
(IPoE).
4.6. Access Node Requirements
This section lists the requirements for an AN that supports the use
cases defined in this document. Note that this document does not
intend to impose absolute requirements on network elements.
Therefore, the words "must" and "should" used in this section are not
capitalized.
4.6.1. General Architecture
The Access Node Control Mechanism is defined to operate between an
Access Node (AN) and a NAS. In some cases, one AN can be connected
to more than one physical NAS device (e.g., in case different
wholesale service providers have different NAS devices). In such a
model, the physical AN needs to be split in virtual ANs, each having
its own Access Node Control reporting and/or enforcement function.
R-37 An Access Node as physical device can be split in logical
partitions. Each partition may have its independent NAS.
Therefore, the Access Node must support at least 2 partitions.
The Access Node should support 8 partitions.
R-38 One partition is grouped of several Access Ports. Each Access
Port on an Access Node must be assigned uniquely to one
partition.
It is assumed that all circuits (i.e., ATM PVCs or Ethernet VLANs) on
top of the same physical Access Port are associated with the same
partition. In other words, partitioning is performed at the level of
the physical Access Port only.
R-39 Each AN partition must have a separate Access Node Control
Adjacency to a NAS.
R-40 Each AN partition must be able to enforce access of the
controllers to their designated partitions.
R-41 The Access Node should be able to establish and maintain ANCP
Adjacencies to redundant controllers.
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4.6.2. Control Channel Attributes
The Control Channel is a bidirectional IP communication interface
between the controller function (in the NAS) and the reporting/
enforcement function (in the AN). It is assumed that this interface
is configured (rather than discovered) on the AN and the NAS.
Depending on the network topology, the Access Node can be located in
a street cabinet or in a central office. If an Access Node in a
street cabinet is connected to a NAS, all user traffic and Access
Node Control data can use the same physical link.
R-42 The Control Channel should use the same facilities as the ones
used for the data traffic. Note that this is actually a
deployment consideration, which has no impact on the actual
protocol design.
R-43 The Access Node must process control transactions in real-time
(i.e., with a specific response latency).
R-44 The Access Node should mark Access Node Control Protocol
messages with a high priority (e.g., Variable Bit Rate - Real
Time (VBR-RT) for ATM cells, p-bit 6 or 7 for Ethernet packets)
in order to avoid or reduce the likelihood of dropping packets
in case of network congestion.
R-45 If ATM interfaces are used, then any Virtual Path Identifier
(VPI) and Virtual Circuit Identifier (VCI) value must be able
to be used for the purpose of supporting the Access Node
Control Channel.
R-46 If Ethernet interfaces are used then any C-VID and S-VID must
be able to be used for the purpose of supporting the Access
Node Control Channel.
4.6.3. Capability Negotiation Failure
R-47 In case the Access Node and NAS cannot agree on a common set of
capabilities, as part of the ANCP capability negotiation
procedure, the Access Node must report this to network
management.
4.6.4. Adjacency Status Reporting
R-48 The Access Node should support generating an alarm to a
management station upon loss or malfunctioning of the Access
Node Control Adjacency with the NAS.
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4.6.5. Identification
R-49 To identify the Access Node and Access Port within a control
domain, a unique identifier is required. This identifier must
be in line with the addressing scheme principles specified in
Section 3.9.3 of TR-101.
R-50 In a Broadband Forum TR-101 network architecture, an Access
Circuit Identifier (ACI) identifying an AN and Access Port is
added to DHCP and PPPoE messages. The NAS must use the same
ACI format in ANCP messages in order to allow the NAS to
correlate this information with the information present in DHCP
and PPPoE messages.
4.6.6. Multicast
R-51 The AN must deny any join to a multicast flow matching the
black list for the relevant Access Port.
R-52 The AN must accept any join to a multicast flow matching the
white list and for which no Bandwidth Delegation is used.
R-53 Upon receiving a join to a multicast flow that matches the
white list and for which Bandwidth Delegation is used, the AN
must perform the necessary bandwidth admission control check
for the new flow before starting the multicast flow
replication. This may involve a decision made locally, or
querying the NAS or external system such as a policy server, to
request additional delegated multicast bandwidth on a given
Access Port.
R-54 Upon receiving a join to a multicast flow which matches the
grey list and for which no Bandwidth Delegation is used, the AN
must support using ANCP to query the NAS to receive a response
indicating whether that join is to be honored or denied. In
this case, the NAS will perform both the necessary conditional
access and the admission control checks for the new flow.
R-55 Upon receiving a join to a multicast flow that matches the grey
list and for which Bandwidth Delegation is used, the AN must
first perform the necessary bandwidth admission control check
for the new flow. If successful, the AN must support using
ANCP to query the NAS to receive a response indicating whether
that join is to be honored or denied.
R-56 In case of Admission Control with AN Bandwidth Delegation, the
AN must support using ANCP to notify the NAS when the user
leaves the multicast flow.
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R-57 In case of Admission Control with AN Bandwidth Delegation, the
AN must support using ANCP to query the NAS to request
additional delegated multicast bandwidth on a given Access
Port; the AN should be able to specify both the minimum and the
preferred amount of additional multicast bandwidth requested.
R-58 In case of Admission Control with AN Bandwidth Delegation, upon
receiving a Bandwidth Delegation Request from the NAS querying
the AN for the delegated multicast bandwidth on a given Access
Port, the AN must support using ANCP to send a Bandwidth
Delegation Response, indicating the currently delegated
multicast bandwidth.
R-59 In case of Admission Control with AN Bandwidth Delegation, it
may happen that the NAS wants to "revoke" all or part of the
delegated bandwidth. Part of the previously delegated
bandwidth may however be in use by multicast services.
Therefore, upon receiving a Bandwidth Delegation Request from
the NAS instructing to decrease the delegated multicast
bandwidth on a given Access Port, the AN must support using
ANCP to send a Bandwidth Delegation Response, indicating the
delegated multicast bandwidth after the decrease (indicating
how much of the delegated bandwidth can be returned to the NAS
without impacting multicast services that are currently
running).
R-60 In case of Admission Control with AN Bandwidth Delegation, the
AN must support using ANCP to send a Bandwidth Release message
to the NAS in order to release unused delegated multicast
bandwidth on a given Access Port.
R-61 If the requested multicast flow is not part of any list
associated with the Access Port, the AN must discard the
message.
R-62 If the requested multicast flow is part of multiple lists
associated with the Access Port, the AN must use the most
specific match.
R-63 If the requested multicast flow has the same most specific
match in multiple lists, the AN must give precedence to the
black list, followed by the grey list, and then the white list.
R-64 The AN must support configuring a "catch-all" statement in the
black, white, or grey list in order to enforce a default
behavior for a join to a multicast flow which doesn't match any
other entry in a list for the relevant Access Port.
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R-65 Upon querying the NAS, the AN must not propagate the join
message before the successful authorization from the NAS is
received.
R-66 Upon receiving a leave for a multicast flow that matches the
grey list, the AN should be able to autonomously stop
replication and advertise this event to the NAS.
R-67 The AN must support using ANCP to send an Information Report
message to the NAS whenever replication starts or ends.
R-68 The AN should support using ANCP to send an Information Report
message to the NAS indicating the multicast traffic volume that
has been replicated on that port.
R-69 Upon request by the NAS, the AN must support using ANCP to send
an Information Report message to the NAS, indicating what
multicast flows are currently being replicated on a given
Access Port.
R-70 Upon request by the NAS, the AN must support using ANCP to send
an Information Report message to the NAS, indicating what
Access Ports are currently receiving a given multicast flow.
R-71 Upon request by the NAS, the AN must support using ANCP to send
an Information Report message to the NAS, indicating what
multicast flows are currently being replicated on each Access
Port.
R-72 Upon receiving an Admission Response from the NAS, indicating
that replication of a multicast flow is to start or stop on a
given access port of the AN, the AN must enforce this decision.
This decision must be taken irrespective of whether or not a
corresponding Admission Request was issued by the AN earlier.
4.6.7. Message Handling
R-73 The Access Node must be designed to allow fast completion of
ANCP operations, in the order of magnitude of tens of
milliseconds.
R-74 The Access Node should avoid sending bursts of ANCP messages
related to notification of line attributes or line state, by
spreading message transmission over time.
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4.6.8. Parameter Control
Naturally, the Access Node Control Mechanism is not designed to
replace an Element Manager managing the Access Node. There are
parameters in the Access Node, such as the DSL noise margin and DSL
Power Spectral Density (PSD), which are not allowed to be changed via
ANCP or any other control session, but only via the Element Manager.
This has to be ensured and protected by the Access Node.
When using ANCP for access-loop configuration, the EMS needs to
configure on the Access Node which parameters may or may not be
modified using the Access Node Control Mechanism. Furthermore, for
those parameters that may be modified using ANCP, the EMS needs to
specify the default values to be used when an Access Node comes up
after recovery.
R-75 When access-loop configuration via ANCP is required, the EMS
must configure on the Access Node which parameter set(s) may be
changed/controlled using ANCP.
R-76 Upon receiving an Access Node Control Request message, the
Access Node must not apply changes to the parameter set(s) that
have not been enabled by the EMS.
4.7. Network Access Server Requirements
This section lists the requirements for a NAS that supports the use
cases defined in this document. Note that this document does not
intend to impose absolute requirements on network elements.
Therefore, the words "must" and "should" used in this section are not
capitalized.
4.7.1. General Architecture
R-77 The NAS must establish ANCP Adjacencies only with authorized
ANCP peers.
R-78 The NAS must support the capability to simultaneously run ANCP
with multiple ANs in a network.
R-79 The NAS must be able to establish an Access Node Control
Adjacency to a particular partition on an AN and control the
access loops belonging to such a partition.
R-80 The NAS must support obtaining access-loop information (e.g.,
net data rate), from its peer Access Node partitions via the
Access Node Control Mechanism.
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R-81 The NAS must support shaping traffic directed towards a
particular access loop to not exceed the net data rate learned
from the AN via the Access Node Control Mechanism.
R-82 The NAS should support reducing or disabling the shaping limit
used in the Hierarchical Scheduling process, according to per-
subscriber authorization data retrieved from a AAA or policy
server.
R-83 The NAS must support reporting of access-loop attributes
learned via the Access Node Control Mechanism to a Policy or
AAA Server using RADIUS Vendor-Specific Attributes (VSAs).
R-84 In a TR-059/TR-101 network architecture, the NAS shapes traffic
sent to a particular Access Port according to the bitrate
available on that port. The NAS should take into account the
layer 1 and layer 2 encapsulation overhead on the Access Port,
retrieved from the AN via the Access Node Control Mechanism.
R-85 The NAS should support dynamically configuring and
reconfiguring discrete service parameters for access loops that
are controlled by the NAS. The configurable service parameters
for access loops could be driven by local configuration on the
NAS or by a policy server.
R-86 The NAS should support triggering an AN via the Access Node
Control Mechanism to execute local OAM procedures on an access
loop that is controlled by the NAS. If the NAS supports this
capability, then the following applies:
* The NAS must identify the access loop on which OAM
procedures need to be executed by specifying an Access
Circuit Identifier (ACI) in the request message to the AN.
* The NAS should support processing and reporting of the
remote OAM results learned via the Access Node Control
Mechanism.
* As part of the parameters conveyed within the OAM message to
the AN, the NAS should send the list of test parameters
pertinent to the OAM procedure. The AN will then execute
the OAM procedure on the specified access loop according to
the specified parameters. In case no test parameters are
conveyed, the AN and NAS must use default and/or
appropriately computed values.
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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).
R-87 The NAS must treat PPP or DHCP session state independently from
any Access Node Control Adjacency state. The NAS must not
bring down the PPP or DHCP sessions just because the Access
Node Control Adjacency goes down.
R-88 The NAS should internally treat Access Node Control traffic in
a timely and scalable fashion.
R-89 The NAS should support protection of Access Node Control
communication to an Access Node in case of line card failure.
4.7.2. Control Channel Attributes
R-90 The NAS must mark Access Node Control Protocol messages as high
priority (e.g., appropriately set Diffserv Code Point (DSCP),
Ethernet priority bits, or ATM Cell Loss Priority (CLP) bit)
such that the aggregation network between the NAS and the AN
can prioritize the Access Node Control Protocol messages over
user traffic in case of congestion.
4.7.3. Capability Negotiation Failure
R-91 In case the NAS and Access Node cannot agree on a common set of
capabilities, as part of the ANCP capability negotiation
procedure, the NAS must report this to network management.
R-92 The NAS must only commence Access Node Control information
exchange and state synchronization with the AN when there is a
non-empty common set of capabilities with that AN.
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4.7.4. Adjacency Status Reporting
R-93 The NAS must support generating an alarm to a management
station upon loss or malfunctioning of the Access Node Control
Adjacency with the Access Node.
4.7.5. Identification
R-94 The NAS must support correlating Access Node Control Protocol
messages pertaining to a given access loop with subscriber
session(s) over that access loop. This correlation must be
achieved by either:
* Matching an Access Circuit Identifier (ACI) inserted by the
AN in Access Node Control Protocol messages with the
corresponding ACI value received in subscriber signaling
(e.g., PPPoE and DHCP) messages as inserted by the AN. The
format of ACI is defined in [TR-101]; or
* Matching an ACI inserted by the AN in Access Node Control
Protocol messages with an ACI value locally configured for a
static subscriber on the NAS.
4.7.6. Multicast
R-95 The NAS must support using ANCP to configure multicast
conditional access information to Access Ports on an Access
Node, using black lists, grey lists, and white lists.
R-96 The NAS must support using ANCP to indicate to the AN whether
or not Admission Control is needed for some multicast flows on
a given Access Port and where needed whether or not the Access
Node is authorized to perform Admission Control itself (i.e.,
whether or not AN Bandwidth Delegation applies).
R-97 Upon receiving a query from the AN for a request to replicate
a multicast flow to a particular Access Port, and no AN
Bandwidth Delegation is used for that flow, the NAS must be
able to perform the necessary checks (conditional access
and/or admission control) for the new flow. The NAS must
support using ANCP to reply to the AN indicating whether the
request is to be honored or denied. This may involve a
decision made locally or querying an external system such as a
policy server.
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R-98 Upon receiving a query from the AN for a request to replicate
a multicast flow to a particular Access Port, and Admission
Control with AN Bandwidth Delegation is used for that flow,
the NAS must be able to perform the conditional access checks
(if needed), and must support using ANCP to delegate a certain
amount of bandwidth to the AN for a given Access Port.
R-99 In case of Admission Control with AN Bandwidth Delegation,
upon receiving a Bandwidth Delegation Request from the AN
requesting to increase the delegated multicast bandwidth on a
given Access Port, the NAS must support using ANCP to send a
Bandwidth Delegation Response indicating the new delegating
multicast bandwidth.
R-100 In case of Admission Control with AN Bandwidth Delegation, the
NAS must support using ANCP to send a request to the AN to
decrease the amount of multicast bandwidth previously
delegated on a given Access Port; the NAS should be able to
specify both the minimum and the preferred amount of decrement
of multicast bandwidth requested.
R-101 In case of Admission Control with AN Bandwidth Delegation,
upon receiving an ANCP Bandwidth Release message, the NAS must
be able to update accordingly its view of the multicast
bandwidth delegated to the AN.
R-102 The NAS must support using ANCP to configure the Access Node
with the "maximum number of multicast streams" allowed to be
received concurrently per Access Port.
R-103 The NAS must support using ANCP to incrementally add, remove,
and modify individual entries in white, black, and grey lists.
R-104 The NAS must support using ANCP to indicate to the AN whether
or not multicast accounting is needed for a multicast flow on
a particular Access Port.
R-105 In case multicast accounting is needed for a multicast flow on
a particular Access Port, the NAS should support using ANCP to
indicate to the AN whether or not additional volume accounting
information is required.
R-106 The NAS must support using ANCP to query the AN to obtain
information on what multicast flows are currently replicated
on a given Access Port.
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R-107 The NAS must support using ANCP to query the AN to obtain
information on what Access Ports are currently receiving a
given multicast flow.
R-108 The NAS must support using ANCP to query the AN to obtain
information on what multicast flows are currently replicated
on each Access Port.
R-109 When Multicast replication occurs on the AN, the NAS must
support using ANCP to revoke the authorization to replicate a
multicast flow to a particular Access Port.
R-110 The NAS should support using ANCP to indicate to the AN that
replication of a multicast flow is to start or stop on a given
access port of the AN, without having received a corresponding
Admission Request from the AN earlier on.
4.7.7. Message Handling
R-111 The NAS must be designed to allow fast completion of ANCP
operations, in the order of magnitude of tens of milliseconds.
R-112 The NAS should protect its resources from misbehaving Access
Node Control peers by providing a mechanism to dampen
information related to an Access Node partition.
4.7.8. Wholesale Model
Broadband Forum TR-058 [TR-058], Broadband Forum TR-059 [TR-059], and
Broadband Forum TR-101 [TR-101] describe a DSL broadband access
architecture and how it enables wholesaling. In such a model, the
broadband access provider has a wholesale agreement with one or more
service providers. The access provider owns the broadband access
network and manages connectivity to the service providers. This
allows service providers to provide broadband services to retail
customers without having to own the access network infrastructure
itself.
When applying the Access Node Control Mechanism to a wholesale
network architecture, a number of additional requirements apply.
R-113 In case of wholesale access, the network provider's NAS should
support reporting of access-loop attributes learned from the
AN via the Access Node Control Mechanism (or values derived
from such attributes), to a retail provider's network gateway
owning the corresponding subscriber(s).
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R-114 In case of Layer 2 Tunneling Protocol (L2TP) wholesale, the
NAS must support a proxy architecture that gives different
providers conditional access to dedicated Access Node Control
resources on an Access Node.
R-115 The NAS when acting as an L2TP Access Concentrator (LAC) must
communicate generic access-line-related information to the
L2TP Network Server (LNS) in a timely fashion.
R-116 The NAS when acting as a LAC may asynchronously notify the LNS
of updates to generic access-line-related information.
5. Management-Related Requirements
This section lists the management-related requirements for the AN and
NAS. Note that this document does not intend to impose absolute
requirements on network elements. Therefore, the words "must" and
"should" used in this section are not capitalized.
R-117 It must be possible to configure the following parameters on
the Access Node and the NAS:
* Parameters related to the Control Channel transport method:
these include the VPI/VCI and transport characteristics
(e.g., VBR-RT or Constant Bitrate (CBR)) for ATM networks,
or the C-VLAN ID, S-VLAN ID, and p-bit marking for Ethernet
networks;
* Parameters related to the Control Channel itself: these
include the IP address of the IP interface on the Access
Node and the NAS.
R-118 When the operational status of the Control Channel is changed
(up>down, down>up) a linkdown/linkup trap should be sent
towards the EMS. This requirement applies to both the AN and
the NAS.
R-119 The Access Node must provide the possibility using SNMP to
associate individual DSL lines with specific Access Node
Control Adjacencies.
R-120 The Access Node must notify the EMS of configuration changes
made by the NAS on the AN using ANCP, in a timely manner.
R-121 The Access Node must provide a mechanism that allows the
concurrent access on the same resource from several managers
(EMS via SNMP, NAS via ANCP). Only one manager may perform a
change at a certain time.
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R-122 The ANCP may provide a notification mechanism to inform the
NAS about configuration changes done by an EMS, in a timely
manner. This applies only to changes of parameters that are
part of the use case "Access-Loop Configuration"
(Section 3.2).
6. Security Considerations
[RFC5713] lists the ANCP-related security threats that could be
encountered on the Access Node and the NAS. It develops a threat
model and identifies requirements for ANCP security, aiming to decide
which security functions are required at the ANCP level.
With multicast handling as described in this document, ANCP protocol
activity between the AN and the NAS is triggered by join/leave
requests coming from the end-user equipment. This could potentially
be used for denial-of-service attacks against the AN and/or the NAS.
This is not a new class of risk over already possible IGMP messages
sent from subscribers to the NAS when the AN uses no IGMP snooping,
and thus is transparent as long as processing of ANCP messages on the
NAS/AN is comparably efficient and protected against congestion.
To mitigate this risk, the AN MAY implement control-plane protection
mechanisms such as limiting the number of multicast flows a given
user can simultaneously join, or limiting the maximum rate of join/
leave from a given user.
We also observe that an operator can easily deploy some protection
against attacks using invalid multicast flows by taking advantage of
the mask-based match in the black list. This way, joins for invalid
multicast flows can be denied at the AN level without any ANCP
protocol interactions and without NAS involvement.
R-123 The ANCP MUST comply with the security requirements spelled
out in RFC 5713.
R-124 The Access Node MUST NOT allow the sending of Access Node
Control Messages towards the customer premises.
7. Acknowledgements
The authors would like to thank everyone that has provided comments
or input to this document. In particular, the authors acknowledge
the work done by the contributors to the activities related to the
Broadband Forum: Jerome Moisand, Wojciech Dec, Peter Arberg, and Ole
Helleberg Andersen. The authors also acknowledge the inputs provided
by Roberta Maglione, Angelo Garofalo, Francois Le Faucheur, and
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RFC 5851 ANCP Framework May 2010
Toerless Eckert regarding multicast. Finally, the authors thank
Bharat Joshi, Stefaan De Cnodder, Kirubaharan Dorairaj, Markus
Freudenberger, Fortune Huang, and Lothar Reith for providing
comments.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2684] Grossman, D. and J. Heinanen, "Multiprotocol Encapsulation
over ATM Adaptation Layer 5", RFC 2684, September 1999.
[RFC5713] Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security
Threats and Security Requirements for the Access Node
Control Protocol (ANCP)", RFC 5713, January 2010.
[RFC894] Hornig, C., "A Standard for the Transmission of IP
Datagrams over Ethernet Networks", STD 41, RFC 894,
April 1984.
[TR-101] Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL
Aggregation", Broadband Forum TR-101, May 2006.
8.2. Informative References
[G.993.2] ITU-T, "Very high speed digital subscriber line
transceivers 2 (VDSL2)", ITU-T Rec. G.993.2, Feb 2006.
[G.997.1] ITU-T, "Physical layer management for digital subscriber
line (DSL) transceivers", ITU-T Rec. G.997.1, Sep 2005.
[RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over
ATM", RFC 2225, April 1998.
[RFC2364] Gross, G., Kaycee, M., Lin, A., Malis, A., and J.
Stephens, "PPP Over AAL5", RFC 2364, July 1998.
[RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
and R. Wheeler, "A Method for Transmitting PPP Over
Ethernet (PPPoE)", RFC 2516, February 1999.
[RFC2881] Mitton, D. and M. Beadles, "Network Access Server
Requirements Next Generation (NASREQNG) NAS Model",
RFC 2881, July 2000.
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RFC 5851 ANCP Framework May 2010
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[TR-058] Elias, M. and S. Ooghe, "Multi-Service Architecture &
Framework Requirements", Broadband Forum TR-058,
September 2003.
[TR-059] Anschutz, T., "DSL Evolution - Architecture Requirements
for the Support of QoS-Enabled IP Services", Broadband
Forum TR-059, September 2003.
[TR-147] Voigt, N., Ooghe, S., and M. Platnic, "Layer 2 Control
Mechanism For Broadband Multi-Service Architectures",
Broadband Forum TR-147, November 2008.
Authors' Addresses
Sven Ooghe
Alcatel-Lucent
Copernicuslaan 50
B-2018 Antwerpen
Belgium
Phone: +32 3 240 42 26
EMail: sven.ooghe@alcatel-lucent.com
Norbert Voigt
Nokia Siemens Networks
Siemensallee 1
17489 Greifswald
Germany
Phone: +49 3834 555 771
EMail: norbert.voigt@nsn.com
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RFC 5851 ANCP Framework May 2010
Michel Platnic
ECI Telecom
30 Hasivim Street
49517 Petakh Tikva
Israel
Phone: + 972 54 33 81 567
EMail: mplatnic@gmail.com
Thomas Haag
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
64295 Darmstadt
Germany
Phone: +49 6151 628 2088
EMail: haagt@telekom.de
Sanjay Wadhwa
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US
Phone:
EMail: swadhwa@juniper.net
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