Network Working Group S. Ooghe
Internet-Draft Alcatel-Lucent
Intended status: Informational N. Voigt
Expires: May 18, 2008 Nokia Siemens Networks
M. Platnic
ECI Telecom
T. Haag
T-Systems
S. Wadhwa
Juniper Networks
November 15, 2007
Framework and Requirements for an Access Node Control Mechanism in
Broadband Multi-Service Networks
draft-ietf-ancp-framework-04.txt
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Abstract
The purpose of this document is to define a framework for an Access
Node Control Mechanism between a Network Access Server (NAS) and an
Access Node (e.g. a Digital Subscriber Line Access Multiplexer
(DSLAM)) in a multi-service reference architecture in order to
perform QoS-related, service-related and Subscriber-related
operations. The Access Node Control Mechanism will ensure that the
transmission of the information does not need to go through distinct
element managers but rather using a direct device-device
communication. This allows for performing access link related
operations within those network elements, while avoiding impact on
the existing OSS systems.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 8
2.2.2. Access Loop . . . . . . . . . . . . . . . . . . . . . 9
2.2.3. Access Node . . . . . . . . . . . . . . . . . . . . . 9
2.2.4. Access Node Uplink . . . . . . . . . . . . . . . . . . 9
2.2.5. Aggregation Network . . . . . . . . . . . . . . . . . 10
2.2.6. Network Access Server . . . . . . . . . . . . . . . . 10
2.2.7. Regional Network . . . . . . . . . . . . . . . . . . . 10
2.3. Access Node Control Mechanism Transport Methods . . . . . 10
2.4. Operation and Management . . . . . . . . . . . . . . . . . 11
2.4.1. 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 . . . . . . . . . . . . . 17
3.4.2. Multicast Admission Control . . . . . . . . . . . . . 20
3.4.3. Multicast Accounting . . . . . . . . . . . . . . . . . 21
3.4.4. Multicast Termination . . . . . . . . . . . . . . . . 22
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. ANCP Functional Requirements . . . . . . . . . . . . . . . 23
4.2. ANCP Multicast Requirements . . . . . . . . . . . . . . . 24
4.3. ANCP Security Requirements . . . . . . . . . . . . . . . . 25
4.4. Protocol Design Requirements . . . . . . . . . . . . . . . 25
4.5. Access Node Control Adjacency Requirements . . . . . . . . 25
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4.6. ANCP Transport Requirements . . . . . . . . . . . . . . . 26
4.7. Access Node Requirements . . . . . . . . . . . . . . . . . 26
4.7.1. General Architecture . . . . . . . . . . . . . . . . . 26
4.7.2. Control Channel Attributes . . . . . . . . . . . . . . 27
4.7.3. Capability Negotiation Failure . . . . . . . . . . . . 27
4.7.4. Adjacency Status Reporting . . . . . . . . . . . . . . 28
4.7.5. Identification . . . . . . . . . . . . . . . . . . . . 28
4.7.6. Multicast . . . . . . . . . . . . . . . . . . . . . . 28
4.7.7. Message Handling . . . . . . . . . . . . . . . . . . . 29
4.7.8. Parameter Control . . . . . . . . . . . . . . . . . . 29
4.7.9. Security . . . . . . . . . . . . . . . . . . . . . . . 29
4.8. Network Access Server Requirements . . . . . . . . . . . . 29
4.8.1. General Architecture . . . . . . . . . . . . . . . . . 29
4.8.2. Control Channel Attributes . . . . . . . . . . . . . . 31
4.8.3. Capability Negotiation Failure . . . . . . . . . . . . 31
4.8.4. Adjacency Status Reporting . . . . . . . . . . . . . . 32
4.8.5. Identification . . . . . . . . . . . . . . . . . . . . 32
4.8.6. Multicast . . . . . . . . . . . . . . . . . . . . . . 32
4.8.7. Message Handling . . . . . . . . . . . . . . . . . . . 33
4.8.8. Wholesale Model . . . . . . . . . . . . . . . . . . . 33
4.8.9. Security . . . . . . . . . . . . . . . . . . . . . . . 33
5. Policy Server Interaction . . . . . . . . . . . . . . . . . . 34
6. Management Related Requirements . . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 37
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.1. Normative References . . . . . . . . . . . . . . . . . . . 38
9.2. Informative References . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . . . . 41
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1. Introduction
Digital Subscriber Line (DSL) technology is widely deployed for
Broadband Access for Next Generation Networks. Several documents
like DSL Forum TR-058 [TR-058], DSL Forum TR-059 [TR-059] and DSL
Forum TR-101 [TR-101] describe possible architectures for these
access networks. The scope of these specifications consists of the
delivery of voice, video and data services. The framework defined by
this document is targeted at DSL-based access (either by means of
ATM/DSL or as Ethernet/DSL).
Traditional architectures require Permanent Virtual Circuit(s) per
Subscriber. Such virtual circuit is configured on layer 2 and
terminated at the first layer 3 device (e.g. Broadband Remote Access
Server (BRAS)). Beside the data plane, the models define the
architectures for element, network and service management.
Interworking at the management plane is not always possible because
of the organizational boundaries between departments operating the
local loop, departments operating the ATM network and departments
operating the IP network. Besides, management networks are usually
not designed to transmit management data between the different
entities in real time.
When deploying value-added services across DSL access networks,
special attention regarding quality of service and service control is
required, which implies a tighter coordination between Network Nodes
(e.g. Access Nodes and NAS), without burdening the OSS layer with
unpractical expectations.
Therefore, there is a need for an Access Node Control Mechanism
between a Network Access Server (NAS) and an Access Node (e.g. a
Digital Subscriber Line Access Multiplexer (DSLAM)) in a multi-
service reference architecture in order to perform QoS-related,
service-related and Subscriber-related operations. The Access Node
Control Mechanism will ensure that the transmission of the
information does not need to go through distinct element managers but
rather using a direct device-device communication. This allows for
performing access link related operations within those network
elements, while avoiding impact on the existing OSS systems.
This document provides a framework for such an Access Node Control
Mechanism and identifies a number of use cases for which this
mechanism can be justified. Next, it presents a number of
requirements for the Access Node Control Protocol (ANCP) and the
network elements that need to support it.
The requirements spelled out in this document are based on the work
that is performed by the DSL Forum ([WT-147]).
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1.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Definitions
o Access Node (AN): Network device, usually located at a service
provider central office or street cabinet, that terminates Access
Loop connections from Subscribers. In case the Access Loop is a
Digital Subscriber Line (DSL), this is often referred to as a DSL
Access Multiplexer (DSLAM).
o Network Access Server (NAS): Network device which aggregates
multiplexed Subscriber traffic from a number of Access Nodes. The
NAS plays a central role in per-subscriber policy enforcement and
QoS. Often referred to as a Broadband Network Gateway (BNG) or
Broadband Remote Access Server (BRAS). A detailed definition of
the NAS is given in [RFC2881].
o Net Data Rate: defined by ITU-T G.993.2, section 3.39, i.e. the
portion of the total data rate that can be used to transmit user
information (e.g. ATM cells or Ethernet frames). It excludes
overhead that pertains to the physical transmission mechanism
(e.g. trellis coding in case of DSL).
o Line Rate: the total data rate including overhead.
o Access Node Control Mechanism: a method for multiple network
scenarios with an extensible communication scheme that conveys
status and control information between one or more ANs and one or
more NASs without using intermediate element managers.
o Control Channel: a bidirectional IP communication interface
between the controller function (in the NAS) and the reporting/
enforcement function (in the AN). It is assumed that this
interface is configured (rather than discovered) on the AN and the
NAS.
o Access Node Control Adjacency: the relationship between an Access
Node and a NAS for the purpose of exchanging Access Node Control
Protocol messages. The adjacency may either be up or down,
depending on the result of the Access Node Control Adjacency
protocol operation.
o Multicast Flow: multicast Any Source Multicast (ASM) group or
multicast Source Specific Multicast (SSM) (S,G) channel. An
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application channel (such as a TV channel) is mapped onto a
Multicast Flow.
o Join: signaling from the user equipment that it wishes to start
receiving a new multicast flow. In ASM, it is referred to as a
"Join". In SSM [RFC4607], it is referred to as a "subscribe". In
IGMPv2, "joins" are indicated through an "IGMPv2 membership
report". In IGMPv3 [RFC3376], "join" are indicated through
"membership report" using different Filter-Mode-Change (ASM) and
Source-List-Change Records.
o Leave: signaling from the user equipment that it wishes to stop
receiving a multicast flow. With IGMPv2 this is conveyed inside
the "Leave Group" message while in IGMPv3, "leave" is indicated
through "IGMPv3 membership report" message using different Filter-
Mode-Change (ASM) and Source-List-Change Records.
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2. General Architecture Aspects
In this section first the concept of the Access Node Control
Mechanism is described. Then, the reference architecture is
described where the Access Node Control Mechanism is introduced.
2.1. Concept of an Access Node Control Mechanism
The high-level communication framework for an Access Node Control
Mechanism is defined in Figure 1. The Access Node Control Mechanism
defines a quasi-realtime, general-purpose method for multiple network
scenarios with an extensible communication scheme, addressing the
different use cases that are described throughout this document.
+--------+
| Policy |
| Server |
+--------+
|
|
+-----+ +-----+ +--------+ +-----+ +----------+
| CPE |---| HGW |---| | | | | |
+-----+ +-----+ | Access | +---------+ | | | Regional |
| Node |---| Aggreg. |---| NAS |---| Network |
+-----+ +-----+ | | | Node | | | | |
| CPE |---| HGW |---| | +---------+ | | | |
+-----+ +-----+ +--------+ +-----+ +----------+
Information Report / Admission Request
-------------------------->
Admission Response / Control Request
<--------------------------
Control Response
-------------------------->
Access Node Control Mechanism
<------------------------->
PPP, DHCP, IP
<---------><------------------------------------->
Figure 1
From a functional perspective, a number of functions can be
identified:
o A controller function: this function is used to receive status
information or admission requests from the reporting function. It
is also used to trigger a certain behavior in the network element
where the reporting and/or enforcement function resides;
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o A reporting and/or enforcement function: the reporting function is
used to convey status information to the controller function that
requires the information for executing local functions. An
example of this is the transmission of an Access Loop data rate
from an Access Node to a Network Access Server (NAS) tasked with
shaping traffic to that rate. The enforcement function can be
contacted by the controller function to enforce a specific policy
or trigger a local action. An example of this is the initiation
of a port testing mechanism on an Access Node. Another example is
enforcing whether a multicast join is to be honored or denied.
The messages shown in Figure 1 show the conceptual message flow. The
actual use of these flows, and the times or frequencies when these
messages are generated depends on the actual use case, which are
described in Section 3.
The use cases in this document are described in an abstract way,
independent from any actual protocol mapping. The actual protocol
specification is out of scope of this document, but there are certain
characteristics of the protocol required such as to simplify
specification, implementation, debugging & troubleshooting, but also
to be easily extensible in order to support additional use cases.
2.2. Reference Architecture
The reference architecture used in this document can be based on ATM
or Ethernet access/aggregation. Specifically:
o In case of a legacy ATM aggregation network that is to be used for
the introduction of new QoS-enabled IP services, the architecture
builds on the reference architecture specified in DSL 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
DSL Forum [TR-101].
Given the industry's move towards Ethernet as the new access and
aggregation technology for triple play services, the primary focus
throughout this document is on a TR-101 architecture. However the
concepts are equally applicable to an ATM architecture based on TR-
059.
2.2.1. Home Gateway
The Home Gateway (HGW) connects the different Customer Premises
Equipment (CPE) to the Access Node and the access network. In case
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of DSL, the HGW is a DSL Network Termination (NT) that could either
operate as a layer 2 bridge or as a layer 3 router. In the latter
case, such a device is also referred to as a Routing Gateway (RG).
2.2.2. Access Loop
The Access Loop ensures physical connectivity between the HGW at the
customer premises, and the Access Node. In case of DSL, the Access
Loop physical layer could be e.g. ADSL, ADSL2+, VDSL, VDSL2 or
SHDSL. In order to increase bandwidth, it is also possible that
multiple DSL links are grouped together to form a single virtual
link; this process is called "DSL bonding". The protocol
encapsulation on the Access Loop could be based on multi-protocol
encapsulation over AAL5, defined in RFC2684. This covers PPP over
Ethernet (PPPoE, defined in RFC2516), bridged IP (IPoE) and routed IP
(IPoA, defined in RFC2225). Next to this, PPPoA as defined in
RFC2364 can be used. Future scenarios include cases where the Access
Loop supports direct Ethernet encapsulation (e.g. when using VDSL or
VDSL2).
2.2.3. Access Node
The Access Node (AN) is a network device, usually located at a
service provider central office or street cabinet, that terminates
Access Loop connections from Subscribers. In case the Access Loop is
a Digital Subscriber Line (DSL), this is often referred to as a DSL
Access Multiplexer (DSLAM). The AN may support one or more Access
Loop technologies and allow them to inter-work with a common
aggregation network technology.
Besides the Access Loop termination the AN can also aggregate traffic
from other Access Nodes using ATM or Ethernet.
The framework defined by this document is targeted at DSL-based
access (either by means of ATM/DSL or as Ethernet/DSL). The
framework shall be open to non-DSL technologies, like Passive Optical
Networks (PON) and IEEE 802.16 (WiMAX), but the details of this are
outside the scope of this document.
The reporting and/or enforcement function defined in Section 2.1
typically resides in an Access Node.
2.2.4. Access Node Uplink
The fundamental requirements for the Access Node uplink are to
provide traffic aggregation, Class of Service distinction and
customer separation and traceability. This can be achieved using an
ATM or an Ethernet based technology.
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2.2.5. Aggregation Network
The aggregation network provides traffic aggregation towards the NAS.
The aggregation technology can be based on ATM (in case of a TR-059
architecture) or Ethernet (in case of a TR-101 architecture).
2.2.6. Network Access Server
The NAS is a network device which aggregates multiplexed Subscriber
traffic from a number of Access Nodes. The NAS plays a central role
in per-subscriber policy enforcement and QoS. It is often referred
to as a Broadband Network Gateway (BNG) or Broadband Remote Access
Server (BRAS). A detailed definition of the NAS is given in RFC2881.
The NAS interfaces to the aggregation network by means of standard
ATM or Ethernet interfaces, and towards the Regional Network by means
of transport interfaces for Ethernet frames (e.g. GigE, Ethernet
over SONET). The NAS functionality correpsonds to the BNG
functionality described in DSL Forum TR-101. In addition to this,
the NAS supports the Access Node Control functionality defined for
the respective use cases throughout this document.
The controller function defined in Section 2.1 typically resides in a
NAS.
2.2.7. Regional Network
The Regional Network connects one or more NAS and associated Access
Networks to Network Service Providers (NSPs) and Application Service
Providers (ASPs). The NSP authenticates access and provides and
manages the IP address to Subscribers. It is responsible for overall
service assurance and includes Internet Service Providers (ISPs).
The ASP provides application services to the application Subscriber
(gaming, video, content on demand, IP telephony etc.).
The Regional Network supports aggregation of traffic from multiple
Access Networks and hands off larger geographic locations to NSPs and
ASPs - relieving a potential requirement for them to build
infrastructure to attach more directly to the various Access
Networks.
2.3. Access Node Control Mechanism Transport Methods
The connectivity between the Access Node and the NAS may differ
depending on the actual layer 2 technology used (ATM or Ethernet).
Therefore the identification of unicast & multicast flows/channels
will also differ (see also Section 2.4.1).
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In case of an ATM access/aggregation network, a typical practice is
to send the Access Node Control Protocol messages over a dedicated
Permanent Virtual Circuit (PVC) configured between the AN and the
NAS. These ATM PVCs would then be given a high priority so that the
ATM cells carrying the Access Node Control Protocol messages are not
lost in the event of congestion. It is discouraged to route the
Access Node Control Protocol messages within the 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 Virtual Path
(VP) that is given a high priority and runs across the aggregation
network. This requires the presence of a VC cross-connect in the
aggregation node that terminates the VP.
In case of an Ethernet access/aggregation network, a typical practice
is to send the Access Node Control Protocol messages over a dedicated
Ethernet Virtual LAN (VLAN) using a separate VLAN identifier (VLAN
ID). This can be achieved using a different VLAN ID for each Access
Node, or, in networks with many Access Nodes and high degree of
aggregation, one Customer VLAN (C-VLAN) per Access Node and one
Service VLAN (S-VLAN) for the Access Node Control Adjacencies of all
Access Nodes. The traffic should be given a high priority (e.g. by
using a high Class of Service (CoS) value) so that the Ethernet
frames carrying the Access Node Control Protocol messages are not
lost in the event of congestion.
In both cases, the Control Channel between NAS and Access Node could
use the same physical network- and routing resources as the
Subscriber traffic. This means that the connection is an inband
connection between the involved network elements. Therefore there is
no need for an additional physical interface to establish the Control
Channel.
Note that these methods for transporting Access Node Control Protocol
messages are typical examples; they do not rule out other methods
that achieve the same behavior.
The Access Node Control Adjacency interactions must be reliable. In
addition to this, some of the use cases described in Section 3
require the interactions to be performed in a transactional fashion,
i.e. using a "request/response" mechanism. In case the response is
negative, the state of the peer must then be rolled back to the state
prior to the transaction.
2.4. Operation and Management
When introducing an Access Node Control Mechanism, care is needed to
ensure that the existing management mechanisms remain operational as
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before.
Specifically when using the Access Node Control Mechanism for
performing a configuration action on a network element, one gets
confronted with the challenge of supporting multiple managers for the
same network element: both the Element Manager as well as the Access
Node Control Mechanism may now perform configuration actions on the
same network element. Conflicts therefore need to be avoided.
Also, there is a possibility to integrate this with a Policy Server
(e.g. RADIUS server) that keeps track of the different Subscriber
related parameters.
2.4.1. Circuit Addressing Scheme
In deployments using an ATM aggregation network, the ATM PVC on an
Access Loop connects the Subscriber to a NAS. Based on this
property, the NAS typically includes a NAS-Port-Id, NAS-Port or
Calling-Station-Id attribute in RADIUS authentication & accounting
packets sent to the RADIUS server(s). Such attribute includes the
identification of the ATM VC for this Subscriber, which allows in
turn identifying the Access Loop.
In an Ethernet-based aggregation network, a new addressing scheme is
defined in TR-101. Two mechanisms can be used:
o A first approach is to use a one-to-one VLAN assignment model for
all Access Ports (e.g. a DSL port) and circuits on an Access Port
(e.g. an ATM PVC on an ADSL port). This enables directly deriving
the port and circuit identification from the VLAN tagging
information, i.e. S-VLAN ID or <S-VLAN ID, C-VLAN ID> pair;
o A second approach is to use a many-to-one VLAN assignment model
and to encode the Access Port and circuit identification in the
"Agent Circuit ID" sub-option to be added to a DHCP or PPPoE
message. The details of this approach are specified in TR-101.
This document reuses the addressing scheme specified in TR-101. It
should be noted however that the use of such a scheme does not imply
the actual existence of a PPPoE or DHCP session, nor on the specific
interworking function present in the Access Node. In some cases, no
PPPoE or DHCP session may be present, while port and circuit
addressing would still be desirable.
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3. Use Cases for Access Node Control Mechanism
3.1. Access Topology Discovery
[TR-059] and [TR-101] discuss various queuing/scheduling mechanisms
to avoid congestion in the access network while dealing with multiple
flows with distinct QoS requirements. One technique that can be used
on a NAS is known as "Hierarchal Scheduling" (HS). This option is
applicable in a single NAS scenario (in which case the NAS manages
all the bandwidth available on the Access Loop) or in a dual NAS
scenario (in which case the NAS manages some fraction of the Access
Loop's bandwidth). The HS must, at a minimum, support 3 levels
modelling the NAS port, Access Node uplink, and Access Loop sync
rate. The rationale for the support of HS is as follows:
o Provide fairness of network resources within a class.
o Better utilization of network resources. Drop traffic early at
the NAS rather than letting it traverse the aggregation network
just to be dropped at the Access Node.
o Enable more flexible Class of Service (CoS) behaviors other than
only strict priority.
o The HS system could be augmented to provide per application
admission control.
o Allow fully dynamic bandwidth partitioning between the various
applications (as opposed to static bandwidth partitioning).
o Support "per user weighted scheduling" to allow differentiated
SLAs (e.g. business services) within a given traffic class.
Such mechanisms require that the NAS gains knowledge about the
topology of the access network, the various links being used and
their respective rates. Some of the information required is somewhat
dynamic in nature (e.g. DSL line rate - hence also the net data
rate), hence cannot come from a provisioning and/or inventory
management OSS system. Some of the information varies less
frequently (e.g. capacity of a DSLAM uplink), but nevertheless needs
to be kept strictly in sync between the actual capacity of the uplink
and the image the BRAS has of it.
OSS systems are rarely able to enforce in a reliable and scalable
manner the consistency of such data, notably across organizational
boundaries. The Access Topology Discovery function allows the NAS to
perform these advanced functions without having to depend on an
error-prone & possibly complex integration with an OSS system.
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Communicating Access Loop attributes is specifically important in
case the rate of the Access Loop changes overtime. The DSL actual
data rate may be different every time the DSL NT is turned on. In
this case, the Access Node sends an Information Report message to the
NAS after the DSL line has resynchronized.
Additionally, during the time the DSL NT is active, data rate changes
can occur due to environmental conditions (the DSL Access Loop can
get "out of sync" and can retrain to a lower value, or the DSL Access
Loop could use Seamless Rate Adaptation making the actual data rate
fluctuate while the line is active). In this case, the Access Node
sends an additional Information Report to the NAS each time the
Access Loop attributes change above a threshold value.
The hierarchy and the rates of the various links to enable the NAS
hierarchical scheduling and policing mechanisms are the following:
o The identification and speed (data rate) of the DSL Access Loop
(i.e. the net data rate)
o The identification and speed (data rate) of the Remote
Terminal(RT)/Access Node uplink (when relevant)
The NAS can adjust downstream shaping to current Access Loop actual
data rate, and more generally re-configure the appropriate nodes of
its hierarchical scheduler (support of advanced capabilities
according to TR-101).
This use case may actually include more information than link
identification and corresponding data rates. In case of DSL Access
Loops, the following Access Loop characteristics can be sent to the
NAS (cf. ITU-T Recommendation G.997.1 [G.997.1]):
o DSL Type (e.g. ADSL1, ADSL2, SDSL, ADSL2+, VDSL, VDSL2)
o Framing mode (e.g. ATM, ITU-T Packet Transfer Mode (PTM), IEEE
802.3 Ethernet in the First Mile (EFM))
o DSL port state (e.g. synchronized/showtime, low power, no power/
idle)
o Actual net data rate (upstream/downstream)
o Maximum achievable/attainable net data rate (upstream/downstream)
o Minimum net data rate configured for the Access Loop (upstream/
downstream)
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o Maximum net data rate configured for the Access Loop (upstream/
downstream)
o Minimum net data rate in low power state configured for the Access
Loop (upstream/downstream)
o Maximum achievable interleaving delay (upstream/downstream)
o Actual interleaving delay (upstream/downstream)
The NAS MUST be able to receive Access Loop characteristics
information, and share such information with AAA/Policy Servers.
3.2. Access Loop Configuration
Access Loop rates are typically configured in a static way. If a
Subscriber wants to change its Access Loop rate, this requires an
OPEX intensive reconfiguration of the Access Port configuration via
the network operator, possibly implying a business-to-business
transaction between an Internet Service Provider (ISP) and an Access
Provider.
Using the Access Node Control Mechanism to change the Access Loop
rate from the NAS avoids those cross-organization business-to-
business interactions and allows to centralize Subscriber-related
service data in e.g. a Policy Server. More generally, several Access
Loop parameters (e.g. minimum data rate, interleaving delay) could be
changed by means of the Access Node Control Mechanism.
Triggered by the communication of the Access Loop attributes
described in Section 3.1, the NAS could query a Policy Server (e.g.
RADIUS server) to retrieve Access Loop configuration data. The best
way to change Access Loop parameters is by using profiles. These
profiles (e.g. DSL profiles for different services) are pre-
configured by the Element Manager managing the Access Nodes. The NAS
may then use the Configure Request message to send a reference to the
right profile to the Access Node. The NAS may also update the Access
Loop configuration due to a Subscriber service change (e.g. triggered
by the Policy Server).
The Access Loop Configuration mechanism may also be useful for
configuration of parameters that are not specific to the Access Loop
technology. Examples include the QoS profile to be used for an
Access Loop, or the per-Subscriber multicast channel entitlement
information, used for IPTV applications where the Access Node is
performing IGMP snooping or IGMP proxy function. The latter is also
discussed in Section 3.4.
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It may be possible that a Subscriber wants to change its Access Loop
rate, and that the operator wants to enforce 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 OSS
system, which could use application specific signaling to notify the
Subscriber of the fact that the change could not be performed at this
time.
3.3. Remote Connectivity Test
Traditionally, ATM circuits are point to point connections between
the BRAS and the DSLAM or DSL NT. In order to test the connectivity
on layer 2, appropriate OAM functionality is used for operation and
troubleshooting. An end-to-end OAM loopback is performed between the
edge devices (NAS and HGW) of the broadband access network.
When migrating to an Ethernet-based aggregation network (as defined
by TR-101), end to end ATM OAM functionality is no longer applicable.
Ideally in an Ethernet aggregation network, end-to-end Ethernet OAM
as specified in IEEE 802.1ag and ITU-T Recommendation Y.1730/1731 can
provide Access Loop connectivity testing and fault isolation.
However, most HGWs do not yet support these standard Ethernet OAM
procedures. Also, various access technologies exist such as ATM/DSL,
Ethernet in the First Mile (EFM) etc. Each of these access
technologies have their own link-based OAM mechanisms that have been
or are being standardized in different standard bodies.
In a mixed Ethernet and ATM access network (including the local
loop), it is desirable to keep the same ways to test and troubleshoot
connectivity as those used in an ATM based architecture. To reach
consistency with the ATM based approach, an Access Node Control
Mechanism between NAS and Access Node can be used until end-to-end
Ethernet OAM mechanisms are more widely available.
Triggered by a local management interface, the NAS can use the Access
Node Control Mechanism to initiate an Access Loop test between Access
Node and HGW. In case of an ATM based Access Loop the Access Node
Control Mechanism can trigger the Access Node to generate ATM (F4/F5)
loopback cells on the Access Loop. In case of Ethernet, the Access
Node can perform a port synchronization and administrative test for
the access loop. The Access Node can send the result of the test to
the NAS via a Control Response message. The NAS may then send the
result via a local management interface. Thus, the connectivity
between the NAS and the HGW can be monitored by a single trigger
event.
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3.4. Multicast
With the rise of supporting IPTV services in a resource efficient
way, multicast services are getting increasingly important.
In case of an ATM access/aggregation network, such as the reference
architecture specified in DSL Forum [TR-059], multicast traffic
replication is performed in the NAS. In this model, typically IGMP
is used to control the multicast replication process towards the
subscribers. The NAS terminates and processes IGMP signaling
messages sent by the subscribers; towards the Regional Network, the
NAS typically uses a multicast routing protocol such as PIM. The ATM
Access Nodes and aggregation switches don't perform IGMP processing,
nor do they perform multicast traffic replication. As a result,
network resources are wasted within the access/aggregation network.
To overcome this resource inefficiency, the Access Node, aggregation
node(s) and the NAS must all be involved in the multicast replication
process. This avoids that several copies of the same stream are sent
within the access/aggregation network. In case of an Ethernet-based
access/aggregation network, this may, for example, be achieved by
means of IGMP snooping or IGMP proxy in the Access Node and
aggregation node(s).
By introducing IGMP processing in the access/aggregation nodes, the
multicast replication process is now divided between the NAS, the
aggregation node(s) and Access Nodes. In order to ensure backward
compatibility with the ATM-based model, the NAS, aggregation node and
Access Node need to behave as a single logical device. This logical
device must have exactly the same functionality as the NAS in the ATM
access/aggregation network. The Access Node Control Mechanism can be
used to make sure that this logical/functional equivalence is
achieved by exchanging the necessary information between the Access
Node and the NAS.
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.
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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" 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.
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 list
or a Black list associated with that Access Port. If it is part of a
White list, the AN can autonomously start replicating multicast
traffic. If it is part of a Black list, the AN can autonomously
discard the message because the request is not authorized.
The White List and Black 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>);
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,
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or when the multicast groups are not known to a client application in
advance. The conditional access control could be tied to a more
complex policy/authorization mechanism, e.g. time of day access, or
location based access or to invoke a remote authorisation server.
For these cases, the AN can use ANCP to query the NAS, that in turn
will respond to the AN indicating whether the join is to be honored
(and hence replication performed by the AN) or denied. This can be
done with the Admission Request and Admission Response messages.
Some examples of using NAS querying are the following:
o Roaming users: a subscriber that logs in on different wireless
hotspots and would like to receive multicast content he is
entitled to receive;
o A related example is that of mobility or seamless handover; in
both cases the burden of (re)configuring access nodes with White
lists or Black lists may be too high;
o "Over The Top Video Partnerships": Service Providers may choose to
partner with Internet video providers to provide video content.
In this case, the multicast group mappings may not be known in
advance, or may be reused for different content in succession.
Querying the NAS before performing a join on the AN may increase
channel join and channel change times because of the additional
message processing involved in the AN, the NAS and potentially the
Policy Server. On the other hand, pre-provisioning per subscriber
profiles potentially different for each subscriber may be a
configuration burden, may result in large delays when the NAS or AN
restarts, or may not be viable when conditional access changes
frequently or are to remain under the control of an external
administrative entity.
In order to account for these operational factors and associated
trade-offs, in some cases, the provisioning and querying techniques
can be combined. In such a model, the AN sends an Admission Request
message to the NAS as a trigger for a particular multicast flow. The
NAS would then send back an Admission Response message to the AN,
including conditional access information for that multicast flow, as
well as for a set of multicast flows sharing the same conditional
access rules. The AN can then autonomously honor or deny requests
for a given user/port for the set of Multicast flows as indicated in
the Admission Response message.
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3.4.2. Multicast Admission Control
The successful delivery of Triple Play Broadband services is quickly
becoming a big capacity planning challenge for most of the Service
Providers nowadays. Solely increasing available bandwidth is not
always practical, cost-economical and/or sufficient to satisfy end
user experience given not only the strict requirements of unicast
delay sensitive applications like VoIP and Video, but also the fast
growth of multicast interactive applications such as
videoconferencing, digital TV, digital audio, online movies and
networked gaming. These applications are typically characterized by
a delay sensitive nature, an extremely loss sensitive nature and
intensive bandwidth requirements. They are also typically "non-
elastic", which means that they operate at a fixed bandwidth, that
cannot be dynamically adjusted to the currently available bandwidth.
Therefore a Connection Admission Control (CAC) mechanism covering
admission of multicast 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 enough "video" bandwidth remaining on the
access line to carry the new flow (in addition to all other existing
multicast and unicast video traffic). The solution needs to cope
with multiple flows per access line and needs to allow access line
bandwidth to be dynamically shared across multicast and unicast
traffic (irrespective of whether unicast CAC is performed by 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
AN) and the entity performing unicast CAC (e.g. the NAS or a 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 both unicast
and multicast CAC for the access line are performed by the NAS.
In this case, the AN can use ANCP to query the NAS, that in turn
performs multicast CAC and responds to the AN indicating whether
the join is to be honored (and hence replication performed by the
AN) or denied. In the process, the NAS may communicate with a
Policy Server. Similarly to what has been discussed in the
Conditional Access use case, in response to a Admission Request
from the AN for admission control of a multicast flow, the NAS may
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send back an Admission Response message to the AN, including
admission control information for that multicast flow, as well as
for other a set of multicast flows sharing the same admission
control rules. The AN can then autonomously honor or deny
requests for a given user/port for the set of Multicast flows as
indicated in the Admission Response message. The ANCP
requirements to support this approach (where the AN queries the
NAS) are specified in this document;
o Another approach is the reverse: it consists of the Policy Server
querying the AN (either 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, that in turn will perform unicast CAC for the
access line and respond, indicating whether the unicast request is
to be honored or denied. In case 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.
3.4.3. Multicast Accounting
It may be desirable to perform accurate per-user or per Access Loop
time or volume based accounting. 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 starts or stops, and
generates the time and/or volume based accounting information per
Access Loop and per multicast flow, before sending it to a central
accounting system for logging. Since the AN communicates with
this 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 starts or stops, 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 can be done with the Information Report message.
The NAS can then generate the appropriate time and/or volume
accounting information per Access Loop and per multicast flow, to
be sent to the accounting system. The ANCP requirements to
support this approach are specified in this document.
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3.4.4. Multicast Termination
The capability to dynamically stop the replication of a multicast
flow can be useful in different scenarios: for example in case of
prepaid service, when available credit expires, the Service Provider
may want to be able to stop multicast replication on a specified
Access Port for a particular user. Another example of applicability
for this functionality is a scenario where a Service Provider would
like to show a "Content Preview": in this case a multicast content
will be delivered just for a fixed amount of time.
In both cases an external entity (for example a Policy Server or an
external application entity), can instruct the NAS to interrupt the
multicast replication of a specified multicast flow to a specified
Access Port or user. The NAS can then use ANCP to communicate this
decision to the Access Node. This can be done with the Admission
Response message. The approach dynamically updates the Black list
associated with the specified Access Port.
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4. Requirements
4.1. ANCP Functional Requirements
o The ANCP MUST address all use cases described in this document,
and be general-purpose and extensible enough to foresee additional
use cases (including the use of other Access Nodes than a DSLAM,
e.g. a PON Access Node).
o The ANCP MUST be flexible enough to accommodate the various
technologies that can be used in an access network and in the
Access Node.
o The Access Node Control interactions MUST be reliable (using
either a reliable transport protocol (e.g. TCP) for the Access
Node Control Protocol messages, or by designing ANCP to be
reliable).
o The ANCP MUST support "request/response" transaction-based
interactions for the NAS to communicate control decisions to the
Access Node, or for the NAS to request information from the Access
Node. Transactions MUST be atomic, i.e. they are either fully
completed, or rolled-back to the previous state.
In case the NAS wants to communicate a bulk of independent control
decisions to the Access Node, the transaction (and notion of
atomicity) applies to the individual control decisions. This avoids
having to roll back all control decisions. Similarly, if the NAS
wants to request a bulk of independent information elements from the
Access Node, the notion of transaction applies to the individual
information elements.
o The ANCP MUST allow fast-paced transactions, in order to provide
real time transactions between a NAS and a fully populated Access
Node.
o The ANCP MUST allow fast completion of a given operation, in the
order of magnitude of tens of milliseconds.
o In large scale networks, Access Nodes are provisioned but not
always fully populated. Therefore the ANCP MUST be scalable
enough to allow a given NAS to control thousands of Access Nodes
(e.g. typically 5000 to 10000).
o The ANCP SHOULD minimize sources of configuration mismatch, help
automation of the overall operation of the systems involved
(Access Nodes and NAS) and be easy to troubleshoot.
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o The implementation of the ANCP in the NAS and Access Nodes MUST be
manageable via an element management interface. This MUST allow
to retrieve statistics and alarms (e.g. via SNMP) about the
operation of the ANCP, as well as initiate OAM operations and
retrieve corresponding results.
o The ANCP SHOULD support a means to handle sending/receiving a
large burst of messages efficiently (e.g. using "message
bundling").
4.2. ANCP Multicast Requirements
o The ANCP MUST support providing multicast conditional access
information to Access Ports on an Access Node, using Black lists
and White lists.
o The ANCP MUST support binding a particular Black list and White
List to a given Access Port.
o The ANCP MUST allow the AN to query the NAS to request an
admission decision for replicating a multicast flow to a
particular Access Port.
o The ANCP MUST allow the NAS to send an admission decision to the
AN indicating whether or not a multicast flow may be replicated to
a particular Access Port.
o The ANCP MUST allow the NAS, when replying to an AN request, to
OPTIONALLY convey information on multiple multicast flows sharing
the same conditional access rules. This allows the AN to take
autonomous decisions for these flows later on.
o The ANCP MUST allow the AN to report to a NAS when replication of
a multicast flow on a particular Access Port starts and stops.
o The ANCP MUST allow the NAS to indicate to the AN when multicast
accounting information is required for a multicast flow on a
particular Access Port.
o The ANCP MUST allow the NAS to revoke a decision to replicate a
multicast flow to a particular Access Port, which had been
conveyed earlier to an AN.
o The ANCP MUST support partial updates of the White lists and Black
lists.
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4.3. ANCP Security Requirements
The ANCP MUST also support the security requirements as described in
[draft-ietf-ancp-security-threats].
4.4. Protocol Design Requirements
o The ANCP MUST be simple and lightweight enough to allow an
implementation on Access Nodes with limited control plane
resources (e.g. CPU and memory).
o The ANCP SHOULD provide a "shutdown" sequence allowing to inform
the peer that the system is gracefully shutting down.
o The ANCP SHOULD include a "report" model for the Access Node to
spontaneously communicate to the NAS changes of states.
o The ANCP SHOULD support a graceful restart mechanism to enable it
to be resilient to network failures between the AN and NAS.
o The ANCP MUST provide a means for the AN and the NAS to perform
capability negotiation and negotiate a common subset.
4.5. Access Node Control Adjacency Requirements
o The ANCP MUST support an adjacency protocol in order to
automatically synchronize states between its peers, to agree on
which version of the protocol to use, to discover the identity of
its peers, and detect when they change.
o The Access Node Control Adjacency MUST be designed such that loss
or malfunction of the adjacency can be automatically detected by
its peers.
o The ANCP SHOULD include a "keep-alive" mechanism to automatically
detect adjacency loss.
o A loss of the Access Node Control Adjacency MUST NOT affect
Subscriber connectivity, nor network element operation.
o If the Access Node Control Adjacency is lost, it MUST NOT lead to
undefined states on the network elements.
o The ANCP MUST be able to recover from loss of the Access Node
Control Adjacency (e.g. due to link or node failure) and
automatically resynchronize state upon re-establishing the Access
Node Control Adjacency.
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4.6. ANCP Transport Requirements
o The Access Node Control Mechanism MUST be defined in a way that is
independent of the underlying layer 2 transport technology.
Specifically, the Access Node Control Mechanism MUST support
transmission over an ATM as well as over an Ethernet aggregation
network.
o The ANCP MUST be mapped on top of the IP network layer.
o If the layer 2 transport technology is based on ATM, then the
encapsulation MUST be according to RFC2684 routed (IPoA).
o If the layer 2 transport technology is based on Ethernet, then the
encapsulation MUST be according to RFC894 (IPoE).
4.7. Access Node Requirements
This section lists the requirements for an AN that supports the use
cases defined in this document.
4.7.1. General Architecture
The Access Node Control Mechanism is defined by a dedicated relation
between the Access Node (AN) and the NAS. If one service provider
has multiple physical NAS devices which represent one logical device
(single edge architecture), then one AN can be connected to more than
one NAS. Therefore the physical AN needs to be split in virtual ANs
each having its own Access Node Control reporting and/or enforcement
function.
o An Access Node as physical device can be split in logical
partitions. Each partition may have its independent NAS.
Therefore the Access Node must support at least 2 partitions. The
Access Node should support 8 partitions.
o One partition is grouped of several Access Ports. Each Access
Port on an Access Node must be assigned uniquely to one partition.
It is assumed that all circuits (i.e. ATM PVCs or Ethernet VLANs) on
top of the same physical Access Port are associated with the same
partition. In other words, partitioning is performed at the level of
the physical Access Port only.
o Each AN partition must have a separate Access Node Control
Adjacency to a NAS and should be able to enforce access control on
the controllers to only designated partitions being bound to one
controller.
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o The Access Node should be able to establish and maintain ANCP
Adjacencies to redundant controllers.
4.7.2. Control Channel Attributes
The Control Channel is a bidirectional IP communication interface
between the controller function (in the NAS) and the reporting/
enforcement function (in the AN). It is assumed that this interface
is configured (rather than discovered) on the AN and the NAS.
Depending on the network topology, the Access Node can be located in
a street cabinet or in a central office. If an Access Node in a
street cabinet is connected to a NAS, all user traffic and Access
Node Control data can use the same physical link.
o The Control Channel SHOULD use the same facilities as the ones
used for the data traffic.
o The Control Channel MUST be terminated at the Access Node.
o For security purposes, the Access Node Control Protocol messages
sent over the channel MUST NOT be sent towards the customer
premises.
o The Access Node must not support the capability to configure
sending Access Node Control Protocol messages towards the customer
premises.
o The Access Node should process control transactions in a timely
fashion.
o The Access Node should mark Access Node Control Protocol messages
with a high priority (e.g. VBR-rt for ATM cells, p-bit 6 or 7 for
Ethernet packets) in order for the packets not to be dropped in
case of congestion.
o If ATM interfaces are used, VPI as well as VCI value must be
configurable in the full range.
o If Ethernet interfaces are used, C-Tag as well as S-Tag must be
configurable in the full range.
4.7.3. Capability Negotiation Failure
o In case the Access Node and NAS cannot agree on a common set of
capabilities, as part of the ANCP capability negotiation
procedure, the Access Node must report this to network management.
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4.7.4. Adjacency Status Reporting
o The Access Node should support generating an alarm to a management
station upon loss or malfunctioning of the Access Node Control
Adjacency with the NAS.
4.7.5. Identification
o To identify the Access Node and Access Port within a control
domain a unique identifier is required. This identifier must be
in line with the addressing scheme principles specified in section
3.9.3 of TR-101.
o To allow for correlation in the NAS, the AN must use the same
Access Circuit Identifier (ACI) format for identifying the AN and
Access Port in Access Node Control Protocol messages, PPPoE and
DHCP messages.
4.7.6. Multicast
o The AN must deny any join to a multicast flow matching the Black
List for the relevant Access Port.
o The AN must accept any join to a multicast flow matching the White
List for the relevant Access Port.
o When a multicast flow matches both in the Black List and the White
List, the AN must use the most specific match.
o Upon receiving a join to a multicast flow which does not match any
entry in the Black List nor in the White List for a specific
Access Port, the AN must support using ANCP to query the NAS to
recieve a response indicating whether that join is to be honored
or denied.
o Upon querying the NAS, the AN should support receiving ANCP
messages from the NAS containing conditional access information of
multiple multicast flows. This allows the AN to take autonomous
decisions for these flows lateron.
o The AN must support using ANCP to send information to the NAS
about when replication starts/stops for the port/multicast flow.
o Upon receiving an Admission Response from the NAS with a
revocation of a previous admission decision, the AN must stop
replication of the corresponding multicast flow to the
corresponding Access Port.
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4.7.7. Message Handling
o The Access Node should dampen notifications related to line
attributes or line state.
4.7.8. Parameter Control
Naturally the Access Node Control Mechanism is not designed to
replace an Element Manager managing the Access Node. There are
parameters in the Access Node, such as the DSL noise margin and DSL
Power Spectral Densities (PSD), which are not allowed to be changed
via ANCP or any other control session, but only via the Element
Manager. This has to be ensured and protected by the Access Node.
When using ANCP for Access Loop Configuration, the EMS needs to
configure on the Access Node which parameters may or may not be
modified using the Access Node Control Mechanism. Furthermore, for
those parameters that may be modified using ANCP, the EMS needs to
specify the default values to be used when an Access Node comes up
after recovery.
o When Access Loop Configuration via ANCP is required, the EMS must
configure on the Access Node which parameter set(s) may be
changed/controlled using ANCP.
o Upon receiving an Access Node Control Request message, the Access
Node must not apply changes to the parameter set(s) that have not
been enabled by the EMS.
4.7.9. Security
The ANCP related security threats that could be encountered on the
Access Node are described in [draft-ietf-ancp-security-threats].
This document develops a threat model for ANCP security, aiming to
decide which security functions are required at the ANCP level.
Additional information is presented in Section 7.
4.8. Network Access Server Requirements
This section lists the requirements for a NAS that supports the use
cases defined in this document.
4.8.1. General Architecture
o The NAS must only communicate to authorized Access Node Control
peers.
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o The NAS must support the capability to simultaneously run ANCP
with multiple ANs in a network.
o The NAS must be able to establish an Access Node Control Adjacency
to a particular partition on an AN and control the access loops
belonging to such a partition.
o The NAS must support learning of access loop attributes (e.g. net
data rate), from its peer Access Node partitions via the Access
Node Control Mechanism.
o The NAS must support shaping traffic directed towards a particular
access loop to not exceed the net data rate learnt from the AN via
the Access Node Control Mechanism.
o The NAS should support a reduction or disabling of such shaping
limit, derived from Policy/Radius per-subscriber authorization
data.
o The NAS must support reporting of access loop attributes learned
via the Access Node Control Mechanism to a Radius server using
RADIUS VSAs.
o The NAS must correlate Access Node Control information with the
RADIUS authorization process and related subscriber data.
o The NAS should support shaping traffic directed towards a
particular access loop to include layer-1 and layer-2
encapsulation overhead information received for a specific access
loop from the AN via the Access Node Control Mechanism.
o The NAS should support dynamically configuring and re-configuring
discrete service parameters for access loops that are controlled
by the NAS. The configurable service parameters for access loops
could be driven by local configuration on the NAS or by a Policy
Server.
o The NAS should support triggering an AN via the Access Node
Control Mechanism to execute local OAM procedures on an access
loop that is controlled by the NAS. If the NAS supports this
capability, then the following applies:
* The NAS must identify the access loop on which OAM procedures
need to be executed by specifying an Access Circuit Identifier
(ACI) in the request message to the AN;
* The NAS should support processing and reporting of the remote
OAM results learned via the Access Node Control Mechanism.
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* As part of the parameters conveyed within the OAM message to
the AN, the NAS should send the list of test parameters
pertinent to the OAM procedure. The AN will then execute the
OAM procedure on the specified access loop according to the
specified parameters. In case no test parameters are conveyed,
the AN and NAS must use default and/or appropriately computed
values.
* After issuing an OAM request, the NAS will consider the request
to have failed if no response is received after a certain
period of time. The timeout value should be either the one
sent within the OAM message to the AN, or the computed timeout
value when no parameter was sent.
The exact set of test parameters mentioned above depends on the
particular OAM procedure executed on the access loop. An example
of a set of test parameters is the number of loopbacks to be
performed on the access loop and the timeout value for the overall
test. In this case, and assuming an ATM based access loop, the
default value for the timeout parameter would be equal to the
number of F5 loopbacks to be performed, multiplied by the F5
loopback timeout (i.e. 5 seconds per the ITU-T I.610 standard).
o The NAS must treat PPP or DHCP session state independently from
any Access Node Control Adjacency state. The NAS must not bring
down the PPP or DHCP sessions just because the Access Node Control
Adjacency goes down.
o The NAS should internally treat Access Node Control traffic in a
timely and scalable fashion.
o The NAS should support protection of Access Node Control
communication to an Access Node in case of line card failure.
4.8.2. Control Channel Attributes
o The NAS must mark Access Node Control Protocol messages as high
priority (e.g. appropriately set DSCP, Ethernet priority bits or
ATM CLP bit) such that the aggregation network between the NAS and
the AN can prioritize the Access Node Control Protocol messages
over user traffic in case of congestion.
4.8.3. Capability Negotiation Failure
o In case the NAS and Access Node cannot agree on a common set of
capabilities, as part of the ANCP capability negotiation
procedure, the NAS must report this to network management.
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o The NAS must only commence Access Node Control information
exchange and state synchronization with the AN when there is a
non-empty common set of capabilities with that AN.
4.8.4. Adjacency Status Reporting
o The NAS must support generating an alarm to a management station
upon loss or malfunctioning of the Access Node Control Adjacency
with the Access Node.
4.8.5. Identification
o The NAS must support correlating Access Node Control Protocol
messages pertaining to a given access loop with subscriber
session(s) over that access loop. This correlation must be
achieved by either:
* Matching an Access Circuit Identifier (ACI) inserted by the AN
in Access Node Control Protocol messages with corresponding ACI
value received in subscriber signaling (e.g. PPPoE and DHCP)
messages as inserted by the AN. The format of ACI is defined
in [TR-101];
* Matching an ACI inserted by the AN in Access Node Control
Protocol messages with an ACI value locally configured for a
static subscriber on the NAS.
4.8.6. Multicast
o The NAS must support using ANCP to configure multicast conditional
access information to Access Ports on an Access Node, using Black
Lists and White Lists.
o The NAS must support using ANCP to configure the Access Node with
the "maximum number of multicast streams" allowed to be received
concurrently per Access Port.
o Upon receiving a query from the AN for a request to replicate a
multicast flow to a particular Access Port, the NAS must support
using ANCP to reply to the AN indicating whether the request is to
be honored or denied.
o Upon receiving a query from the AN for a request to replicate a
multicast flow to a particular Access Port, the NAS should support
sending an Admission Response message containing conditional
access information of multiple multicast flows. This allows the
AN to take autonomous decisions for these flows lateron.
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o The NAS must support using ANCP to indicate to the AN whether or
not multicast accounting information is required for a multicast
flow on a particular Access Port.
o The NAS must support using ANCP to receive information about when
replication starts/stops for a multicast flow on a particular
Access Port.
o When Multicast replication occurs on the AN, the NAS must support
using ANCP to revoke the authorization to replicate a multicast
flow to a particular Access Port.
4.8.7. Message Handling
o The NAS should protect its resources from misbehaved Access Node
Control peers by providing a mechanism to dampen information
related to an Access Node partition.
4.8.8. Wholesale Model
o In case of wholesale access, the network provider's NAS should
support reporting of access loop attributes learned from AN via
the Access Node Control Mechanism (or values derived from such
attributes), to a retail provider's network gateway owning the
corresponding subscriber(s).
o In case of L2TP wholesale, the NAS must support a proxy
architecture that gives different providers conditional access to
dedicated Access Node Control resources on an Access Node.
o The NAS when acting as a LAC must communicate generic access line
related information to the LNS in a timely fashion.
o The NAS when acting as a LAC may asynchronously notify the LNS of
updates to generic access line related information.
4.8.9. Security
The ANCP related security threats that could be encountered on the
NAS are described in [draft-ietf-ancp-security-threats]. This
document develops a threat model for ANCP security, aiming to decide
which security functions are required at the ANCP level. Additional
information is presented in Section 7.
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5. Policy Server Interaction
This document does not consider the specific details of the
communication with a Policy Server (e.g. using RADIUS).
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6. Management Related Requirements
o It must be possible to configure the following parameters on the
Access Node and the NAS:
* Parameters related to the Control Channel transport method:
these include the VPI/VCI and transport characteristics (e.g.
VBR-rt or CBR) for ATM networks or the C-VLAN ID and S-VLAN ID
and p-bit marking for Ethernet networks;
* Parameters related to the Control Channel itself: these include
the IP address of the IP interface on the Access Node and the
NAS
o When the operational status of the Control Channel is changed
(up>down, down>up) a linkdown/linkup trap should be sent towards
the EMS. This requirement applies to both the AN and the NAS.
o The Access Node must provide the possibility using SNMP to
associate individual DSL lines with specific Access Node Control
Adjacencies.
o The Access Node must notify the EMS of configuration changes made
by the NAS on the AN using ANCP, in a timely manner.
o The Access Node must provide a mechanism that allows the
concurrent access on the same resource from several managers (EMS
via SNMP, NAS via ANCP). Only one manager may perform a change at
a certain time.
o The ANCP may provide a notification mechanism to inform the NAS
about configuration changes done by an EMS, in a timely manner.
This applies only to changes of parameters which are part of the
Use Case Access Loop Configuration.
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7. Security Considerations
[draft-ietf-ancp-security-threats] lists the ANCP related security
threats that could be encountered on the Access Node and the NAS. It
develops a threat model for ANCP security, aiming to decide which
security functions are required at the ANCP level.
With Multicast handling as described in this document, ANCP protocol
activity between the AN and the NAS is triggered by join/leave
requests coming from the end-user equipment. This could potentially
be used for denial of service attack against the AN and/or the NAS.
This is not a new class of risk over already possible IGMP messages
sent from subscribers to the NAS when the AN uses no IGMP snooping,
and thus is transparent as long as processing of ANCP messages on the
NAS/AN is comparable efficient and protected against congestion.
To mitigate this risk, the AN MAY implement control plane protection
mechanisms such as limiting the number of multicast flows a given
user can simultaneously join, or limiting the maximum rate of join/
leave from a given user.
We also observe that an operator can easily deploy some protection
against attacks using invalid multicast flows by taking advantage of
the mask-based match in the Black List. This way, joins for invalid
multicast flows can be denied at the AN level without any ANCP
protocol interactions and without NAS involvement.
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8. Acknowledgements
The authors would like to thank everyone that has provided comments
or input to this document. In particular, the authors acknowledge
the work done by the contributors to the DSL Forum related
activities: Jerome Moisand, Wojciech Dec, Peter Arberg and Ole
Helleberg Andersen. The authors also acknowledge the inputs provided
by Roberta Maglione, Angelo Garofalo, Francois Le Faucheur and
Toerless Eckert regarding multicast. Finally, the authors thank
Bharat Joshi, Stefaan De Cnodder, Kirubaharan Dorairaj and Markus
Freudenberger for providing comments.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2881] Mitton, D. and M. Beadles, "Network Access Server
Requirements Next Generation (NASREQNG) NAS Model",
RFC 2881, Jul 2000.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
9.2. Informative References
[G.997.1] ITU-T, "Physical layer management for digital subscriber
line (DSL) transceivers", ITU-T Rec. G.997.1, Sep 2005.
[TR-058] Elias, M. and S. Ooghe, "Multi-Service Architecture &
Framework Requirements", DSL Forum TR-058, September 2003.
[TR-059] Anschutz, T., "DSL Evolution - Architecture Requirements
for the Support of QoS-Enabled IP Services", DSL Forum TR-
059, September 2003.
[TR-101] Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL
Aggregation", DSL Forum TR-101, May 2006.
[WT-147] Voigt, N., Ooghe, S., and M. Platnic, "Layer 2 Control
Mechanism For Broadband Multi-Service Architectures", DSL
Forum WT-147, June 2007.
[draft-ietf-ancp-security-threats]
Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security
Threats and Security Requirements for the Access Node
Control Protocol (ANCP)",
IETF draft-ietf-ancp-security-threats-01.txt, Dec 2006.
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Authors' Addresses
Sven Ooghe
Alcatel-Lucent
Copernicuslaan 50
B-2018 Antwerpen
Belgium
Phone: +32 3 240 42 26
Email: sven.ooghe@alcatel-lucent.be
Norbert Voigt
Nokia Siemens Networks
Siemensallee 1
17489 Greifswald
Germany
Phone: +49 3834 555 771
Email: norbert.voigt@nsn.com
Michel Platnic
ECI Telecom
30 Hasivim Street
49517 Petakh Tikva
Israel
Phone: + 972 3 926 85 35
Email: michel.platnic@ecitele.com
Thomas Haag
T-Systems
Deutsche Telekom Allee 7
64295 Darmstadt
Germany
Phone: +49 6151 937 5347
Email: thomas.haag@t-systems.com
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Sanjay Wadhwa
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US
Phone:
Email: swadhwa@juniper.net
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