Network Working Group Nabil Bitar(ed.)
Verizon
Internet Draft
Intended Status: Informational Sanjay Wadhwa (ed.)
Alcatel-Lucent
Expires: June 02, 2013
Thomas Haag
Deutsche Telekom
Hongyu Li
Huawei Technologies
December 02, 2012
Applicability of Access Node Control Mechanism to
PON based Broadband Networks
draft-ietf-ancp-pon-04.txt
Abstract
The purpose of this document is to provide applicability of the
Access Node Control mechanism to PON-based broadband access. The
need for an Access Node Control mechanism between a Network
Access Server (NAS) and an Access Node Complex (a combination of
Optical Line Termination (OLT) and Optical Network Termination
(ONT) elements) is described in a multi-service reference
architecture in order to perform QoS-related, service-related and
Subscriber-related operations. The Access Node Control mechanism
is also extended for interaction between components of the Access
Node Complex (OLT and ONT). The Access Node Control mechanism
will ensure that the transmission of information between the NAS
and Access Node Complex (ANX) and between the OLT and ONT within
an ANX does not need to go through distinct element managers but
rather uses a direct device-to-device communication and stays on
net. This allows for performing access link related operations
within those network elements to meet performance objectives.
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Status of this Memo
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This Internet-Draft will expire on June 02,2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as
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without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction............................................
4
2. Terminology.............................................
5
3. Motivation for explicit extension of ANCP to FTTx PON.... 7
4. Reference Model for PON Based Broadband Access Network.. 8
4.1. Functional Blocks 11
4.1.1. Home Gateway...............................
11
4.1.2. PON Access................................. 11
4.1.3. Access Node Complex........................
11
4.1.4. Access Node Complex Uplink to the NAS......
12
4.1.5. Aggregation Network........................ 12
4.1.6. Network Access Server......................
12
4.1.7. Regional Network...........................
12
4.2. Access Node Complex Control Reference
Architecture Options 13
4.2.1. ANCP+OMCI ANX Control...................... 13
4.2.2. All-ANCP ANX Control.......................
14
5. Concept of Access Node Control Mechanism for PON
Based Access........................................... 15
6. Multicast.............................................
18
6.1. Multicast Conditional Access 19
6.2. Multicast Admission Control 21
6.3. Multicast Accounting 33
7. Remote Connectivity Check............................. 34
8. Access Topology Discovery............................. 35
9. Access Loop Configuration............................. 37
10. Security Considerations.............................. 37
11. Differences in ANCP applicability between DSL and PON. 38
12. ANCP versus OMCI between the OLT and ONT/ONU......... 39
13. IANA Consideration...................................
40
14. Acknowledgements.....................................
40
15. References.....................................,.....
40
15.1. Normative References 40
15.2. Informative References 41
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1. Introduction
Passive Optical Networks (PONs) based on BPON [G.983.1] and GPON
[G.984.1] are being deployed across carrier networks. There are
two models for PON deployment: Fiber to the building/curb
(FTTB/FTTC), and Fiber to the Premises (FTTP). In the FTTB/C
deployment, the last mile connectivity to the subscriber premises
is provided over the local Copper loop, often using Very High
Speed Digital Subscriber line (VDSL). In the FTTP case, PON
extends to the premises of the subscriber. In addition, there are
four main PON technologies: (1) Broadband PON (BPON), (2) Gigabit
PON (GPON), (3) 10-Gigabit PON (XGPON), and (4) Ethernet PON
(EPON). This document describes the applicability of Access Node
Control Protocol (ANCP) in the context of FTTB/C and FTTP
deployments, focusing on BPON, GPON and XPON. Architectural
considerations lead to different ANCP compositions. Therefore,
the composition of ANCP communication between Access Nodes and
Network Access Server (NAS) is described using different models.
BPON, GPON and XPON in FTTP deployments provide large bandwidth
in the first mile, bandwidth that is an order of magnitude larger
than that provided by xDSL. In the downstream direction, BPON
provides 622 Mbps per PON while GPON provides 2.4 Gbps, and XPON
provides 10 Gbps.
In residential deployments, the number of homes sharing the same
PON is limited by the technology and the network engineering
rules. Typical deployments have 32-64 homes per PON.
The motive behind BPON, GPON and XPON deployment is providing
triple-play services over IP: voice, video and data. Voice is
generally low bandwidth but has low-delay, low-jitter, and low
packet-loss requirements. Data services (e.g., Internet services)
often require high throughput and can tolerate medium latency.
Data services may include multimedia content download such as
video. However, in that case, the video content is not required
to be real-time and/or it is low quality video. Video services,
on the other hand, are targeted to deliver Standard Definition or
High Definition video content in real-time or near-real time,
depending on the service model. Standard Definition content using
MPEG2 encoding requires on the order of 3.75 Mbps per stream
while High definition content using MPEG2 encoding requires on
the order of 15-19 Mbps depending on the level of compression
used. Video services require low-jitter and low-packet loss with
low start-time latency. There are two types of video services: on
demand and broadcast (known also as liner programming content).
While linear programming content can be provided over Layer1 on
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the PON, the focus in this document is on delivering linear
programming content over IP to the subscriber, using IP
multicast. Video on demand is also considered for delivery to the
subscriber over IP using a unicast session model.
Providing simultaneous triple-play services over IP with unicast
video and multicast video, VoIP and data requires an architecture
that preserves the quality of service of each service.
Fundamental to this architecture is ensuring that the video
content (unicast and multicast) delivered to the subscriber does
not exceed the bandwidth allocated to the subscriber for video
services. Architecture models often ensure that data is
guaranteed a minimum bandwidth and that VoIP is guaranteed its
own bandwidth. In addition, QoS control across services is often
performed at a Network Access Server (NAS), often referred to as
Broadband Network Gateway (BNG) for subscriber management, per
subscriber and shared link resources. Efficient multicast video
services require enabling multicast services in the access
network between the subscriber and the subscriber management
platform. In the FTTP/B/C PON environment, this implies enabling
IP multicast on the Access Node (AN) complex composed of the
Optical Network Terminal (ONT) or Unit (ONU) and Optical Line
Terminal (OLT), as applicable. This is as opposed to Digital
Subscriber Line (DSL) deployments where multicast is enabled on
the DSL Access Multiplexer (DSLAM) only. The focus in this
document will be on the ANCP requirements needed for coordinated
admission control of unicast and multicast video in FTTP/B/C PON
environments between the AN complex (ANX) and the NAS,
specifically focusing on bandwidth dedicated for multicast and
shared bandwidth between multicast and unicast.
[RFC5851] provides the framework and requirements for
coordinated admission control between a NAS and an AN with
special focus on DSL deployments. This document extends that
framework and the related requirements to explicitly address
PON deployments.
2. Terminology
- PON (Passive Optical Network) [G.983.1][G.984.1]: a point-to-
multipoint fiber to the premises network architecture in which
unpowered splitters are used to enable the splitting of an
optical signal from a central office on a single optical fiber to
multiple premises. Up to 32-128 may be supported on the same PON.
A PON configuration consists of an Optical Line Terminal (OLT) at
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the Service Provider's Central Office (CO) and a number of
Optical Network Units or Terminals (ONU/ONT) near end users, with
an optical distribution network (ODN) composed of fibers and
splitters between them. A PON configuration reduces the amount of
fiber and CO equipment required compared with point-to-point
architectures.
- Access Node Complex (ANX): The Access Node Complex is composed
of two geographically separated functional elements OLT and
ONU/ONT. The general term Access Node Complex (ANX) will be used
when describing a functionality which does not depend on the
physical location but rather on the "black box" behavior of OLT
and ONU/ONT.
-Optical Line Terminal (OLT): is located in the Service
provider's central office (CO). It terminates and aggregates
multiple PONs (providing fiber access to multiple premises or
neighborhoods) on the subscriber side, and interfaces with the
Network Access server (NAS) that provides subscriber management.
- Optical Network Terminal (ONT): terminates PON on the network
side and provides PON adaptation. The subscriber side interface
and the location of the ONT are dictated by the type of network
deployment. For a Fiber-to-the-Premise (FTTP) deployment (with
Fiber all the way to the apartment or living unit), ONT has
Ethernet (FE/GE/MoCA) connectivity with the Home Gateway
(HGW)/Customer Premise Equipment(CPE). In certain cases, one ONT
may provide connections to more than one Home Gateway at the same
time.
-Optical Network Unit (ONU): A generic term denoting a device
that terminates any one of the distributed (leaf) endpoints of an
Optical Distribution Node (ODN), implements a PON protocol, and
adapts PON PDUs to subscriber service interfaces. In case of an
MDU multi-dwelling or multi-tenant unit, a multi-subscriber ONU
typically resides in the basement or a wiring closet (FTTB case),
and has FE/GE/Ethernet over native Ethernet link or over xDSL
(typically VDSL) connectivity with each CPE at the subscriber
premises. In the case where fiber is terminated outside the
premises (neighborhood or curb side) on an ONT/ONU, the last-leg-
premises connections could be via existing or new Copper, with
xDSL physical layer (typically VDSL). In this case, the ONU
effectively is a "PON fed DSLAM".
-Network Access Server (NAS): Network element which aggregates
subscriber traffic from a number of ANs or ANXs. The NAS is often
an injection point for policy management and IP QoS in the access
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network. It is also referred to as Broadband Network Gateway
(BNG) or Broadband Remote Access Server (BRAS).
-Home Gateway (HGW): Network element that connects subscriber
devices to the AN or ANX and the access network. In case of xDSL,
the Home Gateway is an xDSL network termination 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). In the case of PON, it is often a Layer3 routing device
with the ONT performing PON termination.
-PON-Customer-ID: This is an identifier which uniquely identifies
the ANX and the access loop logical port on the ANX to the
subscriber (customer) premises, and is used in any interaction
between NAS and ANX that relates to access-loops. Logically it is
composed of information containing identification of the OLT (the
OLT may be physically directly connected to the NAS), the PON
port on the OLT, the ONT/ONU, and the port on the ONT/ONU
connecting to the subscriber HGW. When acting as a DHCP relay
agent, the OLT can encode PON-Customer-ID in the "Agent-Circuit-
Identifier" Sub-option in Option-82 of the DHCP messages [RFC3046].
3. Motivation for explicit extension of ANCP to FTTx PON
The fundamental difference between PON and DSL is that a PON is
an optical broadcast network by definition. That is, at the PON
level, every ONT on the same PON sees the same signal. However,
the ONT filters only those PON frames addressed to it. Encryption
is used on the PON to prevent eavesdropping.
The broadcast PON capability is very suitable to delivering
multicast content to connected premises, maximizing bandwidth
usage efficiency on the PON. Similar to DSL deployments, enabling
multicast on the Access Node Complex (ANX) provides for bandwidth
use efficiency on the path between the Access Node and the NAS as
well as improves the scalability of the NAS by reducing the
amount of multicast traffic being replicated at the NAS. However,
the broadcast capability on the PON enables the AN (OLT) to send
one copy on the PON as opposed to one copy to each receiver on
the PON. The PON multicast capability can be leveraged in the
case of GPON and BPON as discussed in this document.
Fundamental to leveraging the broadcast capability on the PON for
multicast delivery is the ability to assign a single encryption
key for all PON frames carrying all multicast channels or a key
per set of multicast channels that correspond to service
packages, or none. It should be noted that the ONT can be a
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multi-Dwelling Unit (MDU) ONT with multiple Ethernet ports, each
connected to a living unit. Thus, the ONT must not only be able
to receive a multicast frame, but must also be able to forward
that frame only to the Ethernet port with receivers for the
corresponding channel.
In order to implement triple-play service delivery with necessary
"quality-of-experience", including end-to-end bandwidth optimized
multicast video delivery, there needs to be tight coordination
between the NAS and the ANX. This interaction needs to be near
real-time as services are requested via application or network
level signaling by broadband subscribers. ANCP as defined in
[RFC5851] for DSL based networks is very suitable to realize a
control protocol (with transactional exchange capabilities),
between PON enabled ANX and the NAS, and also between the
components comprising the ANX, i.e., between OLT and the ONT.
Typical use cases for ANCP in PON environment include the
following:
- Access topology discovery
- Access Loop Configuration
- Multicast
- Optimized multicast delivery
- Unified video resource control
- NAS based provisioning of ANX
- Remote connectivity check
4. Reference Model for PON Based Broadband Access Network
An overall end-to-end reference architecture of a PON access
network is depicted in Figure 1 and Figure 2 with ONT serving a
single HGW, and ONT/ONU serving multiples HGWs, respectively. An
OLT may provide FTTP and FTTB/C access at the same time but most
likely not on the same PON port. Specifically, the following PON
cases are addressed in the context of this reference
architecture:
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- BPON with Ethernet uplink to the NAS and ATM on the PON
side.
- GPON/XPON with Ethernet uplink to the NAS and Ethernet
on the PON side
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 (BBF) [TR-101]. The Ethernet aggregation
network between a NAS and an OLT may be degenerated to one or
more direct physical Ethernet links.
Given the industry move towards Ethernet as the new access and
aggregation technology for triple play services, the primary
focus throughout this document is on GPON/XPON and BPON with
Ethernet between the NAS and the OLT.
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Access Customer
<---------Aggregation-------><-Prem->
Network Network
+------------------+
| Access Node |
| Complex (ANX) |
+---------+ +---+ +-----+ |+---+ +---+ | +---+
| | +-|NAS|--|Eth |--||OLT|-<PON>-|ONT|-|--|HGW|
NSP---+Regional | | +---+ |Agg | |+---+ +---+ | +---+
|Broadband| | +---+ +-----+ +------------------+
|Network |-+-|NAS| |
ASP---+ | | +---+ |
| | | +---+ |
+---------+ +-|NAS| | +---+ +---+
+---| +-<PON>-|ONT|--|HGW|
| +---+ +---+
|
| +---+ +---+
+---|ONT|--|HGW|
+---+ +---+
HGW : Home Gateway
NAS : Network Access Server
PON : Passive Optical Network
OLT : Optical Line Terminal
ONT : Optical Network Terminal
Figure 1: Access Network with PON.
FE/GE/VDSL
+---+ +---+
+----------------+ | |-|HGW|
+---------+ +-----+ | +-----+ +----+| | | +---+
| | +-|NAS |--| |Eth |--|OLT||-<PON>- | |
NSP---+Regional | | +-----+ | |Agg | | || | |ONT| +---+
| | | | | | | || | | or|-|HGW|
|Broadband| | +-----+ | +-----+ +----+| | |ONU| +---+
|Network |-+-|NAS | +----------------+ | | |
ASP---+ | | +-----+ | | | +---+
| | | +-----+ | | |-|HGW|
+---------+ +-|NAS | | +---+ +---+
+-----+ |
| +---+ +---+
+-|ONT|-|HGW|
+---+ +---+
Figure 2: FTTP/FTTB/C with multi-subscriber ONT/ONU serving
MTUs/MDUs.
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The following sections describe the functional blocks and network
segments in the PON access reference architecture.
4.1. Functional Blocks
4.1.1. Home Gateway
The Home Gateway (HGW) connects the different Customer Premises
Equipment (CPE) to the ANX and the access network. In case of
PON, the HGW is a layer 3 router. In this case, the HGW performs
IP configuration of devices within the home via DHCP, and
performs Network Address and Port Translation (NAPT) between the
LAN and WAN side. In case of FTTP/B/C, the HGW connects to the
ONT/ONU over an Ethernet interface. That Ethernet interface could
be over an Ethernet physical port or over another medium. In case
of FTTP, it is possible to have a single box GPON CPE solution,
where the ONT encompasses the HGW functionality as well as the
GPON adaptation function.
4.1.2. PON Access
PON access is composed of the ONT/ONU and OLT. PON ensures
physical connectivity between the ONT/ONU at the customer
premises and the OLT. PON framing can be BPON (in case of BPON)
or GPON (in case of GPON). The protocol encapsulation on BPON is
based on multi-protocol encapsulation over AAL5, defined in
[RFC2684]. This covers PPP over Ethernet (PPPoE, defined in
[RFC2516]), or bridged IP (IPoE). The protocol encapsulation on
GPON is always IPoE. In all cases, the connection between the AN
(OLT) and the NAS (or BNG) is assumed to be Ethernet in this
document.
4.1.3. Access Node Complex
This is composed of OLT and ONT/ONU and is defined in section 2.
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4.1.4. Access Node Complex Uplink to the NAS
The ANX uplink connects the OLT to the NAS. The fundamental
requirements for the ANX 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. The focus in this document is on
Ethernet as stated earlier.
4.1.5. Aggregation Network
The aggregation network provides traffic aggregation towards the
NAS. The Aggregation network is assumed to be Ethernet in this
document.
4.1.6. Network Access Server
The NAS is a network device which aggregates multiplexed
Subscriber traffic from a number of ANXs. 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 802.1Q or 802.1 Q-in-Q Ethernet interfaces, and
towards the Regional Network by means of transport interfaces
(e.g., GigE, PPP over SONET). The NAS functionality corresponds
to the BNG functionality described in BroadBand Forum (BBF) TR-
101 [TR-101]. In addition, the NAS supports the Access Node
Control functionality defined for the respective use cases in
this document.
4.1.7. 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 NAS can be part of the NSP
network. Similarly, the NSP can be the ASP.
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4.2. Access Node Complex Control Reference Architecture Options
Section 3 details the differences between xDSL access and PON
access and the implication of these differences on DSLAM control
vs. OLT and ONT/ONU (access node complex (ANX)) control. The
following sections describe two reference models: (1) ANCP+OMCI
ANX control, and (2) all-ANCP ANX control. That is, the two
models differ in the ONT/ONU control within the ANX.
Implementations, out of the scope of this document, may choose to
implement one or the other based on the ONT/ONU type and the
capabilities of the ONT/ONU and OLT. It is possible for an OLT or
an OLT PON port to connect to ONTs/ONUs with different
capabilities and for these two models to co-exist on the same OLT
and same PON. Section 12 describes the differences between OMCI
and ANCP in controlling the ONU/ONT.
OMCI is designed as a protocol between the OLT and ONT/ONU. It
enables the OLT to configure and administer capabilities on the
ONT/ONU in BPON, GPON and XPON. ANCP is designed as a protocol
between the NAS and access node. It enables the NAS to enforce
dynamic policies on the access node, and the access node to
report events to the NAS among other functions.
4.2.1. ANCP+OMCI ANX Control
Figure 3 depicts the reference model for ANCP+OMCI ANX control.
In this model, ANCP is enabled between the NAS and a connected
OLT, and OMCI is enabled between the OLT and an attached ONT/ONU.
NAS communicates with the ANX via ANCP. The OLT acts as an
ANCP/OMCI gateway for communicating necessary events and policies
between the OLT and ONT/ONU within the ANX and for communicating
relevant policies and events between the ONT/ONU and the NAS. The
functionality performed by the OLT as ANCP/OMCI gateway will be
application dependent (e.g., multicast control, topology
discovery) and should be specified in a related specification. It
should be noted that some applications are expected to require
extensions. Such extensions are expected to be outside of ANCP
scope, and may need to be defined by the ITU-T. It should be
noted that OMCI, in addition to configuration and administration,
provides the capability to report status changes on an ONT/ONU
with AVC (Attribute Value Change) notifications. When ONT/ONU's
DSL or Ethernet UNI attributes change, a related ME (management
Entity) will send a corresponding notification (AVC) to the OLT.
The OLT interworks such notification into an ANCP report and
sends it to the connected NAS via the ANCP session between the
OLT and the NAS. As the ANCP report contains information of
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ONT/ONU's UNI and OLT's PON port, NAS can obtain accurate
information of access topology.
+----------------------+
| ANX |
+---------+ +---+ +---+ |+---+ +-------+ | +---+
| | +-|NAS|--|Eth|--||OLT|-<PON>-|ONU/ONT|-|-|HGW|
NSP---+Regional | | +---+ |Agg| |+---+ +-------+ | +---+
|Broadband| | +---+ +---+ +----------------------+
|Network |-+-|NAS| |
ASP---+ | | +---+ |
| | | +---+ |
+---------+ +-|NAS| | +-------+ +---+
+---| +-<PON>-|ONU/ONT|-|HGW|
| +-------+ +---+
| +---+ +---+
+--|ONT|-----|HGW|
+---+ +---+
ANCP OMCI
+<--------------->+<----------->+
HGW: Home Gateway
NAS: Network Access Server
PON: Passive Optical Network
OLT: Optical Line Terminal
ONT: Optical Network Terminal
ONU: Optical Network Unit
Figure 3: Access Network with single ANCP+OMCI access control
4.2.2. All-ANCP ANX Control
Figure 4 depicts the All-ANCP ANX control reference model. In
this model, an ANCP session is enabled between a NAS and a
connected OLT, and another ANCP session is enabled between the
OLT and a connected ONT/ONU. ANCP enables communication of
policies and events between the OLT and the ANX. The OLT acts as
a gateway to relay policies and events between the NAS and
ONT/ONU within the ANX in addition to communicating policies and
events between the OLT and ONT/ONU. It should be noted that in
this model, OMCI(not shown) is expected to be simultaneously
enabled between the ONT and OLT, supporting existing OMCI
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capabilities and applications on the PON, independent of ANCP or
applications intended to be supported by ANCP.
+----------------------+
| Access Node Complex |
| (ANX) |
+---------+ +---+ +---+ |+---+ +-------+ | +---+
| | +-|NAS|--|Eth|--||OLT|-<PON>-|ONU/ONT| |--|HGW|
NSP---+Regional | | +---+ |Agg| |+---+ +-------+ | +---+
|Broadband| | +---+ +---+ +----------------------+
|Network |-+-|NAS| |
ASP---+ | | +---+ |
| | | +---+ |
+---------+ +-|NAS| | +-------+ +---+
+---| +-<PON>-|ONU/ONT|--|HGW|
| +-------+ +---+
|
| +-------+ +---+
+---|ONU/ONT|--|HGW|
+-------+ +---+
ANCP ANCP
+<----------------->+<---------->+
HGW: Home Gateway
NAS: Network Access Server
PON: Passive Optical Network
OLT: Optical Line Terminal
ONT: Optical Network Terminal
ONU: Optical Network Unit
Figure 4: All-ANCP ANX Reference Model
5. Concept of Access Node Control Mechanism for PON Based
Access
The high-level communication framework for an Access Node Control
mechanism is shown in Figure 5 for the ALL-ANCP ANX control
model. 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 in the sections that follow. The access
node control mechanism is also extended to run between OLT and
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ONT/ONU. The mechanism consists of control function, and
reporting and/or enforcement function. Controller 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.
The reporting function is used to convey status information to
the controller function that requires the information for
executing local functions. The enforcement function can be
contacted by the controller function to enforce a specific policy
or trigger a local action. The messages shown in Figure 5 show
the conceptual message flow. The actual use of these flows, and
the times or frequencies when these messages are generated depend
on the actual use cases, which are described in later sections.
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+--------+
| Policy | +----+
| Server | +--<PON>---|ONT |------- HGW
+--------+ + +----+ +---+
| + +----------|ONT|----HGW
| + | +---+
| +----------------|-------------+
+----+ | +----+ | +-----+ | +---+
|NAS |---------------| | | | |-|----|HGW|
| |<------------->| | | | ONU | | +---+
+----+ ANCP | |OLT |------<PON>----| | |
| | | | | | | +---+
| | | |<------------->| |------|HGW|
| | +----+ ANCP +-----+ | +---+
| +------------------------------+
| | Access Node |
| Control Request | |
| ------------------>| Control Request |
| |-------------------->|
| | Control Response |
| Control Response |<------------------- |
|<-------------------| |
| |Admission Request |
| Admission Request |<--------------------|
|<-------------------| |
|Admission Response | |
|------------------->|Admission Response |
| |-------------------->|
|Information Report | |
|<-------------------| |
Access Node Control Access Node Control
Mechanism Mechanism
<--------------------><-------------------->
PPP, DHCP, IP
<------------------------------------------------------>
Figure 5: Conceptual message flow for Access Node Control
mechanism in all-ANCP ANX control model.
As discussed previously, in different PON deployment scenarios,
ANCP may be used in variant ways and may interwork with other
protocols, e.g., OMCI. In the ANCP+OMCI model described earlier,
the NAS maintains ANCP adjacency with the OLT while the OLT
controls the ONT/ONU via OMCI. The messages shown in Figure 6
show the conceptual message flow for this model. The actual use
of these flows, and the times or frequencies when these messages
are generated depend on the actual use cases.
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+--------+
| Policy |
| Server | +---+ +---+
+--------+ +---- |ONT|--------|HGW|
| | +---+ +---+
| +--------------- |-------------+
+----+ | +----+ | +-----+ | +---+
|NAS |---------------| | | | |-|----|HGW|
| |<------------->| | | | ONU | | +---+
+----+ ANCP | |OLT |------<PON>----| | |
| | | | | | | +---+
| | | |<------------->| |------|HGW|
| | +----+ OMCI +-----+ | +---+
| +-----------------------------+
| | Access Node |
| Control Request | |
| ------------------>| Control Request |
| |-------------------->|
| | Control Response |
| Control Response |<------------------- |
|<-------------------| |
| |Admission Request |
| Admission Request |<--------------------|
|<-------------------| |
|Admission Response | |
|------------------->|Admission Response |
| |-------------------->|
|Information Report | |
|<-------------------| |
ANCP Mechanoism OMCI
<--------------------><-------------------->
PPP, DHCP, IP
<------------------------------------------------------->
Figure 6: Conceptual Message Flow for ANCP+OMCI ANX control model.
6. Multicast
With the rise of supporting IPTV services in a resource-efficient
way, multicast services are becoming increasingly important.
In order to gain bandwidth optimization with multicast, the
replication of multicast content per access-loop needs to be
distributed to the ANX. This can be done by ANX (OLT and ONT/ONU)
becoming multicast aware by implementing an IGMP snooping and/or
proxy function. The replication thus needs to be distributed
between NAS, aggregation nodes, and ANX. In case of GPON, and in
case of BPON with Ethernet uplink, this is very viable. By
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introducing IGMP processing on the ANX and aggregation nodes, the
multicast replication process is now divided between the NAS, the
aggregation node(s) and ANX. This is in contrast to the ATM-based
model where NAS is the single element responsible for all
multicast control and replication. In order to ensure backward
compatibility with the ATM-based model, the NAS, aggregation node
and ANX 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
ANX and the NAS.
An alternative to multicast awareness in the ANX is for the
subscriber to communicate the IGMP "join/leave" messages with the
NAS, while the ANX is being transparent to these messages. In
this scenario, the NAS can use ANCP to create replication state
in the ANX for efficient multicast replication. The NAS sends a
single copy of the multicast stream towards the ANX. The NAS can
perform network-based conditional access and multicast admission
control on multicast joins, and create replication state in the
ANX if the request is admitted by the NAS.
The following sections describe various use cases related to
multicast.
6.1. Multicast Conditional Access
In a Broadband FTTP/B/C 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 based on customer
subscription. Note that, in some environments, application layer
conditional access by means of Digital Rights Management (DRM)
for instance may provide sufficient control so that network-based
Multicast conditional access may not be needed. However, network
level access control may add to the service security by
preventing the subscriber from receiving a non-subscribed
channel. In addition, it enhances network security by preventing
a multicast stream from being sent on a link or a PON based on a
non-subscriber request.
Where network-based channel conditional access is desired, there
are two approaches. It can be done on the NAS along with
bandwidth-based admission control. The NAS can control the
replication state on the ANX based on the outcome of access and
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bandwidth based admission control. This is covered in a later
section. The other approach is to provision the necessary
conditional access information on the ANX (ONT/ONU and/or OLT) so
the ANX can perform the conditional access decisions
autonomously. For these cases, the NAS can use ANCP to provision
black and white lists as defined in [RFC5851] on the ANX so that
the ANX can decide locally to honor a join or not. It should be
noted that in the PON case, the ANX is composed of the ONT/ONU
and OLT. Thus, this information can be programmed on the ONT/ONU
and/or OLT. Programming this information on the ONT/ONU prevents
illegitimate joins from propagating further into the network. A
third approach, outside of the scope, may be to program the HGW
with the access list. A White list associated with an Access Port
identifies the multicast channels that are allowed to be
replicated to that port. A Black list associated with an Access
Port identifies the multicast channels that are not allowed to be
replicated to that port. It should be noted that the black list
if not explicitly programmed is the complement of the white list
and vice versa.
If the ONT/ONU performs IGMP snooping and it is programmed with a
channel access list, the ONT/ONU will first check if the
requested multicast channel is part of a White list or a Black
list associated with the access port on which the IGMP join is
received. If the channel is part of a White list, the ONT/ONU
will pass the join request upstream towards the NAS. The ONT/ONU
must not start replicating the associated multicast stream to the
access port if such a stream is received until it gets
confirmation that it can do so from the upstream node (NAS or
OLT). Passing the channel access list is one of the admission
control criteria whereas bandwidth-based admission control is
another. If the channel is part of a Black list, the ONT/ONU can
autonomously discard the message because the channel is not
authorized for that subscriber.
The ONT/ONU, in addition to forwarding the IGMP join, sends an
ANCP admission request to the OLT identifying the channel to be
joined and the premises. Premises identification to the OLT can
be based on a Customer-Port-ID that maps to the access port on
the ONT/ONU and known at the ONT/ONU and OLT. If the ONT/ONU has
a white list and/or a black list per premises, the OLT need not
have such a list. If the ONT/ONU does not have such a list, the
OLT may be programmed with such a list for each premises. In this
latter case, the OLT would perform the actions described earlier
on the ONT/ONU. Once the outcome of admission control
(conditional access and bandwidth based admission control) is
determined by the OLT (either by interacting with the NAS or
locally), it is informed to the ONT/ONU. OLT Bandwidth based
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admission control scenarios are defined in a later section.
The White List and Black List can contain entries allowing:
- An exact match for a (*,G) Any Source Multicast (ASM)
group (e.g., <G=g.h.i.l>);
- An exact match for a (S,G) Source Specific Multicast
(SSM)channel (e.g., <S=s.t.u.v,G=g.h.i.l>);
- A mask-based range match for a (*,G) ASM group (e.g.,
<G=g.h.i.l/Mask>);
- A mask-based range match for a (S,G) SSM channel (e.g.,
<S=s.t.u.v,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., FTTP) subscribers. For
this application, the IPTV subscription is typically bound to a
specific FTTP home, and the multicast channels 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 ANX can be provisioned
with the conditional access information related to the IPTV
service.
Instead of including the channel list(s) at the ONT/ONU, the OLT
or NAS can be programmed with these access lists. Having these
access lists on the ONT/ONU prevents forwarding of unauthorized
joins to the OLT or NAS, reducing unnecessary control load on
these network elements. Similarly, performing the access control
at the OLT instead of the NAS, if not performed on the ONT/ONU,
will reduce unnecessary control load on the NAS.
6.2. 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 QoS requirements of unicast applications like VoIP and
Video on Demand, but also the fast growth of multicast
interactive applications such as "video conferencing", digital
TV, and digital audio. These applications typically require low
delay, low jitter, low packet loss and high bandwidth. These
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applications are also typically "non-elastic", which means that
they operate at a fixed bandwidth, which cannot be dynamically
adjusted to the currently available bandwidth.
An Admission Control (AC) mechanism covering admission of
multicast traffic for the FTTP/B/C access is required in order to
avoid over-subscribing the available bandwidth and negatively
impacting the end-user experience. Before honoring a user request
to join a new multicast flow, the combination of ANX and NAS must
ensure admission control is performed to validate that there is
enough video bandwidth remaining on the PON, and on the uplink
between the OLT and NAS to carry the new flow (in addition to all
other existing multicast and unicast video traffic) and that
there is enough video bandwidth for the subscriber to carry that
flow. The solution needs to cope with multiple flows per premises
and needs to allow bandwidth to be dynamically shared across
multicast and unicast video traffic per subscriber, PON, and
uplink (irrespective of whether unicast AC is performed by the
NAS, or by some off-path Policy Server). It should be noted that
the shared bandwidth between multicast and unicast video is under
operator control. That is, in addition to the shared bandwidth,
some video bandwidth could be dedicated to Video on Demand, while
other video bandwidth could be dedicated for multicast.
The focus in this document will be on multicast-allocated
bandwidth including the shared unicast and multicast bandwidth.
Thus, supporting admission control requires some form of
synchronization between the entities performing multicast AC
(e.g., the ANX and/or NAS), the entity performing unicast AC
(e.g., the NAS or a Policy Server), and the entity actually
enforcing the multicast replication (i.e., the NAS and the ANX).
This synchronization can be achieved in a number of ways:
- One approach is for the NAS to perform bandwidth based
admission control on all multicast video traffic and
unicast video traffic that requires using the shared
bandwidth with multicast. Based on the outcome of admission
control, NAS then controls the replication state on the
ANX. The subscriber generates an IGMP join for the desired
stream on its logical connection to the NAS. The NAS
terminates the IGMP message, and performs conditional
access and bandwidth based admission control on the IGMP
request. The bandwidth admission control is performed
against the following:
1. Available video bandwidth on the link to OLT
2. Available video bandwidth on the PON interface
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3. Available video bandwidth on the last mile (access-port
on the ONT/ONU).
The NAS can locally maintain and track video bandwidth it manages
for all the three levels mentioned above. The NAS can maintain
identifiers corresponding to the PON interface and the last mile
(customer interface). It also maintains a channel map,
associating every channel (or a group of channels sharing the
same bandwidth requirement) with a data rate. For instance, in
case of 1:1 VLAN representation of the premises, the outer tag
(S-VLAN) could be inserted by the ANX to correspond to the PON
interface on the OLT, and the inner-tag could be inserted by the
ANX to correspond to the access-line towards the customer.
Bandwidth tracking and maintenance for the PON interface and the
last-mile could be done on these VLAN identifiers. In case of N:1
representation, the single VLAN inserted by ANX could correspond
to the PON interface on the OLT. The access loop is represented
via Customer-Port-ID received in "Agent Circuit Identifier" sub-
option in DHCP messages.
The NAS can perform bandwidth accounting on received IGMP
messages. The video bandwidth is also consumed by any unicast
video being delivered to the CPE. NAS can perform video bandwidth
accounting and control on both IGMP messages and on requests for
unicast video streams when either all unicast admission control
is done by the NAS or an external policy server makes a request
to the NAS for using shared bandwidth with multicast as described
later in the document.
This particular scenario assumes the NAS is aware of the
bandwidth on the PON, and under all conditions can track the
changes in available bandwidth on the PON. On receiving an IGMP
Join message, NAS will perform bandwidth check on the subscriber
bandwidth. If this passes, and the stream is already being
forwarded on the PON by the OLT (which also means that it is
already forwarded by the NAS to the OLT), NAS will admit the
JOIN, update the available subscriber bandwidth, and transmit an
ANCP message to the OLT and in turn to the ONT/ONU to start
replication on the customer port. If the stream is not already
being replicated to the PON by the OLT, the NAS will also check
the available bandwidth on the PON, and if it is not already
being replicated to the OLT it will check the bandwidth on the
link towards the OLT. If this passes, the available PON bandwidth
and the bandwidth on the link towards the OLT are updated. The
NAS adds the OLT as a leaf to the multicast tree for that stream.
On receiving the message to start replication, the OLT will add
the PON interface to its replication state if the stream is not
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already being forwarded on that PON. Also, the OLT will send an
ANCP message to direct the ONT/ONU to add or update its
replication state with the customer port for that channel. The
interaction between ANX and NAS is shown in Figures 7 and 8. For
unicast video streams, application level signaling from the CPE
typically triggers an application server to request bandwidth
based admission control from a policy server. The policy server
can in turn interact with the NAS to request the bandwidth for
the unicast video flow if it needs to use shared bandwidth with
multicast. If the bandwidth is available, NAS will reserve the
bandwidth, update the bandwidth pools for subscriber bandwidth,
the PON bandwidth, and the bandwidth on the link towards the OLT,
and send a response to the policy server, which is propagated
back to the application server to start streaming. Otherwise, the
request is rejected.
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+----+
+---<PON>---------- |ONT |------ HGW
+ +----+
+ +----+
+ +--------- |ONT |------ HGW
+----+ +----+ + +----+
|NAS |---------------| |------<PON>
| |<------------->| | + +-----+
+----+ ANCP |OLT | +--------- | |----- HGW
| | | | |
| | |<------------------>| ONU |------HGW
| +----+ ANCP | | +---+
| | | |-----|HGW|
| | +-----+ +---+
| 1.IGMP JOIN(S/*,G) | |
|<---------------------------------------------------------- |
2.| | | |
+=======================+ | |
[Access Control & ] | |
[Subscriber B/W ] | |
[PON B/W & OLT link B/W ] | |
[based Admission Control] | |
+=======================+ | |
| | | |
|-------------------> | | |
3.ANCP Replication-Start| | |
(<S/*,G> or Multicast | | |
|MAC,Customer-Port-ID>| --------------------> | |
| |4.ANCP Replication-Start |
| (<S/*,G> or Multicast MAC,Customer-Port-ID)
|-------------------> | | |
|5.Multicast Flow(S,G)| | |
|On Multicast VLAN |---------------------> | |
| |6.Multicast Flow (S,G) | |
| |forwarded on | |
| |Unidirectional | |
| |<Multicast GEM-PORT> | |
| |on the PON by OLT |------------->|
7. Multicast Flow
orwarded on |
Customer-Port by|
|ONT/OLT. |
| |
Figure 7: Interactions for NAS based Multicast Admission Control
(no IGMP processing on ANX, and NAS maintains available video
bandwidth for PON) upon channel join.
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+----+
+---<PON>---------- |ONT |----- HGW
+ +----+
+ +----+
+ +--------- |ONT |----- HGW
+----+ +----+ + +----+
|NAS |---------------| |------<PON>
| |<------------->| | + +-----+
+----+ ANCP |OLT | +--------- | |---- HGW
| | | | |
| | |<------------------>| ONU |-----HGW
| +----+ ANCP | | +---+
| | | |-----|HGW|
| | +-----+ +---+
| | | |
| IGMP LEAVE(S/*,G) | |
|<-----------------------------------------------------------|
| | | |
+====================+ | | |
[Admission Control ] | | |
[<Resource Released> ] | | |
+====================+ | | |
| | | |
| | | |
| | | |
|-------------------> | | |
ANCP Replication-Stop | | |
(<S/*,G> or Multicast MAC,Customer-Port-ID) | |
| | | |
| |---------------------> | |
| | ANCP Replication-Stop | |
(<S/*,G> or Multicast MAC,Customer-Port-ID)
Figure 8: Interactions for NAS based Multicast Admission Control
(no IGMP processing on ANX, and NAS maintains available video
bandwidth for PON) upon channel leave.
- An alternate approach is required if the NAS is not aware
of the bandwidth on the PON. In this case the OLT does the PON
bandwidth management, and requests NAS to perform bandwidth
admission control on subscriber bandwidth and the bandwidth on
the link to the OLT. Following are operations of various
elements:
ANX operation:
- ONT/ONU can snoop IGMP messages. If conditional access
is configured and the channel is in the Black list (or it is not
on the White list), ONT will drop the IGMP Join. If the channel
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passes the conditional access check, the ONT will forward the
IGMP Join, and will send a bandwidth admission control request to
the OLT. In case the multicast stream is already being received
on the PON, the ONT/ONU does not forward the stream to the access
port where IGMP is received till it has received a positive
admission control response from the OLT.
- OLT can snoop IGMP messages. It also receives a bandwidth
admission control request from the ONT/ONU for the requested
channel. It can be programmed with a channel bandwidth map. If
the multicast channel is already being streamed on the PON, or
the channel bandwidth is less than the multicast available
bandwidth on the PON, the OLT forwards the IGMP request to the
NAS and keeps track of the subscriber (identified by customer-
Port-ID) as a receiver. If the channel is not already being
streamed on the PON, but the PON has sufficient bandwidth for
that channel, the OLT reduces the PON multicast video bandwidth
by the channel bandwidth and may optionally add the PON to the
multicast tree without activation for that channel. This is
biased towards a forward expectation that the request will be
accepted at the NAS. The OLT forwards the IGMP join to the NAS.
It also sends a bandwidth admission request to the NAS
identifying the channel, and the premises for which the request
is made. It sets a timer for the subscriber multicast entry
within which it expects to receive a request from the NAS that
relates to this request. If the PON available bandwidth is less
than the bandwidth of the requested channel, the OLT sends an
admission response (with a reject) to the ONT/ONU, and does not
forward the IGMP join to the NAS.
NAS operation:
The NAS receives the IGMP join from the subscriber on the
subscriber connection. When NAS receives the admission control
request from ANX (also signifying the bandwidth on the PON is
available), it performs admission control against the subscriber
available multicast bandwidth. If this check passes, and the NAS
is already transmitting that channel to the OLT, the request is
accepted. If the check passes and the NAS is not transmitting the
channel to the OLT yet, it performs admission control against the
multicast video available bandwidth (this includes the dedicated
multicast bandwidth and the shared bandwidth between multicast
and video on demand) on the link(s) to the OLT. If the check
passes, the request is accepted, the available video bandwidth
for the subscriber and downlink to the OLT are reduced by the
channel bandwidth, and the NAS sends an ANCP admission control
response (indicating accept) to the OLT, requesting the addition
of the subscriber to the multicast tree for that channel. The OLT
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activates the corresponding multicast entry if not active and
maintains state of the subscriber in the list of receivers for
that channel. The OLT also sends an ANCP request to the ONT/ONU
to enable reception of the multicast channel and forwarding to
the subscriber access port. Otherwise, if the request is
rejected, the NAS will send an admission reject to the OLT, which
in turn removes the subscriber as a receiver for that channel (if
it were added), and credits back the channel bandwidth to the PON
video bandwidth if there is no other receiver on the PON for that
channel. The interactions between ANX and NAS are shown in
Figures 9 and 10.
If the OLT does not receive a response from the NAS within a set
timer, the OLT removes the subscriber from the potential list of
receivers for the indicated channel. It also returns the
allocated bandwidth to the PON available bandwidth if there are
no other receivers. In this case, the NAS may send a response to
the OLT with no matching entry as the entry has been deleted. The
OLT must perform admission control against the PON available
bandwidth and may accept the request and send an ANCP request to
the ONT/ONU to activate the corresponding multicast entry as
described earlier. If it does not accept the request, it will
respond back to the NAS with a reject. The NAS shall credit back
the channel bandwidth to the subscriber. It shall also stop
sending the channel to the OLT if that subscriber was the last
leaf on the multicast tree towards the OLT.
On processing an IGMP leave, the OLT will send an ANCP request to
NAS to release resources. NAS will release the subscriber
bandwidth. If this leave causes the stream to be no longer
required by the OLT, the NAS will update its replication state
and release the bandwidth on the NAS to OLT link.
If the subscriber makes a request for a unicast video stream
(i.e., Video on Demand), the request results in appropriate
application level signaling, which typically results in an
application server requesting a policy server for bandwidth-based
admission control for the VoD stream. The policy server after
authorizing the request, can send a request to the NAS for the
required bandwidth if it needs to use bandwidth that is shared
with multicast. This request may be based on a protocol outside
of the scope of this document. The NAS checks if the available
video bandwidth (accounting for both multicast and unicast) per
subscriber and for the link to the OLT is sufficient for the
request. If it is, it temporarily reserves the bandwidth and
sends an ANCP admission request to the OLT for the subscriber,
indicating the desired VoD bandwidth. If the OLT has sufficient
bandwidth on the corresponding PON, it reserves that bandwidth
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and returns an accept response to the NAS. If not, it returns a
reject to the NAS. If the NAS receives an accept, it returns an
accept to the policy server which in turn returns an accept to
the application server, and the video stream is streamed to the
subscriber. This interaction is shown in Figure 11. If the NAS
does not accept the request from the policy server, it returns a
reject. If the NAS receives a reject from the OLT, it returns the
allocated bandwidth to the subscriber and the downlink to the
OLT.
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+----+
+-------- |ONT |-------- HGW
+----+ +----+ + +----+
|NAS |---------------| |------<PON>
| |<------------->| | + +-----+
+----+ ANCP |OLT | +--------- | |------ HGW
| | | ANCP | ONU |
| +----+<------------------>+-----+-------HGW
| | | |
|1.IGMP Join(s/*,G) +=============+ +=============+ |
|<------------------[IGMP Snooping]---------[IGMP snooping]--|
| +=============+ +=============+ |
| |2.Admission-Request | |
| |(Flow,Customer-Port-ID) | |
| |<---------------------- | |
| 3.+===============+ | |
| [ Access Ctrl ] | |
| [ & PON B/W ] | |
| [ Admission Ctrl] | |
| +===============+ PASS | |
|4.Admission-Request | | |
| <Flow, | | |
| Customer-Port-ID> | | |
|<--------------------| | |
5.| | | |
+=================+ | | |
[Subscriber B/W ] | | |
[& OLT link B/W ] | | |
[Admission Ctrl ] | | |
+=================+PASS | | |
|6.Admission-Reply-Pass | |
|<Flow,Customer-Port-ID> | |
|-------------------->| | |
| 7.+========================+ | |
| [Update Replication State] | |
| +========================+ | |
| | 8.Admission-Reply-Pass | |
| |(<Flow,Cust-Port-ID> | |
| |----------------------> | |
| | 9.+============+ |
| | [Update Repl.] |
| | [ State ] |
+============+
Figure 9: Interaction between NAS & ANX for Multicast Bandwidth
Admission Control in the All-ANCP ANX control model upon success.
Similar functionality will be required when OMCI is enabled between
the OLT and ONT/ONU in the ANCP+OMCI ANX control model. In this
latter case, the OLT will act as ANCP-OMCI gateway.
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+----+
+--------- |ONT |------ HGW
+----+ +----+ + +----+
|NAS |---------------| |------<PON>
| |<------------->| | + +-----+
+----+ ANCP |OLT | +--------- | |----- HGW
| | | ANCP |ONU |
| +----+<------------------>+-----+------HGW
| | | |
|1.IGMP Join(s/*,G) +=============+ +=============+ |
|<------------------[IGMP Snooping]--------[IGMP snooping]-- |
| +=============+ +=============+ |
| |2.Admission-Request | |
| |(Flow,Customer-Port-ID) | |
| |<---------------------- | |
| 2.+===============+ | |
| [ Access Ctrl ] | |
| [ & PON B/W ] | |
| [ Admission Ctrl] | |
| +===============+ PASS | |
|3.Admission-Request | | |
| <Flow,Customer-Port-ID> | |
|<--------------------| | |
4.+==================+ | | |
[Subscriber B/W ] | | |
[& OLT link B/W ] | | |
[Admission Ctrl ] | | |
+==================+FAIL | |
| | | |
|5.Admission-Reply-Fail | |
|<Flow,Cust-Port-ID> | | |
|-------------------->| | |
| 6.+==================+ | |
| [Release PON B/W ] | |
| [Remove Repl.State ] | |
| +==================+ | |
| | 7.Admission-Reply-Fail | |
| |<Flow,Cust-Port-ID> | |
| |----------------------> | |
| | 8.+============+ |
| | [Remove Repl.] |
| | [ State ] |
+============+
Figure 10: Interaction between NAS and ANX for Multicast Bandwidth
Admission Control in the All-ANCP ANX control model upon failure.
Similar functionality will be required when OMCI is enabled between
the OLT and ONT/ONU in the ANCP+OMCI ANX control model. In this
latter case, the OLT will act as ANCP-OMCI gateway.
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+------------+ 1. VoD Request
| App. Server|<-----------------------------------------------
| Server |
+------------+
| 2. Admission-Request (VoD-Flow)
+-------+
|Policy |
|Server |
+-------+
| +
|<-|---3. Admission-Request
| |
+ | 8. Admission-Reply
+----+ + +----+ +-----+
|NAS |---------------|OLT |------<PON>-------|ONT |---HGW--CPE
| |<------------->| | +-----+ |
+----+ ANCP +----+ | |
4.| | | |
+=================+ | | |
[Subscriber B/W ] | | |
[& OLT link B/W ] | | |
[Admission Ctrl ] | | |
+=================+PASS | | |
| | | |
| 5.Admission-Request | | |
|(Bandwidth,PON-Port-ID) | |
|-------------------> | | |
| | | |
| 6.+===============+ | |
| [ PON B/W ] | |
| [ Admission Ctrl] | |
| +===============+ PASS | |
|7.Admission-Reply | | |
| <PON-Port-ID> | | |
|<------------------- | | |
Figure 11: Interactions for VoD Bandwidth Admission Control in
the All-ANCP ANX control model. Similar functionality will be
required when OMCI is enabled between the OLT and ONT in the
ANCP+OMCI ANX control model. In this latter case, the OLT will
act as ANCP-OMCI gateway.
-A third possible approach is where the ANX is assumed to have a
full knowledge to make an autonomous decision on admitting or
rejecting a multicast and a unicast join. With respect to the
interaction between ONT/ONU and OLT, the procedure is similar to
the first approach (i.e., NAS controlled replication). However,
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when the OLT receives an IGMP request from a subscriber, it
performs admission control against that subscriber multicast
video bandwidth (dedicated and shared with Video on Demand), the
PON and uplink to the GWR. It should be noted in this case that
if there are multiple NAS-OLT links, either the link on which the
multicast stream must be sent is pre-determined, needs to be
selected by the OLT based on downstream bandwidth from NAS to OLT
and the selection is communicated to the NAS, or the OLT has to
be ready to receive the stream on any link. If the check passes,
the OLT updates the video available bandwidth per PON and
subscriber. The OLT adds the subscriber to the list of receivers
and the PON to the multicast tree, if it is not already on it. It
also sends an ANCP request to the ONT/ONU to add the subscriber
access port to that channel multicast tree, and sends an ANCP
message to the NAS informing it of the subscriber and link
available video bandwidth and the channel the subscriber joined.
The NAS upon receiving the ANCP information message, updates the
necessary information, including the OLT to the multicast tree if
it is not already on it. It should be noted in this case that the
ANCP message from the OLT to the NAS is being used to add the OLT
to a multicast tree as opposed to an IGMP message. The IGMP
message can also be sent by the OLT with the OLT acting as an
IGMP proxy at the expense of added messages. In this option, the
OLT acts as the network IGMP router for the subscriber.
For unicast video streams, the policy server receiving an
admission request from an application server, as described
before, may query the OLT for admission control as it has all
information. If the OLT has sufficient bandwidth for the stream
it reserves that bandwidth for the subscriber, PON and OLT uplink
to the NAS and returns an accept to the policy server. It also
updates the NAS via an ANCP message of the subscriber available
video bandwidth. If the OLT rejects the policy server request, it
will return a reject to the policy server.
It should be noted that if the policy server adjacency is with
the NAS, the policy server may make the admission request to the
NAS. The NAS then sends an ANCP admission request to the OLT on
behalf of the policy server. The NAS returns an accept or reject to
the policy server if it gets a reject or accept, respectively,
from the OLT.
6.3. Multicast Accounting
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It may be desirable to perform accurate per-user or per Access
Loop time or volume based accounting. In case the ANX is
performing the traffic replication process, it knows when
replication of a multicast flow to a particular Access Port or
user starts and stops. Multicast accounting can be addressed in
two ways:
- ANX 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 ANX
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 [RFC5851]. If the
replication function is distributed between the OLT and ONT/ONU,
a query from the NAS will result in OLT generating a query to the
ONT/ONU.
- ANX 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 ANX communicates
with this accounting system directly, the approach does not
require the use of ANCP. It is therefore beyond the scope of this
document; It may also be desirable for the NAS to have the
capability to asynchronously query the ANX to obtain an
instantaneous status report related to multicast flows currently
replicated by the ANX. Such a reporting functionality could be
useful for troubleshooting and monitoring purposes. If the
replication function in the ANX is distributed between the OLT
and the ONT/ONU, then for some of the information required by the
NAS (such as the list of access-ports on which a flow is being
forwarded or list of flows being forwarded on an access-port), a
query to the OLT from the NAS will result in a query from OLT to
ONT/ONU. The OLT responds back to the NAS when it receives the
response from the ONT/ONU. Also, if the list of PONs on which
replication is happening for a multicast channel or the list of
channels being replicated on a PON is what is desired, the OLT
can return this information.
7. Remote Connectivity Check
In an end-to-end 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
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testing and fault isolation. However, most HGWs do not yet
support these standard Ethernet OAM procedures. Also, in a mixed
Ethernet and ATM access network (e.g., Ethernet based aggregation
upstream from the OLT, and BPON downstream), interworking
functions for end-to-end OAM are not yet standardized or widely
available. Until such mechanisms become standardized and widely
available, Access Node Control mechanism between NAS and ANX can
be used to provide a simple mechanism to test connectivity of an
access-loop from the NAS.
Triggered by a local management interface, the NAS can use the
Access Node Control Mechanism (Control Request Message) to
initiate an Access Loop test between Access Node and HGW or
ONT/ONU. On reception of the ANCP message, the OLT can trigger
native OAM procedures defined for BPON in [G.983.1] and for GPON
in [G.984.1]. The Access Node can send the result of the test to
the NAS via a Control Response message.
8. Access Topology Discovery
In order to avoid congestion in the network, manage and utilize
the network resources better, and ensure subscriber fairness, NAS
performs hierarchical shaping and scheduling of the traffic by
modeling different congestion points in the network (such as the
last-mile, access Node uplink, and the access facing port).
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 in case the last
mile is xDSL based, e.g., in case of "PON fed DSLAMs" for
FTTC/FTTB scenarios), hence cannot come from a provisioning
and/or inventory management OSS system. Some of the information
varies less frequently (e.g., capacity of the OLT uplink), but
nevertheless needs to be kept strictly in sync between the actual
capacity of the uplink and the image the NAS 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 under certain deployment scenarios.
The Access Topology Discovery function allows the NAS to perform
these advanced functions without having to depend on an error-
prone and possibly complex integration with an OSS system.
The rate of the access-loop can be communicated via ANCP
(Information Report Message) from the ONT/ONU to the OLT in the
All-ANCP ANX control model or via OMCI in the ANCP+OMCI ANX
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control model, and then from OLT to the NAS via ANCP.
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, ANX sends an additional Information Report to the NAS each
time the Access Loop attributes change above a threshold value.
Existing DSL procedures are not applicable in this case because
an adapted message flow and additional TLVs are needed.
+--------+
| Policy |
| Server | +---+ +---+
+--------+ +-----------|ONT|---|HGW|
| | +---+ +---+
| +--------------- |-----------------+
+----+ | +----+ | +-----+ | +---+
|NAS |------------ | | | | | |-|-|HGW|
| |<----------> | | | | |ONT/ | | +---+
+----+ ANCP | |OLT |------<PON>--------|ONU | |
| | | | | | | +---+
| | | |<----------------->| |---|HGW|
| | +----+ OMCI +-----+ | +---+
| +----------------------------------+
| | Access Node |
| | |
| |------GPON Ranging------|
| Port Status Message| ONT Port UP |
|<------------------ |<-----------------------|
|Port Configuration GPON Line/Service Profile|
|------------------> |<---------------------->|
| ONT/ONI Port UP| |
|<------------------ | |
| ANCP | OMCI |
<-------------------><----------------------->|
PPP, DHCP, IP
<------------------------------------------------------>
Figure 12: Message Flow for the use case of Topology Discovery
for the ANCP+OMCI access control model.
Figure 12 depicts a message flow for topology discovery when
using the ANCP+OMCI access control model. Basically, when an
ONT/ONU gets connected to a PON, the OLT detects a new device and
a GPON Ranging process starts. During this process the ONT/ONU
becomes authorized by the OLT and identified by ONT/ONU ID, PON
Port ID and max Bandwidth. This port status is reported via ANCP
to the NAS and then potentially the policy server via another
mechanism that is out of scope of this document. In a second step
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after GPON Service profile is assigned from OLT to ONT/ONU, the
OLT reports the final status to NAS with information about
service profile and other information such as the ONT/ONU port
rate to the subscriber for instance.
9. Access Loop Configuration
Topology Discovery reports access port identification to NAS when
sending an Access Port Discovery message. This informs NAS
identification of PON port on an Access Node. Based on Access
Port Identification and on customer identification, service
related parameters could be configured on an OLT and an ONU/ONT.
Service related parameters could be sent to OLT via ANCP before
or after an ONU/ONT is up. Sending of ANCP loop Configuration
messages from NAS can be triggered by a management system or by
customer identification and authentication after Topology
Discovery. It may be used for first time configuration (zero
touch) or for updating/upgrading customer's profile like C-VLAN
ID, S-VLAN ID, and service bandwidth.
Parameters of UNI (subscriber interface to HGW/CPE) of ONU/ONT
can also be configured via ANCP. When the ONU/ONT supports ANCP,
parameters of the UNI on ONU/ONT are sent to the ONU/ONT via
ANCP. If the ONU/ONT does not support ANCP, but only OMCI,
parameters have to be sent from the NAS to the OLT via ANCP
first. Then, the OLT translates such configuration into OMCI and
sends it to the ONU/ONT.
10. 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 for ANCP security, and lists the security functions that
are required at the ANCP level.
With Multicast handling as described in this document, ANCP
protocol activity between the ANX 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 ANX and/or the NAS.
To mitigate this risk, the NAS and ANX may implement control
plane protection mechanisms such as limiting the number of
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multicast flows a given user can simultaneously join, or limiting
the maximum rate of join/leave from a given user.
Protection against invalid or unsubscribed flows can be deployed
via provisioning black lists as close to the subscriber as
possible (e.g., in the ONT).
11. Differences in ANCP applicability between DSL and PON
As it currently stands, both ANCP framework [RFC5851] and
protocol [RFC6320] are defined in context of DSL access. Due to
inherent differences between PON and DSL access technologies,
ANCP needs a few extensions for supporting the use-cases outlined
in this document for PON based access. These specific differences
and extensions are outlined below.
- In PON, the access-node functionality is split between OLT and
ONT. Therefore, ANCP interaction between NAS and AN translates to
transactions between NAS and OLT and between OLT and ONT. The
processing of ANCP messages (e.g., for multicast replication
control) on the OLT can trigger generation of ANCP messages from
OLT to ONT. Similarly, ANCP messages from ONT to the OLT can
trigger ANCP exchange between the OLT and the NAS (e.g.,
admission-request messages). This is illustrated in the generic
message flows in Figures 5 and 6 of section 5. In case of DSL,
the ANCP exchange is contained between two network elements (NAS
and the DSLAM).
- The PON connection to the ONT is a shared medium between
multiple ONTs on the same PON. The local-loop in case of DSL is
point-to-point. In case of DSL access network, the access facing
port on the NAS (i.e., port to the network between NAS and the
DSLAM), and the access-facing ports on the DSLAM (i.e.,
customer's local-loop) are the two bandwidth constraint points
that need to be considered for performing bandwidth based
admission control for multicast video and VoD delivered to the
customer. In case of PON access, in addition to the bandwidth
constraint on the NAS to OLT facing ports, and the subscriber
allocated bandwidth for video services, the bandwidth available
on the PON for video is an additional constraint that needs to be
considered for bandwidth based admission control. If the
bandwidth control is centralized in NAS (as described in option 1
of section 6.2), then the NAS needs to support additional logic
to consider available PON bandwidth before admitting a multicast
request or a VoD request by the user. Accordingly, ANCP needs to
identify the customer access port and the PON on which the
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customer ONT is. If the PON bandwidth control is performed on the
OLT (as defined in second option in section 6.2), then additional
ANCP request and response messages are required for NAS to query
the OLT to determine available PON bandwidth when a request to
admit a VOD flow is received on the NAS (as shown in Figure 9 in
section 6.2) or for the OLT to inform the NAS what stream
bandwidth is sent to the subscriber for the NAS to take
appropriate action (e.g., bandwidth adjustment for various types
of traffic).
- In PON, the multicast replication can potentially be performed
on three different network elements: (1) on the NAS (2) on the
OLT for replication to multiple PON ports, and (3) on the ONT/ONU
for replication to multiple customer ports. In case of DSL, the
replication can potentially be performed on NAS and/or the DSLAM.
Section 6.2 defines options for multicast replication in case of
PON. In the first option, the multicast replication is done on
the AN, but is controlled from NAS via ANCP (based on the
reception of per-customer IGMP messages on the NAS). In this
option, the NAS needs to supply to the OLT the set of PON-
customer-IDs (as defined in section 2) to which the multicast
stream needs to be replicated. The PON-customer-ID identifies the
OLT and the PON ports on the OLT as well as the ONT and the
access-ports on the ONT where the multicast stream needs to be
replicated. Upon receiving the request to update its multicast
replication state, the OLT must update its replication state with
the indicated PON ports, but may also need to interact with the
ONT via ANCP to update the multicast replication state on the ONT
with the set of access-ports (as indicated by the NAS). In case
of DSL, the DSLAM only needs to update its own replication state
based on the set of access-ports indicated by the NAS.
- For reporting purposes, ANCP must enable the NAS to query the
OLT for channels replicated on a PON or a list of PONs and to
specific access ports. The latter should trigger the OLT to query
the ONT for a list of channels being replicated on all access
ports or on specific access ports to the premises. In DSL case,
it is sufficient to query the DSLAM for a list of channels being
replicated on an access port or a list of access ports.
12. ANCP versus OMCI between the OLT and ONT/ONU
ONT Management and Control Interface (OMCI) [OMCI] is specified
for in-band ONT management via the OLT. This includes configuring
parameters on the ONT/ONU. Such configuration can include adding
an access port on the ONT to a multicast tree and the ONT to a
multicast tree. Thus, OMCI can be a potential replacement for
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ANCP between the OLT and ONT/ONU, albeit it may not a be suitable
protocol for dynamic transactions as required for the multicast
application.
If OMCI is selected to be enabled between the OLT and ONT/ONU to
carry the same information elements that would be carried over
ANCP, the OLT must perform the necessary translation between ANCP
and OMCI for replication control messages received via ANCP. OMCI
is an already available control channel, while ANCP requires a
TCP/IP stack on the ONT/ONU that can be used by an ANCP client
and accordingly it requires that the ONT/ONU be IP addressable
for ANCP. Most ONTs/ONUs today have a TCP/IP stack used by
certain applications (e.g., VoIP, IGMP snooping). ANCP may use
the same IP address that is often assigned for VoIP or depending
on the implementation may require a different address. Sharing
the same IP address between VoIP and ANCP may have other network
implications on traffic routing. Using a separate IP address for
the purpose of ONT/ONU management or ANCP specifically may often
be required when supporting ANCP. These considerations may favor
OMCI in certain environments. However, OMCI will not allow some
of the transactions required in approach 2, where the ONT/ONU
sends unsolicited requests to the OLT rather than being queried or
configured by OLT requests.
13. IANA Consideration
This document does not require actions by IANA.
14. Acknowledgements
The authors are thanksful to Rajesh Yadav and Francois Le
Faucheur for valuable comments and discussions.
15. References
15.1. Normative References
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[RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone,
D., and R. Wheeler, "A Method for Transmitting PPP Over
Ethernet (PPPoE)", RFC 2516, February 1999.
[RFC2684] Grossman, D. and J. Heinanen, "Multiprotocol
Encapsulation over ATM Adaptation Layer 5", RFC 2684, September
1999.
15.2. Informative References
[RFC2881] Mitton, D. and M. Beadles, "Network Access Server
Requirements Next Generation (NASREQNG) NAS Model", RFC 2881, Jul
2000.
[RFC5851] Ooghe, S., et al., "Framework and Requirements
for Access Node Control Mechanism in Broadband Networks", RFC
5851, May 2010.
[G.983.1] ITU-T recommendation G.983.1, Broadband optical access
systems based on Passive Optical Networks (PON).
[G.984.1] ITU-T recommendation G.984.1 Gigabit-capable Passive
Optical Networks (G-PON): General characteristics.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC3046, January 2011.
[TR-101] Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL
Aggregation", DSL Forum TR-101, May 2006.
[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.
[OMCI] ITU-T recommendation G.984.4 GPON ONT Management and
Control Interface (OMCI) Specifications.
[RFC6320] Taylor, T., et al, "Protocol for Access Node Control
Mechanism in Broadband Networks", RFC 6320, October 2011.
Authors' Addresses
Nabil Bitar
Verizon
60 Sylvan Road
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Waltham, MA 02451
Email: nabil.n.bitar@verizon.com
Sanjay Wadhwa
Alcatel-Lucent
701 East Middlefield Road
Mountain View, CA, 94043
Email: sanjay.wadhwa@alcatel-lucent.com
Hongyu Li
Email: hongyu.lihongyu@huawei.com
Thomas Haag
Email: HaagT@telekom.de
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