INTERNATIONAL TELECOMMUNICATION UNION
ITU-T G.987.1
TELECOMMUNICATION (01/2010) STANDARDIZATION SECTOR
OF ITU
SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS
Digital sections and digital line system – Optical line
systems for local and access networks
10 Gigabit-capable Passive Optical Network (XG-PON): General Requirements
CAUTION !
PREPUBLISHED RECOMMENDATION
This prepublication is an unedited version of a recently approved Recommendation.
It will be replaced by the published version after editing. Therefore, there will be
differences between this prepublication and the published version.
FOREWORD
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NOTE
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Recommendation ITU-T G.987.1
10 Gigabit-capable Passive Optical Network (XG-PON):
General Requirements
1 Scope
This Recommendation addresses the general requirements of 10 Gigabit-capable Passive Optical Network (XG-PON) systems, in order to guide and motivate the physical layer and the transmission convergence layer specifications. The general requirements include examples of services, User Network Interfaces (UNI) and Service Node Interfaces (SNI), as well as the principal deployment configurations that are requested by network operators. This Recommendation also includes the system and operational requirements to meet the needs of supporting various business and residential applications.
As much as possible, this Recommendation maintains characteristics from [ITU-T G.982], [ITU-T G.983], and [ITU-T G.984] series of Recommendations. This is to promote backward compatibility with existing Optical Distribution Networks (ODN) that complies with those Recommendations. Furthermore, this recommendation provides a mechanism that enables seamless subscriber migration from Gigabit PON (Generic term to represent both G-PON and GE-PON) to XG–PON
using WDM defined in the G.984 series.
There are two flavours of XG-PONs based on the upstream line rate: XG-PON1 featuring a 2.5Gbit/s upstream path and XG-PON2 featuring a 10Gbit/s one. The initial phase of this specification only addresses XG-PON1. XG-PON2 will be addressed at later phase when the technology becomes more mature.
2 References
The following ITU-T Recommendations and other references contain provisions, which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation [ITU-T G.652] ITU-T Recommendation G.652 (2005), Characteristics of a single-mode
optical fibre cable.
[ITU-T G.657] ITU-T Recommendation G.657 (2006), Characteristics of a bending loss
insensitive single mode optical fibre and cable for the access network. [ITU-T G.902] ITU-T Recommendation G.902 (1995), Framework Recommendation on
functional access networks (AN) – Architecture and functions, access types,
management and service node aspects.
[ITU-T G.982] ITU-T Recommendation G.982 (1996), Optical access networks to support
services up to the ISDN primary rate or equivalent bit rates.
[ITU-T G.983.1] ITU-T Recommendation G.983.1 (2005), Broadband optical access systems
based on Passive Optical Networks (PON).
Rec. ITU-T G.987.1 (01/2010) – Prepublished version 1
[ITU-T G.983.2] ITU-T Recommendation G.983.2 (2005), ONT management and control
interface specification for B-PON.
[ITU-T G.983.3] ITU-T Recommendation G.983.3 (2001), A broadband optical access system
with increased service capability by wavelength allocation.
[ITU-T G.984.1] ITU-T Recommendation G.984.1 (2008), Gigabit-capable Passive Optical
Networks (GPON): General characteristics.
[ITU-T G.984.2] ITU-T Recommendation G.984.2 (2008), Gigabit-capable Passive Optical
Networks (GPON): Physical Media Dependent (PMD) layer specifications. [ITU-T G.984.3] ITU-T Recommendation G.984.3 (2008), Gigabit-capable Passive Optical
Networks (GPON): Transmission convergence layer specification.
[ITU-T G.984.4] ITU-T Recommendation G.984.4 (2008), Gigabit-capable Passive Optical
Networks (GPON): ONT management and control interface specification. [ITU-T G.984.5] ITU-T Recommendation G.984.5 (2007), Gigabit-capable Passive Optical
Networks (GPON): Enhancement band for Gigabit-capable Passive Optical
Networks.
[ITU-T G.984.5Am1] ITU-T Recommendation G.984.5 Am1 (2009), Gigabit-capable Passive
Optical Networks (G-PON): Enhancement band. Amendment 1.
[ITU-T G.808.1] ITU-T Recommendation G.808.1 (2006), Generic protection switching –
Linear trail and subnetwork protection.
[ITU-T G.984.6] ITU-T Recommendation G.984.6 (2008), Gigabit-capable Passive Optical
Networks (GPON): GPON optical reach extension (G.984.re).
[ITU-T Y.2201] ITU-T Recommendation Y.2201 (2007), NGN release 1 requirements [ITU-T G.810] ITU-T Recommendation G.810 (1996), Definitions and terminology for
synchronization networks
[ITU-T G.813] ITU-T Recommendation G.813 (2003), Timing characteristics of SDH
equipment slave clocks (SEC)
[ITU-T G.703] ITU-T Recommendation G.703 (2008), Physical/electrical characteristics of
hierarchical digital interfaces
[ITU-T G.8261] ITU-T Recommendation G.8261 (2008), Timing and synchronization aspects
in packet networks
[ITU-T G.8262] ITU-T Recommendation G.8262 (2008), Timing characteristics of synchronous
Ethernet equipment slave clock (EEC)
[ITU-T G.Sup45] ITU-T Series G Supplement45 (2009), Means and impact of GPON power
saving. White Paper
[ITU-T G.987] ITU-T Recommendation G.987 (2009), G.987 definitions, abbreviations and
acronyms
[ITU-T G.987.2] ITU-T Recommendation G.987.2 (2009), 10-Gigabit-capable Passive Optical
Networks (XG-PON): Physical Media Dependent (PMD) layer specification [ITU-T Y.2001] ITU-T Recommendation Y.2001 (12/2004), General overview of NGN. [ITU-T Y.1731] ITU-T Recommendation Y.1731 (02/2008), OAM functions and mechanisms
for Ethernet based networks.
Rec. ITU-T G.987.1 (01/2010) – Prepublished version 2
[ITU-T J.185] ITU-T Recommendation J.185 (02/2002), Transmission equipment for
transferring multi-channel television signals over optical access networks by
FM conversion.
[ITU-T J.186] ITU-T Recommendation J.186 (06/2003), Transmission equipment for multi-
hannel television signals over optical access networks by sub-carrier c
multiplexing (SCM).
[IEEE 1588] IEEE 1588-2008 (2008), IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems
[DSLF TR-156] DSL Forum (also known as the Broadband Forum) TR-156 (2008) Using
GPON Access in the context of TR-101
[MEF 10.1] MEF 10.1 (2006), Ethernet Service Attributes Phase 2
3 Definitions
See [ITU-T G.987], clause 3.
4 Abbreviations and Acronyms
See [ITU-T G.987], clause 4.
5 Architecture of the optical access network
5.1 Network architecture
The optical section of a local access network system can be either active or passive and its architecture can be either point-to-point or point-to-multipoint. Figure 5-1 shows the considered architectures, which range from Fibre to the Home (FTTH), Fibre to the Cell sites (FTTCell), Fibre to the Building/Curb (FTTB/C), to the Fibre to the Cabinet (FTTCab), etc. The Optical Distribution Network (ODN) is common to all architectures shown in Figure 5-1; hence the commonality of this system has the potential to generate large worldwide volumes.
Rec. ITU-T G.987.1 (01/2010) – Prepublished version 3
Figure 5-1 - Network Architecture
Note: An ONU supporting FTTH has been commonly referred to as ONT (See [ITU-T G.987]) The differences among these FTTx options are mainly due to the different services supported and the different locations of the ONUs rather than the ODN itself, so they can be treated as one in this Recommendation. It must be noted that a single OLT optical interface might accommodate a combination of several scenarios described hereafter.
XG-PON should extend the G.984.6 reach extenders capability, inherited from the G.984 recommendations series, to produce extra optical budget to achieve longer distances and/or additional passive split.
5.1.1 FTTB scenario
The FTTB scenario is divided into two scenarios, one for multi-dwelling units (MDU) and the other for businesses or mixed environments (MTU). Each scenario has the following service categories: 5.1.1.1 FTTB for MDU served residential users
– Asymmetric broadband services (e.g., IPTV, digital broadcast services, VOD, file
download, etc.).
– Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance
learning, telemedicine, online-game, etc.).
– POTS - The access network must be able to provide, in a flexible way, narrow-band
telephone services with appropriate using either emulation (complete replication of a legacy
service) or simulation (providing a service that is almost the same as the legacy service). 5.1.1.2 FTTB for MTU served business users
– Symmetric broadband services (e.g., group software, content broadcast, e-mail, file
exchange, etc.).
Rec. ITU-T G.987.1 (01/2010) – Prepublished version 4
– POTS - The access network must be able to provide, in a flexible way, narrow-band
telephone services using either emulation (complete replication of a legacy service) or
simulation (providing a service that is almost the same as the legacy service). – Private line. The access network must be able to provide, in a flexible way, private line
services at several rates.
5.1.2 FTTC and FTTCab scenario
Within this scenario, the following service categories have been considered: – Asymmetric broadband services (e.g., IPTV, digital broadcast services, VoD, file
download, online-game, etc.).
– Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance
learning, telemedicine, etc.).
– POTS - The access network must be able to provide, in a flexible way, narrow-band
telephone services using either emulation (complete replication of a legacy service) or
simulation (providing a service that is almost the same as the legacy service). – xDSL backhaul.
5.1.3 FTTH scenario
Within this scenario, the following service categories have been considered: – Asymmetric broadband services (e.g., IPTV, digital broadcast services, VOD, file
download, etc.).
– Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance
learning, telemedicine, online-game, etc.).
– POTS - The access network must be able to provide, in a flexible way, narrow-band
telephone services using either emulation (complete replication of a legacy service) or
simulation (providing a service that is almost the same as the legacy service). 5.1.4 FTTO scenario
FTTO addresses business ONU dedicated to a small business customer. Within this scenario, the following service categories have been considered:
– Symmetric broadband services (e.g., group software, content broadcast, e-mail, file
exchange, etc.).
– POTS - The access network must be able to provide, in a flexible way, narrow-band
telephone services using either emulation (complete replication of a legacy service) or
simulation (providing a service that is almost the same as the legacy service). – Private line. The access network must be able to provide, in a flexible way, private line
services at several rates.
5.1.5 FTTCell wireless scenario
Within this scenario, the ONU will be called CBU and will have to offer connectivity to wireless base stations:
- Symmetric TDM services (e.g., 2G cell site backhaul)
- Symmetric/Asymmetric packet based broadband services (e.g., 3G/4G cell site backhaul)
- Hot spots
Rec. ITU-T G.987.1 (01/2010) – Prepublished version 5
Within this scenario, the ONU will be called CBU and will have to offer connectivity to wireless base stations.
Figure 5-2 represents exemplary scenarios of XG-PON applications.
XG-PON
FTTCellCBU
BusinessFTTBMTU
XG-PON FTTOSBUOLT
FTTHSFU
ResidentialAggregation SwitchFTTBMDU
XG-PON OLTONUFTTCurb/Cab
- Figure 5-2 - A summary of some XG-PON scenarios
5.1.6 Environment conditions in outdoor scenarios
For supporting the wide range of scenarios and applications, optical parameters for the OLT and the ONU should be determined to allow an outdoor operation.
5.2 Reference configuration
A high level and simple reference configuration of XG-PON is depicted in Figure 5-3, which shows very similar high level reference configuration as G.983 and G.984 series. Rec. ITU-T G.987.1 (01/2010) – Prepublished version 6
Access Network management
functions
ONU
R/S S/R
Service Node ODN OLT functions
SNI ONU (V) Reference
AF point
(a) Reference point UNI
(T) Reference point
User side Network side
Figure 5-3 - High Level Reference Configuration of XG-PON
In addition to Figure 5-3, when XG-PON is deployed with a RF video overlay service, the ODN can
use a WDM device or an optical coupler/splitter to combine XG-PON and RF video signal. The
coupler/splitter can optionally be used to provide a split at the Central Office (CO). Such
architectures are depicted in 错误；未找到引用源。Error! Reference source not found. and 错
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Rec. ITU-T G.987.1 (01/2010) – Prepublished version 7
Figure 5-4 - Reference access network architecture
Figure 5-4 depicts generic optical access network (OAN) reference architecture that applies to the XG-PON. It includes an OLT, ONUs and an Optical Distribution Network (ODN) between them. As shown in Figure 5-4, an XG-PON ODN can consist of a single passive optical distribution segment (ODS), or a group of passive ODSs interconnected with reach extenders (REs) [ITU-T G.987].
5.2.1 ODN architectures
There can be several types of ODN architectures to achieve coexistence between XG-PON1 or XG-PON2 and additional services such as G-PON and video distribution services. Figure 5-5 and Figure 5-6 are reference diagrams of optical access network architectures. The figures assume that wavelength blocking filters (WBF) are used when XG-PON (1 or 2), G-PON and video are shared within the same ODN.
Note that these diagrams simply provide reference configurations of the ODN and WBF, and are not intended to limit future designs and implementations. In addition, the coexistence of XG-PON1 and XG-PON2 is outside the scope of this clause since this would not affect WDM configuration. Rec. ITU-T G.987.1 (01/2010) – Prepublished version 8