IEEE ComSoc Technology Blog

Overview of ITU-T G.9701-2019 (as of May 24, 2019):

Summary:

1.  Previous version: Recommendation ITU-T G.9701-2014 specifies a gigabit broadband access technology that exploits the existing infrastructure of copper wire-pairs that were originally deployed for plain old telephone service (POTS) services. Equipment implementing this Recommendation can be deployed from fibre-fed distribution points (fibre to the distribution point, FTTdp) located very near the customer premises, or within buildings (fibre to the building, FTTB). This Recommendation supports asymmetric and symmetric transmission at an aggregate net data rate up to 1 Gbit/s on twisted wirepairs using spectrum up to 106 MHz and specifies all necessary functionality to support far-end crosstalk (FEXT) cancellation between multiple wire-pairs, and facilitates low power operation.

2. Recommendation ITU-T G.9701-2019 integrates ITU-T G.9701-2014 and all of its corrigenda and amendments, and adds support for the following new functionality: LPM classes, optional extension of probe sequence length, short CLR/CL messages, Annex R – Showtime reconfiguration, and Appendix IV – Targeted generalized vectoring with active G.9701 supporting lines (TGVA). It also adds several clarifications, and fixes various errors and inconsistencies including ANDEFTR support, SRA triggering and PMS-TC parameter requirements, and conditions for an rtx-uc anomaly.

Scope:

This Recommendation specifies the operation of a broadband access technology that exploits the existing infrastructure of wire-pairs that were originally deployed for plain old telephone service (POTS) and, with Amendment 3, adds support for operation over coaxial cables.

This Recommendation supports transmission at an aggregate net data rate (the sum of upstream and downstream rates) up to approximately 2 Gbit/s.

While asymmetric digital subscriber line transceivers 2 (ADSL2) – extended bandwidth (ADSL2plus) uses approximately 2 MHz of the spectrum, and very high speed digital subscriber line transceivers 2 (VDSL2) uses up to 35 MHz of the spectrum, this Recommendation defines profiles using spectrum up to 106 MHz and 212 MHz and specifies all necessary functionality to support the use of far-end crosstalk (FEXT) cancellation between ITU-T G.9701 transceivers deployed on multiple wire-pairs. The availability of spectrum up to 106 MHz or 212 MHz allows ITU-T G.9701 transceivers to provide reliable high data rate operation on very short loops. This Recommendation can be deployed from fibre-fed distribution points located very near the customer premises, or within the buildings. This Recommendation is optimized to operate over wire-pairs up to approximately 250 m of 0.5 mm diameter. However, it is capable of operation over wire-pairs up to at least 400 meters of 0.5 mm diameter, subject to some performance limitations.

This Recommendation defines a wide range of settings for various parameters (such as spectral usage and transmitter power) that may be supported by a transceiver. Therefore, this Recommendation specifies profiles to allow transceivers to support a subset of the allowed settings and still be compliant with the Recommendation. The specification of multiple profiles allows vendors to limit the implementation complexity and develop implementations that target specific service requirements. This edition of the Recommendation specifies transmission profiles for inband spectral usage of up to 212 MHz and maximum transmit power up to +8 dBm. This Recommendation operates in compliance with the power spectral density (PSD) specification in [ITU-T G.9700].

As per ITU-T Recommendations in the ITU-T G.99x series, this Recommendation uses [ITU-T G.994.1] to initiate the transceiver training sequence. Through negotiation during the handshake phase of the initialization, the capability of equipment to support this Recommendation and/or ITU-T G.99x series Recommendations (e.g., [ITU-T G.993.2] defining VDSL2) is identified. For reasons of interoperability, equipment may support multiple Recommendations such that it is able to adapt to the operating mode supported by the far-end equipment.

It is the intention of this Recommendation to provide, by negotiation during the initialization, U interface compatibility and interoperability between transceivers complying with this Recommendation, including transceivers that support different combinations of options. The technology specified in this Recommendation provides the following key application features:

• Best aspects of fibre to the home (FTTH): up to 2 Gbit/s aggregate net data rate;
• Best aspects of ADSL2: customer self-install and operation in the presence of bridged taps, avoiding operator truck-rolls to the customer premises for installation and activation of the broadband access service;

• Coexistence with ADSL2 and VDSL2 on adjacent wire-pairs;
• Low power operation and all functionality necessary to allow transceivers to be deployed as part of reverse powered (and possibly battery operated) network equipment and to adapt to environmental conditions (e.g., temperature);
• Management capabilities allowing transceivers to operate in a zero touch deployment, avoiding truck-rolls to the network equipment for installation and activation of new or upgraded broadband access service;
• Control of the upstream vs downstream transmission time to adapt net data rates to the needs of the business and the residential customers;
• Vectoring (self-crosstalk cancellation) for increased net data rates on wire-pairs that experience far-end crosstalk from ITU-T G.9701 transceivers in the same vectored group operating on other wire-pairs in the same cable or operating on other wire-pairs originating from the same network equipment;
• Network timing reference (NTR) and time-of-day (ToD) transport for network frequency and time synchronization between network and customer premises equipment;
• Configuration of spectrum use, including configuration of the transmit power spectral density (PSD) limitations and notches to meet electromagnetic compatibility (EMC) requirements.

The technology specified in this Recommendation uses the following key functionalities and capabilities:
• Transparent transport of data packets (e.g., Ethernet packets) at an aggregate (sum of upstream and downstream) data rate of up to 2 Gbit/s;
• In-band spectral usage up to 212 MHz;
• Configurable start and stop frequencies, PSD shaping and notching;
• Discrete multitone (DMT) modulation (2 048/4 096 subcarriers with 51.75 kHz subcarrier
spacing);
• Time-division duplexing (sharing time between upstream and downstream transmission);
• Low latency retransmission, facilitating impulse noise protection (INP) between the V and T reference points at all data rates to deal with isolated erasure events at the U reference point of at least 10 ms, without loss of user data;
• Forward error correction based on Trellis coding and Reed-Solomon coding;
• Vectoring (self-FEXT cancellation), where this edition of the Recommendation uses linear precoding;
• Discontinuous operation where not all of the time available for data transmission is used;
• Online reconfiguration (OLR) for adaptation to changes of the channel and noise characteristics, including fast rate adaptation (FRA).

With these functionalities and capabilities, the technology specified in this Recommendation targets the following aggregate net data rates over a 0.5 mm straight wire-pair for 106 MHz profiles:
• 500 to 1000 Mbit/s on a wire-pair shorter than 100 m;
• 500 Mbit/s at 100 m;
• 200 Mbit/s at 200 m;
• 150 Mbit/s at 250 m;
• 500 Mbit/s at 50 m, while operating in the band above 17 MHz.

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.117] Recommendation ITU-T G.117 (2007), Transmission impairments due to speech Processing.
[ITU-T G.994.1] Recommendation ITU-T G.994.1 (2018), Handshake procedures for digital subscriber line transceivers.
[ITU-T G.997.2] Recommendation ITU-T G.997.2 (2019), Physical layer management for ITU-T G.9701 transceivers.
[ITU-T G.9700] Recommendation ITU-T G.9700 (2019), Fast access to subscriber terminals (G.fast) – Power spectral density specification.
[ITU-T O.9] Recommendation ITU-T O.9 (1999), Measuring arrangements to assess the degree of unbalance about earth.
[ITU-T T.35] Recommendation ITU-T T.35 (2000), Procedure for the allocation of ITU-T defined codes for non-standard facilities.
[ISO 8601] ISO 8601:2000, Data elements and interchange formats – Information interchange – Representation of dates and times.

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The complete document is available to ITU-T members with a TIES account.