ITU-T G.9711 PDF

This Recommendation supports transmission at an aggregate net data rate (the sum of upstream and downstream rates) up to approximately 8 Gbit/s (for full duplex (FDX) mode) and 4 Gbit/s (for time division duplexing (TDD) mode) on metallic wires, to provide capabilities supporting internet access with low transmission latency (such as cloud computing, advanced video service, cloud-based 360-degree virtual reality and 8K video services). This Recommendation specifies the operation of a broadband access technology that exploits the existing infrastructure of both wire-pairs that were originally deployed for plain old telephone service (POTS) and coaxial cables that were originally deployed for television (TV) services.

Whilst asymmetric digital subscriber line transceivers 2 (ADSL2) – extended bandwidth (ADSL2plus) uses approximately 2 MHz of the spectrum, very high speed digital subscriber line transceivers 2 (VDSL2) uses up to 35 MHz of the spectrum, and fast access to subscriber terminals (G.fast) uses up to 212 MHz of the spectrum, this Recommendation defines profiles using spectrum up to 424 MHz and 848 MHz. The 424 MHz profiles are fully specified, while the 848 MHz profiles are for further study. For any profile using spectrum up to 424 MHz, it specifies all necessary functionality to support the use of far-end crosstalk (FEXT) and near-end crosstalk (NEXT) cancellation between ITU-T G.9711 transceivers deployed on multiple wire-pairs. The availability of spectrum up to 424 MHz allows ITU-T G.9711 transceivers to provide reliable high data rate operation on 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 twisted pairs between 30 m and 100 m. However, it is capable of operation over twisted pairs and coaxial cable up to at least 400 m, subject to some performance limitations.

This Recommendation defines a wide range of settings for various parameters 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 Recommendation specifies the profile for in-band spectral usage of up to 424 MHz at +4 dBm and + 2 dBm maximum transmit power for operation over twisted pairs and coaxial cable respectively, with the aggregate bit rate upto 8 Gbit/s (for FDX mode) and 4 Gbit/s (for TDD mode). Devices compliant with this Recommendation operate in compliance with the power spectral density (PSD) specification in [ITU-T G.9710].

As do 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 and G.97xx series Recommendations (e.g., [b-ITU-T G.993.2] applicable to VDSL2 and [b-ITU-T G.9701] applicable to G.fast) is identified. For reasons of interoperability, equipment may support multiple Recommendations such that it is able to operate using a mode supported by the far-end equipment.

It is the intention of this Recommendation to provide, by negotiation during the initialization, compatibility and interoperability at the U interface 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 multi-gigabit per second 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 by crosstalk mitigation;

• Coexistence with G.fast on adjacent wire-pairs (connected to the same distribution point unit (DPU)) by crosstalk cancellation;

• 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 scheme to adapt net data rates (especially in the TDD mode) to the needs of the business and the residential customers;

• Vectoring (self-crosstalk cancellation) for increased net data rates on wire-pairs that experience FEXT from other wire-pairs where ITU-T G.9711/G.9701 transceivers operate in the same vectored group, in the same cable or originated from the same network equipment;

• Echo-cancellation and near-end crosstalk cancellation/mitigation for increased net data rates on wire-pairs which are operated in FDX mode using the same frequency spectrum in both directions concurrently;

• Support of ultra-low latency services by improved retransmission and by use of FDX transmission;

• 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;

• Point-to-multipoint (P2MP) operation, when multiple units of customer premises equipment can be connected to the same physical wire and port of network equipment;

• Quality of service (QoS) support by means of support of up to four QoS channels in upstream and downstream direction by the transceivers;

• Showtime reconfiguration (SREC) to reconfigure a line with a specified set of configuration parameters, applied during showtime without requiring a fast retrain or full re-initialization;

• Power saving by dynamic control of the time and frequency band available for data transmission depending on user traffic (using discontinuous time frequency operation (DTFO) functionality).

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 8 Gbit/s;

• This edition of the Recommendation specifies profiles up to 424 MHz with +4 dBm and +2 dBm maximum transmit power;

• Configurable start and stop frequencies, PSD shaping and notching;

• Discrete multitone (DMT) modulation (using an inverse discrete fourier transform (IDFT) with 8192 subcarriers with 51.75 kHz subcarrier spacing for 424 MHz profiles;

• TDD (sharing time between upstream and downstream transmission);

• FDX (transmission in both directions at the same time at the same frequency);

• Improved retransmission techniques and use of proactive retransmissions for support of ultralow latency services;

• Low latency retransmission, facilitating impulse noise protection (INP) between the V and T reference points at all data rates to deal at least with isolated erasure events at the U reference point of 10 ms, without loss of user data;

• Forward error correction (FEC) based on the combination of an inner trellis coded modulation (TCM) and an outer Reed-Solomon coding, or low-density parity-check (LDPC) coded modulation with probabilistic constellation shaping (PCS-LCM) and an outer Reed- Solomon coding;

• Discontinuous time-frequency operation (DTFO) in which the time and frequency band available for data transmission may change dynamically;

• Online reconfiguration (OLR) for adaptation to changes of the channel and noise characteristics.