G.hn

Gigabit Home Networking is a specification for wired home networking that supports speeds up to 2 Gbit/s and operates over four types of legacy wires: telephone wiring, coaxial cables, power lines and plastic optical fiber. Some benefits of a multi-wire standard are lower equipment development costs and lower deployment costs for service providers.

History

G.hn was developed under the International Telecommunication Union's Telecommunication Standardization sector and promoted by the HomeGrid Forum and several other organizations. ITU-T Recommendation G.9960, which received approval on October 9, 2009, specified the physical layers and the architecture of G.hn. The Data Link Layer was approved on June 11, 2010.
Prominent organizations, including CEPca, HomePNA, and UPA, who were creators of some of these interfaces, rallied behind the latest version of the standard, emphasizing its potential and significance in the home networking domain. Moreover, the ITU-T extended the technology with multiple input, multiple output technology to increase data rates and signaling distance. This new feature was approved in March 2012 under G.9963 Recommendation.
The development and promotion of G.hn have been significantly supported by the HomeGrid Forum and several other organizations. The technology was not only designed to address home-networking challenges but also found applications beyond this initial scope, showcasing its versatility and potential in the networking domain.

Technical specifications

Technical overview

G.hn specifies a single physical layer based on fast Fourier transform orthogonal frequency-division multiplexing modulation and low-density parity-check code forward error correction code. G.hn includes the capability to notch specific frequency bands to avoid interference with amateur radio bands and other licensed radio services. G.hn includes mechanisms to avoid interference with legacy home networking technologies and also with other wireline systems such as VDSL2 or other types of DSL used to access the home.
OFDM systems split the transmitted signal into multiple orthogonal sub-carriers. In G.hn each one of the sub-carriers is modulated using QAM. The maximum QAM constellation supported by G.hn is 4096-QAM.
The G.hn media access control is based on a time division multiple access architecture, in which a "domain master" schedules Transmission Opportunities that can be used by one or more devices in the "domain". There are two types of TXOPs:

Contention-Free Transmission Opportunities, which have a fixed duration and are allocated to a specific pair of transmitter and receiver. CFTXOP are used for implementing TDMA Channel Access for specific applications that require quality of service guarantees.
Shared Transmission Opportunities, which are shared among multiple devices in the network. STXOP are divided into Time Slots. There are two types of TS:
* Contention-Free Time Slots, which are used for implementing "implicit" token passing Channel Access. In G.hn, a series of consecutive CFTS is allocated to a number of devices. The allocation is performed by the "domain master" and broadcast to all nodes in the network. There are pre-defined rules that specify which device can transmit after another device has finished using the channel. As all devices know "who is next", there is no need to explicitly send a "token" between devices. The process of "passing the token" is implicit and ensures that there are no collisions during Channel access.
* Contention-Based Time Slots, which are used for implementing CSMA/CARP Channel Access. In general, CSMA systems cannot completely avoid collisions, so CBTS are only useful for applications that do not have strict Quality of Service requirements.
Optimization for each medium

Although most elements of G.hn are common for all three media supported by the standard, G.hn includes media-specific optimizations for each media. Some of these media-specific parameters include:

OFDM Carrier Spacing: 195.31 kHz in coaxial, 48.82 kHz in phone lines, 24.41 kHz in power lines.
FEC Rates: G.hn's FEC can operate with code rates 1/2, 2/3, 5/6, 16/18 and 20/21. Although these rates are not media specific, it is expected that the higher code rates will be used in cleaner media while the lower code rates will be used in noisy environments such as power lines.
Automatic repeat request mechanisms: G.hn supports operation both with and without ARQ. Although this is not media specific, it is expected that ARQ-less operation is sometimes appropriate for cleaner media while ARQ operation is appropriate for noisy environments such as power lines.
Power levels and frequency bands: G.hn defines different power masks for each medium.
MIMO support: Recommendation G.9963 includes provisions for transmitting G.hn signals over multiple AC wires, if they are physically available. In July 2016, G.9963 was updated to include MIMO support over twisted pairs.
Security

G.hn uses the Advanced Encryption Standard encryption algorithm using the CCMP protocol to ensure confidentiality and message integrity. Authentication and key exchange is done following ITU-T Recommendation X.1035.
G.hn specifies point-to-point security inside a domain, which means that each pair of transmitter and receiver uses a unique encryption key which is not shared by other devices in the same domain. For example, if node Alice sends data to node Bob, node Eve will not be able to easily eavesdrop their communication.
G.hn supports the concept of relays, in which one device can receive a message from one node and deliver it to another node farther away in the same domain. Relaying becomes critical for applications with complex network topologies that need to cover large distances, such as those found in industrial or utility applications. While a relay can read the source and target addresses, it cannot read the message's content due to its body being end-to-end-encrypted.

Profiles

The G.hn architecture includes the concept of profiles. Profiles are intended to address G.hn nodes with significantly different levels of complexity. In G.hn the higher complexity profiles are proper supersets of lower complexity profiles, so that devices based on different profiles can interoperate with each other.
Examples of G.hn devices based on high complexity profiles are Residential Gateways or Set-Top Boxes. Examples of G.hn devices based on low complexity profiles are home automation, home security and smart grid devices.

Technical parameters

The chart depicts a summary of the crucial technical specifications of the G.hn standard. Many of these technical elements are consistent across different physical media, with variations seen in areas such as Tone Spacing and frequency ranges. This uniformity is essential as it allows silicon manufacturers to produce a singular chip capable of implementing all three media types, leading to cost savings. Presently, G.hn chipsets are compatible with all three media types. This compatibility allows system manufacturers to create devices that can adjust to any wiring type simply by modifying a software configuration in the equipment.

Spectrum

The G.hn spectrum depends on the medium as shown in the diagram below:

Protocol stack

G.hn specifies the physical layer and the data link layer, according to the OSI model.

The G.hn Data Link Layer is divided into three sub-layers:
* The Application Protocol Convergence Layer, which accepts frames from the upper layer and encapsulates them into G.hn APC protocol data units. The maximum payload of each APDU is 2¹⁴ bytes.
* The logical link control, which is responsible for encryption, aggregation, segmentation and automatic repeat-request. This sub-layer is also responsible for "relaying" of APDUs between nodes that may not be able to communicate through a direct connection.
* The medium access control, which schedules channel access.
The G.hn physical layer is divided into three sub-layers:
* The Physical Coding Sub-layer, responsible for generating PHY headers.
* The Physical Medium Attachment, responsible for scrambling and forward error correction coding/decoding.
* The Physical Medium Dependent, responsible for bit-loading and OFDM modulation.

The interface between the Application Entity and the Data Link Layer is called A-interface. The interface between the Data Link Layer and the physical layer is called Medium Independent Interface. The interface between the physical layer and the actual transmission medium is called Medium Dependent Interface.

Support

HomeGrid Forum

The HomeGrid Forum is a non-profit trade group promoting G.hn. The Forum includes over 50 members, categorized as non-profit contributors, participant service providers, promoters, adopters, and liaisons.

Vendors

Vendors promoting G.hn include MaxLinear, ReadyLinks Inc, Lantiq, devolo AG, microchip manufacturer Intel, system-on-a-chip vendor Sigma Designs, and Xingtera, which announced a product in January 2013.
The first live public demonstration of G.hn interoperability was shown at CES, January 10–13, 2012 by Lantiq, Marvell Technology Group, Metanoia, and Sigma Designs.

Service providers

On February 26, 2009, as part of a HomePNA press release, AT&T expressed support for the work developed by ITU-T creating standards for home networking, including G.hn.
Service providers like AT&T promoted G.hn for:

Connecting to any room no matter what the wiring type may be.
Enabling customer self-install
Built-in diagnostic information and remote management
Multiple silicon and equipment suppliers

Other service providers that are contributors to the ITU-T Study Group include British Telecom, Telefónica, and AT&T.

Equipment vendors

In April 2008, during the first announcement of HomeGrid Forum, Echostar, a manufacturer of set-top boxes for the service provider market, expressed its support for the unified standard: