|ITU-T Home networking Recommendations|
|HomePNA 2.0||G.9951, G.9952, G.9953|
|HomePNA 3.0||G.9954 (02/05)|
|HomePNA 3.1||G.9954 (01/07)|
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Telecommunication Standardization sector (the ITU-T) and promoted by the HomeGrid Forum and several other organizations. The G.hn specifications define networking over power lines, phone lines and coaxial cables with data rates up to 1 Gbit/s.
ITU-T Recommendation (the ITU's term for standard) G.9960, which received approval on October 9, 2009, specified the physical layers and the architecture of G.hn. The Data Link Layer (Recommendation G.9961) was approved on June 11, 2010. The work was done in the ITU Telecommunication Standardization Sector, Study Group 15, Question 4. About 20 companies participated in the work, including telephone, communication equipment, and home networking technology companies.
- 1 Unified communication
- 2 Technical specifications
- 3 Status
- 4 Support
- 5 Applications
- 6 See also
- 7 References
- 8 External links
G.hn is a specification for existing-wire home networking. It is a complementary counterpart to Wi-Fi. G.hn targets gigabit per second data rates and operation over three types of legacy home wires: telephone wiring, coaxial cables and power lines. A single G.hn semiconductor device is able to network over any of the supported home wire types. Some benefits of a multi-wire standard are lower equipment development costs and lower deployment costs for service providers (by allowing customer self-install).
The majority of devices in which G.hn may become embedded (such as televisions, set-top boxes, residential gateways, personal computers or network-attached storage devices) will be AC-powered, so configurations that have at least one power line networking interface are likely to become the most common. This [clarification needed] will also facilitate integration with home control and demand side management applications for AC-powered appliances.
The ITU-T extended the technology [clarification needed] with multiple input, multiple output (MIMO) technology to increase data rates and signaling distance.  The work on MIMO for G.hn at ITU-T is under the G.9963 standard.
By developing dual mode devices [clarification needed], G.hn proponents believe[opinion] it can provide an evolution path from other wired home networking technologies such as Multimedia over Coax Alliance (MoCA), HomePNA 3.1 over coax and phone wires (already an ITU standard G.9954), and HomePlug AV, Universal Powerline Association (UPA) and HD-PLC over powerline. Key promoters CEPCA, HomePNA, and UPA, creators of two of these interfaces, united behind the latest version of the standard in February 2009.
G.hn specifies a single physical layer based on fast Fourier transform (FFT) orthogonal frequency-division multiplexing (OFDM) modulation and low-density parity-check code (LDPC) forward error correction (FEC) 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 (12-bit QAM).
The G.hn Media Access Control is based on a time division multiple access (TDMA) architecture, in which a "domain master" schedules Transmission Opportunities (TXOPs) that can be used by one or more devices in the "domain". There are two types of TXOPs:
- Contention-Free Transmission Opportunities (CFTXOP), 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 (QoS) guarantees.
- Shared Transmission Opportunities (STXOP), which are shared among multiple devices in the network. STXOP are divided into Time Slots (TS). There are two types of TS:
- Contention-Free Time Slots (CFTS), 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 (CBTS), 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 (power lines, phone lines and coaxial cable), 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 (such as coaxial) while the lower code rates will be used in noisy environments such as power lines.
- Automatic repeat request (ARQ) mechanisms: G.hn supports operation both with and without ARQ (re-transmission). Although this is not media specific, it is expected that ARQ-less operation is sometimes appropriate for cleaner media (such as coaxial) 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 media.
- MIMO support: Recommendation G.9963 includes provisions for transmitting G.hn signals over multiple AC wires (phase, neutral, ground), if they are physically available. 
G.hn uses the Advanced Encryption Standard (AES) encryption algorithm (with a 128-bit key length) 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 (in the same domain as Alice and Bob) 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 further away in the same domain. Relaying provides for utilizability of multiple transport media and complex network topologies. 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.
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.
- The G.hn Data Link Layer (Recommendation G.9961) is divided into three sub-layers:
- The Application Protocol Convergence (APC) Layer, which accepts frames (usually in Ethernet format) from the upper layer (Application Entity) and encapsulates them into G.hn APC protocol data units (APDUs). The maximum payload of each APDU is 214 bytes.
- The Logical Link Control (LLC), 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 (MAC), which schedules Channel Access.
- The G.hn physical layer (Recommendation G.9960) is divided into three sub-layers:
The PMD sub-layer is the only sub-layer in the G.hn stack that is "medium dependent" (i.e., some parameters may have different values for each media - power lines, phone lines and coaxial cable). The rest of sub-layers (APC, LLC, MAC, PCS and PMA) are "medium independent".
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 (MII). The interface between the physical layer and the actual transmission medium is called Medium Dependent Interface (MDI).
Recommendation G.9960 was granted approval at the October 2009 Study Group 15 plenary meeting.
Recommendation G.9961 received approval on June 11, 2010. During that meeting, concerns about regulatory conformance were raised and an amendment to the G.hn standard was proposed that eliminated the passband (100 MHz to 200 MHz) and reduced the baseband operational spectrum (from 100 MHz to 80 MHz). Other changes included in the amendment included a reduction of transmit power to meet regulatory complaints raised at the meeting. In June 2011, during a joint Forum held by ITU-T, ITU-R and other organizations, it was recognized that "ITU-T G.hn was considered to have electromagnetic compatibility (EMC) and mitigation techniques that go well beyond those considered essential for protecting radio services", and that "Non-ITU compliant home network equipment may cause problems".
In June 2011, four silicon vendors (Lantiq, Marvell Semiconductor, Metanoia and Sigma Designs) announced their participation in an open interoperability plugfest in Geneva, hosted by Homegrid Forum, Broadband Forum and ITU.
The HomeGrid Forum showcased the world’s first live public demonstration of G.hn interoperability at CES, January 10–13, 2012. HomeGrid Forum members Lantiq, Marvell, Metanoia, and Sigma Designs joined together to highlight real-world G.hn capabilities.
In January 2012, Tangotec Ltd. announced that it will have a fully compliant ITU-T G.hn chipset family available in 2012. Tangotec demonstrated G.hn capabilities over all three media at CES 2012.
In December 2012, Marvell and HomeGrid Forum announced that Marvell's G.hn silicon had passed all compliance tests and was now the first compliance certified G.hn silicon. To be first certified G.hn silicon only interop testing remains.
The HomeGrid Forum is a non-profit trade group promoting G.hn. HomeGrid Forum provides technical and marketing efforts, addresses certification and interoperability of G.hn-compliant products, and cooperates with complementary industry alliances.
HomeGrid Forum members include Allion Test Labs, Inc., ARRIS, AT&T, BC Institute of Technology, Best Buy, British Telecom (BT), Chunghwa Telecom, COMTREND Corporation, Holland Electronics, LLC, Institute for Information Industry (III), Korea Electrotechnology Research Institute (KERI), Korea Polytechnic University (KPU), Kwangwoon University, LAN S.A.R.L, Marvell, Metanoia Communications, Inc., MitraStar, Sigma Designs, Teleconnect GmbH, Telefónica, The University of British Columbia, TRaC Global, and Xingtera Inc.
On February 26, 2009, as part of a HomePNA press release, AT&T (which makes use of wireline home networking as part of its U-Verse IPTV service) 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:
- Connect to any room no matter what the wiring type may be.
- Enable customer self-install
- Built-in diagnostic information and remote management
- Multiple silicon and equipment suppliers
Panasonic, one of the largest manufacturers of consumer electronics, is also a contributor member of HomeGrid Forum.
On February 25, 2009, three home networking organizations that promoted previously incompatible technologies (CEPCA, HomePNA and the Universal Powerline Association), announced they agreed to work with Homegrid Forum to promote G.hn as the single next-generation standard for wired home networking, and to work to ensure coexistence with existing products in the market.
On October 2008, the Continental Automated Buildings Association (CABA) and HomeGrid Forum signed a liaison agreement to support HomeGrid Forum’s efforts in conjunction with ITU-T G.hn to make it easy for consumers to connect devices and enjoy innovative applications using existing home wiring.
On July 2009, HomeGrid Forum and DLNA signed a liaison agreement "setting the stage for collaboration between the two organizations and the approval of G.hn as a DLNA-recognized Physical Layer technology".
On June 2010, Broadband Forum and HomeGrid Forum signed an agreement to deliver a compliance and interoperability testing program for products using G.hn technology. The Broadband Forum will support HomeGrid Forum's validation of G.hn products, their promotion of product conformance and interoperability, and help expedite the total time to market for HomeGrid Forum Certified products. On May 2011, both organizations jointly announced the first open G.hn plugfest.
ITU G.9970 (also known as G.hnta) is a Recommendation developed by ITU-T that describes the generic architecture for home networks and their interfaces to the operators' broadband access networks.
ITU G.9972 (also known as G.cx) is a Recommendation developed by ITU-T that specifies a coexistence mechanism for home networking transceivers capable of operating over power line wiring. The coexistence mechanism would allow G.hn devices which implement G.9972 to coexist with other devices implementing G.9972 and operating on the same power line wiring.
The major motivation for wired home networking technologies was IPTV, especially when offered by a service provider as part of a triple play service, voice and data service offering such as AT&T's U-Verse. Smart Grid applications like home automation or demand side management can also be targeted by G.hn-compliant devices that implement low-complexity profiles. 
In many customers' homes the residential gateway that provides Internet access is not located close to the IPTV set-top box. This scenario becomes very common as service providers start to offer service packages with multiple set-top boxes per subscriber.
G.hn can connect the residential gateway to one or more set-top boxes, by using the existing home wiring. Using G.hn, IPTV service providers do not need to install new Ethernet wires, or 802.11 wireless networks. Because G.hn supports any kind of home wiring, end users might install the IPTV home network by themselves, thus reducing the cost to the service provider.
Although Wi-Fi technology is popular for consumer home networks, G.hn is also intended for use in this application. G.hn is an adequate solution for consumers in situations in which using wireless is not needed (for example, to connect a stationary device like a TV or a network-attached storage device), or is not desired (due to security concerns) or is not feasible (for example, due to limited range of wireless signals).
Consumer electronics (CE) products can support Internet connectivity using technologies such as Wi-Fi, Bluetooth or Ethernet. Many products not traditionally associated with computer use (such as TVs or Hi-Fi equipment) provide options to connect to the Internet or to a computer using a home network to provide access to digital content.
G.hn is intended to provide high-speed connectivity to CE products capable of displaying high definition television.
Integrating the power connection and the data connection provides potential energy savings in CE devices. Given that CE devices (such as home theater receivers) very often run on standby or "vampire power", they represent major savings to homeowners if their power connection is also their data connection - the device could reliably be turned off when it is not displaying any source.
Because G.hn can operate over wires including AC and DC power lines, it can provide the communication infrastructure required for smart grid applications. A comprehensive smart grid system requires reaching into every AC outlet in a home or building so that all devices can participate in energy conserving strategies.
On September 2009, the US National Institute of Standards and Technology included G.hn as one of its standards for the smart grid "for which it believed there was strong stakeholder consensus", as part of an early draft of the "NIST Framework and Roadmap for Smart Grid Interoperability Standards". In January 2010 G.hn was removed from the final version of the "Standards Identified for Implementation".
The broad concept of a smart grid includes applications with overlapping scopes such as demand side management, energy conservation measures, Advanced Metering Infrastructure (AMI) and home networks. 
Because G.hn supports popular protocols like IPv4 and IPv6, G.hn-based networks can easily be integrated with IP-based networks. Well-known network management protocols like the Simple Network Management Protocol (SNMP) can manage IP networks including G.hn devices.
- Ben-Tovim, Erez (February 2014). "ITU G.hn - Broadband Home Networking". In Berger, Lars T.; Schwager, Andreas; Pagani, Pascal; Schneider, Daniel M. MIMO Power Line Communications: Narrow and Broadband Standards, EMC, and Advanced Processing. Devices, Circuits, and Systems. CRC Press. ISBN 9781466557529.
- New ITU standard opens doors for unified 'smart home' network, ITU Press Release
- United Nations ITU-T's G.hn Approved as Global Standard for Wired Home Networking
- DS2 Blog: How fast can G.hn be?
- HomeGrid Forum Webinar: In-Stat's Perspective on Integrated, Segregated & Next-Generation Wired In-Home Networks
- "Technology Organizations Align to Support United Nations' ITU-T G.hn Standard: CEPCA, HomePNA, and UPA Unite with HomeGrid Forum to Promote Next-Generation Home Networking Technology". Press release (HomeGrid Forum). February 25, 2009. Archived from the original on March 10, 2009. Retrieved December 1, 2013.
- HomeGrid Forum White-paper: G.hn Compatibility with Existing Home Networking Technologies, HomeGrid Forum Blog
- HomeGrid Forum - G.hn Technology Overview, (registration required)
- Top Ten Things You Need to Know About the New G.hn Standard
- An introduction to G.hn security
- Updated Issues List for G.hn - Geneva May 2009, (ITU membership required)
- UNITED NATIONS ITU-T RATIFIES G.HN STANDARD FOR WIRED HOME NETWORKING
- Forum highlights radio interference fears
- Sigma Designs Unveils Industry’s First G.hn Chipset
- Lantiq Introduces Family of Chips Supporting Global ITU-T G.hn Standard for Home Networking Applications
- G.hn Moves from Specification to Reality
- ITU-T G.hn Specification Achieves Key Milestone with Successful Consent at Geneva ITU-T Meeting, Significant Progress Towards Unified Standard for Home Networking Endorsed by HomeGrid Forum
- Intel publishes white-paper on G.hn standard
- SIGMA DESIGNS JOINS HOMEGRID FORUM BOARD OF DIRECTORS
- Xingtera G.hn Device Upgrades Home Networks with Radio Frequency (RF) Over Coax
- HomePNA and HomeGrid Sign Liaison Agreement, Groups Work to Promote New ITU G.hn Global Wired Home Networking Standard
- HomeGrid Forum Webinar: A Service Provider's Perspective on G.hn, Tom Starr, AT&T
- BT Joins HomeGrid Forum Board of Directors
- Industry Creates HomeGrid Forum to Develop Technology for Enjoying Multimedia Anywhere in the Home
- HomeGrid Forum Adds New Members, Best Buy Joins Board Of Directors, Consumer Electronics Retailer to Help Drive G.hn Technology
- New G.hn Home Networking Standard Has Significant Potential, ABI Research
- New global standard for fully networked home
- CopperGate Communications Commits to G.hn
- HomeGrid Forum and CABA Ink Liaison Agreement to Promote Development and Deployment of Advanced Intelligent Home Networks
- HOMEGRID FORUM SIGNS LIAISON AGREEMENT WITH DIGITAL LIVING NETWORK ALLIANCE
- Broadband Forum and HomeGrid Forum Reach Definitive Collaboration Agreement With the Aim of Enabling Conformance and Interoperability of G.hn Products
- HomeGrid Forum and Broadband Forum Announce First Open G.hn Chipset Interoperability Plugfest
- Multiple industries converging around the G.hn standard, HomeGrid Forum Blog
- Berger, Lars T.; Iniewski, Krzysztof (April 2012). Smart Grid - Applicacions, Communications and Security. John Wiley and Sons. pp. 1–16. ISBN 978-1-1180-0439-5. 712376.
- "Why do we need a unified standard at all?", HomeGrid Forum Blog
- Commerce Secretary Unveils Plan for Smart Grid Interoperability
- NIST Smart Grid Interoperability Standards Roadmap
- Why the Smart Grid must be based on IP standards
- ITU-T Study Group 15 Question 4
- ITU-T Recommendation G.9960
- ITU-T Recommendation G.9961
- ITU-T Recommendations: Series G
- The HomeGrid Forum Blog, A forum for discussion of ITU-T G.hn
- Everywire, Your Definitive Source for All Things G.hn
- Bluehelmets care for homenetworks - a translated report from Tom's Networking Guide Germany