G.hn

ITU-T Home networking Recommendations
Common Name	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/HomeGrid	G.9960, G.9961
G.cx	G.9972
G.hnta	G.9970

G.hn is the common name for a home network technology standard being developed under the International Telecommunication Union (ITU-T) and promoted by the HomeGrid Forum and several other organizations. and several other organizations. It supports networking over power lines, phone lines and coaxial cables with data rates up to 1 Gbit/s.

ITU Recommendation G.9960, which received Approval on Oct 9th 2009, specifies the Physical Layer 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-T Telecommunication Standardization Sector, Study Group 15, Question 4. Over 20 companies participated regularly, representing a broad cross section of the communications industry including some of the world's largest telephone companies, major communication equipment companies, and some of the leading home networking technology companies.

Unified communication

G.hn is a new specification for existing-wire home networking (a wired and complementary counterpart to the popular Wi-Fi wireless home networking standard). G.hn targets gigabit per second data rates and operation over all three types of legacy home wires: telephone wiring, coaxial cables and power lines. As 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, configurations that have at least one power line networking interface are likely to become the most common. This will also facilitate integration with home control and demand side management applications for AC-powered appliances.

G.hn proponents are working to make G.hn the future universal wired home networking standard worldwide. By developing dual mode devices, G.hn proponents believe it can provide an evolution path from today's incompatible wired home networking technologies including Multimedia over Coax Alliance over coax, 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. In February 2009 the key promoters of two of these interfaces united behind the latest version of the standard. Others are pursuing different initiatives, such as IEEE P1901, MoCA2 and HomePlug AV2 .

One device, any wire

G.hn proponents offer the technical promise that one semiconductor device that can be used for networking over any home wire. Some proposed benefits of a multi-wire standard are lower equipment development costs and lower deployment costs for service providers (by allowing customer self-install). Documents describing these advantages are available.

G.hn opponents believe that this standard has a major deficiency in that it won’t interoperate with legacy wireline standards such as HomePlug (for powerline) and MoCA (for coax). There are millions of deployed devices in the market that are based on these two standards and future G.hn-based products will not interoperate with any of these. Opponents also believe that a single standard for the three different wired mediums will result in a lowest common denominator solution that offers lower performance on all of the wires as compared to current wireline standards that optimize communications for the specific wired environment (i.e. HomePlug AV and IEEE1901 for powerline, MoCA for coax).

Technical specifications

Technical Overview

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 that ensure that performance is maximized when operating over 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's 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's 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.

G.hn security

G.hn uses the 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 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 extended range for large networks. To ensure security in scenarios with relays, G.hn specifies end-to-end encryption, which means that if node Alice sends data to node Bob using node Mallory as an intermediate relay, the data is encrypted in such a way that Mallory cannot decrypt it or modify it. The other alternative (not used by G.hn) would be hop-by-hop encryption, in which data is sent from Alice to Mallory, decrypted by Mallory, encrypted again by Mallory for delivery to Bob and then decrypted by Bob. In this hop-by-hop scenario, data is available in plain text while it's being relayed by Mallory, which makes the system susceptible to a man-in-the-middle attack.

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.

Protocol stack

File:G.hn protocol stack.001.png

G.hn protocol stack

G.hn specifies the Physical Layer and the Data Link Layer, according to the OSI model.

• 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 Physical Coding Sub-layer (PCS), responsible for generating PHY headers.
  • The Physical Medium Attachment (PMA), responsible for scrambling and FEC coding/decoding.
  • The Physical Medium Dependent (PMD), responsible for bit-loading and OFDM modulation.

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).

Status

During 2008 the group completed a Foundation document (Recommendation G.9960) which received "Consent" at the December 2008 Plenary meeting of Study Group 15. G.9960 was subsequently granted final Approval at the October 2009 Study Group 15 plenary meeting .

On May 2009, a new draft of the G.hn Data Link Layer Recommendation (later renamed to G.9961) was approved. In this draft, key elements of the Data Link Layer were adopted as "baseline text" . G.9961 received consent during the January 2010 meeting in Geneva and received final 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.

Post PHY consent claims from DS2 that G.hn products would be available in 2009 would appear to have been optimistic as Coppergate's Michael Weissman, VP Marketing North America, and DS2's Chano Gomez, VP Marketing now claim that G.hn-compliant chips will be available during 2010 . In-Stat analyst Joyce Putscher, estimates that sample quantities of G.hn-compatible chips could be available in the second half of 2010, with "first equipment by 2010" . Unnamed representatives of the ITU stated chips could be out as early as 2010 .

Industry Support

HomeGrid Forum

The HomeGrid Forum is a global, non-profit trade group promoting the International Telecommunication Union’s G.hn standardization efforts for next-generation home networking. HomeGrid Forum promotes adoption of G.hn through technical and marketing efforts, addresses certification and interoperability of G.hn-compliant products, and cooperates with complementary industry alliances.

HomeGrid Forum members are Intel, Lantiq, Panasonic, Best Buy, British Telecom, Texas Instruments, K-Micro, Ikanos Communications, Aware, DS2, Gigle Networks, Sigma Designs, University of New Hampshire InterOperability Laboratory (UNH-IOL), LAN S.A.R.L, IC Plus Corp, Korea Electrotechnology Research Institute (KERI) and Polaris Networks.

Silicon and IP Vendors

Immediately after G.hn's consent four vendors, Aware, CopperGate, DS2 and Ikanos announced support for the new G.hn standard.

Other silicon vendors actively involved in the development of G.hn include DSL vendors Infineon and Metanoia, microprocessor manufacturer Intel (which on June 2009 said "[...] a single networking technology for all three types of existing home wiring will make it easier to expand the market for Intel’s home networking products"), and SoC vendor Sigma Designs, which on July 2009 said "Sigma intends to support the proliferation of G.hn-based products starting with reference platforms that will power the next-generation of home content delivery".

Service providers

On February 26, 2009, as part of a HomePNA press release, AT&T (which makes extensive 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 will benefit from G.hn for several reasons:

• 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

Other Service Providers that are active contributors to the work being done by ITU-T Study Group 15, Question 4, include British Telecom, NTT, Telenor, Qwest, Telefonica, Portugal Telecom and China Telecom.. However, to date only AT&T and BT have expressed public interest in potentially deploying G.hn devices.

Equipment vendors

On 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:

“

"EchoStar is eager to see HomeGrid Forum accomplish its goals. One standard to transfer HD video over a home’s cable or power lines will make installations much easier for service providers." explained Michael Hawkey, vice president of sales, EchoStar.

”

Consumer Electronics

On March 2009, Best Buy (which is the largest retailer of consumer electronics in the United States) joined the board of directors of HomeGrid Forum and expressed its support for G.hn technology as the single standard for wired home networks:

“

“One of the greatest challenges facing consumers today is the many incompatible technologies that exist for wired networking in the home.[...] Best Buy supports the global adoption of the ITU-T’s G.hn next-generation technology as the single wired standard for connecting devices together over coax, powerlines, and phonelines in the home.”

”

Panasonic, one of the largest manufacturers of consumer electronics, is also a contributor member of HomeGrid Forum.

Industry Analysts

On June 2008, Michael Wolf, director at ABI Research said:

“

“We at ABI Research see several applications, such as multi-room high-definition video, that would ultimately benefit from the move towards a single MAC/PHY for multiple media in the home" [...] The effort to build a higher-speed single specification for the three primary in-home wiring types (powerline, coax and phoneline) will provide a roadmap for next-generation service provider deployments. “While it is still early, ABI Research sees promise in the efforts by ITU G.hn,” says Wolf. “Ultimately, if G.hn sees integration into carrier devices by 2010, we expect that in 2013 some 42 million G.hn-compliant nodes will ship into the market, in devices such as set-top boxes, residential gateways and other service provider CPE hardware.”

”

On December 2008, Joyce Putscher, Principal Analyst at market research firm In-Stat, said:

“

“Service operators have been looking for an international standard that encompasses multiple existing-wire mediums for video distribution. G.hn meets that requirement and it seems clear that with significant industry backing from service providers, semiconductor and equipment vendors, and the fast rate at which the process is moving to achieve a standard, we will see first equipment by 2010.”

”

On December 2008, Kurt Scherf, analyst with market research firm Parks Associates, said:

“

“A single, unified technology for multimedia networks over power lines, coaxial cable, and phone lines has the potential to enable a simple, easy-to-use means of networking devices in the home [...] We believe ITU’s work is an important step towards eliminating fragmentation in the industry and in achieving the vision of a networked home.”

”

However, see Kurt Scherf's subsequent statement in the "Criticism" section below.

On December 2008, Steve Rago, principal analyst at market researcher iSuppli, said:

“

"G.hn provides the next-generation standard for networking over customer-owned wiring. It is destined to become the first universal standard for home networking. [...] G.hn nodes will grow at a CAGR of 257% between 2010 and 2013."

”

Other organizations

On February 25, 2009, three home networking organizations that promoted previously incompatible technologies (CEPCA, HomePNA and the Universal Powerline Association), announced that they had 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 worldwide 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 global 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.

Related standards

File:Ghnta.png

Relationship between G.hnta and G.hn

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.

Potential Applications

Although the major driver for wired home networking technologies has been IPTV (especially IPTV offered by a service provider as part of a triple play service, voice and data service offering (such as AT&T's U-Verse)), it is expected that G.hn will also become the dominant wired networking standard for other markets such as the PC and CE industries. Smart Grid applications like home automation or demand side management can also be targeted by G.hn-compliant devices that implement low-complexity profiles.

IPTV Home Networks

One of the problems faced by most providers of IPTV services is that in many customers' homes the Residential gateway that provides connectivity with the Broadband access network is not located in close proximity 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 solves the problem of connecting the Residential Gateway to one or more Set-top boxes, by using the existing home wiring. Using G.hn, IPTV service providers don't need to install new Ethernet wires, and don't need to use 802.11 wireless networks, which usually don't provide the Quality of Service and Security required for IPTV. Because G.hn supports any kind of home wiring, end users will often be able to install the IPTV home network by themselves, thus reducing the cost to the service provider.

Consumer Home Networks

Although Wi-Fi technology is today the most popular choice 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 NAS device), or is not desired (due to security concerns) or is not feasible (for example, due to limited range of wireless signals).

Consumer Electronics devices

A recent trend in many types of Consumer Electronics (CE) is connectivity. It's usual for many CE products to include 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) now 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 (HD).

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.

Smart Grid

Because G.hn can operate over any type of wire (including AC and DC power lines), it can provide the communication infrastructure required for Smart Grid applications in residential, commercial and industrial environments. 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, NIST included G.hn as one of the "Standards Identified for Implementation" 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 this "strong stakeholder consensus" collapsed when G.hn was removed from the final version of the "Standards Identified for Implementation". Additional standards which are relevant to integrating G.hn with the Smart Grid are mentioned in the NIST report.

The broad concept of Smart Grid includes applications with overlapping scopes such as Demand side management (DSM), Energy conservation measures (ECM), Advanced Metering Infrastructure (AMI) and Home Area Networks.

Because G.hn natively supports popular protocols like Ethernet, IPv4 and IPv6, G.hn-based Smart Grid networks can easily be integrated with IP-based networks. Well-known network management protocols like SNMP can be used to manage large-scale IP networks including G.hn devices.

Criticism

The G.hn effort has been criticized by most proponents of other wired technologies, notably MoCA and HomePlug technologies. Also, some industry analysts have questioned the potential adoption of G.hn. They argue that G.hn is incompatible with the established technologies in the market, including HomePlug AV and MoCA. Some claim that the G.hn specification is not sufficient as a next generation technology and that G.hn will be outperformed by backwards-compatible technologies developed by these groups. HomePlug proponents point out that G.hn claims of gigabit-level powerline performance were and are made based on the most optimistic of theoretical calculations and do not take into account the realities of actual powerline networking that must conform to various regulatory restrictions. This criticism seems to be borne out based on a major amendment to the G.hn specification proposed at the recent Geneva meeting in June 2010. Originally, the G.hn specification allowed pass-band operations in the 100 MHz to 200 MHz spectrum and baseband operations up to 100 MHz. At the Geneva meeting, concerns were raised that such operations did not conform to ITU-R (the other branch of ITU) and to various other regulations that must be met in order to be legally deployed worldwide. In order to address these complaints, an amendment to G.hn was proposed that eliminated the passband, reduced the baseband upper limit from 100 MHz to 80 MHz and reduced transmit power. HomePlug proponents say that their standard addresses such issues and that performance of future G.hn-based products will be in line, or lower than, current HomePlug AV or IEEE1901 performance.

Criticism of the G.hn standard also includes the general nature of the document which totals about 300 pages. The HomePlug AV and IEEE1901 standards contain very detailed technical specifications and range to about 1,300 pages. Critics say that the G.hn standard is too general and that the wide technical latitude it affords could cause multi-vendor interoperability issues whenever products are deployed. Parks Associates analyst Kurt Scherf, after recent conversations with European service providers, is convinced that HomePlug has strong backing from that industry. "I do not think that the G.hn effort will fully succeed until they take into account HomePlug and build in some compatibility with it," Scherf is quoted to have said.

G.hn opponents also believe that the claims made for gigabit-level performance are greatly exaggerated and based on theoretical limits that do not take into account many performance-robbing realities, especially over power lines. In a June 15 article bylined by Stephen Lawson of IDG News Service, Scherf is quoted as saying, “The bottom line is that MoCA and HomePlug work -- and seem to work well -- for the service providers that have chosen them. They'd be very reluctant to make a wholesale move to a technology that's not proven in large field deployments."

EDN Analyst Brian Dipert believes that G.hn will not be adopted as a powerline technology "With DS2's demise. if the rumors are correct, seemingly also go the powerline portions of the ITU's G.hn standards group. That is, unless G.hn faces up to de facto standardization reality and incorporates HomePlug AV into its specifications instead."

IDC Analysts Jonathan Gaw and Michael J. Palma believe that G.hn will face an uphill climb to gain industry adoption.

See also

• IEEE P1901

External links

• ITU-T
• ITU-T Study Group 15 Question 4
• ITU-T Recommendation G.9960
• ITU-T Recommendations: Series G
• The HomePNA Blog contains general information about home networking and G.hn
• 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 Germanyca:G.hn

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