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	G.9960, G.9961
G.hn-management	G.9962
G.hn-mimo	G.9963
G.hn-psd	G.9964
G.vlc	G.9991
G.cx	G.9972
G.hnta	G.9970
G.dpm	G.9977
G.sa	G.9978
G.cwmp (TR-069)	G.9980

G.hn is the common name for the "next generation" home network technology standard being developed under the International Telecommunication Union (ITU) and promoted by the HomeGrid Forum. The first Recommendation for G.hn is G.9960, which received consent on Dec 12th 2008. The work is being done in the ITU-T Telecommunication Standardization Sector, Study Group 15, Question 4. Over 20 companies are participating regularly representing a broad cross section of the communications industry including some of the worlds largest telephone companies, major communication equipment companies and some of the leading home networking technology companies.

Overview

G.hn is the next generation standard for existing-wire home networking (a wired and complementary counterpart to the popular WiFi wireless home networking standard). G.hn targets gigabit per second data rates and operation over all three types of home wires: coaxial, power lines and phone wires.

G.hn proponents are working to make G.hn the future universal wired home networking standard worldwide; coexisting with and providing an evolution path from today's existing-wire 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.

Although the "killer" application for existing wire home network technologies is IPTV (especially IPTV offered by a service provider as part of a Triple play (telecommunications) video, 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.

The promise of G.hn is one semiconductor device that can be used for networking over any home wire. Some benefits of the final standard are expected to be lower equipment development costs and lower deployment costs for service providers (by allowing customer self-install).

Technical specifications

Technical Overview

G.hn specifies a single PHY based on FFT OFDM modulation and Low-Density Parity-Check (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 Medium Access Control is based on a 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 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.

Per-medium optimization

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 ensures 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 rates will be used in cleaner media (such as coaxial) while the lower rates will be used in noisy environments such as powerline.
• 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 powerline.
• 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) to ensure confidentiality. 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 can not 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.

Protocol stack

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 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 MAC Service Data Units (MSDUs). The maximum payload of each MSDU 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 MSDUs 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 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" (ie, 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 which was then approved at the December 2008 Plenary meeting of Study Group 15. The standard has been in development since 2006.

Coppergate's Michael Weissman, VP Marketing North America, and DS2's Chano Gomez, VP Marketing claim that G.hn-compliant chips will be available during 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 include Intel, Infineon, Panasonic, Texas Instruments, Best Buy, Ikanos Communications, Aware, DS2, Gigle, Pulse~Link, ACN, Sigma Designs, Westell, University of New Hampshire InterOperability Laboratory (UNH-IOL) and LAN S.A.R.L.

Silicon and IP Vendors

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

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 an 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, France Telecom, NTT, Telenor and Verizon.

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 member of the Board of Directors 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 analyst 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.”

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.

Related standards

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.

Shortly after G.9960 achieved consent, the IEEE P1901 group adopted a baseline (the first early stage in the development of an IEEE standard) that includes three non-interoperable options for PHY and MAC. One of the three PHY/MAC options, which was added in order to get a successful confirmation vote for the baseline text, is compatible with G.hn/G.9960. Although P1901 devices will not necessarily interoperate with each other (because of multiple incompatible PHY/MAC options), the subset of P1901 devices that implement the "G.hn compatible" PHY/MAC will interoperate with ITU-T G.hn devices.

External links

• ITU-T
• ITU-T Study Group 15 Question 4
• 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 Germany