The Digital Living Network Alliance, or DLNA, (http://www.dlna.org/) is an organization established to enhance the interoperability of home networks. The organization issues design guidelines to support the seamless sharing of video, music, photographs and other content through home networks. It also issues a logo for use on products that qualify under these guidelines.

Sony established the DLNA in June 2003 after convincing other manufacturers of the need to improve interoperability through industry-level standardization initiatives. Sony continues to play a leading role in the organization. Today there are over 240 members, including the world's leading manufacturers of electrical appliances, mobile equipment and computers, as well as developers of software, devices, services and applications, and content providers. By supplying a wide variety of DLNA-compliant products, these manufacturers are helping to raise awareness of DLNA as an industry standard for home networking.

Design Guidelines for Seamless Content Sharing within the Home
The DLNA has established a basis for home network interoperability by formulating design guidelines based on various widely used open standards, such as HTTP, UPnP (*1), XML and MPEG. The DLNA protocol stack (*2) is shown in Figure 1.

Connecting Devices to a Home Network/Device Discovery
The network layer consists of Ethernet, a LAN protocol widely used for home networking and Internet access, and an IP network based on wireless LAN technology. Devices on the home network are discovered using DHCP, which automatically assign IP addresses, and SSDP as defined in the UPnP Device Architecture. It is also possible to retrieve the names and functions of devices, and this information can then be used to select devices.

Server Content Discovery/Media Format Compatibility Checking
Using the structure defined in UPnP AV, it is possible to obtain a list of videos, music, photographs stored on a selected device, together with metadata related to this content. The guidelines also stipulate formats, including video formats, such as MPEG-2 and AVC/H.264 (the new MPEG-4 standard) and audio formats, such as linear PCM and MPEG-2 AAC, MP3 as well as media format profile IDs representing these formats.

Content Transfer
At the content transfer stage, compatible content can be selected by using media format profile IDs to check compatibility between the server and the player. The selected content is transferred by HTTP. Link protection technology, such as DTCP-IP, is used when copyright-protected content is transferred.

Design guidelines formulated by DLNA cover the connection of devices to home networks, the discovery of other devices, the discovery of content on servers, media format compatibility checking and content transfers. Their purpose is to allow the seamless sharing of content within the home.

In September 2005, a home network transfer protocol for the ARIB standard for digital broadcasting in Japan was adopted. This protocol, which is based on the DLNA design guidelines and the DTCP-IP standard, will allow broadcast content and other information received through digital tuners to be transferred through a home network.

Figure 2 shows the most common DLNA application. It consists of a digital media server and a digital media player.

The server distributes the content, while the player is operated by the user to control the device that will be used to view the content. The player can display a list of servers on the home network and a list of content on those servers from a different room. When the user selects a content item, the player will request it from the server and play it back as it is received.

The DLNA has so far defined 12 device classes, including digital media servers and digital media players (Figure 3). These device classes are used to create applications based on the three-box model, whereby the system is controlled by a controller other than the player, and applications involved other uses, such as content uploads and downloads, printer control, and connections with mobile devices.

In addition to the formulation of design guidelines, the DLNA has also established systems and infrastructure for the certification of interoperability between products based on the guidelines. It authorizes manufacturers to use the DLNA Certified logo on compliant products.

As shown in Figure 4, products are examined in testing laboratories, where test tools are used to check their conformance with the specifications. Their interoperability with reference devices is also tested. The DLNA has established an interoperability certification system based on these tests in combination with UPnP and Wi-Fi certifications. Other activities include the development of the test tools used in these certification processes, and the selection of reference devices and testing laboratories.

The use of the DLNA Certified logo on devices that pass these tests enables users to see at a glance whether a product has been certified. A list of certified products is also available on the DLNA website.

DLNA Certification and Logo Program began in September 2005. Immediately after its inception, Sony launched numerous DLNA certified products that had passed the certification program.

The DLNA has also produced guidelines for new product categories, including mobile devices and printers. As new technologies and standards, such as power line communication, become available for use, DLNA guidelines will be expanded to accommodate new approaches based on these innovations.

Content and service providers have shown strong interest in linking various types of equipment to home networks. The range of systems covered by the DLNA is expected to expand and diversify in the future.

In March 2006, DLNA Networked Device Interoperability Guidelines and guidelines for related media formats were adopted as international standards with the publication of IEC 62481-1 and IEC 62481-2 by the International Electrotechnical Commission (IEC). In addition, new guidelines established in December 2011 will also, in time, be adopted as IEC standards.