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How DLNA and UPnP will enable easy home video networks (Part 2)

Posted: 12 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:dlna? upnp? home video networ?

Use categories

DLNA has also defined four primary use categories:
A player pulls content from a server.

An example is a digital media adapter (DMA) connected to a digital TV pulling content from a PC for viewing. This is known as a two-box pull.

A server sends content to output device.
Here, a consumer selects content using a media server's user interface which is used to send the content to another device. An example is a laptop being used to send content to a digital TV. This is known as a two-box push.

A server sends content to an output device using a remote.
An example is a wireless PDA being used to find and select content on a server, then select a digital TV for viewing, and finally initiate the transfer of content from the server to the digital TV.

Sending (or receiving) content from a server to a device for future use and/or storage upload/download):
An example is a wireless PDA being used to download images from a PC so they can be taken out of the home. This is known as a two-box upload/download.

Version 1.0 of the guidelines covers only the first use category. The remaining three will be covered by Version 1.5 guidelines, slated for being released later this year. An example of a possible combination of devices and use categories is shown in Figure 2.


Figure 2: An example of DLNA's two-box pull use category

In this case, the four devices are a DMP (digital TV) and two PCs and a laptop that have pictures stored on them (DMSs). The TV's remote control mediates the interaction between the TV and the PCs. The use category is a two-box pull because the TV's remote is used to find and select pictures and then pull them to the TV. Because the source of the pictures is accessed from the viewing device, the action is called a "pull" based on the HTTP-get protocol. If the user interface had been on the PC or laptop then the action of sending the pictures to the TV would be a "push". The push model will be an optional feature in version 1.5 guidelines based on RTP.

Interoperability framework
Describing devices and use scenarios are important first steps but they are only half the interoperability battle. A framework and protocol are needed to actually send video or other media from one device to another.

The DLNA's guidelines for its initial version (V.1.0) have organized interoperability requirements into five major categories:

  • Network connectivity: Setting up connection is the first order of business of practical interoperability. For version 1.0., DLNA has chosen Ethernet (IEEE 803.3u) and wireless LAN (802.11a/b/g) protocols as its baseline network connectivity design guideline. A DLNA V1.0 compliant device must support either Ethernet or WLAN.
  • Device discovery: Here's one place where UPnP plays its role. Connected devices that execute the UPnP protocols can find and identify each other. The DMP device will search for DMS devices that meet its specific criteria. The search is automatic. DLNA has selected UPnP V.1.0 as the baseline technology here.
  • Content discovery: UPnP V.1.0 is also the technology used to search and browse content in specific DMS devices as requested by the DMP.
  • Transport: As noted earlier, the two-box pull model is the only use category supported by DLNA V.1.0. As such, HTTP is the transport protocol of choice. Version 1.5, which is expected to be released in 2nd half 2005, will, in all likelihood, also designate RTP (Real-time Transport Protocol) as an optional technology. RTP will enable two-box push and other "push" use categories to be implemented.
  • Media format profiles: Formats and codecs (because codecs support very specific formats) present the most numerous set of options for a baseline design guideline. There are many screen resolutions, aspect ratios, frame rates and compression ratios from which to choose. Not having a lowest-common-denominator here would cause innumerable interoperability problems. V.1.0. requires JPEG for still images, LPCM for audio, and MPEG-2 for video. Optional formats are: GIF, TIFF, AC-3, AAC, ATRAC3plus, MPEG-1, MPEG-4 and VC-1.

Figure 3 shows not only the baselines for V.1.0 but projections for presently unsupported features such as QoS and digital rights management. Each guideline entry lists the device classes that it applies to, making it easy for device developers to identify mandatory and optional interoperability features.

V1.5. guidelines will include mobile handheld device guidelines with Bluetooth connectivity as well as add upload/download, RTP, WMM priority-based QoS, play lists and new device classes such as networked media controllers (DMC), network controllable media renderers (DMR), printers (DMPr) and mobile handheld device classes.


Figure 3: DLNA interoperability framework

Into the future
Although DLNA version 1.0 have made its first step toward making the dream of a networked home with device interoperability a reality, there is still plenty of work to be done. Progress is required on four fronts: ease of setup and use; digital rights management; network security and quality of service.

  • Ease of setup and ease of use
    Home networking configuration in particular today requires some technology savvy and a fair amount of time. Consumer ease of setup up is the first barrier that needs to be overcome. Studies have shown, however, that the average consumer will return the products to the store if he or she can not complete the setup of a new piece of electronic equipment within 15 to 30 minutes after he or she first takes it out of the box. After the equipment is setup and installed, ease of use is required for daily usage. Eventually, future DLNA certified gear will have to mean systems that require easy and intuitive user configuration and ease of use.

  • Digital rights management
    Robust content protection is required by the premium content owners (e.g. Hollywood studios) to allow their commercial content to be streamed between devices in the home networking. Usually the premium digital content is protected by a specific DRM or conditional access such as Windows DRM10, Apple Fairplay, Real Helix, DVB-CSA or OMA2.0. However home devices cannot share content if the DRM can not be interoperable. Today, there are no DRM interoperability standards in the market although some organizations are working on standards such as DVB-CPCM. There are also proprietary DRM transcription models such as DTCP over IP, Coral and etc.

  • Network security
    With wireless connections, security technologies for all devices have to be in sync. The chief threat is that personal content can be viewed by the neighbors either intentionally or unintentionally without the owner's consent or the owner's credentials can be stolen and/or altered by a "drive by" hacker.

  • Quality of service
    In most digital homes multiple media streams will be the rule not the exception. Potentially multiple video streams, audio, voice and data streams from TiVOs, STBs, DVD players, home media servers, PCs, and mobile devices being used by family members compete for home networking bandwidth. QoS provisioning is required to allocate bandwidth, guarantee latency and reduce jitter. The bandwidth allocation is particularly critical for streaming video and the latency guarantee is critical for voice over IP (VoIP.) In order to guarantee bandwidth, minimum latency and jitter, parametric QoS should be considered instead of priority based QoS. The example of parametric QoS for WLAN is WMM-SA/802.11e.

    In a converged CE, PC and mobile handheld digital home, a programmable TI DSP is a perfect device to do encode, decode, transcode and DRM transcription to ensure format and DRM interoperability. Coupled with ease of setup, QoS and security, the intended A/V content can be securely and seamlessly streamed in the home network to the intended device(s) in order to achieve an unprecedented user experience.

Implementation considerations
The number of codecs, standards and transport methods that a system of near-universal connectivity must support begs the question: How is such a system be best implemented?

The codec explosion began in early 1990s with MPEG2 and broadcast digital STBs. Computing power was all important and the most cost-effective implementations at the time were hardware based fixed function ASICs with a very specific targeted level of functionality.

The widespread utilization of the Internet in the late 1990s brought with it many alternative codecs, protocols and standards. As result, the fact that ASICs support only a subset of possible features became a major liability.

Moreover, as Internet applications continue to grow and diversify, systems will need even more versatility. Software-programmable solutions are the obvious alternative and advances in process technology enable single and multi-processor based software solutions. Software-programmable solutions also make upgrades adapting to modifications of standards easier.

With the emphasis in most codecs on signal-processing capability, DLNA and UPnP applications are ideally suited for DSP solutions. In addition to their processing capabilities, recent generations of DSPs have been optimized to meet low power requirements in a variety of applications as shown in the Figure 4.


Figure 4: DSPs address a wide spectrum of DLNA applications

As the consumer, communications and computer industries enter a new era of connectivity and compatibility, DSP technology appears destined to play a pivotal role.

About the authors
Tim Simerly
has been with TI for over three years and is the lead System Architect for the company's streaming media solutions based on the DM642 digital media processor. He holds a BS (summa cum laude) and MS degree in electrical engineering from Georgia Tech, an MS in systems analysis from the University of West Florida and an MBA from Georgia State University.
Joseph Chou is the Director of Technical Marketing for TI's DSP Streaming Media Group, where he is responsible for the strategic and technical direction of video applications for multimedia content in IP-STB and Digital Media Adaptor (DMA) market. Chou received his bachelor's degree in electronic engineering from Chao Tung University in Taiwan, and an MBA from the University of Dallas.

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