Home multimedia devices will start sporting the Digital Living Network Alliance (DLNA) logo this year, and the number of products adopting this standard will likely increase. Most vendors of multimedia hardware are members of DLNA and have access to its standards. The cost of joining is minimal, and it's a requirement for getting devices DLNA-logo certified.
Meanwhile, we can provide a little insight into the structure and operation of DLNA devices since they're based upon the open Universal Plug-n-Play (UPnP) standard. The DLNA standard specifies the required UPnP subset that every DLNA device must support (see the figure).
It's possible to support more of the UPnP standard, provide more mediaformatted files, and still comply with the standard. UPnP also defines a range of devices that DLNA does not cover, such as lighting controls. Still, all the UPnP devices should be able to coexist if not interact with each other at some level.
A typical mechanism implemented on DLNA media servers, real-time transcoding, lets devices maintain data in a single format but deliver it to another DLNA device in another format. Of course, this means the server requires enough horsepower to handle the transcoding.
DLNA devices use the standard UPnP discovery and control protocols to identify new devices. Application software is still required to handle the presentation and control interaction, but these applications will utilize the UPnP application programming interface (API) standard.
The DLNA standard is likely to expand over time to incorporate more devices and extend the functionality available between devices. Digital rights management (DRM) support is part of the standard, but you will need to become a DLNA member to find out the requirements.
Most UPnP stack developers also have a DLNA variant. This will make the job of creating a DLNA-compatible device easier.