- What does interoperability mean in a HAVi environment?
- Why is this interoperability important?
- What does this interoperability mean for users?
- What are the basic mechanisms in HAVi to achieve interoperability?
- Can several applications execute simultaneously on HAVi devices?
- Do all my devices need to be HAVi devices to be able to use them in a HAVi network?
- How does HAVi handle the problem of incompatible Audio and Video formats?
1. What does interoperability mean in a HAVi environment?
Within a HAVi environment, interoperability means that an application on a HAVi device can detect other HAVi devices that are connected to the HAVi network, and use the functionality offered by that device. The HAVi standard specifies all the protocols over the HAVi network that are required to achieve this interoperability.
2. Why is this interoperability important?
Today, in the world of analog CE (Consumer Electronic) devices, there are proprietary solutions for interoperability between devices from only one manufacturer. In the upcoming digital era, HAVi extends this to true interbrand interoperability -- interaction will be possible regardless of which manufacturers made the devices. The importance of this is clear, since typical consumer home environments have CE devices from multiple manufacturers.
3. What does this interoperability mean for users?
In some cases, the user in a HAVi environment will be using normal audio and video applications, such as watching a TV program or playing a CD, in which the user operates one HAVi device. However, since HAVi devices are connected to each other by the HAVi network, these devices (or, more correctly, applications on these devices) give the user the ability, without any special installation or configuration actions by the user, to have complete functionality and interaction between all HAVi devices in that environment, regardless of which manufacturer made the devices. To give a few examples:
- A VCR could set the time on its own clock by using the clock of a TV that receives signals via a satellite receiver.
- A TV could program a VCR based on the Electronic Program Guide the TV receives. This would be done completely by the TV - the user would not have to program the VCR separately.
When a HAVi device is plugged in or out of the HAVi network, other HAVi devices will detect this and can adapt their functionality. For example:
- When a VCR is unplugged, the TV could inform the user that his programmed recordings are no longer possible and it can try to find another VCR in the HAVi network to use.
- HAVi devices can use the display of other HAVi devices to present a User Interface.
What is the advantage to users of HAVi's remote User Interface capability?
A remote User Interface enables a user to interact with an application via any HAVi device in the network that has a display. For example, a user could program the VCR in the living room from his TV in the bedroom, again, regardless of which manufacturer made either device.
Another important advantage for users is that these display devices need not take part in the application themselves, or even be aware of the functionality behind the User Interface that is shown by an application - the devices simply offer their display to other applications. This allows devices from different manufacturers to access functionality that is not standardized by HAVi. This greatly improves the flexibility of HAVi, since not every application- or device-specific feature, has to be standardized. This will ensure that device manufacturers, or others, can develop these features and bring them to market quickly and efficiently.
4. What are the basic mechanisms in HAVi to achieve interoperability?
The HAVi specification contains a number of distinct Software Elements that each provide a certain functionality. The Software Elements that are needed for interoperability between HAVi devices are the Messaging System, the Registry, the Event Manager, the Resource Manager, the Stream Manager and the DCM Manager. These are called System Software Elements.
There are also Software Elements called Device Control Modules (DCMs) that provide control over device specific functionality such as a VCR or a camera. Applications are also Software Elements. DCMs and applications are installable Software Elements, which means that their presence depends on which devices or functionality is actually present in a particular HAVi network.
Each Software Element offers Application Programming Interfaces (APIs) as mandated by the HAVi specification. A Software Element on a HAVi device can call an API of another Software Element by sending a message to it. The HAVi messaging system ensures that the message is correctly delivered to the intended Software Element which then executes the corresponding function as defined by the API (for example, the "PLAY" API for a VCR). If the Software Element is located on another HAVi device, the HAVi Messaging System is responsible for sending that message over the HAVi network to its peer Messaging System on that device that will in turn deliver it to the intended Software Element. This is transparent to the applications.
5. Can several applications execute simultaneously on HAVi devices?
Yes. A user can gradually extend his HAVi network with new HAVi devices and simultaneously execute applications on them.
HAVi defines a powerful Resource Manager that handles possible conflicts, such as when applications want to control the same DCM. The Resource Manager allows for the possibility of sharing devices. The sharing function is determined by the devices themselves. An example is a set-top box that can simultaneously select different TV programs in the same Transport Stream. The Resource Manager also handles conflicts that could occur, such as when multiple applications attempt to program a VCR (so called Scheduled Actions), or if there are conflicts that arise due to HAVi network resource or bandwidth issues.
6. Do all my devices need to be HAVi devices to be able to use them in a HAVi network?
No. Under certain conditions, HAVi devices can control non-HAVi devices (devices that do not implement the HAVi APIs and protocols). HAVi defines two types of non-HAVi devices: a Base AV device (BAV) and Legacy AV device (LAV). The following conditions must be met for HAVi devices to be able to control a non-HAVi device:
- The non-HAVi device must have an interface over which it can be controlled. This can be a different interface than the HAVi network, such as a wireless link or a proprietary interface.
- At least one HAVi device must support this interface in order to be able to connect the non-HAVi device to the HAVi network. A DCM must be available, and must be installed on a HAVi device that can communicate over this interface.
As explained earlier, a DCM is a Software Element that is installed and executed on a HAVi device and that provides control over device-specific functionality via the HAVi defined APIs (such as the "PLAY" API of a VCR). These APIs can be called by applications on any HAVi device. This action is transparent to the user and the device, and is DCM and device specific.
If the above conditions are met, then the DCM can translate the HAVi defined APIs into corresponding commands over the device-specific control interface.
7. How does HAVi handle the problem of incompatible Audio and Video formats?
The Stream Manager in HAVi is responsible for initiating and terminating the transfer of real-time AV streams between devices on the HAVi network. It relies on other standards such IEC 61883 to specify how this content is transported over the HAVi network. HAVi also defines APIs that control how this content is rendered (such as setting the brightness on a TV or the volume on an audio amplifier). However, the HAVi specification does not mandate that a HAVi device supports any specific content format such as MPEG, DV, AC3 (**), asp, GIF, JPEG, etc.
An example of format incompatibility that HAVi does not address, would be a digital video stream that is delivered to a TV that can only decode MPEG. In this case, the user will see a black screen. It is dependent on the manufacturer of the TV to build in the capability of rendering multiple formats, or of the Digital Video camcorder manufacturer, to build a device that can also produce MPEG. The Stream Manager can in some cases detect these incompatibilities and inform the user.
With the advent of media processors, it becomes possible to offer affordable software-based solutions for this problem. This technology would allow these devices to be upgraded to allow them to handle new formats. It would also allow for the creation of true transcoder devices that can turn one format into another. Whether these devices will actually be built is entirely up to manufacturers and outside the scope of HAVi.
However, HAVi does specify a 'converter DCM' that can be implemented by such a transcoder device. By using the corresponding APIs, HAVi devices can route the stream through this device and have it transcoded to the right format. With the constantly growing number of formats, the need for these transcoders becomes more and more urgent.
|
