HAVi (Home Audio Video interoperability) provides a home networking standard for seamless interoperability between digital audio and video consumer devices.
All audio and video appliances within the network will interact with each other and allow functions on one or more appliances to be controlled from another appliance, regardless of the network configuration and appliance manufacturer.
HAVi will become the de facto standard for high quality A/V networks HAVi will provide for a home network, which is optimized for audio and video devices.
The main reason for having a dedicated HAVi network for the audio and video devices is that for the exchange of high quality digital video and high fidelity audio signals, a much higher bandwidth is necessary than can be provided by other home networks that are optimized e.g. to control home devices such as lighting, heating, air-conditioning, cooking appliances, etc.
The possibility to integrate other home networks such as existing analog links, telephone lines or new wireless technologies into the HAVi network, was built into the HAVi architecture from the beginning and bridges to these networks are likely to be developed in the future.
HAVi is an initiative from eight major Consumer Electronics companies. The eight CE companies are Grundig AG,Hitachi, Ltd., Matsushita Electrical Industrial Co., Ltd. (Panasonic), Royal Philips Electronics, Sharp Corp., Sony Corp., Thomson Multimedia and Toshiba Corp.
The HAVi architecture is open, scaleable in implementation complexity, platform-independent and language neutral, i.e. HAVi can be implemented in any programming language and on any CPU or real-time operating system.
It provides CE manufacturers the freedom to develop interoperable devices while additionally, application developers can write Java applications for these devices using the open Interoperability API that HAVi provides.
Current CE devices, such as Digital STBs and DV camcorders, contain sophisticated digital processing and storage systems. Future devices will contain even more sophisticated resources. By connecting these devices into the HAVi network it is possible to share their resources and use these to build up more sophisticated applications, such as having two VCRs connected to two tuners with either VCR able to record the signal from either tuner.
HAVi allows a device to be a controlling device and a controlled device at the same time. The benefit of a network of interoperable devices is that the whole is greater than the sum of all the components.
In order to be able to handle both commands and multiple digital audio and video streams, HAVi uses the digital IEEE-1394 network, a standard which enjoys broad support from both the CE and IT industries. IEEE-1394 currently provides a bandwidth of up to 400 Mb/s and is capable of isochronous communication that makes it suitable to simultaneously handle multiple real-time digital AV streams.
Longer transmission distances under the IEEE 1394 standard are near to completion and will allow the IEEE-1394 network to span multiple rooms in a home. HAVi is a distributed software architecture, the software elements of which implement basic services such as network management, device abstraction, inter-device communication and device user interface management.
Software elements on different HAVi devices communicate with each other via HAVi defined protocols to offer the desired service and the Interoperability API. The software elements on a HAVi device are implemented on top of a device- and vendor specific platform, such as a real-time operating system. HAVi software architecture include facilities such as:
- Fire wire CMM (Communication Media Manager), which allows other elements to perform asynchronous and isochronous communication over the IEEE-1394 network.
- Messaging System, which is responsible for passing messages between the HAVi software elements.
- Registry system, which allow at any software element to locate other software elements on the network and detect its capabilities and properties.
- Event Manager, which serves as an event delivery service. An event represents a change in state of the HAVi software elements or the HAVi network configuration.
- Stream Manager, which is responsible for managing real-time transfer of AV streams between functional components.
- Resource Manager, which facilitates sharing of resources and scheduling of actions.
- DCM (Device Control Module), a software element that represents a single device on the HAVi network and exposes the HAVi defined APIs for that device. DCMs assure the “plug and play” facility for HAVi elements. If a device is inserted or removed from the network, a DCM for that device needs to be installed or removed respectively in the network. DCMs are central to the HAVi concept and the source of flexibility in accommodating new devices and features into the HAVi network.
- FCM (Functional Component Module). Contained within a DCM are the Functional Component Modules (FCMs) for each controllable function within the device. Currently HAVi defines FCMs and corresponding APIs for functions like a tuner, VCR, disc based storage, AV display, camera, and modem. In the future it can be expected that new FCMs will be defined for HAVi.
- DCM Manager is responsible for installing and removing DCMs.
Applications need to make them selves known in the HAVi network as a software element to enable communication with other software elements such as the Registry or DCMs but also other applications.
- DDI (Data Driven Interaction). DDI is not a software element but only a protocol that is executed between applications or DCMs.
- Havlet. Havlets are Java applications that can be extracted from a DCM or an Application on request of a display device. They are executed on a Java enabled display device and can draw a User Interface on behalf of that DCM or Application by means of a Java Graphical User Interface API (GUI).
All HAVi software elements communicate using a message passing mechanism. Although the actual implementation of the message passing mechanism can differ from device to device and between brands, the format of HAVi messages and the protocol used for their delivery, are fully specified.
HAVi is an open standard, providing compatibility and interoperability between multi-brand AV devices. This provides consumers with a wide choice when designing their personalized audio-video systems, without sacrificing functionality.
Legacy devices can also form part of the network. Because no one device is the master HAVi-controller of the network and the capability to handle new devices as well as non-standard device features was designed into HAVi from the beginning, the network can evolve as new products are introduced giving the user automatic access to this new functionality.
Figure 5.11 The structure of HAVi system