HAVi has a unique combination of features that make it very suitable for the home entertainment environment. It combines support for streaming high-quality audio/video with guaranteed interoperability and hot plug-and-play. This implies that, if two devices of any vendor have HAVi inside, they are designed to work together from the moment they are connected. HAVi makes this possible by building on top of the IEEE-1394 physical and linklayer standard (also known as Firewire or i-Link).

With a current guaranteed bandwidth of 400 Mbits/second and support for bandwidth reservation, the IEEE-1394 bus is well-suited for high-quality audio and video applications. In addition, 1394 provides support for hot plug-and-play by automatically reconfiguring the network each time a device is added or removed.

Interoperability is guaranteed because all network protocol layers-from the physical to the application-are required to be the same for all HAVi devices. Due to those features, network maintenance in HAVi does not require specialized personnel, as is the norm in most business environments. Without HAVi, the connection of a television to a set-top box, personal video recorder, DVD, stereo, PC or camcorder can require complex configuration steps, using a large number of cables and multiple remote controls.

Standardizing on 1394
While standardizing on the powerful IEEE-1394 bus has many advantages for HAVi, it is also one of its limitations. Since HAVi devices must be connected using 1394, only those devices that support the 1394 interface and contain the HAVi software can be part of the HAVi network. But many commonly used devices such as personal digital assistants (PDAs) and most laptops do not support 1394.

Philips has developed a new method called HAVi Markup Language (HAViML), which allows access to HAVi devices from such "non-HAVi" devices, if the latter are connected to the Internet or other Internet Protocol (IP)-based networks. Using that method, the HAVi devices in the home can be controlled by any Internet-enabled device from anywhere in the world, using the same user interface that was used in the home.

There are many advantages in enabling access to a home network from outside. People continue to become increasingly mobile. Given the large amount of time spent away from home, often in far-off places, there is a need to access the home remotely for monitoring (for example, security cameras, and child and baby-sitter monitors), control (setting temperature or VCR recording) or accessing information. By allowing HAVi access from the Internet, all devices connected to the home network can be accessed anywhere, anytime.

Another area where the HAViML method can be valuable is in integrating heterogeneous home networks. Home networking is expected to pick up rapidly in the next five years. According to industrial analysis firm Forrester Research, 15 percent of U.S. households will have broadband access by the end of 2001, and by 2005, 55 percent of U.S. households will demand multidevice broadband Internet access. The primary driver for home networks is to allow broadband Internet access for a variety of computing devices in the home, such as PCs and laptops. A variety of consumer electronics devices are also becoming available that require Internet access, such as MP3 players and Internet radio. All Web-access-related networking is expected to use IP-based wired or wireless Ethernet-based standards such as 802.11.

In the longer term, however, home networks are likely to be heterogeneous, since one type of network will not be suitable for all applications. For example, IP-based networks are at present not suitable for high-bandwidth streaming. The home network is likely to consist of many subnetworks, which may follow different standards. The most popular one is expected to be the IP network. Hence, the ability to control HAVi devices from Internet-enabled devices will be valuable in the home as well. A PDA, Web pad or Internet-enabled entertainment appliance could be used for that purpose from anywhere in the home.

The HAVi home network allows one device to control another device. Usually a "smart" device with greater computing capability is paired with a display, such as a TV, to control less sophisticated devices by providing a better user interface than would be possible on the controlled device. For example, a VCR can be controlled more easily through a TV. Similarly, a security camera positioned at the door can also be controlled through the TV. Images from the camera can be displayed on the TV, and controls from the user interface may be used for changing the pan and tilt positions of the camera.

Communications and control
A HAVi-controlled device typically uses a software application provided by the vendor of the device or a third party. The application executes on the controller device, such as the TV, and communicates with the controlled device, such as the VCR or camera, when it needs to send some commands or transfer data. Communication between the controller and controlled devices is made over the HAVi network, using its Messaging System.

If the security camera of the previous example is to be controlled remotely from an Internet-enabled, non-HAVi device such as a laptop, the laptop cannot communicate directly with the camera. Instead, it uses a standard Web browser to connect to an Internet server provided on the home network. Hence, a residential gateway is required, with an Internet server, so that any Internet device can connect to it through the residential gateway's universal resource locator (URL). The residential gateway should also be part of the HAVi network, so that it can access all HAVi devices in the home.

A typical scenario for accessing the security camera from the laptop is to start a browser and enter the URL for the residential gateway. Once the connection is established, the residential gateway presents a Web page showing a menu of available remote applications. From this menu, the security camera application is selected. This results in an applet being down-loaded from the residential gateway to the laptop, containing the application, and the software required to send HAVi commands over the Internet. Now the security camera application can start executing on the laptop.

If a HAVi device is controlled from the Internet, the controller is not on the HAVi network, and direct communication between the controller and the controlled HAVi device is not possible. Instead, a proxy controller is created on the HAVi network that represents the remote controller present on the Internet. Control commands from the remote controller are sent over the Internet to the proxy controller via the residential gateway. The proxy controller then communicates the commands to the controlled device over the HAVi network.

Results of the command, or any data, are sent from the controlled device to the proxy controller on the HAVi network, and then to the remote controller over the Internet. Multiple remote-control applications can be supported simultaneously by creating one proxy controller for each remote controller, and also saving the mapping of the proxy controller and the remote controller associated with it.

The HAViML method consists of a translation scheme that allows HAVi commands and data to be transferred over the Internet. This is known as the tunneling of HAVi through the Internet. A translation scheme is required because the format of data transfer in the HAVi network is different from that on the Internet. HAVi commands are sent in the HAVi network as binary packets. On the other hand, Internet data is transferred using the Hypertext Transfer Protocol, which is in ASCII form.

In our scheme, we use the existing Extensible Markup Language (XML) and Simple Object Access Protocol (Soap) standards to translate HAVi commands to an Internet-compliant format. The translation is done on the remote site, and the residential gateway translates back from the XML/Soap format to the HAVi format. Note that the response to the HAVi commands is translated to XML/Soap in the residential gateway and returned to the remote site.

This standards-based, rather than proprietary, approach allows the use of standard tools to carry out the translations between the two formats.

A prototype implementation of the HAViML remote-access method described here has been completed. The prototype allows the remote client to access the entire HAVi command set. The demonstration setup consisted of showing remote HAVi access to a HAVi network with a test application capable of sending a large variety of HAVi commands with the proper parameters, and displaying the results of those commands.

The setup for the demonstration consisted of two PCs connected by Ethernet. One of them had the full HAVi software and acted as the residential gateway. The other one was the remote client, with only standard PC software, including a browser. In this setup, all HAVi commands could be sent from the remote client to the home server, and they executed correctly.

Remote interface
The prototype has also been used to execute a user interface for a HAVi device remotely. A HAVi-based user interface has been developed for a DVD player. Within a HAVi network consisting of a TV and the DVD player, the user interface can be shown on the TV, and used for controlling the DVD player. By means of the HAViML method, a laptop computer connected to the Internet, but not directly to the HAVi network, could show the same DVD user interface. Thus, the DVD could be accessed with the same user interface inside and outside the home.

One feature still to be added is "streaming" of audio and video data across the Internet to enable applications such as receiving TV on an Internet-enabled Web pad. However, streaming over the Internet can't offer the same bandwidth guarantees as IEEE 1394. Security is an issue because the ability to access home devices leaves them vulnerable.

The most significant contribution of this work has been to show that HAVi can be extended beyond the 1394 bus to the Internet without modification.

The full version of the article is being presented this week at the IEEE International Conference on Consumer Electronics (ICCE).