Called the home-mobile user interface gateway (HAVi-WAP UI gateway), the feasibility of this approach has been demonstrated with a prototype implementation, in which we have selected HAVi (Home Audio Video interoperability) and WAP (Wireless Application Protocol) as entertainment and communication network technologies. Both have protocol stacks that are stretched out far into the application layer of the OSI (Open System Interconnection) reference model, although the implementations are completely different. A gateway connector between the two networks was chosen instead of a bridge or a router.

The main motivation for developing the HAVi-WAP UI was to extend the control of home network appliances — in particular HAVi appliances — beyond the home to mobile networks. The remote mobile control was accomplished by exchanging user interface commands. The HAVi-WAP gateway performs a user interface protocol translation by mapping the HAVi DDI (Data Driven Interaction) user interface to the WAP WML (Wireless Markup Language).

The reasons for developing the home-mobile gateway were to provide a design guide for implementing user interface based remote mobile control of home appliances and acquire knowledge about integrating such a gateway into control software for home audio-visual appliances. Selecting HAVi and WAP as the gateway satisfied several objectives including support of pull and push technology because the HTML standard does not include a push mechanism and support for small-display user interfaces for data driven interaction.

The home-mobile user interface gateway is expected to be a part of a general purpose residential gateway that can be seen as a further development of existing set top boxes. From one side, the residential gateway is connected to one or more home appliances making up a home network. From the other side, the residential gateway contains interfaces to the outside world, to access networks over the telephone service, cable, DSL and satellites. Examples of such interfaces include a TV/radio tuner or a cable modem. The home-mobile gateway as a subpart of the residential gateway has an HTTP capable connection to mobile server provider gateways via some of these interfaces.

Basically, the home network side consists of a number of services, called DDI targets in the HAVi Level 1 user interface terminology. Each target interacts via the DDI protocol with a DDI controller. The latter is a part of a HAVi-WAP gateway. The DDI protocol is presented in the form of DDI API (Application Programming Interface) calls, specialized for sending information over the HAVi network. The DDI target may be an application, or a DCM (Device Control Module) that operates in an implementation-dependent manner. The DDI target is controlled by the DDI controller that communicates with the user via the input/output capacity of a WAP enabled device which is situated remotely.

The mobile network side consists of a physical WAP-enabled device, e.g. a WAP phone. However, in the prototype, we used a software WAP hand set simulator. In general, various configurations are possible with WAP, depending on the hardware/software and the Internet/private network connection available. The one we selected for experimenting, consists of a WAP software development kit including a browser and a WAP phone emulator. We used the Nokia WAP Toolkit 2.1, available at Nokia's site (www.nokia.com).

The traditional WAP architecture is server-client oriented, as the client is in the wireless domain and the server is in the Internet domain. To connect these two domains WAP uses an HTTP-WAP gateway, translating between WAP and HTTP requests, for example, to standard HTTP GET or POST commands. These HTTP requests are forwarded to an HTTP server that will be a part of the HAVi-WAP gateway. In our experimental setup, we used an Ericsson HTTP-WAP gateway (www.ericsson.com) implementing both pull and push technologies.

The HAVi-WAP gateway has three main parts: a WAP connection controller, a WAP connection handlers holder and an HTTP server providing access to the HTTP-WAP gateway. Any network supporting the HTTP protocol may establish the connection between the latter and the HAVi-WAP gateway. In our implementation, we used the Internet.

In a traditional client-server model, a client requests a service from the server which then responses by delivering the service. This is the well-known pull technology in which the transactions are client-initiated. A pull transaction starts with a request from the WAP client to the DDI target. The HTTP-WAP gateway translates the request to a normal GET request and forwards it to the HTTP server. In the user interface the request can be seen as a WML tag selection.The WAP pull handler requests the DDI-WML mapper to translate the selected WML tag into DDI element and then maps the request into a method call for the DDI controller. As a result of the call, some DDI elements are changed and returned to the DDI controller. The latter asks the DDI-WML mapper to translate these DDI elements into WML tags and to assemble a new WML card deck. Once the card deck is complete, it is sent back to the DDI controller that returns it to the WAP pull handler. The latter forwards it to the HTTP server that takes it as a payload for the GET response to the WAP client.

In contrast to the pull technology, the transactions in the push technology are server-initiated. This means that there is no explicit request from the client before the server transmits its content. A push transaction starts by sending a notification message from the DDI target to the DDI controller. The message arguments provide the DDI controller with information about the DDI elements that have been changed. They are forwarded to the DDI-WML mapper for a translation into WML tags and assembled into a new WML card deck. Then, the WML card deck is returned to the DDI controller that sends it to the WAP push initiator.

This creates a PAP (Push Access Protocol) push message with the WML card deck as a content entity. The PAP message is translated into an HTTP POST request to the HTTP-WAP gateway. The POST request header is either created by the WAP push initiator or by a simple HTTP client running as an application on the HTTP server. Upon receipt of the POST, the HTTP-WAP gateway sends the push message to the WAP client.

The major goal of this work was to demonstrate that the control of home appliances can be extended beyond the home network to wireless mobile networks without any modification in the network specifications. We have done this by developing and implementing a HAVi-WAP gateway that intermediates between a wired home network and a wireless communication network using HAVi and WAP specifications. The gateway accomplishes both pull and push technologies, improves the network integration and raises the necessity of developing applications that combine mobile devices with home network devices.

This article will be presented at ICCE in a paper titled "Remote Mobile Control of Home Appliances."