There are now various home network standards available for networking appliances in the field of the home. In the field of consumer electronics, the bus standard IEEE-1394 has become established, in particular. This allows communication between the consumer electronics appliances at a very high data rate. Data rates of 100, 200 and 400 Mbit/s are supported. In the meantime, the original standard IEEE-1394-1995 has been extended and the current version IEEE-1394b specifies even higher data transmission speeds S800, S1200 and S1600. This is sufficient to transmit both asynchronous data packets for controlling the network subscriber stations (subsequently called network stations for short) and isochronous audio and video data streams in parallel. The typical application for data interchange between consumer electronics appliances involves a title, either a video film or a piece of music, being played back from a video or audio data source, and the associated data stream being transmitted to a further consumer electronics appliance. For this instance of application, a logical data connection is set up between the appliances in question, which interchange data with one another. This data connection is then used for transmitting data packets on a regular basis. This form of data transmission is referred to in the IEEE-1394-1995 standard as isochronous data transmission, which involves data packets being transmitted from the data source to the data sink or data sinks on a regular basis, at particular intervals of time.
In addition, asynchronous data transmission also takes place in the IEEE-1394 network. In this case, data packets are sent as required, so to speak. The quantity of such asynchronous data packets which is sent via the bus is dependent on the volume of data which arises. Asynchronous data transmission is used predominantly for identifying and controlling an appliance in the network using another appliance which is present in the network.
However, the IEEE-1394-1995 standard specifies only the bottom layers of the ISO/OSI reference model for data communication, namely the physical layer, the data link layer and parts of the network layer. The higher layers, namely the transport layer, the session layer, the presentation layer and the application layer, are unspecified, however.
A consortium of consumer electronics companies has set about also defining the higher layers for data interchange between the consumer electronics appliances. This standard is known by the acronym HAVi, where HAVi stands for Home Audio/Video interoperability. This standard specifies “interoperability middleware”, which ensures that products from various manufacturers understand one another, i.e. cooperate with one another, in order to perform tasks via the network together.
As mentioned, the typical instance of application for the network of consumer electronics appliances involves a data source appliance sending AV data, that is to say audio or video data, to one or more other consumer electronics appliances. The target appliances are typically referred to as a data sink appliance. The user wishes to be able to select directly that appliance from which he wishes to send data and that appliance to which the data need to be delivered within the network. This selection of the appliances needs to be as convenient as possible for the user. To this end, the user interface known from computer technology is used very frequently today. A user interface comprises one or more operating menus (which can be shown on a display unit) in which the user can use either a mouse pointer or keys on the remote control (particularly cursor control keys) to select individual menu items directly and can make particular inputs using the keypad.
To set up a logical data connection between two network stations, it is possible for the user to select the data source appliance and the data sink appliance directly. Only after this selection is the data connection set up and is it possible for an audio and/or video data stream to be transmitted via this data connection. One example mentioned is where a user wishes to forward the AV data received via a digital set-top box to a television in order to be able to view and listen to the video programme on the television. To do this, the user would need to select both appliances directly. If the AV data are now likewise also intended to be recorded by a recording appliance, then the user would need to select the data source appliance and the data target appliance (that is to say the recording appliance) again and start the recording function.