The AT&T Broadband Phone system
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Broadband Phone Technology

The Broadband Phone system combines two key underlying technologies:

  • Thin-client technology based on our VNC system means that the Broadband Phone is stateless—no important information is held in the device. The phone simply displays graphics from the server and sends back input from pen-strokes or finger-presses on the screen. This is similar in concept to an existing phone; if it is replaced with another one, the user doesn't lose their phone number or access to any of their services. Compare that with the applications and data on a home PC!
  • SIP-based IP telephony means that the Broadband Phone does not need to plug into a traditional telephone line, but transmits voice in digital form over the network. Signalling and advanced service provision is done using SIP which is very widely seen as the cornerstone of next-generation communication services. Other types of data can be sent alongside the voice so, for example, users can share information or play an interactive game while talking.

System Architecture

The Broadband Phone system consists of a central server (or server cluster), a number of end user platforms (typically, but not necessarily, Broadband Phones) and an optional gateway to the PSTN. Because of our uncompromising thin-client approach, the central server cluster hosts virtually all of the services, right down to the SIP User Agents for each end user platform. Our servers are primarily Linux-based, but the software can also run under Solaris or, without too much modification, Windows NT.

An overview of the Broadband Phone system architecture is depicted in this diagram.

Advantages of the Broadband Phone

The Broadband Phone has many advantages, primarily owing to the thin client approach. For instance, it is:

The phone itself is stateless, with no application software to crash, no information to lose, and zero user maintenance required. A new phone plugged in simply picks up where the old one left off. Nothing is downloaded to the phone, so there is no risk of viruses.
By this we mean cross-platform mobility rather than physical mobility. Because the system is designed to interact with the endpoint using very simple protocols, it can easily be retargeted at different devices. When working at home, your phone could take on all the facilities normally available at your office. Your personal phone display could even be made to migrate to your PC screen, to a callbox, or to your car dashboard. Of course, as wireless networks proliferate and improve, your phone display could also migrate to your wireless PDA in which case cross-platform mobility would become physical mobility.
A major challenge in creating the Broadband Phone architecture was to produce a system which could scale to millions of users worldwide, and yet still be viable for a small enterprise. The solution lies in the network-centric philosophy, which brings an economy of scale through shared resources and centralised management.
Future proof
Because the phone contains no web browser or other applications, and because all data is kept by the service provider, it never needs upgrading with new storage space or processors. The phone simply reflects whatever applications are made available on the network, where it is easy to change the software or hardware as required, for instance to add a new application.

Why 'Broadband'?

  • High-speed, or broadband, networks are becoming the norm, to support the explosive growth in demand for the exciting multimedia services available on the Internet. The Broadband Phone system was designed with such networks in mind, where the maximum benefit can be drawn from the radical thin-client approach. However, the actual bandwidth required for the Broadband Phone varies with the specific applications deployed. For multimedia-intensive applications (e.g. video, high quality stereo audio, real-time interactive games, etc) true broadband is required. In this case, the underlying broadband connection might be Ethernet, cable modem, xDSL, or wireless. For other applications (e.g. telephony, directories, web, email, etc) less powerful network connections will suffice. These include ISDN or even dial-up over a standard telephone line.