ATT Labs

An archive of

AT&T Laboratories

hosted in

Cambridge University Computer Laboratory

The Digital Technology Group

Home Page

Consumer Broadband Home Page

A Consumer Broadband goal: Data on Virtual Circuits which have QoS passes seamlessly from remote servers through the Wide Area Telecomms Network to Broadband Appliances in homes.


Our plan is to develop a software and hardware architecture for the home which can support both data and high quality media. If new network services such as streaming media on demand are to be successful we believe this will require end-to-end Quality of Service across the entire virtual connection from networked server to home appliance.

We are also trialling the integration of this new technology with new fixed wireless access (FWA) systems. The FWA system will be viable for high speed broadband connections before cabled high-speed broadband connections are available and will be able to fill in areas where it is difficult or too expensive to lay cable or fibre.

Ethernet Virtual Circuits

Ethernet is a de facto LAN standard and early adopters are already installing wired and wireless ethernet systems in their homes. It has many advantages over, for example, ATM as a home standard - most importantly it is available, cheap and simple. However, plain ethernet has no support for Quality of Service (QoS). This means that all data connections are treated as having the same priority, and multimedia streams such as video-on-demand, audio-on-demand or phonecalls can be interrupted by other data transfer activity.

To overcome these limitations we have developed the concept of Ethernet Virtual Circuits (EVC). EVCs allow end-to-end virtual circuit connectivity with multiple levels of QoS across mixtures of ATM and ethernet networks - as long as the ethernet networks use EVC-aware switches and EVC-aware appliances. Importantly, EVC networks are compatible with plain ethernet, although the advantages of using virtual circuits would not be available on the plain ethernet section of the network.

The prototype EVC switch.

At present we have built and programmed a number of prototype EVC switches in Cambridge and we have completed an EVC QoS demonstration system. The system consists of an MPEG-2 video server, an MPEG-2 display appliance, some EVC ethernet switches linked by ATM, some Broadband Phones modified to use the EVC QoS mechanism, and some PC's which can blast packets at various QoS priorities. The EVC switches are also programmed to support multicast to endpoints asking for the streams. The demonstration shows how high priority voice traffic is unaffected by lower priority video streams. Packet blasts at lowest priority do not affect either media stream.

An Integrated Wired and Wireless Access Network

Fixed Wireless Access systems have now been developed to the point where they can provide high speed broadband connectivity to the home. In Cambridge we have been trialling an FWA system made by Cambridge Broadband Ltd. The key designers in this company formed one of our spin-offs several years ago, they had previously developed our Broadband Radio ATM Project. The system provides aggregate bandwidth of 60 Mbps bidirectionally within each base station quadrant. Non line of site coverage works at up to 5 Kms. from a base station. The current design is aimed at the European 3.4-3.6 GHz bands.

Virtual Circuits with QoS pass seamlessly through the Access Network and home ethernet from Enterprise Servers to Broadband Home Appliances.

Our interest in this technology is three-fold, First, it lets us leapfrog the development of fibre broadband to the home by providing us with fast connectivity now. Secondly, being ATM based, it supports QoS through multiple levels of priority over the air. Finally, wireless technology will inevitably form part of a complete broadband strategy to reach destinations which are difficult or too expensive to fibre.

A Fixed Wireless Access antenna on our building in Cambridge (top right). Kings College Chapel is in the background.