rds for a similar service and some PTTs LAN, MAN and other existing networks, consequently there are have already installed MANs. adaption layer protocols being defined to provide the necessary Although SMDS is based on MAN technology, it will be possible re-formatting of frames and packets to the ATM Cell format. to link the MANs together later using T3 lines to create Wide Area Figure 55.8 shows the Broadband ISDN protocol model for ATM. Networking. SMDS is a connectionless network unlike ATM which will be connection oriented. True standards based ATM networks are not anticipated to be available until well after Frame Relay and MAN approaches. Major vendors world-wide are developing ATM switches with a close eye on standards. Those with proprietary switches are developing modi- 55.4 Conclusions fications to meet the standards. The major force driving B- ISDN in Europe is the Deutshe Bundespost which is due to end a Broadband It is generally accepted that the network of the 1990s will be some ISDN applications trial (Berkhom project) in 1992. The platforms kind of extremely fast and completely integrated network, combin- used for the trial are STM and proprietary ATM switches. In the ing voice, video, image, data, signalling and high speed LAN United States AT&T has had a 160Mb/s proprietary switch on trial transfers onto one backbone. The fast packet concept addresses for over a year. Public services are not expected to be available until these applications and uses the next generation communication 1994/5. However private networks are already available using pro- technologies for future integrated broadband communications net- prietary ATM approaches and standards compliant private ATM works, which will be capable of handling all narrowband and networks are expected in 1993. broadband services. For further information on ATM see Chapter 41. In the U.S. Frame Relay services have already been announced by major carriers to provide an alternative to traditional leased lines 55.3.2 DQDB Metropolitan Area Networks 