s, which allow flexible routing of optical signals without the need to convert them into electrical form. This kind of fully optical network is called an optical transport network (OTN). These developments will decrease the cost of digital transmission and increase the transmission capacity of the network to meet the growing demands of data, especially Internet, communications. 7.5 Digital Broadcast Systems Current broadcasting systems such as radio and TV use technologies that were originally developed in the 1940s. Even though some updates have been Introduction to Telecommunications Network Engineering made such as color TV, stereo sound, and radio data system (RDS), current systems do not meet the quality requirements of the future. Another problem with these systems is that they do not utilize radio frequencies as efficiently as more modern technologies do. Digital broadcast radio standards were approved many years ago, but digital radio has not become popular. Analog FM broadcast radio is still the main broadcast radio technology and that is because digital radio does not provide much that is new to the listener. The quality is better but FM radio quality is acceptable for most of us. Another reason is that there has not been political pressure to change from analog to digital and analog transmission is allowed to continue. Digital TV standards are also available today. Digital TV will improve quality and provide some additional services and one of its major advantages is more efficient use of the limited resource of broadcast TV frequencies. An additional converter or a new TV set is required for digital broadcast recep- tion. In many countries decisions have been made to phase out analog TV transmissions between 2005 and 2010. The exact time for transition depends on, among other things, the availability of digital TV sets. 7.6 Summary We introduced in earlier chapters the physical basics of electrical communi- cations and current data communications and telecommunications technolo- gies. In the future we