top (OTT) services. These companies are active in the content and services layer of the broadband telecommunications ecosystem. They utilise the broadband infrastructure as retailed by an ISP and replace services tra- ditionally provided by telephone and mobile operators. Revenue lost to OTT service providers can be very significant: it is reported that more than one-third of international voice calls is now carried over the Skype platform (Figure 5.17) [14]. Case Study Questions Why was VoIP market uptake slow? How was Skype successful in establishing its VoIP service and attracting customers? How did Skype-out and Skype-in services help the strategic goals? Why did Skype enter the WiFi hotspot market? Why do you think Microsoft acquired Skype? 35.0% International phone traffic 30.0% Skype share (%) 25.0% 20.0% 15.0% 10.0% Figure 5.17 Skype share of international telephony (based on data from eleGeography [14]) Broadband Telecommunications Technologies and Management Audio Coding Similar to voice, analogue audio is encoded with both lossless and lossy source coders. Several lossless coding techniques exist, with the most widely used being the CD standard. MP3 coders are the most well-known of the lossy audio coding techniques. CD Standard Similar to voice, the rate for A to D conversion of audio signals is also determined by human ability to perceive sound. Human audible sound is in the frequency range of 20-20 000 Hz, and therefore A to D conversion must sample sound at greater than 2x20 000 samples per second to ensure all audible frequencies are captured. Furthermore, the human ear is very sensitive to low and high energy level sound and the audible range is from 10-9 to 104 atmo- spheric pressure, a range of 1013, or 130 dB. Since the range is SO much wider compared with voice, audio needs significantly more quantisation levels compared with the 256 levels used for voice. The CD standard specifies sampling rate at 44 100 samples per second, slightly above the audible frequency range, in order to accommodate 