| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 100 === The evolving mobile technologies have made communications between people easier. Such as Push-to-talk over Cellular(PoC) developed by Open Mobile Alliance in 1990s, similar to analog AM/FM handheld walkie-talkie, but more convenient and cheaper, and can converse over half-duplex communication lines. And besides the wide spread cellular voice services, there are technologies like Voice over Internet Protocol (VoIP) using data network to transmit voice for long distance communication at lower cost and fulfilling the increasing demands, either one-on-one of one-to-many. The next generation of Push-to-talk technologies using VoIP, can provide voice communication and multimedia services over heterogeneous networks, such as WiFi, 3G and LAN, and can connect with devices from Public Switched Telephone Network(PSTN) and Public Land Mobile Network(PLMN). In this study, we use open sources software Linphone with Linux system to implement a Push-to-talk platform in order to increase the voice quality and decrease transition delay by optimizing OS scheduling and device buffer, and discuss its performance within homogenous and heterogeneous networks.
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