The Design Of Voice Transmission Under Android System In DTN

Push-to-talk(PTT) is one class of voice communication system generally employed in cellular phone services. Now, PTT mainly depends on the network infrastructure (such as TCP/IP networks). It must establish a stable point to point communication link to complete the conversation. However, in some remote areas that lack fundamental communication equipment, there are some limits to apply PTT to achieve voice communication. With the expansion of the range of human activities, people’s work environments, such as space, oceans, deserts and other areas, often have the following characteristics:high delay, high error rates and low data transmission rate. We usually define them as challenged environments. And now people are eager to have a talkie which can work in those environments. But in this challenged environment, the node can not establish a stable communication link with using conventional methods. While it has emerged some solutions that can work in Ad-hoc(peer to peer network), they need enough density to the end to end path and eventually fail to communicate in the sparse mobile Ad-hoc environments. In order to solve the above problems, the work that the thesis has done is as follows:Firstly, this paper presents a kind of network architecture-DTN, which it is called Delay Tolerant Networks. It is an overlay network that locates in the above of the area network (including the Internet). Compared with the TCP/IP, it has a conspicuous difference. Between the application layer and the transport layer, DTN adds a Bundle layer for storing data. By storing-carrying-forwarding mechanism, DTN ensures the voice communication working in the limited network.Secondly, the article combines DTN with Android and designs a voice intercom APP:DTN-talkie. It mainly includes four core modules:neighbor discovery module, Voice R/P module, MIME R/P module and Bundle S/R module. In order to transmit voice messages reliably, asynchronous message forwarding method is applied to the DTN-Talkie. In other words, the ferry node will receive message under a good condition, while it will store the information when the conditions are not allowed until it encounters the next relay node. Furthermore, in order to transmit bundle package expediently, the paper describes and adopts a kind of fragmentation mechanism, and it will speed up the session interactively.Thirdly, the GUI and working process are shown in the end of the article. The presentation demonstrates the system can run on the Android phones and completes the voice communication in restricted network environments.Adapting to the challenge environment,the design of voice communication software based on Android platform has some significance:First of all, it provides people who live in the areas lacking sufficient network infrastructure with the voice communication services; Secondly, it helps people working under some special circumstances to share information resources, such as marine communication, deep space communication and Earthquake disaster area communication, and it will reduce the cost of network deployment to some degree; Last but not least, the combination of the DTN with smart phone has some innovative significance.