Design And Implementation Of A Small VoIP System Based On Android Platform

VoIP is a new kind of telecommunication technique which uses IP network to transmit the voice signal. One of Its many advantages is that it can greately reduce the cost of communication without undermining the quality of services. In year 2010, China has removed the network access limits through Wi-Fi. Which means the bandwidth is no longer the problem for mobile phone. Thus, VoIP businesses become more and more attractive to people. However, in these two years, the share of smart phone in market has growed up very quickly, which results in a phenomenon that the traditional VoIP business, especially the voice business, can no longer meet the requirements of people. Therefore, the integration of multi-domain business is becoming a new trend in the development of VoIP business.With such an opinion in mind, this paper design and implement a small VoIP system. This system can provide both voice and video calling services. Besides, it can also provide IM services by allowing users to send video based message. The implemention of this system is divided into three parts which are protocol, server and client. This paper chooses Android as the client OS for a very simple reason that is Android is open to everyone, anyone can use it for its own purpose. In the realm of protocol, this paper choose to use SIP as the main session control protocol. To wrap media data, this paper uses RTP because it is widely used in media streaming. Refering to the STUN protocol, this paper implement a unique method to solve the NAT traversal problem. In video codec, H.264 is chosen. To realize the video message preview, RTSP protocol is implemented on the IM server. Since in the real case, there might be hundreds of thousand clients try to connect to the server at the same time, the design of socket I/O model becomes much more important. To solve this case, this paper implements the IOCP mechanism to core layer of the server and uses lots of other techniques to optimize server's architechture, such as BOOST library, design patterns, etc.This paper first briefly introduces the architechture of the system and some knowledge background related to the system. Then focuses on three important issues and discusses them in detail. These issuals are method to realize a high performance UDP server, NAT traversal technique and video transmitting based on H.264. At last, this paper presents the realization of each model and demonstrate the experiment results. This paper can be a reference to those who want to develop VoIP business on Android.