Research And Design Of Multi-hop Wireless VoIP Terminal Based On Linux

With the popularization of Wireless Local Area Network (WLAN) based on IEEE 802.11 protocol and the rapid development of Voice over Internet Protocol (VoIP) technique, voice communication technique based on WLAN is emerged, which is called VoWLAN. VoIP wireless terminal based VoWLAN can realize the ability of VoIP wireless voice communication through WLAN, which well satisfies the requirements of affordable price, high quality and mobile flexibility. At present, VoWLAN techniques have great prospects in the field of medical health and manufacture industries and are also fit for the requirements at airport, hotel and emporium. However, the available communication distance for wireless VoIP terminal based on IEEE 802.11 is limited in the case of one hop. It usually uses more wireless Access Points (APs) to extend the communication distance, which increases the cost.Aiming at these problems, a wireless VoIP embedded terminal with the function of multihop voice communication is designed and implemented at the ADM5120 platform in this dissertation. The terminal adopts wireless network cards based on IEEE 802.11b/g to access WLAN, employs AODV (Ad hoc On-demand Distance Vector) as routing protocol and extends distance through multihop communication. Thus it could save the cost and is easy to be arranged flexibly. Moreover, this dissertation designs a scheme which applies SIP (Session Initiation Protocol) in the terminal as the signaling control protocol. Therefore this scheme has good compatibility with the WiFi cell phone based on SIP. In this scheme, the signaling exchange between terminals and servers is realized and the real-time media transmission is achieved through RTP/RTCP.Based on the in-depth study of the VoIP technique and SIP protocol, the whole architecture of the wireless VoIP terminal is proposed in the dissertation. In addition, hardware platform design, driver development and application software design of terminal modules is presented and exchange between modules is designed. The design of AODV routing module and the SIP signaling module are illustrated in detail, which are important in software application design. For AODV routing module, an AODV protocol scheme based on Netfilter function architecture is implemented firstly. This scheme doesn't change the kenerl of Linux and could well realize the function of routing request, routing reply, routing update and maintenance. Secondly, the transplant of AODV protocol of the terminal is achieved by the mode of loadable kernel module. Finally, the performance of multihop voice communication is tested. The result shows that the terminal has short delay in the case of less than three hops. For SIP signaling module,the dissertation builds protocol stacks based on the oSIP/eXosip and design a scheme based on modular modeling technology aiming at the layer structure of SIP. This paper also define finite state machine in user module to realize the logic function of User Agent (UA), which decreases the complexity of SIP signaling control.