The Study Of Ethernet-oriented Voice Gateway And Implementation By FPGA And ARM

A new technique solution of Ethernet-oriented PSTN voice gateway is proposed by analyzing and comparing present solutions. The voice data exchanging strategy, the encapsulation mode of Ethernet frame and the used interfaces are the focuses of research. The voice data is directly encapsulated into Ethernet MAC frame; the high-speed data transmission between PSTN and Ethernet is implemented by FPGA; the switch control and network management is implemented by ARM embedded system.The voice data can be directly encapsulated into Ethernet MAC frame, because MAC address is acted as addressing object among the Ethernet, and driving the network interface to send/receive voice data packets directly can wipe off the redundant IP header, through which can avoid long additional time delay. Furthermore, the Ethernet bandwidth is so broad that sending voice data without compression during encapsulation will also reduce the time delay.In the high-speed data transmission between PSTN and Ethernet, the interface to PSTN is mainly to realize encoding/decoding for El line, distilling voice data form time slot and inserting voice data in time slot according to ITU-T Recommendation G.703 ect.. The interface to Ethernet is mainly to realize the encapsulation/decapsulation of Ethernet MAC packets according to IEEE802.3 protocol. The high-performance parallel processing ability of FPGA can satisfy the strict time-control requirement of constant bit rate line and achieve high processing speed.Another Ehernet interface which is implemented by ARM embedded system is used for switch control and network management, through which the link managemet server can realize voice data exchanging by updating the mapping between time solt and MAC address of telephone terminal. The embedded system has been adopted because it can conveniently use embedded OS to extending system management function and high-layer application based on IP protocol and this will be a compensation for the Ethernet interface implemented by FPGA.The solution proposed simplifys the voice data processing policy, syncretizes two current developing techniques, which is of some theory and application value. Relevant works in this thesis provide valuable reference to the research in same field.