SOPC based Network enabled Voice Codec Unit

This paper describes the design and implementation of a SOPC based Network enabled Voice Codec Unit which bridges analog speech I/O (compressed speech well within the perceived MOS) to ethernet network. A custom FPGA based board is designed primarily around a low cost Cyclone II FPGA, AMBE Vocoder chip and a Ethernet single chip MAC+PHY. The objective is to enable one such unit to convert the input analog speech into digital speech samples, encode the speech using the selected AMBE Vocoder mode and then send the compressed bit stream at the rate 2.0 ~2.4 Kbps out as TCP packets over the Ethernet interface. Simultaneously, the compressed bit stream of TCP packets from the other similar unit is read in from the Ethernet interface and decoded back in to digital speech samples. The decoded samples are converted back into analog speech via the codec whose output is sent to both the handset or line-level output connection depending upon the mode selected. In the present work the functionalities of ordinary telephones have been relied to generate voice and signalling information and a custom embedded application over a configurable RISC processor platform employing Niche TCP/IP stack and MicroC-OS II RTOS in the same FPGA to transfer packet based data. Two such Network enabled Voice Codec Units are developed that communicates directly with each other without any intermediary servers.