1. HAT development and experiment 2002. 1. 24. Kyoungae Kim, SNU Korea drizzle@mmlab.snu.ac.kr

2. Outline HAT ? Software design Implementation details Experimental result Future work

3. What’s HAT ?

4. HAT ? High-quality Audio conferencing Tool –Audio conferencing tool using mp3 codec Variable bitrates: e.g., 32, 80, 128kbps –Supports IPv4 and IPv6 : unicast and multicast –Supported OS : Windows 2000 Working on MSR IPv6 stack Will work on MSDN IPv6 stack

5. Software Design

6. Software Components Sound device Encoder process Stdin RTP send Wave data PIPE Stdout Mic process rawPCM voice RTPRecv process Stdout PIPE mp3 data Sound device sound Stdin Decoder process RTP header mp3 data RTP header Sender Receiver

7. At Sender MIC process –audio signal  WAV file Encoder process –WAV file  MP3 data ( LAME ) –MP3 data  RTP payload –Send it as a UDP packet

8. At Receiver Receiver process –RTP data  MP3 data –Maintain participant information and statistics in source database with RTCP Decoder process –MP3 data  sound device ( mpg123 )

9. Implementation Details

10. Inter-Process Comm. -check the condition of every process dies or not -If no response, show error msg.

11. Statistics

12. Options - Adjust bitrate - Adjust system performance - Input participant name

13. Message Exchange UI Receiver 1. Create Process ASK_ALIVE ALIVE, SESSION_INFO Encoder 2. Create Process 3ASK_SSRC, Source Report 4.MY_SSRC ASK_ALIVE ALIVE 2.AFX_BEGIN_T HREAD MIC PIPE 5._popen Decoder

14. Experimental result & Future work

15. Experiment environment ETRI Daejeon SNU Seoul APAN-KR(KOREN)Native IPv6 Network

16. Result – bandwidth PCM (Pulse Code Modulation ) –sample 16bit, two stereo, sampling rate 44.1kHz –16 * 141000 * 2 =~ 1.3 Mbps MP3 encoding –sample 16bit, two stereo, sampling rate 44.1kHz –128 – 256 kbps

17. Result – delay Required maximum delay : 200 ~ 300ms Delay of HAT : 800 ~ 900ms Solution to minimize delay –Optimization of mpg123 for HAT tool Delete useless options –Optimization for real-time data Modify buffer size, frame size

18. Future Work Reduce end-to-end delay Develop MSDN IPv6 version Welcome your participation in experiment of HAT and collaboration You can get more information from http://mmlab.snu.ac.kr/~hat