1. 1 H.323 網路電話音訊監控與錄製系統之研製 The design and implementation of audio monitoring and recording system for H.323-based internet phone Advisor : Dr. Kai-Wei Ke Speaker : Wei-Ying Huang Data : 2008 06/03

2. 2 Outline Introduction Background Related Protocol System Framework Conclusion Future work Reference Demo

3. 3 Introduction VoIP has already been killer application. Requirement of audio recording system. VoIP protocol – H.323 – SIP (Session Initiation Protocol) Transport protocol – RTP – RTCP

4. 4 Background H.323 H.323 related software WinPcap Codec How to Build WAVE File Silence Suppression Handle

5. 5 H.323 H.323 is a multimedia conferencing protocol, which includes audio, video, and data conferencing over packet-switched networks. Element of H.323 system – Terminals – Gatekeeper – Multipoint Control Units (MCU) – Gateway

6. 6 H.323 framework

7. 7 H.323 related software OpenH323 – An open source library for development of applications using the H.323 protocol. – Base on PWLib library. GNU Gatekeeper (GUNGK) – An open-source project that implements an H.323 gatekeeper. – Implement most of these functions based on the OpenH323 protocol stack.

8. 8 WinPcap An architecture for packet capture and network analysis for the Win32 platforms. It is composed of – NPF (Netgroup Packet Filter ) – Packet.dll – Wpcap.dll

9. 9 WinPcap Model

10. 10 Codec RTP PTNameTypeClock rate (Hz) Audio channels References 0PCMUAudio80001RFC 3551 2G721Audio80001RFC 3551 3GSMAudio80001RFC 3551 8PCMAAudio80001RFC 3551 9G722Audio80001RFC 3551 15G728Audio80001RFC 3551 18G729Audio80001

11. 11 How to Build WAVE File WAVE file format is a subset of RIFF (Resource Interchange File Format) specification.

12. 12 WAVE file format BlockAlign = NumChannels * BitsPerSample / 8 ByteRate = SampleRate * NumChannels * BitsPerSample / 8

13. 13 Silence Suppression Handle Stop sending RTP packets during silent periods is known as "Silence Suppression“. How to detect Silence Suppression? – RTP mark bit – RTP timestamp

14. 14 Silence Suppression example 69840 - 69600 = 240 (72480 – 69840) / 240 = 11

15. 15 Related Protocol Q,931 H.225 H.245 RTP

16. 16 Q.931 Header structure NameLength(Octets)Note Protocol Discriminator 1Always 0x08 for ISDN Call Reference.1,2 or 3The call reference field Message Type2Detail IEs (Information Elements) variousDetail

17. 17 H.225 H.225 call signaling is used to establish H.323 call It was derived from Q.931, but was modified to be suitable for use on a packet based network

18. 18 H.245 H.245 is a control channel protocol and involves the line transmission of non- telephone signals. H.245 signaling is intended to be carried out in parallel to H.225 signaling.

19. 19 Important H.245 Message MessageNotePossible reply Master-Slave Determination Determines which terminal is the master. Acknowledge, Reject, Release Terminal Capability Set Contains information about a terminal's capability. Acknowledge, Reject, Release Open Logical Channel Transport of audio and data information. Acknowledge, Reject, Confirm End Session Command Indicates the end of the H.245 session. No other H.245 message

20. 20 RTP Header structure P : Padding Ex : Extension CSRC : contributing source identifiers count M : Mark

21. 21 The Flow of packet Handle

22. 22 Environment of Network

23. 23 H323 Packet Analysis and EveHandleApp interface Callback function – void handleData(int channelID, int evtType, struct tm *timeStamp, string sourceAddr, string destinAddr, char* buff, int buffSize, int xtraInfo); H323 Packet Analysis interface – int RDSysStart(callback _callback); //return: 1 means success, 0 means failure – int RDSysShutdown()

24. 24 H323 Packet Analysis and EveHandleApp interface (cont.) – int GetDrvCap() //return the number of network interface card – int StartpCap(int inum) //input the NIC number //return: 1 means success, 0 means failure – int RDInitChannel(string IPAddr, int& nChannelID); //return: 1 means success, 0 means failure – int ReleaseChannel(string IPAddr) //return: 1 means success, 0 means failure

25. 25 Conclusion This research implements a system that provides H.323 audio phone analysis and audio recover. It can deal with silence suppression problem and multiple H.323 phone at the same time.

26. 26 Future work User interface Deal with synchronization problem Test the capability when there are more H.323 phones Extend the SIP or other protocol analysis

27. 27 Reference OpenH323, http://www.voxgratia.org/documents.htmlhttp://www.voxgratia.org/documents.html GunGK, http://www.gnugk.org/h323manual-zh.htmlhttp://www.gnugk.org/h323manual-zh.html Q.931, http://www.freesoft.org/CIE/Topics/126.htmhttp://www.freesoft.org/CIE/Topics/126.htm http://www.protocols.com/pbook/h323.htm http://www.networksorcery.com/enp/protocol/rtp.htm http://www.voip- info.org/wiki/view/RTP+Silence+Suppression http://www.voip- info.org/wiki/view/RTP+Silence+Suppression WinPcap,http://www.winpcap.org/docs/docs_40_2/html/ main.htmlhttp://www.winpcap.org/docs/docs_40_2/html/ main.html http://ccrma.stanford.edu/CCRMA/Courses/422/project s/WaveFormat/ http://ccrma.stanford.edu/CCRMA/Courses/422/project s/WaveFormat/

28. 28 Demo Other software – openH323 – GUNGK – Golasoft Packet Player

29. 29 Q.931 Message Type ValueNameDirection 0x01AlteringCalled -> Caller 0x02Call ProceedingCalled -> Caller 0x05SETUPCaller -> Called 0x07ConnectCalled -> Caller 0x45Disconnect 0x5ARelease Complete 0x62Facility

30. 30 Q.931 IEs ValueNameNote 0x04BearerRequired bearer service e.g. voice, data etc. 0x08CauseError/termination code/status. 0x28DisplayDisplay user information 0x7EUser-UserConvey information between ISDN users