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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

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Outline

Introduction Background Related Protocol System Framework Conclusion Future work Reference Demo

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Introduction

VoIP has already been killer application. Requirement of audio recording system. VoIP protocol

– H.323– SIP (Session Initiation Protocol)

Transport protocol– RTP– RTCP

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Background

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

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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

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H.323 framework

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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.

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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

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WinPcap Model

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Codec

RTP PT Name Type Clock rate (Hz)Audio

channelsReferences

0 PCMU Audio 8000 1 RFC 3551

2 G721 Audio 8000 1 RFC 3551

3 GSM Audio 8000 1 RFC 3551

8 PCMA Audio 8000 1 RFC 3551

9 G722 Audio 8000 1 RFC 3551

15 G728 Audio 8000 1 RFC 3551

18 G729 Audio 8000 1  

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How to Build WAVE File

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

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WAVE file format

BlockAlign = NumChannels * BitsPerSample / 8

ByteRate = SampleRate * NumChannels * BitsPerSample / 8

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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

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Silence Suppression example

69840 - 69600 = 240

(72480 – 69840) / 240 = 11

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Related Protocol

Q,931 H.225 H.245 RTP

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Q.931 Header structure

Name Length(Octets) Note

Protocol Discriminator

1 Always 0x08 for ISDN

Call Reference. 1,2 or 3 The call reference field

Message Type 2 Detail

IEs (Information Elements)

various Detail

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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

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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.

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Important H.245 Message

Message Note Possible 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

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RTP Header structure

P : Padding Ex : Extension CSRC : contributing source identifiers count M : Mark

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The Flow of packet Handle

Packet Capture

Callback function call

H.323 signal event

Finish

H323 Packet Analysis

EveHandleApp

UDP TCP

RTP analysisOther H.323 signal

analysis

Does this IP need to be recorded

TCP or UDP

Check portIs It H.323

signal

Yes Yes

Yes

Finish

No

No No

Event handle

H.323 signal handleSilence Suppression

handle

Open a thread to deal with RTP

payload decode and file handle

Silence event RTP data event

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Environment ofNetwork

Intranet

企業內部乙太網路

PDASmart Phone

網路電話桌上型電腦網路軟體電話

Switch

無線網路電話

H323Rec_Drv

Wirless Network

IP PBX

Gate Keeper

Gate Keeper

Gate Keeper

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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()

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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

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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.

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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

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Reference

OpenH323, http://www.voxgratia.org/documents.html GunGK, http://www.gnugk.org/h323manual-zh.html Q.931, http://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 WinPcap,http://www.winpcap.org/docs/docs_40_2/

html/main.html http://ccrma.stanford.edu/CCRMA/Courses/422/

projects/WaveFormat/

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Demo

Other software– openH323– GUNGK– Golasoft Packet Player

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Q.931 Message Type

Value Name Direction

0x01 Altering Called -> Caller

0x02 Call Proceeding Called -> Caller

0x05 SETUP Caller -> Called

0x07 Connect Called -> Caller

0x45 Disconnect

0x5A Release Complete

0x62 Facility

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Q.931 IEs

Value Name Note

0x04 Bearer Required bearer service e.g. voice, data etc.

0x08 Cause Error/termination code/status.

0x28 Display Display user information

0x7E User-User Convey information between ISDN users