User Guide for RAT v4.2 - Computer Science Networks and
Contents
1. The personal details below are conveyed to the other conference participants Name Roy Bennett UCL Email IR Bennett amp cs ucl ac uk Phone 44 0 20 7679 7934 Location UCL Note Apply Cancel Figure 3 RAT Preferences Personal Details The details that you enter here will be conveyed to all other conference participants and can be recalled by them by clicking on your name The information is sent periodically and may take some time to update at all receivers Name Enter your name here Email Enter your Email address here Phone Enter your telephone number here Location Enter the location of your site here Box 8 Personal Details 10 RAT User Guide Preferences Figure 4 RAT Preferences Transmission Details RAT User Guide Encoding Sets the format for data transmitted to the network The different types of encoding use different amounts of bandwidth Using a 8Khz sampling rate these are Linear16 128 kbit s Uncompressed 16 bit samples with linear spacing between sample values A Law 64 kbit s a law companded 8 bit samples Very similar to Mu Law but only supported by RAT i e not VAT Mu Law 64 kbit s u law companded 8 bit samples This means that the spacing between sample values is not constant but has more samples in the loudness levels where the ear is most sensitive Quality is very similar to L16 the difference is imperceptible wi2. http www ip multicast com RTP spec RFC 1889 1890 25 RAT User Guide Glossary Bandwidth A term used to show the amount of information flowing through a communications channel Expressed in units of n x1000 bits per second kbit s CODEC COder DECoder A hardware or software processor converting between analogue audio or video and the digital format used for transmission in both directions The term is also used to describe the major hardware component of a videoconferencing system DES Data Encryption Standard DVI Audio encoding standard GSM Audio encoding standard IP address IP Internet Protocol addresses are unique numerical identifiers for each networked host computer Kilobits per second kbit s The kbit s rate enables the participants to track how much bandwidth is being used during a session Lecture mode An optimisation for one way transmission which increases the delay on the layout of the media in order to minimise the loss of data in the network The longer the playout is delayed the more time there is to retransmit lost packets Loss Rate The percentage of packet information lost during transmission LPC Audio encoding standard Linear Predictive Coder 9 kbit s Mbone The multicast capable backbone of the Internet It currently consists of a network of tunnels linking the islands of multicast capable sub networks around the world MTU Maximum Transmission Unit A measurement
3. Layering is broken it hasn t been updated for multiple processes etc Weird interaction with rat 3 0 x seems that we can generate packets which some instances of rat 3 0 won t play You get some people in the session whose tools report receiving your data but they don t play it out Suspect we re hitting the limitations of the old playout algorithm rather than a specific bug and the correct solution is to get everyone to update to rat 4 x Sometimes see messages of the form source c 767 Spike 160 gt 2708390 and hear nothing If a receiving stream contains a lot of jitter and out of order packets it crashes sometimes jitter around 1000 ms and random out of order Reported by Peter Parnes Send doesn t always send Sometimes when you turn on the mike nothing is sent The mike volume bar doesn t move Turning on and off 1 to 3 times can help Reported by Peter Parnes When RAT starts it turns off playback mute on the mike input which gives feedback for the mike Muting it via the audio control turns off the feedback Note that record mute and playback mute is not the same thing Reported by Peter Parnes Request outstanding to allow the changing of RTP sessions whilst RAT is running Requested by many people Robert Olson Joerg Ott etc 22 RAT User Guide Crashes on WinNT if another version of Tcl Tk is installed on the machine Reported by Didier Lamballais lt Didier _Lamballais irisa fr gt Occasional cra
4. left of the participants name If the diamond is green loss less that 5 or orange loss less than 10 then the packet loss is small so ask them to turn their volume up If that does not help ask them to turn off silence suppression Tthis option is available from the Options menu accessible from the RAT main window see Box 11 Audio Details If everyone s audio keeps cutting out A possible cause is your moving windows around on the screen When you do this the processing power of the computer is spent on window management rather than audio decoding and you lose audio quality Try not to move windows around unnecessarily Box 5 If you have problems hearing other people 4 Using RAT RAT consists of a Main window see Figure 1 a Preferences window see Boxes 6 10 and a number of user info windows see section 1 3 3 below The following sections discuss the Main window and the Preferences window in greater detail The different command line options are described at the end of the section 4 1 RAT main window The Main Window see Figure 1 of RAT is split into three sections In the middle is a list of conference participants Your own name will always appear at the top of this section Names are highlighted whenever anyone speaks Clicking on the name of a participant including your own will display a Preferences panel with the category Personal Details selected see Figure 2 RAT User Guide In this panel
5. the default is TTL 16 DVI coding The option is useful for example for transcoding between low and high bandwidth sessions over a slow link version Displays the version number of RAT Box 16 RAT Command Line Options 20 RAT User Guide Examples To start a unicast session between the current host and the host myhost example ac uk using port number 12000 type rat myhost example ac uk 12000 To join a multicast session on group address 224 2 2 2 and port 8000 type using primary encoding of DVI and a secondary encoding of LPC rag r Chal loe 224 2272 SOOO Box 17 RAT Examples Packet Overheads There is an overhead associated with each audio packet sent When RAT is operating as an audio tool the RTP header is 96 bits per packet it is longer when RAT is acting as mixer and there are multiple contributing sources in each packet The UDP IP overhead is 224 bits per packet Thus transmitting with 20 ms packets has an overhead of 11 2 kbit s whereas 80 ms only incur an overhead of 2 8 kbit s Initially RAT starts with 2 units represents 40ms packets of DVI coded data at 8Khz This represents a trade off between bandwidth quality and the ability of receiver based repair techniques to work successfully Box 18 RAT Packet Overheads 5 Known bugs as of RAT 4 2 6 There are a number of known bugs and a list of desirable improvements for this version of RAT Those that are re
6. Simon Lockhart Mel x Participant Simon Lockhart Mel x Category Playout Category Decoder Actual Playout ms 163 Audio encoding DVI 8K Mono Target Playout ms 140 Packet duration ms 40 Arrival Jitter ms 45 Loss from me 0 Packets Dropped jitter 0 Loss to me 101 Spike Events 2 Packets received JS Packets Dropped spike 10 Packets lost 1291 Relative Clock Rate 0 997 Packets misordered 1 Packets duplicated 0 Round Trip Time ms Figure 10 RAT Participant information panel Playout and Decoder The 3D positioning and Audio options allow the user to change RAT settings The images in Figure 11 below show the default settings If you activate 3D positioning by checking the appropriate box you can then select the further options Filter type HRTF Head Reflected Transfer Function is the default filter and should be the one you use It models the signal to simulate the normal hearing experience where sound is reflected off ears and shoulders Identity provides the basic signal and should be used if HRTF gives any problems Echo is a filter which is being developed in a research environment and should not be selected Length This is a feature which when implemented fully will enable users to adjust quality at present it is fixed at 32 Azimuth This setting allows you to set individual participants on a virtual half circle in front of you The scale runs from 90 repre
7. hear other people at all rssrsnnnnnrrnnnnnnnnnnnnnnnnrrrrnnnnnnnnnnn 5 Box 4 If other people can t hear you rrnnrrrrrnnnnnnnnvnnnnnrrrrnnnnnnnnrrnnnnnrrrnnnnnensennn 5 Box 5 If you have problems hearing other people rrrrrnnnnnnnnrnnnnnrrrrnnnnnnnnnnn 6 Box 6 Silence Suppression rnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnannnnnannnnnnnnnnnnsnee 8 BKT PISTO Aka 8 RAT User Guide Box 8 Personal Details eee Box 9 Transmission Details sssseeeeeneer ennen Box 10 Reception Details aa Box 11 AUGIO DEMS 22 dere reeks iddaa BOX T RCOdEES ane Box 13FSeturity Details avvek Box 14 Interface Details ua BOX 15 SD POSIIOMING ran REN a Box 16 RAT Command Line Options u ssseeereeeeerernnen nn renee Box 17 RAT Examples ae Box 18 RAT Packet Oven Gass ss Soaks ets a ate si aa Cala ts Figures Figure 1 Main RAT Window errnnnnnnnonnnnnnrrrrnnnnnnnnrnnnnnrrrrnnnnnnnsrrnnnnnrrrnnnneeesssnn Figure 2 RAT Participant information panel Personal Details Figure 3 RAT Preferences Personal Details wrrrnnnnnrrrnnnnnnnnnnrnnnnnrrrnnnnn Figure 4 RAT Preferences Transmission Details rrrrrrnnnnnnnnnnnnnnnrrrnnnnn Figure 5 RAT Preferences Reception Details rrrnnnnrrrrnnnnnnnnrrnnnnnrrnnnnnn Figure 6 RAT Preferences Audio Details nnrrnnnnnnnnnrrnonnnnnnnnnnnnnnnnnnnnnnn Figure 7 RAT Preference Codecs rrrrrnnn
8. if the microphone is not powerful enough If whatever is causing the silence suppression to cut you off cannot be rectified you have to disable silence suppression in the RAT Control Window see Figure 6 RAT Preferences Audio Details and use push to talk see Box 7 Push to Talk Box 6 Silence Suppression Push to talk If you prefer to leave your microphone muted when you are not talking for example if you have switched off silence suppression or if you are listening to a lecture you can use push to talk It means that you keep your microphone muted and only un mute it when talking The easiest way of achieving this is by right clicking anywhere within a RAT window which will toggle the Ta k button check This is why is it called push to talk because you push the right mouse button when you talk Box 7 Push to Talk When checked the Listen and Talk buttons mute incoming and or outgoing audio You can mute the outgoing audio i e microphone or line out by holding down the right mouse button with the pointer anywhere within the RAT Window This muting will continue only while the mouse button is depressed RAT User Guide 4 2 RAT options window Pressing the options button in the Main RAT Window brings up a Preferences window allowing the operation of RAT to be modified There are several categories of options that can be altered and you can browse through them by using the Category Menu Opt
9. same protocol RAT Robust Audio Tool Receive only A condition where a tool is used to receive information but cannot transmit Redundant audio encoding Also known as redundancy A technique to protect against packet loss where a second low bandwidth version of the original encoding is piggy backed onto the preceding packet so that when single packets are lost the redundant version is played back instead of silence See RFC 2198 RTP Real Time Protocol is an application level protocol that provides real time support for multimedia communication See RFC 1889 1890 Silence suppression Silence suppression is used in packet voice systems to reduce the output bandwidth of an audio system by exploiting the on off nature of speech 50 savings are possible TTL TTL stands for time to live and determines how far multicast packages can travel over the Internet Roughly the values can be interpreted as 16 Site 47 UK 63 Europe 127 World Unicasting A unicast connection is a point to point connection between two specific machines 27
10. you can display other technical details by selecting other options on the Category menu Playout Decoder Audio and 3D Positioning see section 4 3 below for details Participant Martin Mauve Universit Elie EG Category Personal Details Name Martin Mauve University of Mannheim Email mauve dpid informatik uni mannheim de Phone Location Note Tool RAT v4 2 4 Linux 2 2 16 22 i686 CNAME mauve 134 155 48 19 SSRC 1d100f3e Figure 2 RAT Participant information panel Personal Details The top section of the main window is divided into sections input to the left and output to the right Checking the boxes labelled Listen and Talk will enable the devices shown below them If you do not check the appropriate box you will be unable to hear and or to be heard Individual participants can be selectively muted by clicking on their names with the middle mouse button or on machines that have a two button mouse by holding down the control key on the keyboard and left clicking on their names By default the output device is Speaker and the input device is Microphone Depending on your hardware configuration Line in and CD may be available for input and Line out and Headset for output To change between these options you click on the small triangular buttons on either side of the device description Beneath the input and the output device is a slider to set sound levels which also gives
11. 97 Karl Lehenbauer and Mark Diekhans This product includes software developed by the Computer Systems Engineering Group and by the Network Research Group at Lawrence Berkeley Laboratory Encryption features of this software use the RSA Data Security Inc MD5 Message Digest Algorithm RAT User Guide Contents ad OCG HOM RE ET EE T 1 2 Before you st l ua uensnnesnnnnmnmnmeraneenneeennnnnrnvnsnn 2 3 Getting startedu nimmmasmnssmnnansinsssnsn svissinvvmin 2 3 1 Starting RAT from SDR or SCS G Gu u usseeeeeeeeeerrrrr nerne renerne 2 3 2 Starting RAT from the command line onnnnnnnnvonnnnnnnnnnnnnnnnnnnnnnnnnnnnn 2 3 2 1 Command lines for a multicast conference rrnnnnnnnnnnnnnnrnnnnnn 2 3 2 2 Command lines for a unicast conference 1 4 3 9 Quiek guide to using RAT srein a aa 4 ar BEING RAT chloe ib tuohatichanetoristiaulacihientagitanubacthiinlatiohisediabbinnlathinulacthinbecihivitiaus 6 44 R T man window pre eee 6 4 2 RAT options window LE 9 4 3 RAT participant WINJOWS ssrrrnnnnnvrrrnnnnnnnnvrnnnnnrrrrnnnnnnnnrrnnnnnrrnnnnene 18 4 4 Command line features mrrnrrnnnnnnvvvnnnnnnnnnrnnnnnnrnnvnnnnnnnnnnnnnnnnnnnnnne 20 5 Known bugs as Of RAT 4 2 6 mnnnnnnvvvnnnnnnnnnnnnnnnnnvvnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 21 Further Reading u issvnmnmmussnusnnunsmenesinrin niekvnssnssiesdnnis 24 Gs renne 26 Boxes Box 1 Unicast and Multicast ae 1 Box 2 TTL and Admin scope Lee katter 3 Box 3 If you can t
12. RAT User Guide User Guide for RAT v4 2 O University College London Computer Science Department RAT User Guide Acknowledgements This user guide was originally written for the UKERNA SHRIMP project Version history RAT 3 0 Original version Louise Clark RAT 3 2 Revision 1 Kristian Hasler RAT 4 2 Revision 2 Roy Bennett Disclaimer UCL cannot accept any responsibility for any loss or damage resulting from the use of the material contained in this document The information is believed to be correct but no liability can be accepted for any inaccuracies RAT User Guide Copyright note Copyright O 1995 1998 University College London All rights reserved Redistribution and use in source and binary forms with or without modification is permitted for non commercial use only provided that the following conditions are met 1 Redistributions of source code must retain the above copyright notice this list of conditions and the following disclaimer 2 Redistributions in binary form must reproduce the above copyright notice this list of conditions and the following disclaimer in the documentation and or other materials provided with the distribution 3 All advertising materials mentioning features or use of this software must display the following acknowledgement This product includes software developed by the Computer Science Department at University College London 4 Neither the name of the University no
13. Sample Rate Conversion Allows the conversion of audio sources which are not using the sampling rate supported by the sound card This requires significantly more processing power The options are high medium and low quality and the Microsoft converter Playout Delay You can limit the playout delay within the range 0 to 2000 ms Lecture Mode If checked the playout delay at the receiver is increased This results in better performance in the presence of variable network delay at the expense of reduced interactivity It is most useful when listening to broadcast lectures hence the name This is automatically turned off if you start to transmit audio 3D Audio Rendering If checked allows you to alter the sound for each participant giving the effect that they are virtually placed around you when using headphones See also section 4 3 Box 10 Reception Details 13 RAT User Guide Preferences JOP Category Audio This panel allows for the selection of alternate audio devices and the configuring of device related options Audio Device TBS Audio Mixer CCO4 4 Sample Rate Channels 8 kHz Mono Silence Suppression Additional Audio Options C Off amp Automatic Manual M Automatic Gain Control Manual Silence Threshold F Audio Loopback FEE 100 I Echo Suppression I Tone Test Apply Cancel Figure 6 RAT Preferences Audio Details Audio Device Use this to change b
14. a numeric indication on a scale from 0 to 100 next to the device indicators This numeric indication is useful when setting appropriate levels with other users at the start of a conference providing a precise indication of your level settings Immediately above the slider is a graphical indication of the output volume and the input gain RAT User Guide In the bottom section of the window is the session name the conference address and port number the TTL and six control buttons From left to right these buttons have the following functionality 1 File control when playing from or recording to files 2 Enabling display of the reception quality matrix 3 Enabling the balloon help facility 4 Options Displaying the various preferences which can be set see section 4 2 below 5 About Shows credits copyright information and feedback methods 6 Quit Closes RAT and ends the session Silence suppression By default RAT starts up with silence suppression turned on The silence suppression attempts to ensure that only audio above a certain level is transmitted This means that you can leave your microphone open i e un muted throughout the conference and the silence suppression feature will ensure that background noise is not transmitted However sometimes the silence suppression will cut out speech as well as background noise This can happen if your microphone is a long way away from your mouth making your voice sound faint or
15. checking the box labelled Talk at the top right of the main window with your left mouse button or by holding down the right mouse button whilst the pointer is in the RAT window If you are using headphones rather than a microphone and speakers you can leave the microphone unmuted all the time If you are using a microphone and speakers without an echo cancellor connected the microphone should only be unmuted when you wish to talk You should now be able to use RAT for taking part in conferences but be aware that you may encounter problems with hearing and being heard These problems can result in your not hearing or not being heard at all often the more difficult problems to solve are those which cause degradation of the sound The most likely problems their possible causes and the solutions are given in boxes 4 to 6 below RAT User Guide If you can t hear other people Make sure that the Listen button is checked If the Listen button is not checked the incoming audio will be muted and the power meter will be plain black Make sure that someone is actually talking You can see that someone is talking when the left power meter in the RAT audio window is active and a name in the participants list is highlighted Check that your headset is plugged into the computer correctly Check the output volume setting Make sure that the volume slider for the speaker or headphones is not too far to the left Check the output type set
16. ems with feedback or echo when using headphones Tone Test This option is for research use only Box 11 Audio Details Preferences Iof x Category Codecs This panel shows available codecs and allows RTP payload re mapping Codec Details 1116 8K Mono Short name L16 8K Stereo Sample Rate Hz L16 16K Mono Channels L16 16K Stereo Bitrate kbps L16 32K Mono RTP Payload L16 32K Stereo Capability L16 44K Mono Layers L16 44K Stereo L16 48K Mono L16 48K Stereo PCMU 8kK Mono PCMU 8K Stereo PCMU 16K Mono RTP payload Map Codec Apply Cancel Figure 7 RAT Preference Codecs Description Codec Details When you click on a codec in the window its details are displayed To use the selected codec click on Map Codec RTP payload You can remap the RTP payload using this feature It is not often necessary to do this Box 12 Codecs 15 RAT User Guide Preferences Figure 8 RAT Preference Security Details Key This is the key used to encrypt the audio data using DES The key can be any combination of letters and number but you must have the same key as those you wish to communicate with Enabled When checked encryption is enabled and your communication with others will be limited to those having the same key Box 13 Security Details 16 RAT User Guide Preferences OP x Category Interface The following feature
17. erence IDC 99 21 23 September Madrid Spain 1999 L Lambrinos P T Kirstein amp V Hardman Improving the Quality of Recorded Mbone Sessions using a Distributed Model to be presented at IDMS 1999 V Hardman amp O Hodson Speech and Music Transmission over the Best Effort Internet to be published in Handbook of Communications Technologies The Next Decade published by CRC Press LLC C S Perkins O Hodson amp V Hardman A Survey of Packet Loss Recovery Techniques for Streaming Audio IEEE Network Magazine September October 1998 I Kouvelas V Hardman amp J Crowcroft Network Adaptive Continuous Media Applications Through Self Organised Transcoding Proceedings of Network and Operating Systems Support for Digital Audio and Video NOSSDAV 98 8 10 July 1998 Cambridge UK C S Perkins amp O Hodson Options for Repair of Streaming Media IETF Audio Video Transport Working Group June 1998 RFC2354 V Hardman M A Sasse amp I Kouvelas Successful Multiparty Audio Communication over the Internet Communications of the ACM Vol 41 5 1998 I Kouvelas O Hodson V Hardman amp J Crowcroft Redundancy Control in Real Time Internet Audio Conferencing Proceedings of the 1997 International Workshop on Audio Visual Services Over Packet Networks 15 16 September 1997 24 RAT User Guide 1996 1995 C S Perkins I Kouvelas O Hodson V Hardman M Handley J C Bolo
18. etween multiple audio devices If No Audio Device is selected then no audio can be recorded or played out This will happen automatically if other software is using the audio device when RAT is started Sample Rate Changes the sampling rate Higher sampling rates improve the sound quality but also require greater network resources When using higher sampling rates the encoding schemes available are limited to ones that support that sampling rate Channels Allows you to change between mono and stereo Silence Suppression This feature ensures that periods of silence within a conversation including background noise will not be transmitted hence reducing network traffic If you leave the default setting Aufomatic RAT will take care of it If you have problems with the automatic setting you can switch to Manual and increase the silence threshold using the slider It is recommend that you use some method of silence suppression see also Box 6 Silence Suppression Automatic Gain Control If checked the microphone gain will be controlled automatically i e the volume will remain relatively level despite your shouting or speaking quietly Audio Loopback If checked and if the soundcard supports this option the audio is looped back so that you hear your own audio 14 RAT User Guide Echo Suppression lf checked RAT will suppress i e not transmit your audio whilst another participant is active This prevents probl
19. f you have problems hearing other people If the other participants audio is too faint ask them to turn up their volume You can adjust the volume of your microphone with the slider bar beneath the word Microphone in the input segment at the top right of the main window With most audio cards you will not hear yourself in your headset or through the speakers when you are talking if you do hear yourself in this way you can turn off this effect Whether you can hear yourself or not you will have to rely to a certain extent on the power meter to adjust your microphone volume if you can hear yourself the volume you hear is not necessarily related to the volume other participants will hear When you speak the power meter should not go all the way into the red area at the top as this volume level will cause you to sound distorted Generally you have to rely on the other participants in the conference to tell you whether your volume is set correctly The numeric indication on a scale from 0 to 100 labelled Gain can be useful for indicating to others the level at which you are transmitting If the audio from another participant is very broken up The most likely causes of this are either network congestion causing the loss of their data packets or the other user speaking too quietly for the audio tool to distinguish them from the background noise You can tell if you are losing packets from another participant by looking at the diamond to the
20. g RAT from the command line from SDR and from the Secure Conference Store SCS Using one of the latter two is easier as they automatically configures the tool for use 3 1 Starting RAT from SDR or SCS When joining a conference with audio using SDR or SCS RAT will start up automatically All parameters will be set automatically 3 2 Starting RAT from the command line The commands vary with platform and conference type A full list of the command line options is given in section 4 4 below 3 2 1 Command lines for a multicast conference The format for setting up RAT from the command line is as follows Unix Prompt gt rat options lt address port gt Windows95 98 NT4 0 Click on the Start button in the bottom left hand corner of the screen Select Run In the Run Window type the following in the open field Open rat options lt address port gt Multicast addresses should be in the range 224 2 0 0 224 2 255 255 except when using admin scope see Box 2 The port number should be an even RAT User Guide number and at least 1024 RAT uses both the port specified and also the next port So as an example this line would start RAT with a TTL of 47 see Box 2 for an explanation of TTL on the multicast address 224 2 2 60 and port number 5004 Prompt gt Open rat t 47 224 2 2 60 5004 In the example above the user has used the option t to specify the TTL TTL determines how far the audio packets w
21. ill go i e how far away you can talk to people A TTL of 47 is generally large enough for communication within the UK All participants must use the same multicast address and port number in order to talk to one another TTL TTL stands for Time To Live and determines how far the audio that you transmit will travel As a rough guide a TTL of 15 will reach other parts of a campus a TTL of 47 will reach all parts of a country in Europe or a state in the USA a TTL of 63 reaches a continent and 127 world wide These values can differ depending on your location and you should confirm them by contacting your local network administrator The default for RAT is a TTL of 16 The maximum TTL allowed is 255 Admin scope Admin scoping assigns different ranges of multicast addresses that determine how far your audio will be transmitted Using admin scope will limit conferences more accurately and is more sophisticated than specifying a TTL Like TTL scopes admin scopes need to be set up by the network administrator When the scopes have been configured you will get a range of addresses for each of the scopes defined Using an address in the range provided will limit your conference to that scope Example If local scope is defined as addresses in the range of 239 0 0 0 239 100 255 255 any conference on addresses in this range will be restricted to the local area as defined by the network administrator TTL scoping is still widely used b
22. in Bytes of the largest packet size which a network is capable of transmitting Multicasting Multicasting is sending audio video etc on the Internet in way which ensures that anybody who is interested in receiving the information can receive it but only people who are interested will receive it Think of it as being in between unicast like most telephone calls between two telephones only and broadcast TV the signals are sent to you whether you want to watch or not 26 RAT User Guide Multicast address Addresses used for multicast conferencing should be in the range 224 2 0 0 224 2 255 255 Note Multicast addresses must be agreed upon in advance of the multicast session either through e mail or phone or assigned using a tool such as SDR Network congestion A condition in an IP network where the amount of traffic injected into the network is too great for the routers to handle and some packets are discarded PCM Audio encoding standard Pulse Code Modulation 64 kbit s 8 bit u law encoded 8 kHz Port A UDP User Datagram Protocol number unique to the broadcast session and should be over 5000 Note The port number must be agreed upon in advance either through e mail or phone or assigned using SDR Protocol A set of standards that govern the transfer of information between computers over a network or via telecommunications systems To reduce errors the computers at both ends of a communications link must follow the
23. ions can be set for the current session by clicking on the Apply Preferences button or kept for future sessions by clicking on the Save amp Apply Preferences button Clicking on the cancel button will cancel any changes made These are some of the options you May need to change often If other participants complain that your audio keeps cutting out and it is not due to packet loss try turning up your microphone volume If that does not help turn off Suppress Silence see Box 6 Silence Suppression If you turn silence suppression off you should mute your microphone whenever you are not speaking otherwise you will be transmitting background noise continuously see Box 7 Push to talk If you are only listening for example to a lecture you should turn Lecture Mode on When Lecture Mode is switched on RAT delays the playout of the audio for a short while allowing more time for packets to be received Lecture Mode is automatically switched off when you talk You may want to change your name as it appears in the Main RAT Window You can do that by clicking in the Name field editing the information Likewise you can change your e mail address phone number and location These details will be available to other participants if they click on your name in the Main RAT Window For a thorough description of the options available in the RAT Preferences Window see Boxes 6 10 RAT User Guide Preferences OP x Category Personal
24. levant to users are listed here The full list is included in the documentation with the software at the end of the file named MODS under the heading TODO Assorted audio driver problems e FreeBSD driver bug on SoundBlaster 16 has small write buffers and stops working full duplex mode after a time Hard to fix because of cushion e Crashes on FreeBSD 4 0 reported by Lars Eggert and Joe Love Due to bugs in FreeBSD 21 RAT User Guide e Broken auddev_pca with adding of audio interface conversion code FreeBSD 3 1 pca audio does not seem to work anymore e SunVideoPlus interface code does not work properly The driver Sun distributes only works in 8k mono MMAC produce the card and wrote a driver for Sun an exceptionally buggy and unstable driver MMAC now has a better version but expect you to pay for the developer kit to access features 1200 for a card that does not perform as advertised The marketing blurb states it has G728 G722 and CD Quality audio it may do but you can t access them e SGI O2 s don t have autosensing audio interface selection like Indy s e Thierry Turletti still has problems with the NM256 card and device pairing e Maestro2 cards only support stereo recording you need to hack auddev_oss to deal with this Joseph Eggleston Disabling participant list doesn t work if the window has been resized not sure if this is a feature of Tk or the window manager but there s little we can do about it
25. nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnne Figure 8 RAT Preference Security Details rrrrrrrnnnnnrrrrnnnnnnnnvnnnnnnrrrnnnnn Figure 9 RAT Preferences Interface Details orrnnnnnrrrrnnnnnnnnrrnnnnnrrnnnnnn Figure 10 RAT Participant information panel Playout and Decoder Figure 11 RAT Participant information panel 3D positioning and Audio RAT User Guide 1 Introduction RAT v4 2 6 Untitled session M Listen 52 3 kb s I Talk 0 0 b s gt Speaker Vol 76 Microphone 3ai 76 a DRoy Bennett UCL Tdusan US Martin Mauve University of Mannheim Jurc Barcelona lt P Luis Costa LIP6 France pi an Gerke Pion crowcroft lt PJan Gerke Tarso Savanovic IJS Ljubljana Slovenia Untitled ERE Address 129 132 66 2 Port 7000 TTL 63 gje al Options About Quit Figure 1 Main RAT Window RAT Robust Audio Tool is an audio conferencing tool RAT can be used for either point to point unicast conferencing involving a direct link between two computers or for multiparty multicast conferencing when many participants in different locations are linked via a multicast capable network see Box 1 Unicast and Multicast A unicast connection is like a telephone call which has one connection between two telephones for the duration of the call You should use unicast if there are only two people in the conference and if one
26. of you does not have access to multicasting In order to set up a unicast connection you must know the name of the computer to be used by the person with whom you want to have a conference A multicast connection can in principle have an unlimited number of participants Multicast networking is available on Local Area Networks LANs and in parts of the Internet You must use multicast if there will be more than two participants in the conference Tools like RAT VIC NTE WB and SDR have been specially developed for multicasting Box 1 Unicast and Multicast RAT User Guide 2 Before you start In order to receive audio there must be either a speaker or a pair of headphones connected to your computer In order to transmit audio you Must have a microphone plugged into your computer You should also have a full duplex soundcard installed RAT only supports full duplex sound cards Check your sound card s instruction booklet to see if it has a full duplex mode before using RAT It is recommended that headphones are used in preference to speakers Using headphones allows you to listen and talk at the same time this is known as full duplex audio If you do not use headphones the output from the speakers may interfere with the input to the microphone causing unpleasant feedback The only other way of avoiding this feedback is to use an expensive echo cancellor 3 Getting started There are three ways of startin
27. p sample as a replacement You can specify how to encode the backup sample and also set the offset from the original packet the backup sample should be sent in This type of loss protection is also supported by FreePhone from INRIA Interleaving works by interleaving the order in which the packets can be sent This tries to prevent against large gaps in network loss The size of the packets to interleave and the separation between each interleave can be altered using Units and Separation respectively This should only be used with other participants using RAT3 2 or above Box 9 Transmission Details 12 RAT User Guide Preferences olx Category Reception Repair Scheme Pattern Match Sample Rate Conversion High Quality F Limit Playout Delay Minimum Delay ms Maximum Delay ms 0 2000 bh T Lecture Mode F 3D Audio Rendering Apply FE Figure 5 RAT Preferences Reception Details Repair Scheme There are five options none of which affect the data sent to the network Pattern match repeats a suitable segment of audio from before the loss occurred and with no discontinuity in phase This sounds better than packet repetition but involves more calculation Repeat patches over the gap left by a missing packet with the previous packet Repeat similar scheme but more sophisticated Noise introduces a random pattern None means that no attempt is made to repair losses
28. r is primary encoding secondary encoding etc A maximum of seven levels of encoding are possible although only two are available from the user interface See Box 12 for description of the CODECs and their recommended usage allowloopback Causes RTP packets to be looped back during multicast sessions Mainly used for debugging hame name Sets the RAT window title to the value of name p priority Sets the thread priority on the Windows 32 bit version The following values are observed 1 above normal priority level 2 time critical thread priority 3 highest thread priority You should not need to change this option repair method Specifies the use of receiver based repair techniques based on method This can currently be either none or repeat t TTL Specifies the TTL Time To Live value set in the packet headers This limits the scope of the packets The following values are generally considered appropriate 16 campus organisation 64 continent 47 country and 127 world T addr port TTL CODEC addr port TTL CODEC Causes RAT to operate as an RTP transcoder mixer In this mode the user interface is not displayed and no audio is played out Instead RTP packets received from either group are transcoded into the format specified for the other group multiple sources are mixed together and the result transmitted to the other group In each case addr may be either unicast or multicast and the TTL and CODEC specifiers may be omitted
29. r of the Department may be used to endorse or promote products derived from this software without specific prior written permission Use of this software for commercial purposes is explicitly forbidden unless prior written permission is obtained from the authors THE SOFTWARE AND DOCUMENTATION IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS AS IS AND ANY EXPRESSED OR IMPLIED WARRANTIES INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT INDIRECT INCIDENTAL SPECIAL EXEMPLARY OR CONSEQUENTIAL DAMAGES INCLUDING BUT NOT LIMITED TO PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES LOSS OF USE DATA OR PROFITS OR BUSINESS INTERRUPTION HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY WHETHER IN CONTRACT STRICT LIABILITY OR TORT INCLUDING NEGLIGENCE OR OTHERWISE ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE This software is derived in part from publically available source code with the following copyright Copyright 1991 1993 Regents of the University of California Copyright 1992 Stichting Mathematisch Centrum Amsterdam Copyright 1991 1992 RSA Data Security Inc Copyright 1992 Jutta Degener and Carsten Bormann TU Berlin Copyright 1994 Paul Stewart Copyright 1996 Regents of the University of California Copyright 1992 19
30. s may be disabled to conserve processing power M Powermeters active I Balloon help M Reception quality matrix Participant list F File Control Window Apply Cancel Figure 9 RAT Preferences Interface Details Powermeters active If checked audio power meters will be displayed in the main RAT window Disabling power meters is not usually necessary unless you are on a very slow machine Balloon help If checked help text is displayed in small balloons when you pass the mouse over buttons This can be controlled also with the icon on the main RAT window Reception quality matrix Toggles a window that displays a matrix based on each participant and the quality of the audio received from them This can be done also with the icon on the main RAT window Participant list Toggles the participant list in the main RAT window File Control Window Toggles a window that allows you to play and record sound samples To play or record a sample you first need to click on the relevant disk icon to select the file You can then use the buttons much like a standard CD player to control the sample This can be done also with the icon on the main RAT window Box 14 Interface Details 17 RAT User Guide 4 3 RAT participant windows The Playout and Decoder information options show technical details which may be of use in the event of problems but will not normally be of interest to users Participant
31. senting your extreme left to 90 on your extreme right Zero is the position straight in front If you are viewing individual video images of the participants you can set the sound to appear to come from the same relative positions as the images on the screen Box 15 3D Positioning 18 RAT User Guide Participant Simon Lockhart OP Participant Roy Bennett UCL Ox Category 3D Positioning Category Audio These options allow the rendering of the VE The signal from the participant can j participant to be altered when 3D be scaled and muted with the controls below rendering is enabled I Mute F 3D Audio Rendering Gain IT 1 00 Filter Type Identity Length 32 HRTF Echo Azimuth o Apply Default Figure 11 RAT Participant information panel 3D positioning and Audio The audio category allows you to adjust the volume gain for yourself and for other participants in the conference You can also silence individuals by checking the mute button an option available from the main window also 19 RAT User Guide 4 4 Command line features RAT Synopsis rat options adar port rat T options addr port TTL CODEC addr port TTL CODEC The following command line options are supported crypt key or k key Enable encryption with the specified key Encryption is done using DES f c1 c2 cn Specifies the encodings used when transmitting audio The orde
32. shes due to too many blocks allocated with many allocations in channel_types c 29 channel_types c 34 playout c 188 and source c 893 Seems to be due to packets being received off the network but never played out Reported by Angel Mateo and also observed at UCL Not yet reproducable Problems with the configure script on Irix 6 2 This works for some users and not for others Must be something in the environment or a software version issue but we don t know what Excessive end to end delay on Windows Reported by Gerry Wolfson Bob Olson reported While changing settings from 48khz GSM to 16khz L16 got this rat 4 2 4 media source c 1588 source process Assertion md gt nrep lt 5 amp amp md gt nrep gt 0 failed FYI just triggered this same failure inadvertently at another site by transmitting at 48khz when they were set to receive at 16khz Occasional weird behaviour of the playout buffer where sources are buffered for several minutes before being played out Reported by Steven Dawson on the CAIRN list 23 RAT User Guide Further Reading 2000 1999 1998 1997 O Hodson C S Perkins amp V Hardman Skew detection and compensation for Internet audio applications Proceedings of the IEEE International Conference on Multimedia and Expo New York July 2000 A Bouch amp M A Sasse Network Quality of Service What do users need Proceedings of the 4th International Distributed Conf
33. t A Vega Garcia amp S Fosse Parisis RTP Payload for Redundant Audio Data IETF Audio Video Transport Working Group September 1997 RFC2198 C S Perkins V Hardman Kouvelas amp M A Sasse Multicast Audio The Next Generation In Proceedings of INET 97 Putra World Trade Centre Kuala Lumpur Malaysia June 1997 C S Perkins amp J Crowcroft Real Time Audio and Video Transmission of IEEE Globecom 96 over the Internet Presented at the IEEE Engineer s Conference at Networld Interop Las Vegas May 1997 C S Perkins amp J Crowcroft Real Time Audio and Video Transmission of IEEE Globecom 96 over the Internet IEEE Communications Magazine Volume 35 Number 4 April 1997 I Kouvelas amp V Hardman Overcoming Workstation Scheduling Problems in a Real Time Audio Tool In Proceedings of the USENIX Annual Technical Conference Anaheim January 1997 V Hardman amp M Iken Enhanced Reality Audio in Interactive Network Environments in Proceedings of the FIVE Technical Conference Pisa Italy December 1996 I Kouvelas V Hardman amp A Watson Lip Synchronisation for Use Over the Internet Analysis and Implementation Proceedings of IEEE Globecom 96 November 1996 London UK V Hardman M A Sasse M Handley amp A Watson Reliable Audio for use over the Internet In Proceedings INET 95 Hawaii 1995 See also http www mice cs ucl ac uk multimedia software
34. th most soundcards headphones DVI ADPCM 32 kbit s 16 bit samples compressed to 4 bits per sample The basic idea is to send the first sample and then difference from it to the next sample and so on although in practice it s not quite as simple as this This sounds marginally worse than Mu Law but is generally acceptable Probably the best compromise between processing requirements and bandwidth GSM 13 2 kbit s This encoding is used in mobile phones and is specially designed for voice signals it works by modelling the way the vocal tract works and hence is not suitable for music Uses a lot of processing power but works over a modem connection LPC 5 8 kbit s Generates a synthetic representation of speech which sounds slightly artificial It works by the same principle as GSM but less information is calculated and sent Should only be used if bandwidth is very limited Loss Protection Redundancy and Interleaving Two types of loss protection are possible redundancy and interleaving If the conference includes any users of other audio tools that don t support redundancy redundancy should be turned off i e No Loss Protection should be set However if all users are using RAT and packet loss is being experienced the use of a loss protection will vastly improve sound quality Redundancy works by piggy backing a low quality duplicate sample onto the next packet so that if a packet is lost then the next packet has a backu
35. ting Make sure that the description of the output is correct Headset if using a headset and Speaker if using speakers You can change between the output types available by clicking on the small triangles on either side of the description Some audio cards will automatically send audio to headsets if they are plugged in and speakers if not In this case the description will not toggle but will always display Speaker Check that you are not running any other audio programs If you are you should exit from them and re start RAT Check in the audio options that your audio device is selected See Box 11 Audio Details Check sample rate of sender If other participants are using a different sample rate then check in the Reception options that a sample rate converter has been selected see Box 10 Reception Details Box 3 If you can t hear other people at all If other people can t hear you Make sure that your microphone is not muted when you talk The microphone is muted when the Talk button in the RAT audio window is checked and the powermeter is plain black If you have started rat from the command line make sure that the TTL is high enough see Box 2 TTL and Admin scope If your TTL is too low you may still be able to hear a remote participant even though they cannot hear you To change the TTL you will have to restart RAT Box 4 If other people can t hear you RAT User Guide I
36. ut you should contact your local systems administrator to see if admin scopes have been set up and if not you should ask for it to be done Box 2 TTL and Admin scope RAT User Guide 3 2 2 Command lines for a unicast conference The command format is as follows Unix Prompt gt rat options lt remote hostname port gt Windows95 NT4 0 Click on the Start button in the bottom left hand corner of the screen Select Run In the Run Window type the following in the open field Open rat options lt remote hostname port gt So as an example this line would start RAT for a unicast conference with someone on the computer called myhost example ac uk Prompt gt Open rat myhost example ac uk The person at the other end in this case the person who is working on myhost example ac uk will have to do the same command but with the name of your computer instead of myhost example ac uk port number can be specified but if one is not then RAT uses the default port 5002 TTL is not applicable in unicast sessions 3 3 Quick guide to using RAT In the Main RAT Window you use the slider bar at the top left to adjust the volume of the speaker or headphones When someone is talking the power meter above the left slider will be activated and the name of the speaker will be highlighted in the main window see Figure 1 In order to talk to other people you must unmute your microphone This can be achieved either by
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