LAN Based Real Time Audio-Graphics Conferencing System

L.F.G. Soares * * * S.L. Martins * * T.L.P. Bastos *

+ PUC/RJ-Departamento de Informatics Rua Marques de Si0 Vicente 225- Gavea

22453 - Rio de Janeiro-Brad

ABSTRACT

The increase of communication eficiency brings an enormous gain in performance of all business activities in an ofice environment. In particular, teleconferencing is attracting a great deal of attention due to advantages it creates, such as reduction of cost and time spent in conferences and meetings. LANBRETA-GCS is a LAN based real time audio-graphics teleconferencing system that is being developed by PUC/RJ and RIO-SC of IBM Brad and is the subject of this pa- per. The paper’s first part classifies the system within a taxonomy based on observations of various other systems’ characteristics. The second part deals with the specification of the system. At first, the environment where the system is being implemented is introduced. Then, the general specification is presented, together with justifications of the several choices made. Although LANBRETA-GCS is being implemented in a local area network environment, utilizing an IBM token ring and the functions of DOS, NETBIOS and the PC LAN Program, its implementation is much more general. The current im- plementation is just an example among many other possible imple- mentations. This implementation is commented within the text, in order to demonstrate the system’s viability in a local area network environment.

1. INTRODUCTION

Nowadays one of the greatest demands for better com- munication services comes from the office automation area. In this area, it is reported that managers spend ap- proximately 40% of their total working time attending conferences and meetings [ 11 [2]. Therefore, many efforts are being made to increase the efficiency of the commu- nication tasks in this area, in order to enhance the effi- ciency of all business activities in an office environment. In particular, teleconferencing is a service that is attract- ing a great deal of attention due to advantages it offers in reducing cost and time required in attending conferences and meetings.

In a teleconference, it is important to give the maximum of information to the participants, such as the environ- ment of each location participating in the communication, the participants’ reactions to an explanation, in short, the conference atmosphere. Such information is usually very important in conferences where relevant decisions have to be taken, or in conferences where mutual understanding should be achieved. The introduction of voice and data integrated systems and, even better, of image, voice and

617 CH2702-9/89/0000/0617$01.00 0 1989 IEEE

+ + IBM Brad-Centro Cientifico Rio Estrada das Canoas 3520

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data integrated systems fulfills these needs. In this paper, only real-time conferencing systems are discussed. Other types of multi-individual interactions (like electronic mail, computer conference [3] etc) are excluded. In a real-time conferencing system, every participant can be sat in his office in front of a workstation, which can contain a high-resolution terminal, a keyboard, a pointing device, a microphone, a loudspeaker and possibly a camera and a video monitor, with all these components working to- gether to achieve simultaneous communication with all other participants.

LANBRETA-GCS is an audio-graphics conferencing sys- tem for local area networks, and is one of the components of the voice and data integrated services system, which is being developed by the Rio Scientific Center (Rio-SC-IBM Brasil) in cooperation with the Catholic University of Rio de Janeiro (PUC/RJ). The major func- tional specification of this system is the subject of this paper. Before describing specifically the LANBRETA-GCS, a hierarchical classification of con- ferencing systems is made in section 2. Section 3 presents the assumptions of LANBRETA-GCS and, in section 4, the organization of the system being implemented is dis- cussed. The conclusions are presented in section 5 .

2. HIERARCHICAL CLASSIFICATION OF CONFERENCING SYSTEMS

As mentioned, a teleconferencing system is interpreted here in its narrow sense being defined as [6] [7]: ”The set of telecommunication facilities which enables participants of two or more locations to carry on bidirectional com- munications through electrical communication media, while simultaneously sharing common acoustic and visual space”.

The functions and performance required from a telecon- ferencing system are greatly dependent on the input/output information media that are used to share the teleconferencing common space. Thus, teleconferenc- ing systems have conventionally been classified as: Audio Conferencing, Audio-graphics Conferencing and Video Conferencing. However, many problems arise by using

this classification, in relation to some systems. To avoid these problems, teleconferencing systems are classified here in a similar way to that found in [6].

Audio conferencing - Those where only audio and control signals are transmitted through the intercon- nection network. Any document is previously distrib- uted. Audio-document conferencing - Conference similar to audio conferencing systems, differing in the way the documents are treated. The access and manipulation of documents are performed in real-time and simul- taneously, employing distribution of pointers etc. Audio-graphics conferencing - Those conferences in which beyond the transmission of audio, control signals and documents, visual images (still pictures, facsimile, graphics etc. ) are transmitted, at least part of the time. Freeze-frame video conferencing - Conference similar to audio-graphics conferencing systems, where in ad- dition, conferees images are regularly distributed to all other participants. Video conferencing - Conference similar to audio- graphics conferencing systems, where in addition, full-time moving pictures are transmitted between all participants. Teleseminar - Conferences in which an event occur- ring in one location is distributed (sound and vision) to the other locations, with only one signal return path (voice for example).

Even within this classification, there are some systems that will not present all characteristics of the systems de- fined above, therefore they are approximately classified. This is the case of LANBRETA-GCS, which can be classified as an audio-document conferencing system as well as an audio-graphics conferencing system. Future expansions are expected to be accomplished in the system, therefore the latter classification was chosen. It is im- portant to note that the definition order presented above does not correspond necessarily to the systems complex- ity. There are, for example, various audio-document con- ferencing systems that present a greater complexity than audio-graphics conferencing systems.

3. SPECIFICATION DECISIONS OF LANBRETA-GCS

3.1- Introduction

There are many differences between voice and data signal handling to be recalled when integrated systems are being developed. They will not be treated in this section, unless they directly affect the specification decisions of a tele- conferencing system. The decisions discussed refer mainly to an audio-graphics conferencing system. Prob- lems related to signals integration, such as encoding, si- lence detection, packet losses, absolute delay, variance of delay, synchronization of voice samples clocks, and oth-

ers, are assumed to be solved in this system and they are only mentioned when relevant to a specific decision. Ref- erence [SI describes the environment where LANBRETA-GCS is being implemented and also dis- cusses in depth the solutions to those problems mentioned above. Several other discussions about this matter can be found in [9] [ 101 and [ 1 1 1 .

The next section presents the system environment fol- lowed by the system specification. What follows is only a macro specification of LANBRETA-GCS, stressing the major system functions. The detailed specification can be found in reference [ 191.

3.2 - The Environment

LANBRETAS (LAN Based REal Time Audio System) is a set of integrated voice and data application systems for local area networks. This set has three basic compo- nents:

LANBRETA-DTS (LAN Based REal Time Audio- Data Telephony System) [12] [13] - consists of a set of applications associated with telephony, such as call by subscriber name, subscriber following, selective answer, selective messages and automatic re-dial. LANBRETA-DMS (LAN Based REal Time Audio- Data Message System) [12] [14] - consists of a set of applications associated with a mail system that han- dles voice, data and integrated voice and data mes- sages. LANBRETA-GCS (LAN Based REal Time Audio- Graphics Conferencing System) [8] - consists of a system that allows the setup of an audio-graphics conference in a local area network. It is the subject of this paper.

LANBRETAS is being developed by the Catholic Uni- versity of Rio de Janeiro and the Rio Scientific Center of IBM-BRASIL. It has a local area network similar to an IBM Token Ring as the base of the system, intercon- necting many IBM-PC and IBM-PS microcomputers.

In order to integrate voice into the system, an intelligent extension board to the microcomputers was developed, based on the Intel 80188 system, called Voice Board [15]. This board is responsible for many tasks, such as, digitization and recovery of voice signal, packet assembly and disassembly, silence detection, compensation of delay variance, signalling (user interface), synchronization be- tween the transmitter and receiver, cryptography (op- tional), echo treatment and other functions needed for system operation.

The implementation is being done using the services of- fered by DOS, NETBIOS and the PC LAN Program. Extra functions are being added to these systems in'order to treat real time voice packets properly. Section 4 will show to what extent LANBRETA-GCS depends on these three systems.

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It is important to note that although this system is being implemented in an IBM token-ring network using the fa- cilities offered by DOS, NETBIOS and the PC LAN Network Program, its specification is much more general and the implementation in progress is only an example of one implementation among many others.

3.3 - The System

entry requests and the invited participants list. This new list will be used later in selection of the partic- ipant to get the floor. LANBRETA-GCS is not re- sponsible for negotiation of the conference time, and for distribution of the conference time, the access password, or documents. These tasks should be done by other programs [ 161 [ 171. In the present system, the PC LAN Program and PROFS accomplish these tasks.

In general, almost all conferences demand a certain de- gree of control concentrated in one single person: the teacher in a classroom, the chairman in a conference, the president in a parliamentary session, the manager in a business meeting, in short, a person responsible for the accomplishment of a series of organizational tasks. As these control tasks are usually performed by only one person, the distribution of their implementation does not bring, in general, any significant benefit to the system. Therefore, LANBRETA-GCS assumes as a basic as- sumption the existence of a conference chairman, who is responsible for the organizational and managerial tasks of the conference, such as establishment, control etc. As it will be shown, various other premises of the system are derived from this basic one.

Other conference members are the participants and the listeners. The participants can speak, alter shared docu- ments, vote, and also access the conference status infor- mation. The listeners can only listen to the conference, view the shared window (described later), and access some of the status information. There is also the role of the secretary. Every conference that deals with shared documents must name a secretary, who is the only mem- ber allowed to file a new version of a shared document. The role of secretary can be played (according to the chairman’s decision) by a participant, by the chairman himself or by a user who is dedicated exclusively to this task. In this last case, the secretary is forbidden to edit shared documents and to vote. The secretary’s station is not able to store parts of the participants’ speeches, which are relevant during the preparation of the conference proceedings, because a large storage capacity is not available in the current implementation environment . Future implementations of the system can easily include this facility.

Conference Setup - The assembly method is used. Every conference has an access password and an in- vited participants list (that associates to each partic- ipant a priority and speech time), which are created a t conference setup by the chairman. The users who desire to participate in a certain conference should communicate with the manager ( a program running on the chairman’s station) by sending an entry request. In order to establish this communication, the user must know the conference access password. The entry requests can arrive a t any time during the con- ference and it is up to the manager to analyze each request, and decide if the user can participate. The manager will generate the access control list from the

0 Conference Termination - The conference only ter- minates after the departure of all participants or when the time interval (given by the conference chairman to all participants) to leave the conference has expired. The autonomy of the conference mem- bers is maintained throughout the conference. They are free to leave whenever they want (except the chairman). Participants and listeners join and re-join a conference a t the chairman’s discretion, who is able to temporarily or permanently prevent insertions.

0 Conference Control - The control is centralized, as seen before. There are different ways of handling entry requests. When participant insertion is allowed, only participants included in the invited participants list have their entry requests automatically accepted, other requests are judged by the chairman. Whenever a user is accepted in the conference, he is inserted in the access control list, as shown before. Similarly, a conference member informs the manager the instant he leaves the conference in order to permit the access control list to be updated. In an open conference, all entry requests sent by participants are accepted. Lis- teners are only accepted in the conference if the chairman has allowed them to join at the beginning. The secretary does not send entry requests, but ad- vises the chairman that he is active and waits to be named (in this case the secretary cannot perform any other role in the conference). The manager may, a t any instant, send messages preventing the partic- ipants from speaking or from controlling shared data. These messages are sent in three cases. The first when a participant’s speech time has expired. The second case is when the conference chairman or the secretary wants to intervene, for example, to inform a partic- ipant how much time to speak he still has. The third case is when more than one participant tries to get the conference floor (the control of shared data and the right to speak) at the same time. In this last case, the participant with the highest priority gets the floor while the others are prevented from speaking. The manager is responsible for the control of all confer- ence activities. In addition, he is the only participant that can terminate the conference.

0 Document Handling - The previous storage of con- ference documents in a file server is performed by the PC LAN Program (as known, a system out of LANBRETA-GCS). There are three types of pass- words to access shared documents: reading password

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- allows the document to be read but not changed; editing password - allows to create a copy of a shared document and re-edit it; writing password - allows a re-edited copy to be filed under the original docu- ment’s name. The reading and editing passwords are sent to the participants when they are accepted in the conference; the writing password is sent only to the secretary. The conference members’ screen can be divided in two areas: a shared window and an indi- vidual window. On the individual screen, several at- titudes (functions), that can be adopted by the user according to his role in the conference, are shown. Shared documents view can only be handled inside the shared window. Document alteration is permitted to only one participant at a time, usually the partic- ipant that has the floor. Nevertheless, this participant can pass his alteration right to another, whenever he wants. At regular intervals, the page being edited is sent to all other members and exhibited on their shared window. Despite of transmission and recov- ering delays, one can say that all conference members follow the document edition in real-time. The altered shared document can only be stored in the file server by the secretary, to whom an oral storage request has to be sent - this request can be challenged, also orally, by any other participant. The decision is up to the secretary.

Signal Mixing - Since during most of the conference only one person is speaking, the selection technique (where one participant is selected to speak and have his voice sent to all other conference members) has approximately the same effect of the conventional sum of signals. Human factors studies [IS] have shown little performance loss using this technique and that in many instances it is preferred by the users. The same situation occurs with the sending of partic- ipants’ data pointers. Therefore, LANBRETA-GCS adopts the selection technique, which quite simplifies the signal mixing procedures (for example, it is not necessary to have bridges).

Floor Selection - In a teleconferencing system there is always a participant that has the right to speak a t each instant. During his speech time, this participant has the highest priority to intervene in the teleconfer- ence and also has total resource control. Only the manager (and in special cases the secretary) can in- terrupt a participant who has acquired the right to speak.

There are two basic modes in which a participant can request the right to speak: using control push-buttons or using silence detection. There are other selection techniques implemented in existing systems but a great deal of them are derivations from those men- tioned above. Experience with teleconferencing sys- tems has shown that a teleconference can work satisfactorily using any selection technique. However, human factors [ 181 have shown that silence detection

technique is preferred, because it is easier to learn. In addition, the push-button selection may lead to situations where the participant places himself in the access queue and rehearses his speech instead of pay- ing attention to the conference.

Selection by silence detection demands the existence of a silence detection mechanism. In this technique, a participant can start sending voice packets only when the system is silent for a certain time interval. When two or more participants start speaking together after the same silence interval, the resultant collision is re- solved by the manager, using a priority criterion es- tablished by the access control list, in a way that all colliding participants are inhibited, except the one with the highest priority. A user knows that he has thefloor when he speaks and does not receive in re- turn another participant’s voice. Since the silence detection technique offers a great number of advan- tages and all network stations possess this facility, this technique was chosen.

The floor also confers the right to alter shared docu- ments. The participant can, however, pass this right to any participant in the conference. Nevertheless, this new participant loses the alteration right when the participant that has delegated it to him, loses the floor. Therefore the participant that has obtained the permission to alter data from another participant has to Day attention to the manager message that informs that the speech time is over. The loss of the floor, as already mentioned, can only happen either by the conference chairman’s personal intervention, or by the end of the speech interval time associated with the participant, or by the own participant’s will.

Application Programs - LANBRETA-GCS includes a voice and data editor integrated to the system that offers document handling facilities mentioned before. This editor can run either in the shared or in the in- dividual window without any restriction. Moreover, the system also allows the execution of external ap- plication programs without leaving the conference environment. In this first implementation of the con- ferencing system, the user is responsible for the in- stallation of each external application program on the desired window, otherwise, the system would be very inefficient, because in DOS environment, every at- tempt to write on the screen memory has to be inter- cepted in order to send the data to the correct window. A future version of the system based on a multi-task operating system like Unix could easily of- fer this facility. Another problem arises when an ex- ternal application program is running in the shared window and the user who is executing it loses the al- teration right. The user is responsible for closing all files opened by the program before he actually loses the alteration right, otherwise the integrity of the shared data handled by the application could be af- fected. To avoid this, the user does not lose this right

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immediately after his speech time (or the speech time of the user who has passed the alteration right to him) expires. The system just warns the chairman that the user’s time was over. The chairman ought to make sure that the shared files are closed, before the user loses the alteration right. This can be achieved using, for instance, an oral communication provided by the system.

Voting - In LANBRETA-GCS the participants vote in parallel. The opening and closing of voting is up to the chairman. When a voting is opened, the system asks for several parameters such as name, short ab- stract of voting subject, voting period (that can be extended according to chairman’s will), voting choices and the number of options per vote. These parame- ters are stored in a file server under the voting’s name and the reading password. The arrival of a vote ac- tivates a routine that verifies if the voter is a partic- ipant, if he has already voted and identifies which are his choices, if he can vote. When the voting period expires, the chairman activates vote tally. The results are then appended to the file associated with the vot- ing, allowing the other participants to take note of them. The voting scheme implemented allows the opening of a voting where every voter knows the votes of the others or only the final result. It is possible to maintain various (up to four in the current imple- mentation) independent votings in parallel. Conference Status - The conference status presenta- tion should be simple but it has to contain all infor- mation needed for total conferencing environment control by a participant. The first version of LANBRETA-GCS offers the following information: a short abstract of the conference subject matter (supplied by the chairman when the conference is created), a list of the current and invited participants, who is the conference chairman, who currently has the floor, when a participant has left or joined the conference, and finally, when a participant has passed the floor control (accomplished by a conference his- tory maintained by the manager in a file server). Some status information remains onscreen in special fields during the conference, such as: the current speaker’s name, the name of whoever is altering doc- uments, the chairman’s name, the secretary’s name, the time of the end of the conference, among others.

These were the principal decisions of the LANBRETA-GCS specification. In the next section an overview of the system organization is presented.

4 - SYSTEM ORGANIZATION

4.1 - Introduction

The LANBRETA-GCS specification determines four dis- tinct processes: the manager, the secretary, the participant

and the listener. The first is associated with conferencing management, the second is responsible for the integrity of shared documents and the last two take charge of the members’ entrics, departures, and communications with the manager. There are two distinct types of messages exchanged by these processes: global and individual mes- sages. The first ones are received by those inserted in a conference group (NETBIOS’ group name), and the other ones are addressed to a particular conference member. Due to the complexity of these processes, only a global view of the system is presented. The procedures are being implemented in C, using the facilities offered by DOS, the PC LAN Program, NETBIOS, LANBRETA-DTS and LANBRETA-DMS.

4.2 - Conferencing Groups

When a user is accepted into the conference, he is inserted in the conferencing groups created by the chairman at the conference setup. Some messages exchanged during the conference are redirected by NETBIOS to routines asso- ciated with each group. The routines’ algorithm varies according to the role of each member. There are three different groups used to send three distinct types of mes- sages. Besides this, these groups also have routines acti- vated by the arrival of those messages, as follows:

Voice group - The manager’s routine has the function of allowing only the speech of whoever has the right to speak, controlling the end of the speech time. arbitrating in any contention for the right to speak during silence in- tervals, and reproducing voice packets in the Voice Board (only those packets associated with whoever has the right to speak). The other members’ routines simply reproduce the voice packets in the Voice Board.

Shared Data Group - The manager’s routine always verifies the message source before taking any action. If the sender has the alteration right, the message is exhib- ited on the shared window; otherwise, the manager sends an error mcssage to the source. The other members’ rou- tines simply exhibit the shared data on a shared window. There are three possible screen configuration modes: in MODE1 only the individual window is shown, in MODE2 only the shared window is shown and in MODE3 both windows are shown simultaneously. If MODE1 is active when shared data arrives, the routines should also be able to inhibit MODE1 and then activate MODE3.

Control Group - The manager uses this group only to send messages. The other member’s routine receives a periodical refresh of thc global control variables of the system, such as, name of who is speaking etc, information about the conference termination and alert against any attempt of violation by any user or member. The listen- er’s routine also receives expulsion messages, if the chair- man decides that they shall not continue taking part of the conference.

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4.3 - Individual Messages 5 - CONCLUSIONS

Some messages are addressed to a particular member. Every user that has his entry request accepted must fur- nish a unique identification name, his individual address, to the system. NETBIOS can, from now on, redirect ev- ery individual message to a routine that is associated with this name. The only members excluded from individual message exchange are the listeners. Moreover, it is desir- able that some members have more than one individual name (address).The main reason is to avoid the long time spent in message recognition and treatment. Therefore, there are three types of individual messages, and for each one of them a unique name is provided.

Control Messages are exchanged between an individual user and the manager. Some of them are exchanged via a session, others via datagrams. Sessions are opened be- tween the manager and the member who has the floor, to exchange control information like gain/loss of the floor, temporary inhibition of alteration right or right to speak, recovery of these rights, etc. Messages sent in form of datagrams are the expulsion of the conference, temporary inhibition of a participant's speech request, the secretary naming, and the secretary's answer to the naming. The chairman possess also a unique control name that must be known by every user that wants to join the conference. Packet arrivals to this name are redirected to a routine that is responsible for member insertions and deletions. The distribution of this access password is not, as already told, a task executed by the conferencing system.

Votes are sent from participant to chairman through datagrams. These datagrams should be directed to a unique name in the chairman's station in order to be properly handled. This unique name is not determined by the chairman as the name for control messages ex- change mentioned before, but is derived by the manager's process. The votes must be acknowledged in order to as- sure a reliable voting process.

Notes and Files are private communications between members (once the chairman has allowed private ex- changing). When a note arrives, it will be stored in a memory buffer that can be consulted anytime. The sec- retary can receive notes from everyone but can only send notes to the chairman. File transfer is provided using the file server. The sender stores the file in a server under a password, and then sends the file name and the password to the intended receiver. When a file message arrives, the receiving station adds the file name and its password to its individual conferencing directory, which can be con- sulted anytime. Files can be exchanged only between chairman and participants.

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This paper has presented the specification of an audio- graphics teleconferencing system, LANBRETA-GCS. The first part of the paper classified the system within a taxonomy determined from observations of characteristics of various other systems.

The second part dealt with the system specification. At first, the system implementation environment was intro- duced. Then, the specification was presented along with justifications of several choices made.

As mentioned along the text, although LANBRETA-GCS is being implemented in a local area network environment, using an IBM token ring and the functions of DOS, NETBIOS and the PC LAN Program, its implementation is much more general and the current implementation is only one example among many others. The specification presented is not a specification of a particular system implementation. The objective of this paper was to present the basic functions of the system, a macro system specification and an example of a system implementation, demonstrating its viability under a local area network environment. Reference [8] should be con- sulted in order to obtain a more detailed system specifi- cation. Reference [19] deals with the current system implementation.

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