Communication Technologies for Virtual Laboratories


Prof Dr. Konrad Froitzheim

Freiberg University of Mining and Technology , Department of Computer Science

E-Mail: frz@tu-freiberg.de



Table of Contents

Abstract

1 The Term 'Virtual Laboratory'

2 A Taxonomy of Virtual Laboratory Tools

  2.1 Person-Person
  2.2 Person-Equipment (person-experiment)
  2.2.1 Teleoperation
  2.2.2 Teleprogramming
  2.3 Person-Metamachine

3 Transmission of digital media

  3.1 Media parameters
  3.2 Compression and delay
  3.3 Media and Document Formats
  3.3.1 Text
  3.3.2 Object-graphics
  3.4 Quality of Service (QoS)- the core problem of synchronous communication tools

4 Tool overview for Person-Person Communication

  4.1 E-mail
  4.2 ftp
  4.3 WWW
  4.4 Computer Supported Cooperative Work (CSCW)
  4.5 Chat
  4.6 Whiteboard
  4.7 Internet telephony
  4.8 Video conferencing
  4.9 MBone tools
  4.10 Application sharing
  4.11 Virtual awareness

References


Abstract

The omnipresence of the telephone network and the Internet have changed the way people work. As communication technologies evolve from horizontal infrastructure means to vertical applications (often called 'solutions') even laboratories become subject of 'virtualization'. In this case virtualization not only means telecommunications between humans and extensive use of remote and networked computers, but also the remote use of laboratory equipment.
After an attempt to define 'virtual laboratories' and a first taxonomy, we will look at foundation technologies such as the transmission of digital media streams and formats. Example communication tools and an assessment of their applicability to virtual laboratories build the second part of this overview.


1 The Term 'Virtual Laboratory'

The evaluation of current and future Internet communication technology for virtual laboratories should start with a clear statement of the purpose and the configuration of virtual laboratories. We do not want to deduce such a definition here, we quote from:
A "Virtual Laboratory" (VL) is a project-driven collaboration of personnel from multiple institutions usually operating on a fixed time scale to deliver results (or "deliverables") to the sponsor(s) of the project..
A VL is distinguished from a "Real Laboratory" (RL) or a "Traditional Laboratory". However, a VL is not viewed as a replacement for, or a competitor with, a RL. Instead, VL's are possible extensions to RL's and open new opportunities not realizable entirely within a RL at an affordable cost..>
Alternative terms encompassing the concept of a VL include "Collaboratory", "Virtual Workgroup", and "Distance Collaboration Group"..
Neither is it the intention of this paper to develop a taxonomy of virtual laboratories. We should however quote an idea for such a taxonomy that was proposed anonymously to the virlab mailing list:
- a large scale facility with remote access;
- a network of tools (e.g. telescopes/WET p.14) or of laboratories (PIRCS)
- a network of scientists, characterized by a clear membership to a given community (such as expatriated national scientists).
What this paper has to do however is to identify communication tools for such virtual laboratories, to discuss existing tools and pertinent technologies, and possibly describe areas where development opportunities exist. The discussion of computational tools for research or electronic management software for virtual laboratories is beyond the scope of this document.
Based on the definition of a virtual laboratory, it is clear that communication tools are at the heart of such an undertaking, virtual laboratories spanning multiple institutions are usually geographically distributed. They are also heterogeneous wrt. computing and communication equipment.


2 A Taxonomy of Virtual Laboratory Tools

The field of networking, multimedia communication tools, and distributed computing is a big and very active part of computer science, electrical engineering, and the industry. Several classifications and taxonomies of communication services and tools have been developed - the ISO OSI reference model being the most prominent of them. This model however deals with the transmission of data and not so much with the communication tools building on these services.
Considering the short VL-taxonomy quoted above, one arrives at two major communication tool classes (compare [3]):
- person to person communication in a network of scientists
- person to equipment communication to control a network of tools
The first category in the VL-taxonomy is probably not specific enough in terms of interaction models to form a tool group.
John Rose has argued in the virlab mailing list, that a 3rd communication class may be relevant to virtual laboratories: person to metamachine. The concept of metamachines has been discussed in the November 1998 issue of Communication of the ACM [2], [1]. The idea is that scientific projects will be increasingly based on large, distributed datasets manipulated by transformation algorithms on supercomputers. Access to the data (digital library) and control of the computing power may therefore become part of a VL-communication infrastructure. This class of communication will be called
- person to metamachine
in this document.
The next 3 sections are devoted to a more detailed analysis of the three classes.

2.1 Person-Person
The communication services in this class are typically modeled after conventional techniques of human interaction such as a conversation, a telephone call, a book, TV, or a letter. The computer supported analoga are video conferences, Internet telephony, the WWW, and E-mail. The standard - almost classic - approach to their classification is a division along temporal relationships (synchronous versus asynchronous, see table 1).
synchronous asynchronous
chat, telephony
Internet audio,
video conference
teleteaching
virtual awareness
application sharing
E-mail, file exchange
CSCW, joint authoring
project management,
WWW
Table 1: Person-Person communication
The ITU is using the interactivity of the service to build subclasses: interactive services and distribution services. Another option is to divide along roles such as producer and consumers leading to a consumptive class and a cooperative class [4]. A scale based on roles versus interactivity is the most appropriate (see figure 1) approach to reflect the characteristics of the services.
gif-grafik
Figure 1: Person-Person Communication

2.2 Person-Equipment (person-experiment)
An important part of many virtual laboratories are experiments. They can be operated by certain manipulators and the results are collected by measuring equipment, which can again be controlled. In virtual laboratories this operation and control can be performed remotely.
The control of the equipment can either be performed interactively (typically called teleoperation) or asynchronously with a predefined procedure, script or program (teleprogramming). Depending on the chosen method, synchronous feedback to the scientist may be necessary.

2.2.1 Teleoperation
In the teleoperation scenario a scientist gives commands to remote equipment. The equipment is typically a measuring device (telescope, camera), a manipulator, or a probe. These commands can be of a 'strategic' nature (move to position x, fill tank, explode, etc). Fine control will be performed by the equipment itself, which also prevents catastrophic behavior. In this case the feedback channel (mostly video or sample streams) is used to inform the remote scientist of the status of the system and whether a strategic goal has been achieved.
gif-grafik
Figure 2: Operator-Controller-Equipmen
In the second mode the commands are on a lower level (move right, pour fluid, stop). In this mode the feedback channel is of utmost importance, since very high interactivity is required. The critical nature of the feedback imposes high quality of service requirements on the communication channel wrt. delay and throughput.
gif-grafik
Figure 3: Operator-Motor-Equipment
The result of the experiment, i.e. the data (media) stream obtained can either be collected and stored at the equipment site for later transfer, or it can be transmitted live to the user site. The second is mostly the case when the feedback channel also contains results.
Examples:
- the interactive model railroad at the University of Ulm, Germany is a small model railroad. It can be controlled through a WWW based interface. Feedback is given through WWW-based video - WebVideo.
http://rr-vs.informatik.uni-ulm.de
- remote controlled robot at the university of Western Australia has a WWW-based user interface for all 6 degrees of freedom. Feedback is again provided with WebCams, several of them in this case [5].
http://telerobot.mech.uwa.edu.au
Application sharing can be used as a tool for teleoperation. The local computer based equipment control program to operate the experiment will in this case be used remotely. The application sharing service transmits the user interface of this program to the remote site and the remote input is fed back into the program. Application sharing systems include WTS (Windows Terminal Server, Citrix), Proshare, and Timbuktu.
WWW-based control interfaces are implemented with a WWW-server and the CGI-mechanism or by integrating a small WWW-server into the instrument control software. The user-interface is then based on simple or advanced html-pages with certain embedded links pointing to the equipment control software complete with parameters. The Internet Model Railroad, WebIR - a WWW-based infrared remote control for VCRs, the Materials MicroCharacterization Collaboratory (http://tpm.amc.anl.gov/mmc/) and various WebCams (see http://www.nuspectra.com) are examples for this technology.

2.2.2 Teleprogramming
Teleprogramming is an asynchronous approach to the operation of equipment in a virtual laboratory. The scientist creates a series of commands for the device which is then downloaded into the device and executed. The result stream is recorded and later sent back for evaluation by the scientist.
This command series is in many cases either a script or a program. Most programming languages can be used as long as the equipment manufacturer supports them. Today Java is certainly a good choice, as long as the programs created are not time-critical. Two problem should be mentioned in this context:
- As everybody knows programming is a task intimately associated with errors, bugs. Since the remote programming task is especially tedious wrt. turnaround times, local simulation of the programs is very important. Such a simulation environment helps reducing the time until the program works and it avoids catastrophic errors. Simulation environments for experiments and equipment are however not very common. They are a critical part of teleprogramming in a virtual laboratory.
- In order to write a program for a given experiment, a formal description of the functionality of the equipment and of the controllable parameters is a prerequisite. This can be in the form of interface files or distributed programming interfaces (CORBA, RMI-objects, etc). Again not every equipment manufacturer supports this.
These two problems lead to the fundamental problem of abstract equipment description, that should be solved in order to simplify remote experimentation.

2.3 Person-Metamachine
The concept of metamachines has been discussed in the November 1998 issue of Communication of the ACM [2], [1]. The idea is that scientific projects will be increasingly based on large, distributed datasets manipulated by transformation algorithms on supercomputers. Access to the data (digital library) and control of the computing power may therefore become part of a VL-communication infrastructure.
[1] gives 2 examples of such problems. The first is the digital sky project, where a huge multi-wavelength database of astronomy-data is provided on-line, so that statistical analysis of this data in many different supercomputers will become possible. The second area presented is the 'Mapping the brain' effort, where neuroscientists deal with multiple gigabytes of volumetric data.
The data sets are typically stored in huge databases, they are then filtered to extract pertinent data for certain questions, and finally transformed and analyzed by sophisticated algorithms in supercomputers or networks of distributed processors.
Several techniques related to this communication class have been used in computing and networking for a while:
- client-server computing (Corba, RMI, ODBC, JDBC, Java, ?)
- remote database clients
- remote computer operation based on Telnet, X-Window, and application-sharing (Windows Terminal Server, Timbuktu, QuiX) can be used to operate the supercomputers remotely.
- remote program preparation for the supercomputers
- Agent technology is an interesting approach to the data-filtering task described above.
Problems lie in the areas of consistency (databases!) and throughput between the data storage and the processing resource. In the case of remote operation of the equipment (application sharing), network QoS (bandwidth and delay) is critical.
A systematic taxonomy of this class is not known to the authors. Research has to explore this field in more depth to make recommendations to the architects of virtual laboratories.


3 Transmission of digital media

The transmission of digital media - asynchronous as files and synchronous as streams - is a field of rapid development, intense commercial competition, and scientific research. This document cannot give a decent discussion of the technical and scientific implications nor can it predict future developments. It will give an overview of media, formats and a rather simple requirements table.
Although this chapter may sound very technical to those who are not in the business of communication tool design, it is important to understand that the transmission characteristics and media parameters are of utmost importance to the implementor of a virtual laboratory. The triangle desired services, media parameters, and network capacity constitutes the design rules for the virtual laboratory.

3.1 Media parameters
Media parameters describe the principal requirements from the transmitted data to the network. The selection of the media, which shall be communicated, results in a list of required network service qualities. This list has then to be compared to the available infrastructure quality.
The digitization of continuous media (sound, pictures, movement) requires discrete sampling of the media in space and time. The resolution of the digitized medium is of course critical for the quality of the media stream presented to the human viewer. On the other hand finer resolution increases the data size resp. the data stream bandwidth. It is furthermore very important for media processing algorithms used to evaluate the stream from scientific experiments. Most media streams have a very large size immediately after digitization. In order to transmit them economically, they are compressed.
Compression of the media streams is based on the removal of redundancy and discarding of 'unimportant' information. Lossless compression schemes (LZ-77, LZW, Huffman, Arithmetic Coding) are applied to measurement data, files, text and formatted text, and geometric data. Compression schemes for pictures, audio, and video rely typically on the introduction of small loss into the data, which is hopefully not noticeable by human sense (or the brain). MPEG-1, MPEG-2, MPEG-4, MP-3, GSM audio compression, and JPEG are examples.
Compression is sometimes of limited use in typical Internet small bandwidth scenarios. A good example for the audio case is given in the following table:
compression scheme rate 500 byte 20 msec
high quality (MP-3) 192 kbit/s 21 msec 500 byte
reasonable 32 kbit/s 125 msec 80 byte
low (GSM) 13 kbit/s 307 msec 32.5 byte
very low 4 kbit/s 1 sec 10 byte
Table 2: Compressed audio in Internet packets

The problem lies in the small packet size - Internet routers do not process small packets efficiently (the computational load is the same regardless of the packet size) and the payload/overhead ratio is unfavorable.
It should be noted however, that lossy compression cannot be used on media objects which are to be processed at the receiving end: losses will for example influence image processing and image enhancement algorithms.

3.2 Compression and delay
Conversational (interactive) services such as telephony require short round trip times. Long delays from the sender to the receiver and back impede standard human interaction and lead to
Service medium recommended throughput
file transfer text
formatted text
1 - 10 kbyte/s
2 - 10 kbyte/s
telephony PCM-audio 64 kbit/s
video-telephony MPEG-audio Video H.261 CIF 64 kbit/s 384 kbit/s
teleconference
with n
participants
2 channel MPEG-audio
video M-JPEG
graphics
participants · 192 kbit/s
participants · 10 frames· 40 kbit/s
1 kbit/s - 4 Mbit/s
TV-quality MPEG-2 AV
HDTV
4 Mbit/s
17 Mbit/s
Table 3: Recommended data rates for certain media streams
a serious loss in productivity. Delays do not only appear in transmission and compression, the can also result from assembling a reasonably sized IP packet. Table 2 shows unacceptable delays for the assembly of IP-frames from audio-codecs such as GSM or CELP. Low bitrate audio formats are only useful for distribution services such as the RealAudio system or certain MBone-tool applications such as teleteaching.
Although low bitrates do typically not occur as the result of video compression, the compression delay that schemes like MPEG introduce, are again only acceptable in distribution scenarios. Hardware accelerators improve the situation only marginally, they typically make heavy use of piplining.

3.3 Media and Document Formats
Design and efficient implementation of compression schemes for all kind of media and media streams are very active fields of research. This research has not lead to wonders however, we are still bound by the Shannon's limit.

3.3.1 Text
Text, i.e. human language written on paper or any other display device, is built out of symbols for characters or syllabi. The coding of the symbols depends on the set of characters or syllabi used in the particular language. Code sets range from simple ASCII (for US-English), ISO 8859-X (for Roman, Slavic, Arabic, Hebrew, and Greek character based languages), to Unicode (which includes representations for Chinese, Korean and Japanese). The RFC 822 standard for Internet E-mail is for example built around the ASCII set. Other character sets are not easily transmitted with RFC 822.
Text is typically compact in terms of size with a high amount of information. It is furthermore simple to compress text. Transmission of uncompressed text is rather tolerant against bit errors, packet loss however damages text severely.
Formatted Text includes information on the rendition of the text for presentation. The importance of formatting such as boldface, italic, font type, size, and other attributes for the readability of text should not be underestimated. Most word-processors come with their own document format. The commercial success of Microsoft Word has promoted the Word file format to a universal document format despite of it's shortcomings. MIF, the Framemaker file format is another example of an application that has created a de-facto document format standard. True standards such as X.420 have not been nearly as successful. In those communities of science, that make extensive use of formulae in publications, the latex format is very popular. It should be noted that it's use is today limited physics, mathematics, and theoretical computer science. Other areas of science such as biology, chemistry, or engineering do not profit from latex.

3.3.2 Object-graphics
Object graphics are an important means to convey conceptual information. The relation between Object graphics and bitmap graphics can be compared to text and speech. Pixel graphics contain at least an order of magnitude more redundancy than Object graphics. Furthermore this redundancy is not easily identified and removed by compression algorithms.
Object graphics formats are today often defined by a computer graphics system such as X-Window, Windows-Metafile, or QuickDraw-Pict. They are either transmitted as streams of drawing commands of stored in files and transmitted asynchronously. Other standards are IGES, VRML, and many other.
The required QoS for graphics transmission is typically higher than text and comparable to formatted documents: medium data rates (64 kbit/s) and no errors.
Text and vector-graphics data types are typically compressed offline with compression and archiving utilities. Programs such as StuffIt store multiple files in one document and they use a variety of compression algorithms (LZW, LZ-77, ArithCoders, Huffman) to compress the files. They typically analyze the data and apply the coder with the best results to the data. Some can even mix compression schemes to achieve optimal compression.
Although the human hearing apparatus is able to identify very small elements of sound and it is very susceptible to errors, Audio compression schemes have reached high compression rates for specific sound types. Table 4 shows typical standards and data-rates.
Name sound-type bitrates [kbit/s] quality
ADPCM voice 16, 32 reasonable
GSM voice 7, 13 low
CELP voice 2.4, 4 very low
MP3 music 128, 192 superb
Table 4: Audio compression

Pixelmaps are typically rectangular areas with graphical information, pictures, and formatted text. Many formats and compression standards for this data type exist: simple schemes such as Fax G.3 (T.4), BMP, TIFF, mixed mode formats such as Fax G.4 (T.6), and advanced formats such as GIF, JPEG, JBIG. Many include compression algorithms with or without transformation based loss introduction (DCT-JPEG, Wavelet, Fractals).
Video can be compressed with astounding factor as high as 1:100 and it is still useful for many purposes. Video quality is determined by 2 factors: spatial resolution (pixel count horizontal and vertically) and temporal resolution (frames). As an example TV has a resolution of 720 * 486 pixels and 30 frames/second.
Simple techniques compress the individual frames for the video with pixelmap techniques. Reducing the resolution (pixels and frame rate) can be used to adapt the data rate or the size. More advanced and more effective compression is based on temporal correlations between the frames. All the standardized video compression schemes that exploit temporal redundancy are however not scalable in the network (network filtering), frames cannot be dropped in the network without seriously damaging the stream. Another aspect of temporal compression is a high degree of error susceptibility.
Although the application of JPEG to video streams has never been formally standardized, Motion-JPEG is widely used to transmit video over the Internet. The compression rates are not overwhelming (20:1), the resulting stream is scaleable and error resilient. Another commonly used format are GIF-streams: GIF allows for updates in picture areas. The animated ad banners on almost every WWW-page are a living example.
State of the art video compression schemes are MPEG-1, MPEG2 and MPEG-4. They use JPEG and exploit temporal redundancy to achieve compression rates between 1:30 up to 1:200 at good to acceptable quality. The ITU-standard H.261 and it's variants are slightly less effective.
Compound Documents are primarily file resp. transmission formats to combine several media types: Word, Framemaker, ODA (Office Document Architecture), MHEG, or Fax G.4 (T.6).
Programs: Many good and useful programming languages have been created over the years. Many of them are highly specialized for certain types of problems. Universal languages such as ANSI-C, C++, and Java seem to be the most useful to virtual laboratories, although process control languages may become relevant for the teleprogramming type of the person-to-experiment class. The main problem in this area is however in the interfaces and APIs, which can be used: has the target system the same set (functionality and versions) of the dynamic link libraries as the source?

3.4 Quality of Service (QoS)
- the core problem of synchronous communication tools
Quality of service is a set of performance parameters associated with a certain service, especially with data transmission services. Typical parameters are:
- throughput, the amount of data (packets, bits) transmitted time unit [packets/sec]
- delay, the time a packet needs from entering the network to delivery [seconds]
- delay jitter (variations of the delay)
- error probability (lost packets, bit errors)
- error detection probability (effectiveness of checksums)
- error correction measures (retransmission, forward error correction)
- topology (unicast, anycast, multicast, broadcast)
- availability (probability of a successful connection set-up)
A given network may always provide certain values of these parameter (guaranteed QoS), achieve them on average over a given time (statistical QoS), or just strive to maintain the values (best-effort) QoS. Guaranteed QoS is for example provided by the ISDN telephone system wrt. data rate, but not in all the other areas.
gif-grafik
Figure 4: Media stream size versus error-tolerance
The current publicly available Internet is based on the best-effort QoS paradigm. In reality Internet-QoS is completely unpredictable. Although research and development is trying to add true QoS to the Internet (IntServ, DiffServ), reliable QoS in today's Internet is based overdimensioning the system (links and routers).
Dramatic improvements in overall Internet bandwidth have taken place and will be achieved in the immediate future. However:
Internet performance for the individual user will not increase as long as the user number growth remains in the double-digit range.


4 Tool overview for Person-Person Communication

We will now discuss the services together with their requirements to the infrastructure such as computers, networks (quality of service - QoS), and document formats. We will only review Person-person tools, because there is a stable supply of tools. The other fields (person-experiment, person-metamachine) are not as well developed, there is no palette of existing, well know tools available.

4.1 E-mail
Electronic mail is the exchange of text or multimedia documents in electronic form. It is usually performed by a distributed system of servers, which store messages and / or forward the messages to other servers. Messages are composed and read by humans with personal computers.
Examples for electronic mail services are
- Internet mail based on the standards RFC 821 (SMTP protocol), RFC 822 (syntax and format), and RFC 1341 Multipurpose Internet Mail Extensions (MIME).
- X.400 based on the X.420 document format.
As servers and end-systems are very simple, low performance computers suffice.
EQoS-requirements are very moderate: low bandwidth and reasonably reliable transmission.
Unfortunately common document formats for E-mail are either unsatisfactory (RFC822+MIME) or not widely used (ODA etc.). Users typically resort to attaching native documents to mails, thus creating a major incompatibility problem.

4.2 ftp
File transfer, the client controlled transmission of files of unknown type, is used to exchange data between users. The data is produced and later presented by specific applications, which are not part of the service.
Examples are the Internet file transfer ftp or distributed files systems (nfs, Appleshare, Novell, ?) which are usually associated with operating systems. Computer requirements for the servers vary depending on the number and size of stored documents and service users. The requirement to the client computers are determined by the applications working with the files.
QoS requirements focus on a very reliable transmission without bit-errors and reasonable bandwidth. In low bandwidth environments where multiple users need access to the same files a caching/pre-fetching mechanism based on mirror-servers can be used.

4.3 WWW
The World Wide Web is a distributed hypertext system. Servers store documents linked with so-called Hyperlinks to enable easy referencing and navigation. Multimedia content such as pictures is also embedded with the Hyperlink mechanism. Client programs such as Netscape or Internet Explorer help users navigate the Web and display media-rich documents.
Computer requirements for the servers vary with the number and size of stored Web pages and service users. The browser software on the client computers is demanding in terms of memory and execution speed. This is especially true if Java applets are embedded in the pages.
The Web uses a wide variety of data formats: simple formats such as text, html, or GIF to very sophisticated proprietary compression schemes for video (Real Networks, QuickTime).

4.4 Computer Supported Cooperative Work (CSCW)
Computer supported co-operative work (CSCW) tries to co-ordinate the work of many persons on one entity such as a document or a process. Workflow management falls in this area or the management of file collections associated with an object or an event. Newer systems feature a WWW-based front-end.
The foundation of generic (horizontal) CSCW-systems such as BSCW is basically a file server. The system then adds co-operation support: access management, revision control, a comment process, archiving, etc. Vertical CSCW-systems are specific to the application. They usually model a business or administrative process, e.g. the design of a paperclip or the response to a customer complaint. Since vertical CSCW tools are mostly custom or heavily customized software, they are typically very expensive. Virtual laboratories in the scope of this report will therefore have to write their own vertical CSCW tools.
Generic CSCW-tools such as BSCW need medium QoS, basically the combined bandwidth and interactivity requirements of ftp and WWW. The endsystems should be somewhat more powerful than ftp and WWW servers combined.
Joint authoring of documents is a special form of CSCW: the asynchronous editing of documents such as publications by multiple authors. Tools add a transactional semantic to file management based on version and access rights.
Another subset of the CSCW-tools are distributed project management tools such as calendars, delivery date planning, milestone supervision are typically proprietary applications with very specific data formats and distribution characteristics. Standards employed in this area are CORBA, DCE, RMI, COM/DCOM, and RPCs.
For both joint authoring and project management QoS requirements include reliable delivery of messages, multicast or broadcast topologies, and specific delivery semantics, which are provided by additional software layers. They can be very demanding wrt. network delay in order to provide reasonable interactivity.

4.5 Chat
This ancestor of Internet real-time communication tools is a text-based synchronous conversation. Early forms of chat are Telex or UNIX talk. It is basically the text-equivalent of a telephone call. Today chat is very popular among young people. IRC (Internet Relay Chat), ICQ (an Internet community and chat service), and many chat servers that can be attached to a WWW-site exist today.
The requirements on the end systems vary with the platform used. Special chat programs are not demanding, Java-based chat in browsers is more dependant on fast computers.
Network-QoS requirements are simple too: low bandwidth is sufficient, but the delay should be reasonably low (< 500 msecs) to guarantee interactivity.

4.6 Whiteboard
These applications allow the exchange of visual information such as writing text and drawing sketches (or formulae as pixelmaps) on a board. The paradigm is that of a teacher and his students using the board in the classroom. The exchange of information is typically based on drawing operations or bitmaps. Telepointing is another important component of the service. Although these tools seem easy to program at first, they are actually hard to implement so that they are really useful and easy to use.
Examples are the MBone-tool wb (see below) and built-in components of video conferencing tools.
Both chat and whiteboard are very generic - they exchange simple text and simple graphics (pixelmaps and drawing primitives such as line, circle, rectangle, and a few more). More complex, application oriented symbols are typically not supported. Chat and/or whiteboards with scientific symbol capabilities for collaboration events between Physicists, Mathematicians, Engineers, Students, etc. are not widely available. In a virtual laboratory these kind of tools that allow sharing of equations, formulae, chemical symbols, etc. will play an important role. A multi-platform "ScientificTalk" prototype is currently under development at ICTP (Trieste, Italy). It is an example of a 'vertical' chat/whiteboard for the natural science community to help researchers work on 'unfinished' scientific material with remote peers.

4.7 Internet telephony
This variation of the classic telephone service is based on audio compression and transmission in IP packets. Although many prototypes exist, they are not very useful. The bright future that analysts predict for IP-telephony will probably base on specially built networks based on Internet technology (packet switching, soft-state, RSVP). These networks will be considerably over-dimensioned in order to guarantee appropriate QoS. They will be carefully managed by the operators. And there will be charging similar to the current telephony service. The only price advantage for the users will result from increased competition and lower cost to the operator.
IP-based telephony is also available in the general public Internet. However the QoS provided here is unpredictable due to the best-effort nature of this part of the Internet. Problems include frequent pauses due to packet losses, jitter, and very noticeable round trip delays (in the order of seconds). One should not expect free telephony with ISDN-QoS in the foreseeable future.
Examples: see below under video conferencing.

4.8 Video conferencing
Video conferencing in the public Internet has similar problems as IP-telephony, because the audio part is based on the same tools. Although the throughput requirements for video itself are higher than audio, QoS-problems such as dropped frames and jitter are a lot less disturbing for the viewer as in audio streams. The video-component can therefore be useful as an added media-stream for PSTN-telephony.
Examples: Intel ProShare, PictureTel, Netscape Conferencing, Microsoft NetMeeting, CUSeeMe, VocalTec and many others. Most of these tools include other functions such as whiteboards.

4.9 MBone tools
This collection of real-time media distribution programs is most suitable to producer-consumer scenarios. In a typical multicast session a few stream sources generate video, audio, and whiteboard graphics, which are then viewed by many consumers in a geographic area or even around the globe. Tools include vat (visual audio tool), rat (robust audio tool), nv (network video), vic (video conferencing), wb (whiteboard), ivs (audio and video from Inria), nte (network text editor), sdr (session directory), and other tools such as session recorders.
The most important ingredient of this system is however the MBone itself - the Multicast Backbone network. That is a subnetwork of the Internet consisting of special multicast routers and packet transmission tunnels between them.
It should be noted that a working MBone and tool infrastructure requires significant maintenance. A good example are computer science conferences, where 5 to 10 UNIX gurus frantically work for more than hour before the actual session and during the whole event to enable the MBone session. In terms of QoS all the rules for audio and video apply: high bandwidth, low delay, and configurable error recovery.

4.10 Application sharing
The remote use of computers over a network is an early concept of computing. Systems to use programs on a computer from another computer of the same or a different kind are no longer simple 'terminals'. The application to be shared executes normally on the host computer. The application sharing service intercepts all screen output of this program and transmits it (i.e. the user interface) to the remote site and the remote input is fed back into the program. Thus the program can be used from the remote site. Application sharing can is very useful to work together in a videoconference, to work from home in the office environment, to control lab-equipment remotely, and in many other situations.
Examples: Application sharing systems include WTS (Windows Terminal Server, Citrix), Proshare, and Timbuktu. All of them require goof network quality of service (throughput, delay, error-resilience) to ensure functionality and interactivity.

4.11 Virtual awareness
A relatively new form of WWW-based communication is centered around the notion of virtual vicinity. The idea is to add typical human interaction patterns to WWW-surfing. Virtual Presence Services allow Web-users to see each other while they are present on a Web-page or on linked page. The users can then start synchronous communication such as chat, telephony, and conferencing (see above). The proximity of users, i.e. whether they are in a vicinity, is measured with metrics such as time, link distance, document similarity, etc.
CoBrow is such a service. It uses a client server model, where the server is typically co-located with a Web-server. The client component can either be a Java-applet, a standalone program, or a html-based user interface page. QoS requirements are less than the requirements of WWW-surfing. This does however not count the synchronous communication once it is started.


References

[1] More, R. / Prince, Th.A. / Ellisman, M.: Data-Intensive Computing and Digital Libraries; Communications of the ACM, 41(1998)11, 56-62
[2] Communications of the ACM, 41(1998)11
[3] Fluckiger, F.: Networked Multimedia; Prentice Hall, 1994
[4] Froitzheim, K.: Multimedia-Kommunikation; dpunkt, Heidelberg, 1997
[5] Sayers, C.: Remote Control Robotics; Heidelberg, 1998