an educator's an educator's guide guide

An Educator’sAn Educator’sGuideGuide

Timothy M. Logan

Associate Director, Information Technology Center

Instructional Technology and Distance Education

Baylor University

and

Joseph R. Radke

Program Specialist

Virtual Teaching Center

Center for Occupational Research and Development

© 1997, Center for Occupational Research and Development, Waco, Texas

Published and distributed byCORD Communications, Inc.P.O. Box 21206Waco, Texas 76702-1206800/231-3015

Printed in the United States of America

ISBN 1-57837-107-4

iii

Contents

11 Introduction 1

22 Overview of Videoconferencing Technology 1Networking Technologies 1

Cabling 5

Videoconferencing Components 7

Networking Components 10

Standards 12

33 Applications 15Simple Single-Classroom Setup 15

Distance-Learning Classroom 16

Multiple Classrooms 17

District or Regional Network 18

44 Conclusion 21

1 IntroductionVideoconferencing is the transmission of video and audio between two

sites in relatively real time. This allows interaction between participants atboth sites similar to that which would be possible if they were in the sameroom. Videoconferencing has been used in business for years. Now it isbeginning to make its way into education.

This guide is an introduction to the technology of videoconferencing andits uses in education. It will begin by discussing the different componentsrequired for videoconferencing. This includes not only the videoconferencingequipment and networking technology but also the international standardsthat make them all work together. The guide will then look at somehypothetical situations and explain how videoconferencing is applied in each.We hope you find this guide useful in developing a technology plan toincorporate the many opportunities afforded by the rapidly changingtechnology now becoming available to the educational community.

2 Videoconferencing Technology: An Educator’s Guide

2 Overview of VideoconferencingTechnology

The technology involved in videoconferencing ranges from simplecameras and microphones to sophisticated and powerful networkingequipment. The technology seems to be constantly changing and improving.It doesn’t have to be hard to understand though. The following sections willexplain, as simply as possible, some of the equipment, cables, andtelecommunications techniques used in videoconferencing.


Networking technologiesToday there are several ways to get data, including videoconferencing

signals, from the sender to the receiver. In evaluating these differenttechnologies, certain factors are important. Bandwidth, the amount of datathat can be transmitted in a given amount of time, is a major consideration.This will be the main determinant of audio and video quality. Bandwidth isusually measured in bits per second. A bit is the basic unit of digital data. Athousand bits is known as a kilobit (kb), and a million bits is a megabit(Mb).

Certain technologies are limited to private point-to-point connectionswhile others are public-switched services. Public-switched services canconnect with any other end-point that has the same type of service. Unlessyou have an unlimited budget, cost will also be a concern. Finally, theservice must be available in your area.

Plain Old Telephone Service (POTS)

The most basic telecommunication technology available today is plainold telephone service, known as POTS. This is the system you use everytime you pick up the telephone. The maximum bandwidth available throughPOTS is 33.6 kilobits per second (kbps). As you will see, this is slowcompared with other technologies. The big advantages of POTS are that itis widely available—nearly every home and business has at least onetelephone line—and it is inexpensive.

T1

A T1 is a digital trunk phone line, capable of transmitting at the rate of1.544 megabits per second (Mbps). It carries 24 channels of data at 64 kbpsper channel. Each channel is referred to as DS-0. There are differentformats for transmitting data on a T1 circuit. Alternate Mark Inversion(AMI) and Binary 8 Zero Suppression (B8ZS) refer to the electricalcharacteristics of signal as it is put on the line. D4 and Extended Superframe(ESF) concern the size of blocks (frames) of data transmitted. B8ZS andESF are recommended for videoconferencing applications. T1 connectionsare dedicated point-to-point connections. Since the connection is alwaysactive, you pay a flat monthly fee and get unlimited usage of the line. A T1is also very reliable. T3 is a related but higher-speed technology. It has abandwidth of over 45 Mbps, the equivalent capacity of 28 T1s.

Overview of Videoconferencing Technology 5

Integrated Services Digital Network (ISDN)

ISDN is a fully digital switched service available from local and longdistance telephone companies. It is similar to POTS in that you are assigneda telephone number or numbers. Since it is fully digital, higher bandwidthsare available. ISDN comes in two types:

1. Basic Rate Interface (BRI) ISDNBRI ISDN is made up of two channels of 64 kbps, called B channels,and one 16-kbps channel, called a D channel. Because of thisconfiguration, BRI ISDN is sometimes call 2B+D. The D channel isused by telephone companies for signaling. The customer has accessto the two B channels for a total accessible bandwidth of 128 kbps.BRI lines can be combined to achieve higher bandwidths. Thisprocess is called inverse multiplexing or IMUXing. Each B channel isusually assigned a separate telephone number. Each B channel is alsoassigned a service profile identification number, known as an SPID.The service profile to which the SPID refers contains information onthe capability of the channel. Channels can be provisioned for voice ordata. For videoconferencing, both B channels should be provisionedfor data. When configuring ISDN BRI equipment it is often necessaryto know your SPIDs as well as the type of switch the telephonecompany is using and the ISDN standard the switch uses. 5ESS andDMS250 are common switch types. Most ISDN telephone companyswitches conform to the National ISDN 1 (NI1) or National ISDN 2(NI2) standard, although some are custom configurations. Theavailability of ISDN is not as great as POTS but is constantlyincreasing. Usage charges per B channel are similar to regular tollcharges.

2. Primary Rate Interface (PRI) ISDNPRI ISDN has a bandwidth of 1.536 kbps. It consists of 23B channels of 64 kbps and one D channel also of 64 kbps. ESFframing and B8ZS line coding are used on PRI circuits. PRIs arerelatively expensive to install. Usage charges are based on the numberof B channels used and the duration and distance of a call.


CablingCables connect the parts of videoconferencing network systems. They

carry signals, as either electricity or light, from one component to the next.Different types of cable have different capabilities and costs and thusdifferent applications. You may encounter the following types of cables.

Twisted Pair

As the name implies, twisted-pair cables are made up of coated copperwires twisted around one another. The twists help reduce interference thatcan develop when wires run beside each other. Twisted-pair cable comes intwo varieties: shielded twisted pair (STP) and unshielded twisted pair(UTP).

STP has an extra covering that shields it from external electricalinterference. This may be necessary when running the cable close tomachinery or devices that create a lot of electrical noise.

UTP is rated into five categories. Category 3 (cat 3) cable or above isadequate for most telephone applications, including ISDN. Category 5 (cat5) cable is required for some higher-speed networking. Because of its lowprice, ease of installation, and flexibility use, cat 5 cable is one the mostpopular networking cables in use today.

Figure 1Twisted pair

cable

Coax

Coax cable is also made of copper wire. It has a single strand surroundedby insulation and a grounded shield. Because of the extra shielding, coax isless susceptible to interference than UTP cable. It has a higher bandwidthcapacity and can run longer distances. It is, however, harder to install andmore expensive. Coax is used on some digital networks. It is also used tocarry analog audio and video signals.


Figure 2Coax cable

Fiber-Optic

Unlike other cables, fiber-optic cables do not carry electricity. They carrylight. Fiber-optic cables are constructed from flexible glass or plastic. Theycan carry data faster and farther than any copper cable. The main drawbacksof fiber-optic cable are the cost and the difficulty of installation. Currently,the main application of fiber-optic cable is as a high-speed backbone forother networks.

Figure 3Fiber-optic

cable

V.35

A V.35 cable consists of up to 34 wires. It can transmit data at as muchas 2 Mbps. V.35 cables are limited to 100 feet in length before data lossstarts to occur. Therefore, they are not used for general networkinginstallations. In videoconferencing, they are used to connect thevideoconferencing hardware to networking equipment. V.35 cables useM-34 connectors. These connectors have 34 gold-plated pins and built-inscrews for secure connection.


Figure 4V.35 interface

RS-366

RS-366 cable, like V.35 cable, is used primarily to connect to pieces ofequipment directly. It is much slower and less expensive than V.35. RS-366is used primarily for transmitting dialing information, such as ISDNtelephone numbers, to networking equipment. DB-25 connectors, like thosefound on most parallel printer cables, are used on RS-366 cable. The cablehas a length limit of 100 feet.

Figure 5RS-366

interface

Videoconferencing componentsSo far, we have covered how data are transmitted over

telecommunication networks. We looked at the features of variousnetworking technologies and the capacity and application of several cabletypes. Let us now turn our attention to how our images and words arecaptured and converted into the data that race along these networks.


Codec

Codec stands for coder/decoder. This is the heart of thevideoconferencing system. A codec takes the incoming audio and videosignals from the cameras and microphones and converts (codes) them to adigital format. During the coding, the data are also compressed. A regulartelevision signal contains 90 million bits of information per second. Thisinformation must be transmitted across lines with a bandwidth of as little as128 thousand bits per second. That is a ratio of over 700:1 for video alone.The codec must select which pieces of information are important and codethem in an efficient manner. It also takes the incoming data signal anddecodes it back into audio and video signals. Codecs can be a complexseries of electronics in a custom chassis or as simple as a card installedinside a computer. They can even be just software and use componentsalready installed in a multimedia computer. In general, the more complexthe codec, the more expensive and higher quality.

Cameras

The basic function of a camera is to capture video information and sendit to the codec. Simple cameras used in some desktop videoconferencing dolittle more than perform this task. More sophisticated remote-control pan-tilt-zoom (PTZ) cameras offer the ability to rotate side to side (pan) or upand down (tilt) and change focal length (zoom). These cameras may also beable to store preset locations that can be recalled with the push of a button.

Some camera systems have the capability to track the instructor. Thetracking system can be an infrared device worn by the instructor or a video-pattern-recognition system incorporated into the codec. Others havesophisticated audio camera control systems that use multiple sensors tolocate the speaker in the room and then instruct the camera to move to thatlocation. The use of 3 CCD or digital cameras is not necessary invideoconferencing. Since much of the video information is discarded by thecodec, these types of high-quality, expensive cameras do little to improvepicture quality. They may even make the job of the codec harder byproviding more data to be compressed.

A document camera is another type of video input used invideoconferencing. A document camera has a lens mounted on an arm overa small flat platform. Paper documents, transparencies, or 3-D objects canbe placed on the platform and transmitted to the codec.


Monitors

Monitors are video output devices. They range from computer monitors,used mainly for desktop videoconferencing, to large-screen TVs andprojectors. Television monitors in North America and Japan follow theNTSC standard. Other countries use PAL or SECAM standards. Monitorsshould be large enough to be easily seen by all participants. It is frequentlynecessary to add more monitors in the classroom for student viewing. Asmall, indecipherable video image will soon lose the attention of thestudents participating in the videoconference, so special attention must bepaid to providing the students with a clear view of monitors located closeenough for comfortable viewing. In addition, the instructor needs the abilityto see both the far-end and near-end views while presenting.

Lighting

Lighting in the room should provide sufficient illumination for thecameras to do a good job of picking up and transmitting the video fromeach classroom. Fluorescent lighting with even coverage in the room oftensuffices, but additional lights may be needed to illuminate the instructor.Diffuse or angled lighting helps to eliminate harsh shadows under the eyesand chin. Outside windows should be covered with blinds or drapes toeliminate sunlight during a videoconference. Video cameras are not able toadapt well to the differences in brightness between artificial lighting andsunlight.

Audio systems

Good-quality audio reproduction is extremely important in the design ofa distance-education facility. Good video with bad audio is nearly useless;good audio with bad video is less than ideal, but still functional in aninstructional setting. Good audio systems incorporate two elements: pickupand reproduction.

Pickup is accomplished by microphones. Tabletop microphones allowstudents to ask questions. These microphones are frequently the push-to-talk variety. Microphones of this type are muted until a button is pushed toactivate them. This allows microphones to be placed throughout the roomwithout picking up unwanted noise of pages turning, students’ sideconversation, or pencils tapping. While ceiling-mounted microphones seemto offer a technically simple solution for student questions and responses,many vendors and consultants strongly recommend that tabletopmicrophones be used instead to ensure that ambient noise and extraneousnoises do not interfere with the educational experience.

Instructor microphones are usually either podium mounted, worn (calledlavalier or lapel microphones), or carried (hand held). A wireless lavalier


microphone allows the instructor to retain a natural teaching style whileproviding clarity for effective instruction and meaningful student interaction.

Reproduction is accomplished with speakers. Proper placement ofspeakers in each classroom allows clear transmission of the spokeninstructional material and questions, ensuring that the interaction betweenstudent and teacher is not interrupted by problems in an inadequate audiosystem. With the significant expenses associated with other aspects ofvideo-based instruction, the proper design and installation of audio systemsare often overlooked. It is imperative that significant attention be paid to theclassroom audio systems that are part of a distance-education facilitydesign.

Networking components

Inverse Multiplexer (IMUX)

An IMUX takes the signal produced by the codec and breaks it intopieces for transmission over separate lines. For example, a384-kilobit-per-second signal would be broken into three 128-kbps signalsfor transmission over ISDN BRI lines (3 × 128 = 384). The IMUX alsotakes the incoming three signals and reassembles them into one before thesignal enters the codec.

Wide Area Network (WAN) Access Switch

In businesses and schools, there isn’t a separate telephone line for eachphone in the building. Usually, there is a PBX system that allocates a limitednumber of incoming lines to extensions on an as-needed basis. A WANaccess switch performs the same type of function. By using a switch, youeliminate the need to run lines to every videoconferencing unit. The switchwill allocate available lines to whatever unit is making a call. IMUXing isoften performed by the switch as well. In this case, the switch assignsmultiple lines to each call. Some switches are slotted chassis. This meansthat cards can be inserted into them to customize their configuration. Asyour videoconferencing needs grow, additional cards can be added.

Channel Service Unit/Data Service Unit (CSU/DSU)

A CSU/DSU is required at each end of a T1. It is responsible for the linecoding and framing of the signal. It also performs diagnostic functions tohelp troubleshoot problems on the circuit.


Demarc

The demarc is not a piece of equipment but a place. It is the location atwhich the telephone company terminates its lines in your building. It marksthe end of the telephone company’s responsibility.

NT1

ISDN BRI lines come into your building on two copper wires. This two-wire interface is called an U interface. Most videoconferencing andnetworking equipment require four wires, known as an S/T interface. AnNT1 device converts the U interface to a usable S/T interface. Byterminating the network, NT1s also provide the telephone company theability to perform testing on your line. If an NT1 is turned off for anextended time, the telephone company may assume there is trouble on theline and turn the line off. Some ISDN cards and networking equipment haveNT1s built in, eliminating the need for an external one.

Multipoint Control Unit (MCU)

When three or more sites want to conference together at the same time,an MCU is required. All sites connect to the MCU, and it connects the sitesto one another. During multipoint calls, all sites must connect at the samespeed and use the same algorithms. There are a number of options fordetermining which site’s video image and audio appear at the otherparticipating sites. The MCU can manage the conference so that the sitespeaking appears on all screens. The MCU can also rotate among theparticipating sites, showing each site in turn for a selectable amount of time.Some MCU systems allow one location to be designated as the chair site,controlling which site appears on the participants’ screens. Other MCUoptions include the ability to divide the screen into four parts, displaying upto four separate locations simultaneously at all sites. This option is calledcontinuous presence or, more informally, “Hollywood Squares.”


Figure 6Continuous

presencemultipoint

conference

Remote Distance Modules (RDM)

V.35 and RS-366 cables are used to connect CSU/DSUs, IMUXes,switches, and other networking components to codecs. These cables have adistance limit of only 100 feet. What happens when you want to place thecodec more than 100 feet from this equipment? The answer is that you buya set of remote distance modules (RDM). An RDM can convert the V.35and RS-366 signal to a format that can be carried over cat 5 UTP or fiber-optic cable. An RDM on the other end of the cable, as much as over a mileaway, converts the signal back.

StandardsAll the equipment in the world will do you no good if it can’t

communicate. A standard is a common language that differentmanufacturers’ equipment speaks, allowing it to communicate with others.Imagine having a telephone and being able to call only someone with thesame make and model of telephone. That was the world ofvideoconferencing before standards. The International TelecommunicationsUnion (ITU) is the United Nations body responsible for setting thestandards for videoconferencing. Each standard is given a letter and anumber.


H.320

H.320 is actually a group of standards for ISDN and T1videoconferencing. It includes a standard for compressing audio, calledG.711, a standard for compressing video, called H.261, and a standard fortransmitting these signals, called H.221. By using these standards, anyH.320 system should be able to connect to any other H.320 system. AllH.320 systems are not created equal, however. To meet the standard,systems are required only to have a frame rate of 7.5 frames per second(fps). Regular television pictures and better videoconferencing system run at30 fps, producing a much higher-quality image. G.711 also providestelephone-quality audio. Other optional audio standards that providediffering sound quality. G.722 requires more bandwidth but providesexcellent audio. G.728, on the other hand, requires only 16 kbps ofbandwidth and provides less than ideal quality.

H.323 and H.324.

H.323 specifies how videoconferencing is done over the Internet andlocal area networks. H.324 concerns videoconferencing over analogtelephone lines. Neither of these methods provides sufficient quality fordistance instruction.

T.120

T.120 is a group of emerging standards. Instead of dealing withvideoconferencing, T.120 is concerned with data and graphics conferencing.It address such topics as application sharing, file transfer, and whiteboardingamong multiple sites. With T.120, participants at several different locationscan work on a document or receive a graphical presentation from a singlesite. This standard can work alone or with an H.320 videoconferencingsystem that is T.120 compatible.

Applications 15

3 ApplicationsNow that we know all the components that go into a videoconferencing

network, let’s take a look at how this technology is applied. Below aresample applications for videoconferencing in education. In each case, theappropriate level of technology was selected for the desired outcome.Although the solutions presented here are complete and workable, they arenot the only solutions. Each situation you encounter will be different as willthe required approach.


Simple single-classroom setupMs. X wanted to set up a small system in her classroom to allow students

to take virtual field trips and have guest speakers she would not normally beable to get into the classroom. Since she already had a multimedia-equippedcomputer, she ordered an H.320-compatible desktop videoconferencingpackage. When it arrived, she installed the videoconferencing card in anavailable expansion slot in her computer and plugged the included camera,microphone, and speaker into the card.

In the meantime, the technology director for the school ordered a singleBRI ISDN line to be installed at the school’s demarc. From the demarc, heran cat 5 UTP cable to an NT1. Through a patch panel, the directorconnected the NTI to Ms. X’s classroom. He had the telephone companyprovision both B channels for data. Ms. X received the SPIDs, switch type,and ISDN standard from the technology director. She plugged a cat 5 cablefrom the wall jack to the videoconferencing card in the computer andinstalled the software. She then dialed a test number provided by her softwarevendor and confirmed that her system was working. Ms. X now has a 15-fpsdesktop videoconferencing system in her classroom. She can connect withany other H.320-compatible system with an ISDN connection any place in theworld. She ordered a little more expensive system and received a remote-control camera and the ability to add an extra video source.

Ms. X now brings speakers in from around the world. Among other uses,Ms. X’s students have watched a session of the state legislature and laterquestioned their representative on the proceedings.

Figure 7Simple single-

classroomsetup

Applications 17

Distance-learning classroomSeveral people had come to Mr. Y, information technology director for

the school district, requesting videoconferencing services. Mrs. Z had beenapproached by several rural schools to share her calculus course. Miss Q, theguidance counselor, wanted students to be able to take a CAD course at thetechnical school across town without busing them back and forth. Finally,Principal H wanted to get more training for her teachers without spending alot of money on travel and substitute teachers.

Mr. Y purchased a group videoconferencing system. It is H.320compatible and has T.120 capabilities. Three BRIs were ordered, provisionedfor data on all B channels, and installed by the telephone company. Mr. Yalso purchased an IMUX with built-in NT1s. He programmed the IMUXwith the SPIDs and directory numbers of the ISDN lines and the switchinformation. The IMUX was mounted directly in the videoconferencingsystem’s cart. An existing computer lab was converted for distant learning. Asimple audio system was installed, and extra lighting was added. The 3 BRIswere connected with cat 5 cable through the patch panel to the room.

Now, Mrs. Z teaches her course to three rural schools that cannot offerthe course. Students take the CAD course for college credit before theygraduate from high school. They use the T.120 capabilities to share theirwork with the instructor on the other side of town. Teachers receive regularprofessional development sessions without leaving school.

Figure 8Distancelearning

classroom


Multiple classroomsA university has made a major commitment to videoconferencing. The

business department both delivers and receives distance education courses. Inaddition, they offer virtual job interviews for graduating students. Themedical school has a partnership with a local hospital to researchtelemedicine. Finally, the dean wants a desktop system to conference withother administrators in the state system.

At the center of this complex system is a slotted WAN access switch. Thisswitch is outfitted with cards for T1 and PRI coming into the switch from thetelephone company. It also needs V.35 cards for the two group systems and aBRI card for the desktop system. A PRI with B8ZS line coding ESF framingis installed to connect to the public telephone network. A T1, configured thesame way, is installed between the switch and a similar switch at the hospital.Two sets of RDMs are installed, one between the switch and the medicalschool’s telemedicine laboratory. The other RDM is installed between theswitch and the business school’s distance-learning classroom. A cat 5connection is made between the switch and the dean’s office. Although this isnot a BRI provided by the telephone company, the switch makes it appear assuch to the desktop videoconferencing system.

The T1 provides the medical school with high-quality, low-delay audioand video required for telemedicine. The medical school can also call outusing the PRI to reach other H.320-compatible sites. The business school hasthe flexibility to offer distant education courses to sites around the world andbring prospective employers on campus electronically. The dean can attendimportant meetings without leaving his office.

Figure 9Multiple

classrooms

Applications 19

District or regional networkThe university is selected to be a hub for a videoconferencing network of

area schools, libraries, and hospitals. Since multipoint conferencing is a majorpart of the project, an MCU is included in the plan. Additional cards arebought for the switch to accommodate a connection to the MCU and T1s.T1s are installed from the switch to an IMUX at each site. Each site sets up alocal system similar to those described above.

Any site on the network can make a point-to-point call to any other site.Three or more sites can participate in a multipoint call. Each site now alsohas access to the PRI installed at the university. All these connections aremanaged through the switch at the central site.

Figure 10District of

regionalnetwork

4 ConclusionThe development of videoconferencing technology has opened countless

opportunities for educators. The ability exists today to bring the world rightinto the classroom in an effective and affordable way. The future will be onlybrighter. Videoconferencing systems are getting better and less expensive.New network technologies promise to bring higher-bandwidth connections tomore places around the world. These capabilities, if used correctly, can openwhole new horizons for teachers, administrators, and students.

an educator's an educator's guide guide

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