Well-designed, planned, narrated and produced audio content has the facility to engage the audience and transport the listener, providing the right cognitive environment for learning or entertainment or whatever goal the podcast seeks to achieve. As the old story goes, “there are better pictures on the radio.” Denis Nowlan, Deputy to the Controller for BBC Radio 4 describes this as

the wonder of radio [and sound] …the conjuring of magical sounds, Prospero-like, out of the silently teeming air. And the sense of joining, instantly, with a vast community of listeners.

(2005)

Of course, this cognitively experienced sense of “being there” is a completely artificial construct, none more so when you consider audio podcasting. The journey the podcaster takes us on is based on nothing in nature; that is, a narrative transmitted as binary data: electronically-mediated zeros and ones.

I will discuss this phenomenon in detail next time, but for now, read on…

Digital audio is actually very similar in concept to motion film, where a rapid series of still photographs make up a “motion picture.” Digital recording reproduces audio signals by taking many still “pictures” – or samples – of an audio waveform and then reconstructing the waveform for playback digitally (see Figure 1).

Figure 1. Digital Sampling of Audio Waveform
[Click to Enlarge]

In film, the number of still images (frames) we move through the projector per second improves the smoothness and quality of picture we see. Similarly, the size of the film’s light-sensitive crystals in each frame determines the visual resolution of the image – and we all know movies look better in 70mm as opposed to the 35mm or 16mm film.

In digital audio, an analog signal is typically sampled 16 or 24 times a second – that is, 16 or 24 bits of data. A sample is created by taking a “snapshot” of the amplitude (or strength) of an analog audio signal at a particular moment in time. and converting that amplitude into a binary number.

The number of samples contained in each second of audio is called the sample rate. The greater the number of samples per second, the greater the resolution of the audio signal.

Let’s return to the film analogy: the faster the film rate through the camera, the better the ability of the film to pick up motion. For example, if you crank a film camera too slowly, then motion past a camera is not smooth since the frame rate does not capture enough frames in a given amount of time to stop the motion from appearing to jump or jerk – too much action happens in front of the camera “between frames” for the motion to appear natural.

Time for an example: The resolution of an audio CD is 16 bits and the sample rate is 44.1KHz. This means that the audio is sampled 44,100 times a second and a series of 16 zeros and ones is used to define the amplitude of the waveform at each of those 44,100 points.

This resolution – commonly called “CD Quality” and should be your baseline for recording a podcast. When recording voice-over narration, capture all of your audio at 16 bit, 44.1KHz, in mono using the WAV format in Windows, Au format for Unix-based systems (like Linux), and AIFF for Apple Mac.

More…

__________

References:

Nowlan, D. (2005). Radio: where the pictures are better: Denis Nowlan speaks for the medium which leads you by the ear. [Internet] Available from: http://findarticles.com/p/articles/mi_m0KZH/is_1_19/ai_n15928065/ Accessed 12 August 2009.

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The term pace has already entered this series of E-Learning Curve Blog articles about creating podcasts. In this post I will discuss pace, and then the related concepts of pitch, projection, and pausing, over the next few days.

Now read on…

Famously, there are three major elements in human face-to-face communication: body language, voice tonality, and words. According to Mehrabian and Ferris (1967, pp.248-52)

• 55% of impact is determined by body language – facial expressions, eye contact , body posture, gestures,
• 38% by tone of voice
• 7% by the content or the words used in the communication process

Anyone who has ever taken a course on presenting will have heard the instructor assert the axiomatic 55-38-7 formula to their learners as if it were inviolable, like fundamental physical constants like 0 Kelvin, c, or that TOS is better than TNG*.

David Lapakko (1997) asserts that this formula for communication is part of the “catechism” (p.63) of linguistics, proxemics, and psychology.

And that there is good empirical evidence that it is wrong.

According to Lapakko,

A closer look at the Mehrabian and Ferris (1967) study reveals severe limitations that call for prudence in interpreting their results… the findings may be an artifact of [a] small sample size.

(p.64)

His views are supported by other researchers’ findings, including Burgooon, Buller, and Woodall (1898) and Hegstrom (1979). Burgoon et al consider that:

[The 55-38-7 estimate] is erroneous. It is based on extrapolation of two studies, one comparing vocal tone to facial cues… and one comparing vocal tone to single words… rather than comparing all three.

(p.155)

Hegstrom agrees that:

The formula was pieced together from two different studies.

(p.135)

Indeed, Mehrabian himself believes that his findings are “often misquoted.” In Intercultural encounters: The fundamentals of intercultural communication (1995) he wrote that :

…all my findings …dealt with communications of feelings and attitudes…Clearly it is absurd to imply of suggest that the verbal portion of all communication constitutes only 7% of the message.

The refutation of the 55-38-7 formula is great news for podcasters in general and e-learning professionals in particular, because of course it means that we’re not operating in some notional margin of communication, but in its mainstream, as anyone who has ever created a podcast (or even used a telephone) to communicate meaningful information already knows.

In a sense, content delivery works independently of content; some people, as the saying goes, can make the phone book sound interesting. For those of us without this gift, we have to consider how to maintain interest and engage the audience. One of the ways we do this is to pace the dialog appropriately. I would assert that a narrative must be kept moving at a fairly brisk rate. The secret of pace is:

Allow enough time to each learning point for it to be well understood. Then move on.

Pace is impossible without intelligibility. Conversely, it depends in part by not going too fast. Pace depends on the precise shaping of the meaning and the words in time, and it provides the foundation upon which everything else is built.

When a podcast has a lack of pace, it is often down to another, subtler fault: a lack of organization in the underlying form of a podcast’s content. In the design of almost any good podcast, there should be a series of basic units of information, each occupying a few minutes. Each of these should contain one major learning point and sufficient supporting detail to help establish it as clearly as possible. The format of the podcast should provide light and shade within a piece, allow details to emerge, and a story to develop.

Certain types of verbal and linguistic construction don’t work in podcasts: they contain too much content, too little time, or both. For example, the cold, clear logic of a computer language like Java, or a turgid mass of detail are both death to clear, intelligible verbal constructions in sound.

With that in mind, here is the latest episode from my ‘Other’ Podcast – Transatlantic: the Flying Boats of Foynes (’New and Notable’ according to the iTunes Podcast Store). If you choose to listen to the podcast, you’ll notice that the piece is not merely a narrator telling a story: along with narration, there’s dramatization, eye-witness accounts, and incidental and background music. Other sound elements included in the series of podcasts include archive recordings, wild track, and a very cool sound collage to set the scene for the outbreak of World War 2 in September 1939.

In Part 4 of Transatlantic: The Flying Boats of Foynes

It’s 1939.

In Ireland, the town of Foynes in County Limerick becomes a boomtown because of its airport, and a tourist attraction because of the flying boats. The ground staff of Pan Am, and BOAC became part of the community, and the various Irish, British, and American communities live, work and play together.

But in Europe, events leading to the greatest conflict of the 20th Century are beginning to move apace as Fascism rises in Europe.

Autocratic single-party regimes in Germany and Italy have become totalitarian dictatorships. As their military might grows, their leaders lay their plans against the nations of the West…

Click here to listen to the podcast.

Click here to view the transcript of this podcast (PDF, 26K).

The observant among you will notice that the piece isn’t about e-learning. That’s OK – the point of e-learning is to provide training professionals with a means of creating and distributing content that enables people to acquire information, knowledge, skills, and expertise on a diverse range of subjects: as e-learning practitioners, it’s our job to facilitate this process.

More…

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*Humorous Remark Alert! No Trekkie flames please; we all know that Picard is a better captain than Kirk…

__________

References:

Burgoon, J. K., Buller, D. B., & Woodall, W. G. (1989). Nonverbal communication: The unspoken dialogue. New York: HarperCollins/Greyden Press

Hegstrom, T. (1979). Message Impact: What percentage is nonverbal? The Western Journal of Speech Communication, 43, 134-142.

Lapakko, D. (1997) Three Cheers for Language: A Closer Examination of a Widely Cited Study of Nonverbal Communication. Communication Education, 46. [Internet] Available from: http://resourcemagazine.co.uk/acatalog/lapakko.pdf Accessed 31 July 2009

Mehrabian, A. (1995). Intercultural encounters: The fundamentals of intercultural communication (3rd ed.). Englewood, CO: Morton Publishing Company.

Mehrabian, A., & Ferris, S. (1967). Inference of Attitude from Nonverbal Communication in Two Channels. The Journal of Counselling Psychology, 31.

–

Anthony Bates, author of Technology, e-learning and distance education (2005) states that audio (via radio broadcast) has been used in education for over seventy years. Examples of its uses include school broadcasting, informal general education, social action programming, and adult basic education and literacy (p.117).

Since its inception in 1969, the British Open University supplied about one-fifth of its output via radio programming. Typically it such programming centered around:

Discussions of course material or issues covered in printed materials

• Alternative viewpoints to those contained in the printed materials (i.e. guest speakers interpreting a text)
• Source materials for analysis (i.e. children’s speech patterns)
• ‘Performance’ pieces, including poetry readings, dramatizations of literature, musical performances

There are of course drawbacks to delivering content via radio broadcast or via analog tape. Radio broadcasts are wholly dependent on the broadcaster’s schedule, and minority programming is usually relegated to inconvenient “graveyard slots” – the learner has no flexibility around the schedule. Similarly, broadcasted material happens in real-time – the learner has no facility to ‘rewind and play back’ a presentation if they miss a point, unless they tape the program ‘off the air’ (if you’re old enough to remember, you’ll recall that this could be a messy business).

Cassette tapes had their problems too: analog recordings deteriorate with use and over time, tapes cassettes have many moving parts, the actual magnetic tape can break and become degaussed, and if you have a lot of them, they’re bulky to store.

The introduction of CD-ROMs in the late 1980’s mitigated most of these issues, and in a sense were the hardware breakthrough that presaged the beginnings of e-learning as we know it today. However, CD-based materials were expensive to produce, many pre-Pentium and PowerPC processors couldn’t handle the multimedia requirements needed to view and listen to the material delivered via this medium (800×600 CRT monitor, anyone?).

It was the emergence of the internet that genuinely facilitated audio and visual media-based learning. But that, my friends, is a tale that’s still being told, so I’m not going to discuss it here.

The Open University today, on iTunes U

All I will say here is that the internet enables access to e-learning content:

• For Anyone. E-Learning resources are available on-demand, via synchronous and asynchronous channels
• Anywhere. Digital content can be distributed just as easily on a home-based PC, a laptop, or (increasingly) via a mobile device. Content can be viewed both online and offline for maximum flexibility.
• At Any Time. You no longer need to rely on an IT department for distribution of large media files; content is easily delivered on demand to facilitate self-paced, OTJ and just-in-time learning.

Now read on…

The purpose of this long pre-amble was to emphasize the importance of understanding your target audience. When you start work on a podcast, you must be aware of not only what is to be said, but also to whom you want to say it. This is not merely a matter of your audience’s intelligence, but also of background, experiences and outlook. It is also powerfully related to the things that the listener would like to do – ranging from learning Spanish for a vacation, to passing their Microsoft Office User Specialist certification.

Podcasts – like blogs – develop a distinctive ‘personality’ according to the characteristics of the source material, the type of audience that material is aimed at, and the individual or team who produce the podcast. So, a Wired News podcast reviewing the latest and greatest computer technologies will sound very different from a podcast about conversational French for beginners.

A study in to the effect of BBC educational broadcasts noted that too many ‘teaching points’ (what we usually call learning objectives) – more than six per 15 minutes of programming were definitely bad for the user’s learning curve. Interestingly, where long, complex sentences with difficult vocabulary and a lot of prepositions did appear to have an adverse effect on intelligibility, the presence of a large number of adverbs and adjectives did not.

The conclusion was drawn that an apparent excess of facts, figures and descriptive terms is no disadvantage, because although they may not be assimilated themselves, they help maintain interest during the learning intervention.

More…
___________

References:

Bates, A. W. (2005). Technology, e-learning and distance education. Oxford: Routledge Falmer

Read more: http://elearningcurve.blogspot.com/2009/07/exploring-podcasting-for-e-learning-and.html#ixzz0MjnglJ8i

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Discuss.

–

First a little about podcasting…

A podcast is one in a series of digital media files (usually in either  audio MP3 or video M4V format) that is released periodically and made available for download by means of web syndication.

This syndication aspect of the content delivery is what differentiates podcasts from other ways of accessing files, such as simple download or streaming. Special client software applications called RSS aggregators (also known colloquially as podcatchers) such as Apple  iTunes or Nullsoft Winamp can  automatically identify and retrieve new podcast files in a given series when they are made available, by accessing a centrally-maintained ‘feed’ that lists all files currently associated with that particular series.

New files can be downloaded automatically by the podcatcher and stored locally on the user’s computer or other media device for offline use, enabling the audience to download content that is released episodically without having to manually check that new material has been made available.

According to the Horizon Report (2006) podcasting is

At the leading edge of a wave that will last for the next several years and beyond, personal broadcasting takes advantage of small, easy-to-use devices that people already carry to capture and share personal experiences, information, and events. This trend, which has roots in text-based media (personal websites and blogs), is expanding to include audio and video, as the tools for capturing and sharing those media become smaller and better. From podcasting to video blogging (vlogging), personal broadcasting is an increasingly popular trend that is impacting… audiences.

(p.11)

It’s easy to see why podcasts have value in e-learning. Will Richardson states in Blogs, Wikis, Podcasts, and Other Powerful Web Tools for Classrooms that the

underlying technology here is digital recording and the idea that it is now very easy to create and publish these recordings… As long as you have a way to make the recording, and as as long as your students have access to the Internet, you can make this work.

(p.113)

Now that I have started publishing podcasts, I’m obviously going to write a series of articles about developing and delivering content using this learning channel. What’s more, I will discuss podcast authoring using production techniques, based upon my experiences as a radio documentary maker in a ‘previous life’ – I’ll be talking about the craft of writing for audio, as well as the technical aspects of the process.

Now, [drum roll] I want to introduce you to the E-Learning Curve’s Other Podcast. This podcast service is about subjects that interest me other than e-learning. Topics I’ll be covering include aviation, history and music, among others. The first set of podcasts is called Transatlantic: the Flying Boats of Foynes:

July 2009 is the 70th anniversary of the first scheduled trans-Atlantic airplane passenger service. Told against a backdrop of the momentous events of World War Two, this eight-part podcast documentary series by Michael Hanley tells the story of a unique era in world aviation.

Airlines like Pan American Airways (PAA) and the British Overseas Airways Corporation (BOAC) with their flying boats like the Short series of planes, and the massive Boeing 314 ‘Clippers’ were welcomed to the seaport of Foynes, in the embrace of the River Shannon estuary on the Western edge of Europe. Come with me now as we fly back in time to the Golden Age of Aviation, a era of adventure, conflict – and the invention of Irish Coffee.

Parts 1 and 2 of the series are now available. You can listen and subscribe to each episode here, or you can access the podcast via iTunes. The next installment, The Glamour of Travel will be released on Tuesday July 28th, 2009.

The more observant among you will have noticed that this podcast channel is called the Other Podcast, which implies that there is a regular E-Learning Curve Podcast, discussing subjects associated with learning and development.

Yes there is. And it’s on it’s way soon. More about this closer to its launch.
___________

References:

The New Media Consortium (2006). 2006 Horizon Report. [Internet] Available from: http://www.nmc.org/pdf/2006_Horizon_Report.pdf Accessed 15 July 2009

Richardson, W. (2006) Blogs, Wikis, Podcasts, and Other Powerful Web Tools for Classrooms. Thousand Oaks, CA: Corwin Press.

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I’ve mentioned in the past that I’m a Space nut; I believe the ongoing endeavor to explore, live, and work in space to be the epitome of the human spirit and our imperative to learn and to understand that  which is currently beyond out ken. I also share a birthdate (but not the age) with Neil Armstrong, first man on the Moon and utterer of the infamous "One small step…" epigram. And because this is the E-Learning Curve Blog, I’m also going to discuss this event in the context of learning technology, particularly the role of asynchronous media in supporting cognitive events. But I’m not doing that last bit: today, I’m going to sit back and enjoy the events of July 1969.

Now read on…

The first site you can check out is the "official" NASA 40th Anniversary website, which has a variety of informative resources that will teach you about the historic mission. When you ‘land’ (sorry) on the page, you’ll find a brief of the historical events surrounding the mission, as well as a listing of anniversary events for those of you lucky enough to be close to these commemorations. To supplement its own coverage, NASA has also posted several videos of user-generated videos detailing peoples’ impressions of the lunar landing and why it was so important to them.

Next Google Moon. When you search for Apollo 11 on Google Moon, you’ll find basic information such as the astronauts’ biographies. Once you zoom in on their landing site in Mare Tranquillitatis (the Sea of Tranquility), you’ll find nearly 20 landmarks that describe everything from where the TV camera was placed, where Armstrong’s famous first footprints were left, to where location of Eagle, their Lunar Module. It also has images of all the landmarks. It’s a nice way to learn more about Apollo 11.

The Project Apollo Archive is the most extensive collection of high-quality Apollo images, featuring images scanned for Eric Jones’ Apollo Lunar Surface Journal. Many image and multimedia resources on this website are courtesy of the National Aeronautics and Space Administration, specifically the NASA History Office, Kennedy Space Center and Johnson Space Center. The site also features:

• Mission Chronology
• Crews
• Spacecraft
• Diagrams and Maps
• Memorabilia
• A (very tough) Lunar Lander Simulator
• Links
• Mailing Lists / Groups

Back on Earth and in the here-and-now, Steve Eves build and launched a 1/10th Scale working model of the Saturn V rocket. This is possibly the only build of the rocket that is completely re-usable, as all the stages safely parachuted back to earth (the original rockets’ components either burned up in Earth’s atmosphere, crashed into the Moon, or are still in orbit around the Sun. 

Best of all, please check out We Choose the Moon – "an interactive experience recreating the historic Apollo 11 mission to the Moon in real time."

Using Flash, and a range of social media technologies and products, the site does an amazing job of recreating the experience of going to the Moon. As I sit here writing this blog post, I’m tuned in to the pre-launch sights and sounds. The site is Flash based, has three Twitter feeds (cleverly taking the audio from CapCom, Columbia (the command module) and Eagle (the lunar lander), as well as an Adobe Air-based desktop and FaceBook widget.

Fantastic.

Finally, if you’re of a mischievous turn of mind, check out how The Onion is remembering Phurba Dorje, the unsung hero of the lunar landing who, according to Buzz Aldrin "…was as much a member of that team as anyone. Probably more than [Michael] Collins was."

Normal service tomorrow: just going to enjoy myself at We Choose the Moon today!
–

iPhone users now have another way to access and view their spreadsheets and charts: software development house MeLLmo have released RoamBi, an app that lets you view the static data from spreadsheets and tables as interactive charts that can be published on an iPhone or iPod touch. The free-to-use RoamBi Visualizer app is available for download from the  iTunes App Store.

The RoamBi app displays data on your iPhone, giving you access to your stats and figures from your free-to-use online RoamBi account. The app works well with CVS- and Microsoft Excel-formatted data, and can manage Salesforce.com account reports, business process outsourcing (BPO) key performance indicators. Users of the enterprise version of RoamBi can also import SAP Crystal Reports and SAP BusinessObjects Web Intelligence data into the app.

According to MeLLmo’s Santiago Becerra,

It’s the first real enterprise-grade app that allows users to transfer all the info they use on a day-to-day basis onto the iPhone.

Your spreadsheet, BPO and KPI data is stored on the app’s accompanying Web site. Developed in Adobe Flex (the open source Flash-based framework for building and maintaining expressive web applications), you upload your content to RoamBi Designer, where you can customize views for delivery to the iPhone. The finished views are published from the Web tool to your phone through an Amazon-hosted server. MeLLmo state that the resultant outputs are

like a mini-app that allows you to navigate through a particular set of data in a way that feels very natural to you.

RoamBi has a number of views including

• CataList – organizes data into different hierarchical levels, interpreting those levels based on the metadata from the spreadsheet.
• Cardex – a 3-D rolodex-style view of records
• Pie View – presents data a spinnable pie chart
• SuperList – displays data in a tabular format with fixed column and row titles.

I recently commented on the growing acceptance of the iPhone as an enterprise-level communications solution. I would assert that we are now beginning to see the emergence of a virtuous circle: now that the popular demand is there, software houses will invest in developing productivity apps like RoamBi, which will in turn drive more business users to the device, which will result in more business functionality being ported to the device. I hope this will lead to an upswing in the number and range of knowledge-sharing, informational, and educational applications for this and other personal mobile devices.

–

iPhone users now have another way to access and view their spreadsheets and charts: software development house MeLLmo have released RoamBi, an app that lets you view the static data from spreadsheets and tables as interactive charts that are published via an teh iPhone or iPod Touch. The free-to-use RoamBi Visualizer app is available for download from the iTunes App Store.

The RoamBi app displays data on your iPhone, giving you access to your stats and figures from your free-to-use online RoamBi account. The app works well with CVS- and Microsoft Excel-formatted data, and can manage Salesforce.com account reports, business process outsourcing (BPO) key performance indicators. Users of the enterprise version of RoamBi can also import SAP Crystal Reports and SAP BusinessObjects Web Intelligence data into the app.

According to MeLLmo’s Santiago Becerra,

It’s the first real enterprise-grade app that allows users to transfer all the info they use on a day-to-day basis onto the iPhone.

Your spreadsheet, BPO and KPI data is stored on the app’s accompanying Web site. Developed in Adobe Flex (the open source Flash-based framework for building and maintaining expressive web applications), you upload your content to RoamBi Designer, where you can customize views for delivery to the iPhone. The finished views are published from the Web tool to your phone through an Amazon-hosted server. MeLLmo state that the resultant outputs are

like a mini-app that allows you to navigate through a particular set of data in a way that feels very natural to you.

RoamBi has a number of views including

• CataList – organizes data into different hierarchical levels, interpreting those levels based on the metadata from the spreadsheet.
• Cardex – a 3-D rolodex-style view of records
• Pie View – presents data a spinnable pie chart
• SuperList – displays data in a tabular format with fixed column and row titles.

I recently commented on the growing acceptance of the iPhone as an enterprise-level communications solution. I would assert that we are now beginning to see the emergence of a virtuous circle: now that the popular demand is there, software houses will invest in developing productivity apps like RoamBi, which will in turn drive more business users to the device, which will result in more business functionality being ported to the device. I hope this will lead to an upswing in the number and range of knowledge-sharing, informational, and educational applications for this and other personal mobile devices.

–

iPhone users now have another way to access and view their spreadsheets and charts: software development house MeLLmo have released RoamBi, an app that lets you view the static data from spreadsheets and tables as interactive charts that are published via an teh iPhone or iPod Touch. The free-to-use RoamBi Visualizer app is available for download from the iTunes App Store.

The RoamBi app displays data on your iPhone, giving you access to your stats and figures from your free-to-use online RoamBi account. The app works well with CVS- and Microsoft Excel-formatted data, and can manage Salesforce.com account reports, business process outsourcing (BPO) key performance indicators. Users of the enterprise version of RoamBi can also import SAP Crystal Reports and SAP BusinessObjects Web Intelligence data into the app.

According to MeLLmo’s Santiago Becerra,

It’s the first real enterprise-grade app that allows users to transfer all the info they use on a day-to-day basis onto the iPhone.

Your spreadsheet, BPO and KPI data is stored on the app’s accompanying Web site. Developed in Adobe Flex (the open source Flash-based framework for building and maintaining expressive web applications), you upload your content to RoamBi Designer, where you can customize views for delivery to the iPhone. The finished views are published from the Web tool to your phone through an Amazon-hosted server. MeLLmo state that the resultant outputs are

like a mini-app that allows you to navigate through a particular set of data in a way that feels very natural to you.

RoamBi has a number of views including

• CataList – organizes data into different hierarchical levels, interpreting those levels based on the metadata from the spreadsheet.
• Cardex – a 3-D rolodex-style view of records
• Pie View – presents data a spinnable pie chart
• SuperList – displays data in a tabular format with fixed column and row titles.

I recently commented on the growing acceptance of the iPhone as an enterprise-level communications solution. I would assert that we are now beginning to see the emergence of a virtuous circle: now that the popular demand is there, software houses will invest in developing productivity apps like RoamBi, which will in turn drive more business users to the device, which will result in more business functionality being ported to the device. I hope this will lead to an upswing in the number and range of knowledge-sharing, informational, and educational applications for this and other personal mobile devices.

–

…I think that the technology decision has to include consideration of the client capabilities of the audience you are serving as well as the network you will ultimately be streaming into and their openness to the ports and protocols. Most enterprise networks close the streaming ports.

Communications and collaboration using streaming media platforms only work if the client side has the facility to access the content. If you or your organization has a requirement to deliver content (on-demand courseware or a pre-sales demo, for example ) to a customer, you are probably familiar with the refrain " I can’t see the content" from the prospective attendee or viewer. There are many reasons why this may occur, but all other things being equal, the probability is that the client cannot access the content because their firewall is blocking the data delivery.

According to Wikipedia, a firewall is

a part of a computer system or network that is designed to block unauthorized access while permitting authorized communications. It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all (in and out) computer traffic between different security domains based upon a set of rules and other criteria.

To control the flow of data, numbered ports in the firewall are either opened or closed to specific types of packets. The firewall reviews two pieces of information in each arriving or departing packet: the protocol through which the packet is being delivered and the port number to which it is being sent. If the firewall is configured to accept the specified protocol through the targeted port, the packet is allowed through. The most commonly-known example of this process is probably Port 80, the access point for TCP, UDP, and the Hypertext Transfer Protocol (HTTP).

Firewall policy management is beyond the remit of this blog, but suffice it to say that most organizations are understandably cautious about providing ‘open house’ access to their networks. The downside of this caution is that when a legitimate need arises to provide access via a rarely-used port, most organizations’ IT departments have reservations (to say the least) about granting access. 

Table 1 describes all of the ports needed to facilitate the delivery of unicast streaming via Microsoft Media Server 9.

Table 1 Delivering a Unicast Stream via MS Media Serve 9

Table 1 only represents a small portion of Windows Media Server 9’s requirements, the platform has separate port access requirements for:

• Delivering a multicast stream
• Streaming from an encoder
• Distributing content
• Administering the server remotely

Apple, on the other hand, provides proxy server software to get around firewalls, by the IT department maintaining the firewall must install the proxy software.

The Flash Streaming Server platform uses what Michael Topic (2002) calls a "drastic solution" to negotiate this problem: HTTP tunneling

Where [Real Time Protocol] RTP packets are wrapped inside ordinary HTTP packets so that they can pass through the firewall.

(p.99)

"Unfortunately" he notes, this approach adds "significant overhead to the stream" taking up more bandwidth. Adobe Systems solution to this issue (and the one implemented by Digital Chalk, as well as a broad  range of e-learning vendors and other enterprises and institutions) is to implement the proprietary Real-Time Messaging Protocol for streaming audio, video and data over the Internet, between a Flash player and a server..

According to Adobe

The Real-Time Messaging Protocol (RTMP) was designed for high-performance transmission of audio, video, and data between Adobe Flash Platform technologies, including Adobe Flash Player and Adobe AIR. RTMP is now available as an open specification to create products and technology that enable delivery of video, audio, and data in the open AMF, SWF, FLV, and F4V formats compatible with Adobe Flash Player.

The protocol works by a client (such as the Flash Player) communicating with a Flash Communication Server (for example via a corporate Adobe Connect solution) using RTMP protocol over port 1935. If that fails, it will try again over ports 443 and 80 in an attempt to get around firewall policies within an organization, which prevent TCP/IP connections over non-standard ports.

According to Adobe this approach allows "approximately 96% of all users to access publicly accessible Flash Communication servers."

More…
___________

References:

Adobe DevNet (2009). Real-Time Messaging Protocol (RTMP) specification. [Internet] Available from: http://www.adobe.com/devnet/rtmp/ Accessed 11th July 2009

Adobe TechNote (2009). HTTP Tunneling protocols [Internet] Available from: http://kb2.adobe.com/cps/166/tn_16631.html Accessed 11th July 2009

Nelson, D. (2007) Firewall Information for Windows Media Services 9 Series. [Internet] Available from:  http://www.microsoft.com/windows/windowsmedia/forpros/serve/firewall.aspx Accessed 11th July 2009

Topic, M. (2002) Streaming Media Demystified. McGraw-Hill Professional. eBook, United States.

Wikipedia (2009) Firewall. [Internet] Available from: http://en.wikipedia.org/wiki/Firewall Accessed 11th July 2009

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