by Peter Maag
Distance education models must overcome significant challenges in creating an environment that encourages participation. Keeping this in mind, the most successful deployments have addressed issues of lighting and acoustics, resolved the technical hurdles involved in effectively incorporating multiple locations, and provided educators and students with the functionality they need via user-friendly interfaces. To maintain students’ attention and to foster interactivity, these models have also focused on eliminating poor picture quality, bad lip synch, and transmission delays. Supporting all of these features and capabilities is an advanced network video delivery technology, leveraged over a telecom-grade system that provides consistent performance day in and day out without requiring continual intervention from IT staff.
The setting
The network video technology behind distance learning initiatives at high schools, universities, and other educational institutions around the world, connect students, classrooms, and teaching resources across buildings, campuses, and cities. A primary room might use one camera to focus on the presenter/teacher and a second to zoom automatically to a participant, such as a student asking a question. In what is called a 2x3 configuration, this setup uses two cameras along with two encoders to send video to the remote site, as well as decoders to feed incoming video from the remote site to three large displays. The model can be expanded to include additional remote sites, thereby creating a more expansive distance education network and sharing resources more extensively.
Linking learning facilities with live, high quality, two-way video brings immediacy to remote learning, allows participating speakers and students to share their enthusiasm, and gives students access to a compelling and engaging learning environment. The technology therefore needs to ensure a high level of performance for interactive media communications, using the latest industry trends like H.264 / MPEG-4 AVC compression technology, to deliver a true-to-life video communication experience at low bandwidth and low latency.
The question of latency
Latency is among the foremost requirements of an effective network video delivery system, particularly in applications such as distance education where clear, responsive interactivity between sites is critical for success. For remote video collaboration, the established acceptable end-to-end transmission latency (from camera to screen) is below 200 milliseconds, or two tenths of one second), latencies rising above 200 milliseconds cause delays that, in turn, cause fatigue and often lead participants to lose focus. This is especially important for extended use sessions, such as hour long classes, and where a high level of interaction is required, such as with language instruction or applied sciences.
There are various elements including camera latency, encoder latency, network topology and transmission distance, decoder latency, and display latency, that contribute to total video latency. While each of these must be considered during the design and engineering of a distance learning model, encoders and long-distance networks have proved to be the most significant contributors to end-to-end latency. And although network latency is a contributor, it is primarily dependent on distance. As a result, the choice of encoder (or codec when considering an encoder/decoder system) deserves special consideration.
Encoders and codecs are available with a wide variety of characteristics suiting many needs. Encoders that are typically used in broadcast applications add between 300 and 4,000 ms of latency to the video transmission. Some encoders are tailored for web streaming applications, balancing the high quality of broadcast-oriented systems against the bandwidth constraints of network video delivery, but also add significant delay and are unsuitable for any interactive application. Lower latency traditional videoconferencing codecs allow for higher interactivity, but they tend to be difficult to use, provide unstable performance, and feature limited interoperability with common streaming infrastructure elements, such as soft players, set top boxes, and streaming servers. Effective distance education requires near broadcast quality encoding coupled with both low latency performance and telecom grade reliability.
Interoperability is crucial
Distance learning classrooms are designed to foster the immediacy of live communication, but today institutions are looking to get more from their systems in order to offer a greater service to the student population. They are looking beyond the classroom, to the computer desktops and handheld devices that we all turn to. It is most important that any investment that such institutions make is immediately extensive to these mediums. Relying on H.264 is certainly the safest decision, but assuring compatibility with standards based recorders, streaming and distribution systems, and soft players and set top boxes is critical. More and more institutions are moving away from constrained and difficult-to-manage conferencing solutions to open, dynamic, and extensible streaming based solutions.
Adding ease to distance learning
One of the most important requirements in education is ease of use. Teachers cannot fumble with systems, and certainly IT staff cannot be on stand-by for every class. Systems must connect readily and work. Many systems are automatically provisioned by a central scheduler that has been programmed with an entire year of class schedules. Some are controlled by simple wall-mounted control panels resembling light switches, with just a few buttons controlling streaming/reception, on/off functions for the projector, and mute functions for the speakers and microphones.
When manually operated, straightforward control allows teachers to launch two-way sessions at any time without having to input technical details, dial out, or reconfigure the system in any way. To stimulate participation amongst remote sites, interactive voting handsets also can be employed to allow students at multiple locations to vote collaboratively and participate more actively in presentations.
