This article originally appeared in the July 2011 issue of NGN.
The promotion of high-speed mobile broadband services is in full swing as evidenced by a flurry of new television commercials from U.S. mobile service providers. A recent ad shows how a sports event video is interrupted as a critical play is about to be viewed by a sports fan on his mobile device. The commercial shows the ubiquitous animated pinwheel displayed as the video stream is interrupted. All of us have seen this on either our fixed or mobile broadband connections when streaming high-quality audio or video content. Consumers of these services on mobile devices are being told by service providers that going with the fastest mobile network will directly translate to a better user experience. But is this the case?
Mobile video first became popular by enabling access to news/sports portals and to user- generated content via websites such as YouTube (News - Alert). This usage is in fact is characterized by a one-way streaming delivery of this video content. The other case for mobile video usage that has recently become popular is when a mobile subscriber connects to another person for a video call. This case is characterized by establishing a two-way video communication between the video call participants. Both of these video usage scenarios started out as free services, but this is changing as mobile service providers look to monetize video services. IP protocols have been the foundation of the Internet and have made these freemium services possible, but they are not inherently deterministic and cannot eliminate the buffering pinwheel or gaps in audio/video communications. This has resulted in a large number of freemium services where users just learn to cope with interruptions in these services.
In the one-way media content delivery case, the push for monetization has been to offer premium media streaming services that provide higher quality audio and video content. This, in most cases, is licensed material such as the music offered by Pandora (News - Alert) or the movies available from Netflix and Vudu. This has created a new class of streaming media users who sign up for various subscription models offering licensed music and movies. To capitalize on this, over-the-top service providers have taken advantage of technology called content distribution networks. As an IP network overlay, CDNs strive to minimize the buffering issue and enforce usage constraints on licensed media content. The key functional elements of CDNs that help minimize media buffering include a network design with careful physical distribution or caching of content at the edge of the network closer to users, media redundancy schemes, along with adaptive delivery speed techniques that can mask interruptions in the media flow.
In the two-way video communication case it is not enough to just eliminate network latency since the video has to be kept synchronized between communicating parties in real-time. This is in contrast to the just-in-time nature of one-way video, where caching and endpoint buffering can be applied. Two-way video communications require that a real-time session is established between the videoconferencing participants at the start. This can be done using the session initiation protocol to set up the video sessions. The introduction of session management for two-way video communications is an overlay to IP transport networks just as content distribution mechanisms are for one-way media streaming.
This has given rise to the term session delivery networks. SDNs are focused on delivery of real-time, high-quality, two-way communications over IP networks. When real-time session management is integrated with application service logic, service providers can offer their users high-value, rich media services that service providers can monetize. SDNs are focused on keeping end-to-end two-way communications whole, whereas CDNs are focused on bringing the media closer to the endpoint in hopes of getting there without interruption. Also, in addition to addressing quality of service, SDNs are focused on quality of experience factors that encompass session security, interoperability, and regulatory compliance.
In combination with core IMS network elements, the SDN is able to establish that the network capacity is available make a video call in the first place. SDNs will continue to play a prominent role as 4G mobile networks evolve to support end-to-end IP communications and network speeds reaching well over 100mbps.
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Edited by Stefania Viscusi