There are signs of convergence toward common standards shared by fixed networks for mobile video. But, for now, operators have to blend an array of technologies to deploy rich media services on any scale. For mobile video, there are also different sections of the delivery chain to consider, with an obvious distinction between the radio access network, the backhaul serving the cell towers and the core fixed line network behind that. The backhaul itself can be wireless using microwave, but is increasingly served by fiber given the high bandwidth now called for to serve the fast-growing amount of video traffic. For radio access, there will be two options over the coming years: 4G LTE within cellular networks, and Wi-Fi, within the home and in public hotspots, with different technical requirements.
The two main challenges are the same as for fixed-line Over The Top (OTT) video delivery: quality of experience and bandwidth efficiency. These are related to the extent that infinite bandwidth can deliver perfect quality in theory but is not practical or affordable, meaning a compromise has to be reached. It is this factor that has led to use of adaptive bit-rate streaming (ABRS) combined with caching out in the network, to achieve the best quality possible over limited and varying bandwidth. On this count, the issues for mobile video delivery are essentially the same as for OTT as far out as the backhaul network or even the cell tower (or Wi-Fi router), with both converging around ABRS.
The story began with Real Time Streaming Protocol (RTSP), which was widely implemented for streaming on early video capable mobile devices. Meanwhile, for fixed-line OTT, Adobe’s Flash came to dominate, and brought its own proprietary protocol, Real Time Messaging Protocol (RTMP). Then, this was rudely shoved aside by Apple on the back of the iPhone and iPad boom, with Apple’s proprietary version of HTTP streaming called HTTP Live Streaming (HLS).
At the least, this established HTTP streaming as the agreed method for video delivery to both fixed and mobile devices, but with several variants. Adobe fell into line by introducing its version, HTTP Dynamic Streaming (HDS), when it brought out Flash 10.1, while Microsoft introduced Smooth Streaming for Silverlight. These are now being folded into the ISO-MPEG standard initiative called MPEG-DASH, which is being adopted by both fixed and mobile operators. (See Figure 1.)
“MPEG-DASH is where we will likely end up for OTT or mobile delivery, eventually,” said David Springall, chief technical officer at mobile video platform vendor Yospace, whose cloud-based service is being used in the U.S. by Hearst-based TV stations for delivering short-form content.
However, MPEG-DASH was only ratified early this year. In the mean time, service providers have to work with existing streaming protocols while they consider how to migrate to the common standard. YoSpace is among vendors providing help, releasing a Software Development Kit (SDK) that allows app developers to enable smartphones or PCs using Flash players to receive HLS content. YoSpace will follow with a version that also supports MPEG-DASH, which will be significant because it will help service providers migrate to the common converged platform. This will involve replacing Flash with HTML5, which has become the commonly agreed mark-up language for formatting and presenting multimedia content across multiple web-connected platforms. HTML5 was designed to run efficiently on low-powered battery devices, and this has led to rapid adoption on mobile handsets. One survey from Strategy Analytics predicts there will be 1 billion HTML-compatible handsets by 2013, which does not leave much room for Flash or anything else.