Delivering an acceptable quality of service for mobile video is magical if you stop to think about it.
To watch a video on the train using an iPhone (News - Alert), the video must be formatted for the device and the bandwidth available to give a consistent playback experience. It also must take into account the number of users on the network node at the moment of playback, as well as the rapidly changing conditions of the radio signal delivering the video as the user potentially changes locations.
The magic of mobile video is handled relatively well by mobile network operators (MNOs), especially as 4G LTE finds adoption. However, there still is inefficiency and times when the quality of experience for mobile video is functionally inadequate. This is especially the case with rapidly changing network conditions, perhaps the biggest mobile video issue still facing MNO.
Adaptive Guaranteed Bit Rate technology eases the problem
The current best practices approach used by many MNOs is combining Guaranteed Bit Rate (GBR) with HTTP Adaptive Streaming (HAS) with in-network situations and transcoding or transrating for out-of-network video streaming.
Implemented mostly by content providers, HAS incorporates a network-aware approach to video optimization that adjusts the codec rate based on the bandwidth or data rate available between the video server and the client. But HAS cannot rapidly adjust to the rapidly changing radio conditions of wireless networks.
Then there is the network side with GBR, transcoding and transrating.
“The primary advantage of out-of-network methods is their in-depth knowledge of the video characteristic requirements,” according to Colin Kahn and Harish Viswanathan in a recent article for Alcatel-Lucent’s (News 
- Alert) TechZine. “However, they cannot take into account the latest real-time radio conditions, nor can they affect RAN resource allocation for the various video flows.”
When the user is in-network, GBR is used to provide bandwidth stability using quality of service mechanisms, according to the article by Kahn and Harish. But improvements in video performance often come at the expense of lower throughput for best-effort traffic, and GBR doesn’t provide the flexibility needed to respond rapidly to radio congestion.
That’s where Adaptive Guaranteed Bit Rate (AGBR) comes into the equation.
Employed at the node level, AGBR uses an intelligent algorithm to dynamically adapt the network’s GBR in response to increasing or decreasing network congestion.
“This dynamic adjustment of GBR is the key to ‘coding awareness’ in the radio access network,” noted the paper. “It allows more stable bandwidth to be delivered to each HAS client, which is crucial for good HAS video quality in unpredictable wireless environments.”
AGBR also creates an automated “control knob” for balancing video quality and resource utilization, as MNOs can set the level of video quality in relation to other network traffic. No longer must video hog network resources in the service of providing viewers an acceptable viewing experience.
So while mobile video already is magical, it may get even better in the near future as MNOs learn this new trick.
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Edited by
Peter Bernstein
