Why Latency Matters to Mobile Backhaul - O3b Networks

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Why Latency Matters to Mobile Backhaul Figure 6 – End to end latency distribution for a voice call with GEO satellite backhaul. For O3b’s MEO constellation, the fiber return path adds 30ms of latency, representing the case of more than 5000km of optical fiber. The following diagram shows the resulting MOS scores for these two cases. Figure 7 – Voice Quality / MOS score degradation as a function of latency A side-by-side comparison of end-to-end latency values results in an MOS score of 4.4 for O3b’s MEO constellation and a MOS score of 3.8 for traditional GEO satellite. www.o3bnetworks.com 8
Why Latency Matters to Mobile Backhaul Interactive user services The impact of latency on interactive services is more subjective. As the delay increases, the applications continue to function. However, the sense of immediacy and the usability degrades. At some point, the user becomes less tolerant of waiting for the response, eventually giving up and moving on to something more satisfying. A great deal of research has been done by companies whose revenues are impacted when users abandon their transactions. The importance of latency on web commerce was first showcased by Zona Research in 1999 with the popular “8-second rule”. Zona found that more than $4 billion e-commerce sales were lost due to poor site performance, which ultimately led to transaction abandonment. In a follow up study in 2006, Jupiter Research concluded that the threshold had been reduced to 4 seconds, as more users experience the performance of high-speed broadband. Google discovered that the number of web searches and ad revenue declined as they increased the number of user search results from 10 to 30. Further research found the result was due to the additional time required to compute and present more results to the user. Increasing the results from 10 to 30 required an additional 500ms to compute and resulted in a 25% drop in the number of searches done by users. Following this initial study, Google performed additional tests focused exclusively on the latency. They injected artificial delay into the display of the search results. An increase in display time of 400ms actually decreased the number of searches per users by 0.44% to 0.76%. While these drops in usage appear small, they had a direct and meaningful impact on ad revenue. Similarly with Amazon: “We tried delaying the page in increments of 100 milliseconds and found that even very small delays would result in substantial and costly drops in revenue,” said researcher Greg Linden. Linden provides a precise figure: -1% sales for 100ms or more latency. (Greg Linden in “Make Data Useful”, Data Mining course Stanford in 2006). Steve Souders from O’Reilly adds more examples in a blog posting http://radar.oreilly.com/2009/07/velocity-making-your-site-fast.html. In “Performance Related Changes and their User Impact,” Eric Schurman (Bing) explains that Bing researchers have conducted tests adding a static delay of 50 ms to 2 seconds to their servers. A negative impact on the Bing performance indicators resulted as soon as the delay increased by more than 50ms. The degradation noticed was linear. www.o3bnetworks.com 9
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Why Latency Matters to Mobile Backhaul - O3b Networks

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