Why Latency Matters to Mobile Backhaul - O3b Networks

Why Latency Matters to Mobile BackhaulFigure 12 shows that the maximum TCP throughput degrades rapidly aslatency increases.The same illustration for an interactive service is considered: an HSPAaccess over satellite to Internet service (c.f. Figure 9 and Figure 10 for detailon each case).The maximum throughput for TCP Reno will be 2.1 Mbps for O3b and775 kbps for GEO satellite. This will be the maximum achievable rate for aTCP connection, such as a single user communicating with a server. Table 5estimates the transfer time for various media for both backhaul links for asingle TCP stream.O3bGEO2 MB Song 10 seconds 28 seconds1.5GB Movie 1.66 Hours 4.5 Hours3.8GB HD Movie 4.25 Hours 11.4 HoursTable 1: Estimated transfer time comparison between O3b and GEO backhaulThe subscriber QoE for these types of services is directly related to thedownload time. The lower latency of the MEO case results in a hugeimprovement in download times and subscriber QoE.Non real time video streamingVideo streaming was traditionally transported over UDP, but major websites such as YouTube and DailyMotion now use either Adobe Flash Video orHTML5:− HTML5 is delivered using HTTP over TCP.− Adobe Flash Video can be delivered using:− FLW or SWF Files downloaded using a browser with HTTP over TCP− Progressive download over HTTP over TCP− Real Time Messaging Protocol over TCP directly or through HTTP tunnelover TCP− HTTP Live Streaming format over TCP.With all the major providers of web video streaming now using TCPtransport for video streaming, the latency impact on the degraded userexperience will be exactly the same for Internet video streaming as it is fordata file transfer.www.o3bnetworks.com 13