Why Latency Matters to Mobile Backhaul - O3b Networks

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Why Latency Matters to Mobile Backhaul End to end latency, or so called “mouth to ear” has a strong impact on the voice quality, as illustrated by the following figure extracted from the G.114 recommendation. Figure 14: End-to-end latency effect on R factor (ITU G.114) The higher the latency, the lower the voice quality. And as shown in the right side of the graph, voice quality is directly related to user’s QoE and overall satisfaction. www.o3bnetworks.com 16
Why Latency Matters to Mobile Backhaul Finally, the absolute quality of the voice and latency impact is related to the codec selected. Although in any case, higher latency means a decrease in quality. For Mobile backhaul, AMR-12.2 is widely used and corresponds to GSM-EFR codec. Ie= 0 5 7 10 15 19 19 20 26 ms G.711 GSM-EFR G.726 @32 G.729 G.728 @16 ~0 94 87 G.723.1 @6.3 G.729A +VAD w/2% loss G.723.1 @5.3 G.723.1 @ 6.3+VAD w/1% loss GSM-FR IS-54 G.729A +VAD w/4% loss 50 93 86 83 74 67 100 92 87 85 82 77 73 73 72 66 150 90 85 83 80 75 71 71 70 64 200 87 82 80 77 72 68 68 67 61 250 80 75 73 70 65 61 61 60 54 300 74 69 67 64 59 55 55 54 48 350 68 63 61 58 53 49 49 48 42 400 63 58 56 53 48 44 44 43 37 450 59 54 52 49 44 40 40 39 33 Note 1 – R-values in this table have been calculated using the indicated values for Ie and T (T=Ta=Tr/2) along with the default values from Table 6 for all other parameters. Note 2 – Unless indicated otherwise, examples do not include packet loss or Voice Activity Detection (VAD). Note 3 – Blackened cells indicate combinations of delay and codec that are impossible to realize. Figure 15: R rating values for various voice codecs depending on End to end delay (ITU G. 108 Annex B) Annex 2 TCP details and throughput calculation This annex gives more details on TCP Flow Control and TCP Congestion and Maximum TCP throughput and TCP transfer duration. Flow control Flow control is achieved using a feature called “sliding windows”. The receiver advertises the amount of data it can accept through time (generally related to buffering capacity). The transmitter is allowed to transmit data up to this advertised value until it receives an ACK message. www.o3bnetworks.com 17
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Why Latency Matters to Mobile Backhaul - O3b Networks

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