Why Latency Matters to Mobile Backhaul - O3b Networks

Why Latency Matters to Mobile BackhaulFinally, the absolute quality of the voice and latency impact is related tothe codec selected. Although in any case, higher latency means a decreasein quality. For Mobile backhaul, AMR-12.2 is widely used and correspondsto GSM-EFR codec.Ie= 0 5 7 10 15 19 19 20 26msG.711 GSM-EFRG.726@32 G.729G.728@16~0 94 87G.723.1@6.3G.729A+VADw/2%lossG.723.1@5.3G.723.1@6.3+VADw/1% lossGSM-FRIS-54G.729A+VADw/4%loss50 93 86 83 74 67100 92 87 85 82 77 73 73 72 66150 90 85 83 80 75 71 71 70 64200 87 82 80 77 72 68 68 67 61250 80 75 73 70 65 61 61 60 54300 74 69 67 64 59 55 55 54 48350 68 63 61 58 53 49 49 48 42400 63 58 56 53 48 44 44 43 37450 59 54 52 49 44 40 40 39 33Note 1 – R-values in this table have been calculated using the indicated values for Ie and T (T=Ta=Tr/2) alongwith 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. 108Annex B)Annex 2 TCP details and throughput calculationThis annex gives more details on TCP Flow Control and TCP Congestion andMaximum TCP throughput and TCP transfer duration.Flow controlFlow 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 allowedto transmit data up to this advertised value until it receives an ACKmessage.www.o3bnetworks.com 17