Tham khảo tài liệu 'voip technologies part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 216 VoIP Technologies SIR Fig. 16. Measured R factor a and MOS b vs WLAN traffic data rate for different SIR visible in fact Rmax is nearly 22 Mbit s for SIR 6 dB and 22 Mbit s for SIR 1 dB as shown by the two upper curves which in the range 22 - 34 Mbit s assume very high values 70 dB . In this case further measurements should be performed at lower data rate to determine the corresponding values Rmax below which packet loss becomes negligible or even null 2. in terms of jitter Fig. 15 shows that scenario A is rather immune even to the simultaneous presence of AWGN interference and concurrent data traffic. In fact the estimated jitter curves appear very close one with another with values not higher than 12 ms that means quite negligible with respect to the 150 ms threshold. A different effect can instead be noted in the wireless-wireless setup where packet loss significantly worsens upon the increasing of AWGN interference intensity. Also in this case the effect of AWGN interference is clearly visible for SIR valures equal to or lower than 1 dB 3. Fig. 16 finally shows that at application layer the simultaneous presence of both competitive WLAN data traffic and AWGN interference is very detrimental even with data rate values in the range 22 25 Mbit s and for any considered SIR value. The obtained R factor highlights that very satisfied levels of voice quality cannot be obtained for concurrent data rate levels higher than 22 Mbit s. Further tests have been performed at the same setup conditions but with different audio codecs . the aforementioned and . The following results have been observed A. In terms of packet loss is the audio codec that provides better results. In particular a nearly 10 worsening of packet loss is observed for both and regardeless of the considered intereference data rate. B. is also better in terms of jitter which for the codec assumes very high values even up to nearly 75 ms for an interference
