Abut, Fatih2025-01-062025-01-0620192148-268310.31590/ejosat.585736https://doi.org/10.31590/ejosat.585736https://search.trdizin.gov.tr/tr/yayin/detay/359077https://hdl.handle.net/20.500.14669/728Voice over IP (VoIP) is gaining more and more importance and displaces the traditional telephony. For example, more than 300 millionmonthly active users worldwide use the popular VoIP application \"Skype\". However, a big problem in the VoIP environment is the voicequality. The purpose of this study is to investigate the effects of background TCP traffic on perceived voice quality of a VoIP conversationat the user-level using the G.711 codec. Two different playout buffering policies including static buffering and optimal buffering havebeen applied by the VoIP server. For comparison purposes, the same experiments have also been repeated when no playout bufferingpolicy has been used by the VoIP server. A three-hop network topology consisting of a source, a transit, and a destination subnetworkwas simulated whereas the end-to-end capacity of the entire network was limited by a 1.5 Mbps Asymmetric Digital Subscriber Line(ADSL) link. Multiple simultaneous TCP connections with different segment sizes were established to simulate the various conditionsof background traffic. By using the ns2voip framework, an enhancement to the popular Network Simulator 2 (ns-2), extensive simulationexperiments for analyzing the VoIP user-level performance have been carried out and the voice quality has been evaluated by calculatingthe Mean Opinion Score (MOS). The results show that the voice quality is strongly negatively affected by background TCP traffic, evenin the presence of a single TCP flow with 1500 Byte segments. Also, the size of background TCP segments significantly influences theachievable MOSs of VoIP conversations. However, it has also been observed that aggregating multiple speech frames into a single IPpacket can increase the MOS. Particularly, depending on the number and segment size of background TCP flows, aggregation of theoptimal number of speech frames into the same IP packet improves the MOSs up to 14.61% over a 1.5 Mbps ADSL link.eninfo:eu-repo/semantics/openAccessBilgisayar BilimleriYazılım MühendisliğiBilgisayar BilimleriSibernitikBilgisayar BilimleriBilgi SistemleriBilgisayar BilimleriDonanım ve MimariBilgisayar BilimleriTeori ve MetotlarBilgisayar BilimleriYapay ZekaArticle645166383590770