Investigation of Voice Traffic in Wi-Fi Environment Jukka Kantanen, 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment Topics IEEE 802.11b WLAN Some Basics of Voice Traffic What is VoIP? Parameters Affecting VoIP Quality Measurement Setup Results Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment IEEE 802.11b WLAN Operating in the ISM band at 2.4 GHz Uses CSMA/CA for channel sharing Also RTS/CTS can be used for that Manufacturers have Wi-Fi compatibility if the products are tested Max. data rate 11 Mbit/s Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment IEEE 802.11b WLAN PHY layer headers transmitted at 1 Mbit/s Hidden node problem IEEE 802.11b AP Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Some Basics of Voice Traffic Voice (speech) is processed in frames using voice codecs => small bit rate G.711 64 kbit/s, G.723.1 6.3 or 5.3 kbit/s, G.729 8 kbit/s. G.711 provides toll quality Speech tolerates more packet errors than data traffic Delay bounds exist for conversational speech Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Some Basics of Voice Traffic The effect of overheads is significant Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment What is VoIP? Transmission of voice traffic using an IP network => more overheads VoIP connections are established using signaling protocols, e.g. SIP an H.323 Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Parameters Affecting VoIP Quality Delay due to buffers and channel access methods Packet losses due to collisions, bad radio channel and buffer overflow Delay variation - even 1 ms counts Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Parameters Affecting VoIP Quality Delays greater than 150 ms begin to decrease the quality Packet loss rate 1 % mostly acceptable. Depends on the codec used Delay variations must me compensated using buffers (static or adaptive) buffer frames Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment Measurement Setup The goal was to measure the delay, packet losses and delay variation of IEEE 802.11b network of a G.711 VoIP call The end user devices were not considered Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment Measurement Setup Indoor office environment Hidden node situation and max. interference RTS/CTS on/off One/two interfering STAs Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment Results G.711 is a good choice for voice codec, because it is robust against packet losses One STA can’t model several interfering STAs Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – one interfering STA One STA can’t interfere the VoIP call much Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – two interfering STAS RTS/CTS could be more useful in VoIP if more contending STAs were used Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – two interfering STAs Interference of 1 Mbit/s was enough Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Investigation of Voice Traffic in Wi-Fi Environment Conclusions ITU-T E-model was used for VoIP quality evaluation. VoIP call quality was fair when interference < 1 Mbit/s. These measurements describe only a specific situation (worst-case). The measurements should be done again in the actual environment Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

The End Thank You!

Results – one interfering STA Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – one interfering STA with RTS/CTS Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – one interfering STA Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Results – two interfering STAs with RTS/CTS Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Additional information Measurements with one interferer Measurements with two interferers Bit rates of STA B [Mbit/s] Bit rates of STA B1 [Mbit/s] Bit rates of STA B2 [Mbit/s] 0.1 0.05 0.3 0.15 0.5 0.25 0.7 0.35 0.9 0.45 1 3 1.5 5 2.5 Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019

Additional information Protocol Overhead in bytes RTP 12 UDP 8 IP 20 LLC 4 802.11b MAC MAC 34 802.11b PHY with short preamble 15 with long preamble 24 Investigation of Voice Traffic in Wi-Fi Environment 28.6.2019