Measuring of One-Way Delay in Wireless Mesh Networks

Sammanfattning: Wireless mesh networks are multi-hop networks which consist of radio nodes in mesh topology. These networks can use different wireless technologies such as IEEE 802.11, IEEE 802.16, and cellular technology. In recent years, wireless Internet broadband access has become an important aspect for current and future business. Cellular networks often deliver this service with low data rates, high coverage, and expensive cost. Also other types of wireless networks suffer from lack of mobility and the line of sight in the metropolitan areas. Lately, wireless mesh networks have appeared as an alternative to mitigate these problems and provide wireless Internet broadband access with low cost, high data rates, and satisfactory QoS. Consequently the amount of studies on network performance of these networks has been rapidly increased. One-way delay, as one of the key network performance parameters, has become more important Since SLA contracts consider it to guarantee QoS levels. Moreover, accurate one-way delay measurements are difficult to achieve due to challenges in proper synchronization of clocks and existence of asymmetric links. Recently, new methods and infrastructures have been proposed to mitigate this issue. In this thesis, we have investigated the impact of packet rate, payload size, and number of hop counts on measurement accuracy of a tool named TOM. To do so, we used real one-way delay results obtained from DPMI as reference for comparison. To evaluate TOM measurement accuracy, TOM and DPMI were adapted to each other via source code modifications in order to deliver same measurable delay. Also, an experimental setup was also designed for this purpose. Additionally we computed theoretical lower band for one-way delays to evaluate reliability of DPMI and TOM. In the other part of this thesis, we analyzed the effect of TCP and UDP traffic flow on one-way delay performance with respect to data rate, packet size, and number of hop count, while network traces were captured with DPMI. From the results, we concluded that TOM does not have acceptable accuracy in low packet rates, and its accuracy increases linearly as the packet rate increase. Moreover, varying payload size does not have noticeable effect on TOM accuracy compared to packet rate. Absolute error of TOM measurements for single hop scenario is accumulated as number of passing hop increases. From TCP and UDP experiments, we observed that TCP has higher one-way delay compared to UDP due to existing acknowledgements and retransmissions. Interestingly, TCP and UDP are more sensitive to packet size in multi hop tests rather than single hop tests. Also, for a fixed packet size UDP performs better in high data rates.