Understanding Cross-Layer Effects on Quality of Experience for Video over NGMN

The evolution of wireless network standards, e.g., GSM/GPRS, UMTS, WiFi, WiMAX, and end-user devices has paved the way towards Next Generation Mobile Networks (NGMN), where users are always connected through multiple radio access networks. NGMN technologies target to improve the user experience especially for mobile data and multimedia services, which are in line with user expectations evident from, for instance, the increasingly popular mobile HTTP video streaming. To understand the quality that can be offered to the user in NGMNs, we compare the Quality of Experience (QoE) for HTTP streaming in a prototype NGMN testbed with WiFi and 3G UMTS/HSDPA support. We use CUBIC TCP as the transport layer protocol as it is typically the default TCP variant, e.g., in Android phones. We complement the QoE estimations with network QoS parameters such as throughput and delay, and transport layer statistics. The results of our evaluation show that (i) video QoE remains stable in WiFi even for high packet losses compared to UMTS, (ii) QoE in UMTS is sensitive to packet loss even for low loss rates due to high variations in the network QoS, namely, throughput and delay, (iii) the decrease in QoE and QoS in HSDPA is due to its negative interactions with the aggressive congestion control of CUBIC TCP, and (iv) handover from WiFi to HSDPA degrades QoE.