Mobile network delay characteristics and interactions with the transport layer

Abstract

Mobile networks have become an integral part of every day life, and many users rely on its presence and performance. In the past years user num bers and traffic volume has skyrocketed, as adoption of the technology continues to increase. The popularity of internet based services in mobile networks and the increase in user numbers makes the available resources precious and ever more important to use them: a user's satisfaction is inversely proportional to the time it takes for the requested content to load. While the mobile network sets an upper bound on the transmission rate, it is up to the delivering end point to make use of these resources, which for many applications is in the hands of the Transmission Control Protocol (TCP). As TCP has to make the best use of the resources in every situation, it is vital to understand the interactions between the protocol and the mobile network in order to achieve best performance. This work is a measurement based study on the performance of TCP in Finnish 3rd generation (3G) and 4th generation (4G) mobile networks. First, it is investigated how the round-trip time (RTT) behaves throughout end-to-end connections traversing mobile networks, on long term as well as on short term in the form of delay spikes. Second, the proper way for TCP to deal with these delay spikes is examined. Lastly, the interactions of TCP with the mobile network is investigated in real-life situations and causes for sub-optimal performance is extracted. The thesis concludes with a discussion on what is necessary to improve TCP performance in mobile networks, and the changes coming with future networks and algorithms.