Connected WiFi

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 37).TCP was originally designed to function over static hosts. So, a connection is established between two IP addresses which are assumed to never change of the period of the connection. On the other hand, when TCP is deployed on mobile hosts a number of new factors that are the results of the node's mobility, such as frequent disconnections and changing IP addresses, are introduced into the model. TCP may timeout and quit as a response to these events and therefore yield a suboptimal performance. This work introduces Armadillo, a protocol to hide intermittent connectivity from TCP applications on mobile hosts to increase performance. In contrast to all the previous work to our knowledge, our protocol requires no changes to the TCP stack or application on the either end. In a typical scenario we assume that a mobile host uses a WiFi access point (AP) for internet connectivity. Because of the limited range of the AP and the mobility of the host it is going to move out of the range and disconnect. As a consequence, the TCP connection is going to timeout and finally quit. The two important problems we address in this report are the following: (1) preventing the TCP application from timing out and eventually breaking as a result of disconnections and (2) handling the switching between APs so the change of IP addresses is transparent to the TCP application. We evaluate our system under real-world conditions and discuss results.by Tural Badirkhanli.M.Eng