Analysis of data transfer delays in wireless networks subject to roaming

Samo Vodopivec (2010) Analysis of data transfer delays in wireless networks subject to roaming. EngD thesis.

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Abstract

Wireless networks are constantly increasing in size, both in the number of users as well as in the amount of data being transmitted through them. In an effort to provide users with better working conditions we constantly increase the number of access points within a network. These access points form the basis of a wireless network, their common feature being the same network name. Physically they are placed at various locations, and in order to avoid mutual interference, they operate on different channels. The goal is to ensure the highest quality of network operation, regardless of movement of the user within the network's coverage area. Roaming is the process which connects a user with closer access points in an automated way. In order to choose a new (better) access point, the network client must be familiar with its neighborhood, which is explored by searching. A suspension of the users data stream is required while the network client is searching through different channels. Data flow is also interrupted during the roaming, because the processes of association and authentication are being performed. In the thesis I presented the operation of an extended wireless network and properties of access points and clients related to switching access points, in particular the processes of searching and roaming. I also presented the Eduroam network as well as the network hardware and software that I used for measurements, including the testing parameters. Measurements in different configurations were made in a test network and the Eduroam network. The results show that the use of roaming in its simplest form is not appropriate for services requiring minimal interruptions of data flows. Thus, VoIP services that can tolerate interruptions of up to 50ms, cannot be used in combination with roaming. Also provided are some ideas for certain improvements to shorten the search and roaming processes.

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