S. Ortmann, P. Langendörfer, and M. Maaser. Proceedings of the 5th ACM international workshop on Mobility management
and wireless access, page 184--187. Chania, Crete Island, Greece, ACM, (2007)
{. Shen, and P. Dewan. Proceedings of the 1992 ACM conference on Computer-supported cooperative
work, page 51--58. Toronto, Ontario, Canada, ACM, (1992)
C. Ardagna, S. di Vimercati, and P. Samarati. Data and Applications Security XX, volume 4127/2006 of Lecture Notes in Computer Science, Springer Berlin / Heidelberg, (July 2006)