Computer Laboratory

Technical reports

Pocket Switched Networks: Real-world mobility and its consequences for opportunistic forwarding

Augustin Chaintreau, Pan Hui, Jon Crowcroft, Christophe Diot, Richard Gass, James Scott

February 2005, 26 pages


Opportunistic networks make use of human mobility and local forwarding in order to distribute data. Information can be stored and passed, taking advantage of the device mobility, or forwarded over a wireless link when an appropriate contact is met. Such networks fall into the fields of mobile ad-hoc networking and delay-tolerant networking. In order to evaluate forwarding algorithms for these networks, accurate data is needed on the intermittency of connections.

In this paper, the inter-contact time between two transmission opportunities is observed empirically using four distinct sets of data, two having been specifically collected for this work, and two provided by other research groups.

We discover that the distribution of inter-contact time follows an approximate power law over a large time range in all data sets. This observation is at odds with the exponential decay expected by many currently used mobility models. We demonstrate that opportunistic transmission schemes designed around these current models have poor performance under approximate power-law conditions, but could be significantly improved by using limited redundant transmissions.

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BibTeX record

  author =	 {Chaintreau, Augustin and Hui, Pan and Crowcroft, Jon and
          	  Diot, Christophe and Gass, Richard and Scott, James},
  title = 	 {{Pocket Switched Networks: Real-world mobility and its
         	   consequences for opportunistic forwarding}},
  year = 	 2005,
  month = 	 feb,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-617}