In some specific applicable scenarios, nodes are placed in some geographical areas and limited to move in their own community. We investigate the tradeoff between the delivery delay and the number of transmissions in the above multi-community delay tolerant networks by propagating a data packet in a carefully chosen segment of community. First, three restricted epidemic routings are proposed: the shortest community-hop path scheme, the rectangle scheme, and the parallelogram scheme.
Second, the ratios of the average number of communities that can propagate the data packet in the proposed schemes to those that can propagate in the epidemic routing are analyzed. The ratios are found to be small and to decrease with the increase in the number of communities. The tail distribution of the inter-meeting time of any two nodes in the neighboring communities is then demonstrated to be exponential. Third, the delivery delay of the proposed schemes is analyzed by Markovian chain tool. The experiments show that the theoretical model proposed here is reliable, and that the proposed schemes can significantly decrease the number of transmissions, even if these schemes increase the delivery delay to some extent.