## 2 Related Work  
Store-carry and forward relaying has been proposed in the past as an effective mechanism to provide connectivity in intermittently connected networks where, either due to the spatial node sparsity in the network or due to the temporal communication patterns, end-to-end connectivity can not be achieved [2; 3; 4]. In those cases, a delay in the end-to-end path had to inevitably occur so that the end nodes could establish communication. A review of the design objectives and challenges of SCF routing in delay tolerant networks (DTNs) can be found in [5, 6].  
However for the scenario we consider in this work, delay in the forwarding paths is incurred in a controlled fashion and forwarding paths are formed in a coordinated way. Note that within the cell, the BS provides an almost 100% coverage. Therefore all nodes can communicate directly with the BS and hence centralized decisions can be taken for the optimal forwarding paths under the different quality of service constraints. In addition, due to the centralized control offered by the BS, messages are not arbitrarily replicated (as it happens most of the cases within sparse networks, using for example epidemic routing [7] to propagate information messages) but the replication is orchestrated by a centralized node, which can be for example the BS. The main problem with epidemic routing is that it consumes a significant portion of network resources in terms of bandwidth and buffering, since information messages need to be copied at every node encounter without any discretion. Therefore, for our envisioned strategies of improving the performance of cellular networks that are discussed here, such a routing scheme is impractical. A number of different works have looked into the problem of more efficient routing in DTNs by reducing the number of copies using several criteria such as the number of copies already send by a node and the mobility pattern of the nodes. To reduce the number of copies the authors in [8] proposed that only the sender could make a copy; this would dramatically reduce the overhead in the network but at the same time message delivery delay could be substantially increased depending on the mobility pattern and actual distance between sender and receiver. An alternative technique that provides copies of messages with a controllable probability has been proposed in [9]. The above schemes assumes isolated mobile nodes and no infrastructure support. In an architectural framework similar to the one we assume in this paper, the authors in [10] explore the potential of infrastructure based wireless networks for aiding store-carry and forward routing. The authors present both analytical and experimental studies and use a variety of routing protocols with emphasis on the RAPID [11] scheme. The Resource Allocation Protocol for Intentional DTN (RAPID) routing protocol estimates the utility of creating a copy of the message (in terms of propagation delay), and copies the message to the node which has the highest value. Further, the authors in [12] devise a routing algorithm that computes shortest paths in DTNs based on the node contact probabilities while satisfying end-to-end reliability constraints. In [13, 14] the authors consider the placement of small and inexpensive autonomous wireless nodes (termed as throw-boxes) in between the physical routes of mobile nodes to increase the capacity of the underlay DTN. The authors devised optimal deployment strategies and energy efficient algorithms for information dissemination.  
In contrast to the above mentioned cases, for which delay is expended while waiting future contact opportunities, here network connectivity and information communication is not an issue. However, for elastic data services, delay is considered as an additional resource in the system that can be traded off to achieve savings in the communication energy consumption or improvements in the network performance as explained in the sequel.