We study the impact of different levels of relay cooperation on the throughput of a two-hop amplify-and-forward relaying network, where n single-antenna source-destination pairs communicate through a set of single-antenna relays. We focus on two levels of cooperation among the relay nodes, where the relays share either channel state information (CSI) or both CSI and received signals. The high level of cooperation is justified for a case where the relaying role is fulfilled by infrastructure nodes that can communicate through a wired backbone without an overhead on the wireless channel. The generalized and the optimal system throughput for both cases are analyzed. We show that in the first case, at least n2 relays are needed to achieve linear scaling of the system throughput versus n. In the second case, exchanging the received signals at the relays can reduce the needed number of relays to n in order to achieve linear scaling. It is also shown that the second cooperation scheme achieves a strictly positive per node throughput, where the total number of nodes accounted for includes the relays.