A problem that manifests in wireless networks where some of the nodes are unaware of each other. Specifically, it can occur when two nodes waiting to transmit, each to a different target node, are aware of each other but not of the other's target. One node transmits and, in accordance with the network protocol, the other waits for it to finish. In fact, the second node need not wait because it is transmitting to a different node; but it cannot know this. The addition of handshaking to the protocols is a partial cure, but no complete solution has yet been found. Compare hidden terminal problem.