systems and methods for transmitting content to a client via a communication network are provided . according to one embodiment , an insertion server running within a firewall device of a network observes a content request of an application protocol by monitoring or proxying transport communication protocol connections established through the firewall device . the content request is originated by a client device coupled to the network , directed to a destination device coupled to the network and associated with one of the multiple transport communication protocol connections . responsive to observing the content request , the insertion server determines whether one or more conditions are satisfied . if so , the content request is negated by causing a canceling message of the transport communication protocol to be sent to the destination device and unsolicited content is selected and delivered to the client device via the application protocol .