In order to control traffic, a network router, A periodically sends a message to its neighbor, B, telling it to increase or decrease the number of packets that it can handle. At some point in time, Router A is flooded with traffic and sends B a message telling it to cease sending traffic. It does this by specifying that the number of bytes B may send (A's window size) is 0. As traffic surges decrease, A sends a new message, telling B to restart transmission. It does this by increasing the window size from 0 to a positive number. That message is lost. As described, neither side will ever transmit. What type of deadlock is this?