An apparatus includes ports to transmit and receive packets, each packet being associated with one of a plurality of sessions, and a packet buffer to store the packets. A classifier identifies packets that include data representing a transmit window size for one of the sessions. A processor determines whether to reduce the transmit window size for the one of the sessions by comparing a size of the packet buffer to a sum of (i) the transmit window size for the one of the sessions and (ii) transmit window sizes for others of the sessions. The processor modifies the data representing the transmit window size for the one of the sessions to reduce the transmit window size for the one of the sessions before one or more of the ports transmits the packets comprising the data representing the transmit window size for the one of the sessions.