1. A method of data communication between a first plurality of applications running on a first computer and a second plurality of application running on a second computer, the method comprising: establishing a tightly flow-controlled packetized data connection from the first computer to the second computer according to a first protocol in which transmission of first data packets is controlled by an availability of a sufficient number of free buffer spaces at the second computer, wherein each free buffer space at the second computer is represented by a token that is sent from the second computer to the first computer, wherein the first protocol limits a number of the first data packets that the first computer can send to the second computer to a number of tokens received from the second computer, and wherein the first protocol requires that the number of tokens received from the second computer be decremented by one for each of the first data packets sent to the second computer over the established tightly flow-controlled connection; in response to a number of tokens available to the first computer being less than a threshold, inserting a generated request for additional tokens in at least one of the first data packets sent from the first to the second computer, wherein the request for additional tokens is a piggyback message; establishing a plurality of loosely flow-controlled packetized data connections for sending second data packets between a specified one of the first plurality of applications and at least one specified one of the second plurality of applications according to a second protocol that is different from the first protocol; and sending the second data packets of one of the plurality of loosely flow-controlled packetized data connections over the tightly flow-controlled packetized data connection according to the second protocol.