Abstract: An extensible data communication protocol is described that operates between remote computers and a server computer on the same network, where the computers exchange data messages while the server manages addressing of the communication, so that applications running on the computers can communicate without reference to the underlying network addresses, but rather by means of virtual addressing based on some other label or indicia of identity, including the identity of the computer sending the data message and the identity of the intended recipient computer. Other improvements to data packet and network address management are also part of the invention are presented.