i'm using the Xbee 3G global in transparent mode and i've come across a pattern.
after all parameters setup appropriately; i can successfully make five TCP/IP requests in succession - which is effectively a HTTP request where the client has requested closed connection and the server forces a close connection. when the six attempt is made; the request is never made - as if there is no longer an available socket.
a potential bug possibly? reported to digi support.
what it seems is that when a TCP/IP port is open; even when it has been closed; the port remains flagged as open. this is contradictory to what the documentation says on the matter. the resolution i was forced to use was to issue a network reset AT command (ATNR 0) that resets the transport layer; effectively forcing close any ports.
then i can continue to create new TCP/IP connections without failure.