1. A method of converting application data to transport data in a power line communication system, the method comprising: receiving application data in a transport protocol layer from an application in a device through a service access point, the service access point being one of a plurality of service access points of the transport protocol layer; applying classifier rules associated with the service access point to the application data received through the service access point to determine if a connection through a lower protocol layer exists for the application data, including: determining if the application data matches matching criteria of a particular classifier rule; and if the application data matches matching criteria of the particular classifier rule, associating a globally unique connection identifier with the particular classifier rule, encapsulating the application data into a payload of a transport message, associating the globally unique connection identifier with the transport message and the service access point, and transmitting the transport messages through a connection of the power line communication system identified by the globally unique connection identifier of the particular classifier rule, wherein each classifier rule includes a priority; applying the classifier rules includes applying the classifier rules to the application data in an order defined by the priorities of the classifier rules; wherein the connection includes the globally unique connection identifier and a connection type selected from at least one of a continuous grant service (CGS) type, a period grant service (PGS) type, and a priority aperiodic grant service (PAGS) type; and the connection identifier is globally unique over the power line communication system and identifies the connection to which the transport message carrying the application data payload belongs; and transmitting through the connection includes transmitting through the connection having the selected connection type.