Participant lists identify members of a session and are used for opening connections. Upper protocols interested in establishing a connection will construct the participant list and pass it to the lower protocol as a parameter of an open routine. The lower protocol will then extract information from the participant list, possibly passing the participant list on to its own lower protocol.
Each participant in the list contains a participant address stack, designed to facilitate a general method of communicating encapsulated address information between protocol layers. By using pointers to address information, one layer can pass address information through a lower layer without having the lower layer manipulate the address information at all, not even by copying. The address information for each participant is kept as a stack of void * pointers to address components and the lengths of each component. The component pointers are pushed or popped onto the stack by utility functions.