通信子网 Application Application. protocol Application APDU Presentation Representation protocol resentation PPDU Session ession_protocol Session SPDU Tr ranson Transport protocol Transport Segment Network Netwo【wEwo【 Network Netwo水k Packe Data Link Data Link Data Link Data Link Data Link Frame Physical i Physical Physical vl Physicall Physical BitsApplication protocol Representation protocol Session protocol Transport protocol 通信子网 APDU PPDU Frame Bits Packet SPDU Segment