code: def process_npdu(self, npdu):
          
          if _debug: DeviceToDeviceServerService._debug("process_npdu %r", npdu)
  
          # broadcast messages go to peers
          if npdu.pduDestination.addrType == Address.localBroadcastAddr:
              destList = self.connections.keys()
          else:
              if npdu.pduDestination not in self.connections:
                  if _debug: DeviceToDeviceServerService._debug("    - not a connected client")
                  return
              destList = [npdu.pduDestination]
          if _debug: DeviceToDeviceServerService._debug("    - destList: %r", destList)
  
          for dest in destList:
              # make device-to-device APDU
              xpdu = DeviceToDeviceAPDU(npdu)
              xpdu.pduDestination = dest
  
              # send it down to the multiplexer
              self.service_request(xpdu)
docs: encode NPDUs from the service access point and send them downstream.