3.2.4.5 Query for Responder Charge
Charge is abstracted away from higher-layer applications and protocols. There is no direct higher-layer event to query for the responder charge. However, a mapper MAY query for responder charge in response to a network topology test issued by a higher-layer application or protocol for a specific responder (see section 3.2.4.3).
Before querying for the current charge, the mapper must first check the Network Topology Test Session List for an entry for the responder. If no entry exists, or if there is an outstanding request (the Pended Request field is not empty), then the mapper MUST NOT query for current charge and MUST ignore the higher-layer application or protocol request for the network topology test.
If there is an entry and no outstanding request, the mapper sends an acknowledged Charge frame using the sequence number in the Sequence Number field of the entry and stores the frame in the Pended Request field. Acknowledged Charge frames MUST be padded to the size of a Flat frame in order to carry enough implicit charge for the Flat frame response.
Once the Flat frame has been received, the mapper can continue to charge the responder.