Mission Operations Reference Model. Draft ... - CCSDS

DRAFT RECOMMENDED PRACTICE FOR MISSION OPERATIONS REFERENCE MODEL4.6.2 MESSAGE RECEPTION SEQUENCEFigure 4-14 shows the message reception sequence for the Transport layer. It includes theerror cases as alternative fragments.Transport LayerAccess ControlMALMessage SourceReceive MessageDecrypt messagePre-check messagealt Message check failureLog error locallyCheck digital signaturealt Security check failureLog error locallyDecode messagealt Message transport failureTransmit decoding erroralt If message from a ProviderReceive decoding errorReceive messageFigure 4-14: Transport Layer Reception SequenceThe basic outline of this sequence from the high-level sequence (figure 4-3) is that theTransport layer receives a message and passes it up to the MAL.a) The message source passes the message to the Transport layer using whatevermechanism is appropriate for that messaging technology.b) The Transport layer decrypts the message and then checks to ensure that it containsall the required aspects for the layer itself. If it fails these checks, then an error maybe logged locally. No error message is passed upwards or returned to the source,because it may be a spoof message.c) If there was an error, then the sequence ends at this point.d) The layer then checks the digital signature, if applicable. If the digital signaturecomponent rejects the message, then it returns an error using an implementationspecificmechanism to the Transport layer. The Transport layer then may log thatCCSDS 520.1-R-1 Page 4-18 October 2009