Sending of unexpected Configuration update complete NAS message.

[bjoern-r]

Issue Description

corescope is sending an configuration update complete response when it is not requested to by the core.
According to 3GPP TS 24.501 Section 5.4.4.3.:

If "acknowledgement requested" is indicated in the Acknowledgement bit of the Configuration update indication IE in
the CONFIGURATION UPDATE COMMAND message, the UE shall send a CONFIGURATION UPDATE
COMPLETE message.

Setup Details

running corescope against an instance of of the open5gcore from Fraunhofer FOKUS.

Expected Behavior

No reply was expected to the configuration update command message.

Actual Behaviour

corescope replies with a configuration update complete message.

Steps to reproduce the problem

send a NAS PDU with the following contens to corescope:

NG Application Protocol (DownlinkNASTransport)
    NGAP-PDU: initiatingMessage (0)
        initiatingMessage
            procedureCode: id-DownlinkNASTransport (4)
            criticality: ignore (1)
            value
                DownlinkNASTransport
                    protocolIEs: 3 items
                        Item 0: id-AMF-UE-NGAP-ID
                        Item 1: id-RAN-UE-NGAP-ID
                        Item 2: id-NAS-PDU
                            ProtocolIE-Field
                                id: id-NAS-PDU (38)
                                criticality: reject (0)
                                value
                                    NAS-PDU: 7e02ff3205d5027e0054431510004f00700065006e003600470063006f00720065450910…
                                        Non-Access-Stratum 5GS (NAS)PDU
                                            Security protected NAS 5GS message
                                                Extended protocol discriminator: 5G mobility management messages (126)
                                                0000 .... = Spare Half Octet: 0
                                                .... 0010 = Security header type: Integrity protected and ciphered (2)
                                                Message authentication code: 0xff3205d5
                                                Sequence number: 2
                                            Plain NAS 5GS Message
                                                Extended protocol discriminator: 5G mobility management messages (126)
                                                0000 .... = Spare Half Octet: 0
                                                .... 0000 = Security header type: Plain NAS message, not security protected (0)
                                                Message type: Configuration update command (0x54)
                                                Network Name - Full name for network
                                                Network Name - Short Name

Additional Information

[Any additional information, configuration or data that might be necessary to reproduce the issue]