[ippm] Discussion of DTLS during IPPM/draft-ietf-ippm-capacity-protocol

["MORTON JR., AL" <[e-mail]>]

Hi IPPM,

Thanks to Martin and Tommy, the meeting clarified that DTLS only performs reordering and retransmission during the DTLS Handshake Protocol.

When looking into the RFC (9147), I found that [0] 
"Each DTLS record contains a sequence number to provide replay protection." 
...and...
"Duplicates are rejected through the use of a sliding receive window."

AFAICT, this means that the DTLS records are not delivered transparently to the measurement application, and that any Duplicate packets arising during transfer would be discarded by the DTLS receiver.

The lack of transparency is a major drawback, especially for measuring radio access where Duplicated packets can occur during handover between stations or when the radio technology changes due to coverage limitations (mmWave coverage, for example). And given other discussion of the scope of this protocol, I have reproduced the portion of the Status feedback measurement PDU below, with fields for loss, reordering (Ooo), Duplication (Dup), one-way and round-trip delay variation results. This PDU is unchanged for about 3 years.

So, I think we are again looking for solutions other than DTLS, for the reasons above.

regards,
Al


[0] https://datatracker.ietf.org/doc/html/rfc9147#section-4.5.1 


from: https://datatracker.ietf.org/doc/html/draft-ietf-ippm-capacity-protocol-03#section-7.2


// Status feedback header for UDP payload of status PDUs
//

        uint16_t statusId;  // Status ID = 0xFEED
        uint8_t testAction; // Test action
        uint8_t rxStopped;  // Receive traffic stopped indicator (BOOL)
        uint32_t spduSeqNo; // Status PDU sequence number (starts at 1)
        //
        struct sendingRate srStruct; // Sending Rate Structure (28 octets)
        //
        uint32_t subIntSeqNo;      // Sub-interval sequence number
        struct subIntStats sisSav; // Sub-interval Saved Stats Structure  (52 octets)
        //
        uint32_t seqErrLoss; // Loss sum
        uint32_t seqErrOoo;  // Out-of-Order sum
        uint32_t seqErrDup;  // Duplicate sum
        //
        uint32_t clockDeltaMin; // Clock delta minimum (either RTT or 1-way delay)
        uint32_t delayVarMin;   // Delay variation minimum
        uint32_t delayVarMax;   // Delay variation maximum
        uint32_t delayVarSum;   // Delay variation sum
        uint32_t delayVarCnt;   // Delay variation count
        uint32_t rttMinimum;    // Minimum round-trip time sampled
        uint32_t rttSample;     // Last round-trip time sample
        uint8_t delayMinUpd;    // Delay minimum(s) updated observed, communicated in both directions.
        uint8_t reserved2;      // (alignment)
        uint16_t reserved3;     // (alignment)
        //
        ...