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DP83822I: Auto MDIX vs Robust Auto MDIX

Expert 4455 points
Part Number: DP83822I

Hi, 
Customer is asking for the exact purpose of Robust Auto MDIX function. Is the following assumption correct or are there further differences?

  • When both link partner support normal Auto MDIX, robust Auto MDIX is not needed regardless whether you have a straight or crossover cable.
  • When link partner A does not support Auto MDIX (ie the PHY is forced to either MDI or MDIX), robust Auto MDIX enabled for link partner B ensures to establish the link. If link partner B supports only normal Auto MDIX, there might be cases where you run into a deadlock situation.

Thanks and BR,
KF

  • Hi KF,

    Yes, Robust AutoMDIX is used in cases which are outside the normal autonegotiaton, auto-mdix use case. Another case where Robust AutoMDIX can use used is when host is configured for Force 100Mbps communication and Auto-MDIX. This is not a use case defined in IEEE standards and Robust AutoMDIX can be used to resolve that. Please note that Robust AutoMDIX is a special mode designed to be used in non-standard use cases. The most common use case is to have Auto-negotiation ON and Auto-MDIX ON. If Auto-negotiation is disabled (forced speed) then Auto-MDIX should also be disabled (Force MDI or Force MDIX).

    -Regards
    Aniruddha