family plus helper selection schemes. With a sufficiently large finite field, we can explicitly construct an [*exact-repair*]{} code with $(\alpha,\beta)$ equal to the MBR point $(\alpha_{\text{MBR}},\beta_{\text{MBR}})$ computed by the min-cut-based analysis , , and . That is, [*the necessary condition is also sufficient for the MBR point $(\alpha_{\text{MBR}},\beta_{\text{MBR}})$ of the tradeoff curve.*]{}

As will be discussed in Section \[subsec:fhs\_analysis\], the MBR point is the point when good helper selection results in the largest improvement over the BHS scheme. Since our focus is on studying the benefits of helper selection, the above partial statement proved in Part II is sufficient for our discussion.

Comparison with Existing Codes {#sec:comparison}
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                     Original RC [@dimakis2010network; @wu2009reducing; @rashmi2009explicit; @shah2012interference; @rashmi2011optimal]   Locally Repairable Codes [@gopalan2012locality; @papailiopoulos2012locally; @kamath2014codes; @rawat2012optimal; @kamath2013explicit]                          Dynamic Helper Selection
  ------------------ -------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------- -----------------------------------------------------------------------------------------------------
  Repair Mode        Functional/Exact-Repair                                                                                              Exact-Repair                                                                                                                                                   Functional-Repair
  Helper Selection   Blind                                                                                                                Stationary (Fixed over time)                                                                                                                                   Dynamic (helper choices may depend on failure history)
  $(n,k,d)$ range    Designed for $k\leq d$.                                                                                              Designed for $k>d$.                                                                                                                                            Allow for arbitrary $(n,k,d)$ values
  Contribution       Storage/repair-bandwidth tradeoff for the worst possible helper selection                                            Storage/repair-bandwidth characterization for the specific stationary helper selection of the proposed exact-repair local code, which may/may not be optimal   First exploration of the storage/repair-bandwidth tradeoff for the 