[Din] draft-mazieres-dinrg-scp-04 peer priority algorithm

Piers Powlesland <pierspowlesland@gmail.com> Tue, 07 August 2018 16:58 UTC

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From: Piers Powlesland <pierspowlesland@gmail.com>
Date: Tue, 7 Aug 2018 17:58:10 +0100
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Subject: [Din] draft-mazieres-dinrg-scp-04 peer priority algorithm
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Hello,

On page 10 of https://tools.ietf.org/pdf/draft-mazieres-dinrg-scp-04.pdf
an algorithm is described to determine the priority of peers for a
given node.

Peers are selected from a set "neighbours" based on a priority
calculated for each peer. The "neighbours" set is constructed by
taking the set of peers that constitute the quorum slices for a node
and then filtering them to remove any peer for which

sha-256(slot_number || 1 || nomination_round || peer_id ) < 2^256 *
weight(peer_id)

Where "||" means concatenation of serialised values and
"weight(peer_id)" is the fraction of slices containing peer_id.

As I understand, this filtering could lead to a situation where the
neighbours set is empty, since there is no guarantee that any hash
calculated above will be less than '2^256 * weight(peer_id)'. Is this
intentional? Also what is the motivation for creating the "neighbours"
set as opposed to simply selecting a peer from all peers based on
their priority weighted by their weight?