If α =0, it becomes unweighted random walk and creates the issue of approving too many lazy tips. To overcome the issues, IOTA introduced a parameter α to control the ‘weight’ of the weighted random walk. *I introduced my own word orphan which may not be accurate in accordance with the IOTA white paper. The Tangle system will end up having many unapproved transactions, or orphans. If we insist that every approval of the transactions must follow the rule strictly, we will do away with randomness completely and many tips will be left unapproved. However, even the weighted random walk method has its own weakness. In our example, transaction 3 has a weight of 6, therefore the walker will choose this path and eventually reach transaction 14 and approve it. Instead, it will look for the path that has the highest cumulative weight. However, transaction 5 only has a cumulative weight of 1, therefore the walker will not continue on this path. In order to approve tip number 13, the walker needs to walk to transaction number 5. The approvers could both be direct or indirect approvers. It means that the higher the number of approvers, the higher the cumulative weight and vice versa. Here we introduce a term called cumulative weight to denote the number of approvers of the transactions. The bias strategy involves choosing a path that has the highest approved transactions over the path that has very few approved transactions. Weighted random walk uses the bias strategy to select the path towards a particular tip. The method is called the weighted random walk(WRW). Therefore, IOTA opted for the persuasion method. It implements a built-in incentives system that rewards the participants to approve the recent transactions. However, this coercive way is against the principles of decentralization and democracy, the core essence of decentralized ledger technologies. How should we overcome the ‘Lazy Tips’ phenomenon? We might impose a rule that requires all incoming transactions to approve the recent transactions. In such situation, the Tangle structure will just stop propagating and eventually crumbles. In the diagram above, we notice that the transactions 30 to 38 chose to approve very old transactions, leaving transactions 25 to 29 unapproved, or became orphans. If there are too many lazy tips exist in the system, the Tangle will become stagnated or simply failed, as illustrated in the diagram below. Their behaviors would not even be penalized by the IOTA system. If we employ the unweighted random walk selection method, these two tips have equal chances to get approved as other tips. With reference to the diagram above, transaction 17 and transaction 18 are lazy tips as they only approved some old transactions, as shown clearly in the diagram. Instead, they choose to broadcast its transactions based on old data. We label them lazy tips because they could not be bothered to update the latest state of the IOTA Tangle network. Lazy tips are tips that choose to approve some old transactions rather than actively looking to approve new transactions. The main issue of using the URW algorithm is the occurrence of lazy tips. In this article, I shall introduce the concept of WRW with the help of some illustrations. Fortunately, there is a better tips selection method known as the weighted random walk(WRW). However, URW has its weakness that could crash the IOTA ecosystem. In the previous article, I have introduced the concept of tips selection using unweighted random walk (URW) algorithm.
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