The number of blockchain projects and the infrastructure built on them is increasing, which leads to the existence of many independent blockchains.



 This poses a problem for their interaction with each other, making it necessary to develop technologies for "communication" between blockchains. In this article, we will discuss some of the ways in which the problem of (in) compatibility of blockchains is being addressed.

One major step towards linking blockchains was the BTC Relay project of the ConsenSys and Ethereum teams, which allows interaction between the Bitcoin and Ethereum blockchains. Securely generating random numbers in Ethereum smart contracts is one of the most difficult tasks but can be made safer by using BTC Relay. Sidechains are another option, but they are not appropriate for all projects. Polkadot is an ambitious relay blockchain project that aims to provide security and coordination by having blockchains rent parachains validated by Polkadot miners.

Cosmos and Polkadot offer different benefits. Cosmos is more flexible in development and cheaper but has a limited number of projects compared to Polkadot. Polkadot maintains chain safety and offers simplified messaging between threads. Polkadot's Substrate software development kit also offers 3 consensus algorithms out of the box: GRANDPA, Rhododendron, and Aurand.

The Cosmos network allows each blockchain to use any consensus algorithm that complies with the ABCI specification, which standardizes communication between chains, but only Tendermint is currently compliant. Tendermint has the advantage of being asynchronous but its speed is inversely proportional to the number of transactions.

In Polkadot, only a limited number of chains can run on the relay chain, determined by an auction requiring a large number of DOT tokens. On the other hand, anyone can build a hub or zone on the Cosmos network, and hubs are sovereign blockchains that connect numerous other blockchains. This hub-and-zone model makes cross-chain communication more efficient because each blockchain only needs to connect to a hub instead of multiple other blockchains.

The Block Collider/Overline has not been mentioned in this article. Is the purpose of this article to provide a review? If so, that is acceptable. Moving forward, what are the plans for publications related to this topic?

It is important to note that there may be other developments and projects related to blockchain communication that have not been covered in this article. As the field of blockchain continues to evolve, it is crucial to stay updated on new technologies and advancements.