Each day the number of blockchain projects is increasing (as well as the size of the infrastructure built on them).
A problem arises - the existence of many independent blockchains, the interaction of which is difficult with each other. Become necessary technologies for "communication" of blockchains among themselves. Below I talk about the ways in which they try to solve the problem of (in) compatibility of blockchains.
The first major step towards linking blockchains was the BTC Relay project of the ConsenSys and Ethereum teams. BTC Relay is a bridge between the Bitcoin and Ethereum blockchains — that is, it allows you to interact with Ethereum smart contracts from the Bitcoin blockchain. How it might manifest:
payment with bitcoins inside smart contracts;
BTC Relay can transfer info about the Bitcoin blockchain to a smart contract;
you can use Bitcoin blocks to generate random numbers, instead of Ethereum (which is much safer).
Securely generating random numbers in Ethereum smart contracts is one of the most difficult tasks.
The job of BTC-Relay is that it pays commissions to "relays" - those who transmit the block header from the Bitcoin blockchain to the BTC Relay. At the same time, charging gas from smart contracts that use BTC Relay.
A sidechain is a chain that is two-way connected to the parent blockchain. If you do not create a separate blockchain, but create a side chain for an existing one (for example, Ethereum), then this will combine the advantages of: your own chain, compatibility with the parent blockchain.
True, sidechain is not appropriate for all projects, so I will not dwell on this option. Anyway, sidechains were primarily created to increase the scalability of Ethereum, and not for compatibility with other projects.
Polkadot is an ambitious relay blockchain project. The main idea is that blockchains do not need their own validators to keep the network running. Blocks will be validated by Polkadot miners, and projects will rent the parachain.
Parachains are built parallel to each other around the main blockchain. These parachains can be considered as clients of the main relay blockchain, the purpose of which is to provide security and coordination.
What's the difference anyway?
First, briefly the general points, and then the differences in the technical part.
Cosmos is more flexible in development;
Prominent projects have already been built on the Cosmos SDK, including (!) Binance Chain;
Cheaper than Polkadot;
Unlimited number of projects unlike Polkadot.
Benefits of Polkadot:
Chain safety is maintained by Polkadot, not by the project developers, as in Cosmos;
Simplified messaging between threads.
Relay chain Polkadot uses a consensus algorithm that allows many blocks from all parachains to be completed quickly and can also accommodate a large number of validators (over 1000).
This is because not all validators need to vote for every single block - instead, validators can vote for the single highest block they consider valid, and the algorithm will transitively apply the vote to all ancestors of that block. Polkadot's Substrate software development kit has 3 consensus algorithms out of the box: GRANDPA, Rhododendron, and Aurand.
In the Cosmos network, each blockchain can use any consensus algorithm that complies with the ABCI specification. This specification was created to standardize communication between chains. In fact, only Tendermint is now ABCI compliant.
Tendermint, on the other hand, has a big advantage and a big drawback - on the one hand, it is asynchronous, that is, when a block is completed, it cannot lose validity even when the chain is split, on the other hand, because of that, the speed of Tendermint is inversely proportional to the number of transactions.
There is only one relay chain in Polkadot, with limited chains that can run on it. At the moment, it is 100 chains, which are distributed through an auction - you need to hold a large number of native tokens of the project (DOT) in order to start and maintain the chain.
On the Cosmos network, on the other hand, there are no fixed membership rules - anyone can build a hub or zone. Hubs themselves are sovereign blockchains created for the purpose of connecting numerous other blockchains.
The hub-and-zone model makes cross-chain communication extra efficient because instead of connecting to any other block chain, each block chain should only connect to a hub.
Didn't mention Block Collider/Overline.
Purpose of this article? Review? If yes, then it's okay. Further, which are the plans for the direction (in terms of publications in this direction)?