Polkadot and Cosmos are both protocols that provide interfaces for machines of different states to communicate with each other. Both protocols are predicted based on the fact that the future will have multiple blockchains that need to interact with each other rather than individual blockchains existing individually.

paradigm

Polkadot uses a shard model in which every shard in the protocol has an abstract state transition function (STF). Polkadot uses WebAssembly (Wasm) as its “super protocol”. The shard’s STF can be abstract as long as the validator on Polkadot runs it in the Wasm environment.

The shards of Polkadot are called “Parachains”. Every time the Parachain wants to make a state transition, it sends a block (a series of state transitions) along with a proof of state that the Polkadot validator can independently verify. These blocks are finalized for the parachains as they are finalized by the main chain of the relay chain system. Thus, all parachains share the state with the entire system, which means that the reorganization of a chain from only one parachain would require the reorganization of all parachains and relay chains.

Cosmos uses a bridge hub model that connects tendermint chains. A system can have multiple hubs (the main hub is the “Cosmos Hub”), but each hub connects a group of external chains called a “Zone”. Each region is responsible for securing the chain with a fully decentralized and delimited validator. Regions send messages and tokens to one another through the hub using a protocol known as blockchain communication (IBC). Since regions do not have a common status, reorganizing one region will not reorganize other regions, which means that every message is tied to the recipient’s trust in the recipient’s confidentiality.

Architecture

Speckle

Polkadot has a relay chain that acts as the main chain of the system. All validators in Polkadot are in the relay chain. Parachain has a colator for creating and recommending Parachain blocks for validators. The comparator has no security responsibility and therefore does not need a strong incentive system. The collation can send a unique parachain block for each relay chain block every 6 seconds. After the parachain submits a block, the validator performs a series of availability and validity checks before adding it to the final chain.

Parachain positions are limited and so parachain candidates enter the auction to hold their seats for up to 2 years. For chains that don’t have funding for parachain placement or don’t need to run with a 6 second block time, Polkadot also has parathreads. Parathreads run on a pay-as-you-go basis, so they only pay to run a block when they need it.

To interact with chains that want to use their own finalization process (e.g. Bitcoin), Polkadot has bridged parachains that provide two-way compatibility.

cosmos

Cosmos has a main chain called “Hub” that connects other blockchains called “Regions”. Cosmos can have multiple hubs, but this article will look at a single hub. Each region must maintain its own status and therefore has its own validator community. When one area wants to communicate with another, it sends packets via IBC. The hub maintains a multi-token ledger with token balances (undelivered messages are forwarded, but their status is not stored in the hub).

Zones monitor the status of the hub using a lightweight client, but the hub does not monitor the status of the zone. Zones must use a full deterministic algorithm (currently all use Tendermint) and implement an IBC interface in order to be able to send messages to other threads through the hub.

The cosmos can also interact with external chains using a “peg area”, similar to a bridged parachain.

consensus

Polkadot uses a hybrid consensus protocol with two sub-protocols: BABE and GRANDPA, collectively called “Fast Forward”. BABE (Blind Assignment for Blockchain Extension) uses a Verifiable Random Function (VRF) to assign slots to validators and a fallback rotation model to ensure that each slot has an effect. GRANDPA (GHOST-based Recursive Ancestor Deriving Prefix Agreement) is more correct for chains than for individual blocks. BABE can generate candidate blocks to extend the mature chain, and GRANDPA can complete them in batches (up to millions of blocks at a time).

Such a division of tasks offers a number of advantages. First, it reduces shipping complexity for both block making and finishing. BABE has a linear complexity, which makes it easy to scale to thousands of block producers with little network overhead. GRANDPA is quadratic in complexity, but is reduced by the latency factor, or the number of blocks it completes in a stack.

Second, the ability to extend the chain with incomplete blocks allows other checkers to perform extensive availability and validity checks to ensure that there are no invalid state transitions.

Cosmos (both hubs and regions) use Tendermint Consensus, a circular protocol that allows for immediate completion. Block production and completion are on the same path of the algorithm, which means that blocks are generated and completed one after the other. Because it is a PBFT-based algorithm (like GRANDPA), it has a quadratic transport complexity but can only complete one block at a time.

Locking mechanism

Polkadot uses the Nominee Proof of Stake (NPoS) to select validators with the sequential Phragmén algorithm. The size of the validator set is determined by the administration (1,000 validators planned) and stakers who do not want to operate the validator infrastructure can specify up to 16 validators. Phragmén’s algorithm chooses the optimal stake allocation, the optimization being based on having the most even stakes.

All validators in Polkadot have the same weight in consensus protocols. That is, to get more than 2/3 support for a chain, more than 2/3 of the validators have to commit to it instead of 2/3 of the effort. Likewise, the validators’ rewards are tied to their activity, mostly block production and proof of completion, not stakes. This creates an incentive to nominate validators with lower stakes, as they achieve a higher return on the tokens they use.

Cosmos Hub uses Bonded Proof of Stake (a variant of Delegated PoS) to select validators. Stakers have to deposit and send an authorization transaction for each validator they want to authorize, along with the number of tokens to be authorized. Cosmos Hub plans to support up to 300 validators.

Consensus voting and rewards are both stake-based in Cosmos. In the case of consensus voting, instead of 2/3 of the validators, more than 2/3 of the assignments must be committed. Validators also receive 10% rewards with 10% of the total stake.

Finally, at Cosmos, the validators take over their voting rights if a stakeholder does not vote in a referendum on governance. For this reason, many validators in Cosmos do not take commission for more control over the protocol. At Polkadot, governance and staking are completely separate; the nomination of the validators does not assign the validators any administrative voting rights.

Forward Embassy

Polkadot uses cross-chain message passing (XCMP) for parachains to send arbitrary messages to each other. Parachain opens connections with each other and can send messages through their established channels. The collaborator are the full nodes of the parachain and the full nodes of the relay chain, so the comparator nodes are an important part of the message transmission. Messages do not go through the relay chain, especially the evidence of posts and channel activities (opening, closing, etc.) go into the relay chain. This improves scalability by storing data on the system.

In the case of a chain reorganization, messages can go back to the reorganization point based on evidence of posts in the relay chain. The common state between the parachains means that the messages have no confidence limits and they are all working in the same area.

Polkadot has an additional protocol called SPREE that provides common logic for cross-chain messages. Messages sent with SPREE contain additional guarantees about the origin and interpretation of the received string.

Cosmos uses a cross-chain protocol called Inter-Blockchain Communication (IBC). The current Cosmos implementation uses the hub to transfer tokens between regions. Now Cosmos has a new specification for any data transmission. However, because threads do not share status, the receiving thread must trust the security of the message origin.

administration

Polkadot has a cross-departmental governance system with multiple ways to approve proposals. All proposals ultimately go through a public referendum, in which the majority of tokens can always control the outcome. For referendums with a low turnout, Polkadot uses adaptive quorum trends to set a pass threshold. The referral program can include a variety of proposals, including the allocation of funds from the on-chain Treasury Department. Decisions are made on-chain and are binding and autonomous.

Polkadot has some parts in the chain, no permit required. The main body is the council, which consists of a collection of accounts elected in the style of the phragmén. The Council represents minority interests and therefore proposals adopted unanimously by the Council will have a lower approval threshold in a public referendum. There is also a technical committee that makes technical recommendations (e.g. upgrade …