> For the complete documentation index, see [llms.txt](https://fogcomputingchain.gitbook.io/fog-computing-chain/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fogcomputingchain.gitbook.io/fog-computing-chain/key-technology/cross-chain.md).

# Cross-chain

The key to cross-chain technology is to solve the transfer problem between backbone and side chain, and to have a mechanism to ensure that the transfer between backbone side chain is safe and credible.To this end, Adam Back et al. Have proposed a technique called two-way anchoring (Two-waypeg) to address the transfer of assets between the two chains.The basic principle is based on SPV to verify that transactions do exist on another chain, but this is the premise to save all of each other's block header information.

Main chain and side chain are 1-to-many relationships, using symmetrical bidirectional anchoring, there is no problem with saving only the whole block head information of the side chain. If the backbone needs to save all side chain header information, it is unacceptable, so symmetrical SPV-based bidirectional anchoring can not be used on the main side chain architecture of FOGR.

FOGR adopts different mechanisms for the transfer in the two directions between the main and side chains.

{% content-ref url="/pages/OQN8wG02dQWS1TKxUVxB" %}
[Backbone to side chain transfer](/fog-computing-chain/key-technology/cross-chain/backbone-to-side-chain-transfer.md)
{% endcontent-ref %}

{% content-ref url="/pages/kTjALJBwye3OdiEFIIV3" %}
[Side chain to the backbone transfer](/fog-computing-chain/key-technology/cross-chain/side-chain-to-the-backbone-transfer.md)
{% endcontent-ref %}

{% content-ref url="/pages/2Jxmi6TGHrr78zDDW41z" %}
[Arbitrator](/fog-computing-chain/key-technology/cross-chain/arbitrator.md)
{% endcontent-ref %}


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