层1和层2分别是物理层和数据链接层，通过以太网实现。

Layers 1 and 2 are the physical and data link layers, respectively, fulfilled by the Ethernet network.

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每一层都使用它下面的层，因此网络层不必担心网络上的每次跳转如何使用物理和数据链接等问题。

Each layer USES the layers beneath it, so the network layer does not need to worry about how each hop on the network USES the physical and data link layers and so forth.

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