A.承載層 B.控制層 C.物理層 D.接入層
A.25%:25%:25%:25% B.12.5%:12.5%:12.5%:12.5%:12.5%:12.5%:12.5%:12.5% C.22.6%:25.8%:25.8%:25.8% D.23.3%:26.7%:23.3%:26.7%
A.1 B.2 C.3 D.4