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4.9 The “root path cost” (RPC) of a bridge is defined as the summation of the transmission costs of the bridges along the path from the bridge to the root bridge. Consider the following BLAN configuration, the RPC of bridge 2 is __(a)___, and the RPC of bridge 4 is ___(b)___. 一個橋接器的 “根路徑費用 (RPC)“ 定義為該橋接器到根橋接器的路徑上所有傳輸成本的總合. 下列橋接網路架構中，橋接器 2的根路徑費用為___(a)___，而橋接器4的根路徑費用為__(b)__.
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| (a) | |
| (b) | |
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4.10 Let (A) be the procedure to find the “root bridge” of a BLAN, (B) be the procedure to find the “root port” of a bridge, and (C) be the procedure to find a “designated bridge” of a LAN, (D) be the procedure to find a “designated port” of a LAN. What is the sequential procedure to establish the spanning tree of a BLAN ? 令 (A)為尋找橋接網路中的根橋接器的過程。(B)為尋找橋接器根埠 (root port) 的過程。 (C)為尋找區域網路的代理橋接器(designated bridge)的過程。(D)為尋找區域網路代理埠 (designated port) 的過程。下列哪個是建立一個橋接網路上擴張樹的順序?
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| A, B, D | |
| A, C, B | |
| A, C, D | |
| B, A, C | |
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4.11 Consider the following state diagram of a bridge port. Initially, a port is in the “blocking” state. The state of a port is changed to “listening” state when a port is selected as a “root” (R) port or a “designated” (D) port. The state of a port is changed to “blocking” state when a port is no more an R port or a D port. The state of a port is changed to “learning” state from “listening” state after a forwarding delay. The state of a port is changed to “forwarding” state from “learning” state after another forwarding delay. Which of the following statements are correct ? 參考下列關於一個橋接器埠的狀態轉換圖。初始時，一個埠會處在 “blocking” 狀態. 該埠會在其被選為”根埠”或”指定埠”時，轉為“listening” 狀態。一個埠的狀態將會在當其不再是”根埠”或”指定埠”時轉為 “blocking” 狀態。一個埠的狀態將會在經過一個轉送延遲(forward delay)後，由“listening” 狀態轉為“learning” 狀態. 一個埠的狀態將會在一個轉送延遲後，由“learning” 狀態轉為“forwarding” 狀態 . 下列哪些敘述是正確的 ?
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| Before the spanning tree is completely constructed, the state of a port may be changed among these four states. 在擴張樹完全確定建立前，一個埠的 狀態可能會在上述的四個狀態間做轉換。. | |
| After the spanning tree is constructed, the state of a port is either in the “learning” state or “forwarding” state. 擴張樹建立完成後，每一個埠的狀態將會是“learning” 狀態或“forwarding” 狀態。 | |
| A port in the “forwarding” state will be an R port or a D port. 一個在“forwarding” 狀態的埠將會是”根埠”或”指定埠”. | |
| A port in the “learning” state is able to learning the source MAC address of a received frame but unable to forward frames. 一個處於 “learning” 狀態的埠可以學習一個接收訊框的來源MAC位址，但無法轉送訊框. | |
| A port in the “forwarding” state is able to forward or filter the received frames. 一個處於“forwarding”狀態的埠可以過濾或轉送收到的訊框. | |
