課程影片與練習
課程簡介
第1週：網路架構與七層參考模式簡介
第2週：IEEE 802.3 乙太網路 (Ethernet)
第3週：IEEE 802.11 無線區域網路 (Wireless LAN)
第4週：IEEE 802.1D 交換機的擴張樹演算法 (Spanning Tree Algorithm)
第5週：IEEE 802.1Q 虛擬區域網路 (Virtual LAN)
第6週：區域網路可靠傳輸技術 －－ 滑動視窗技術
第7週：路由器運作原理以及網路互連技術
第8週：TCP 與網路阻塞偵測與控制技術
※觀看影片請點擊影片名稱後方的"YOUTUBE"或"YOUKU"，
觀看YOUKU影片，請輸入密碼：mooc01004
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8.14 In TCP fast retransmission mechanism, when a packet arrives out of order, the TCP resends the same acknowledgment it sent last time. This second transmission of the same acknowledgment is called a “duplicate ACK”. Which of the following statements are correct ?
在 TCP 快速重送機制中，當一個封包非以原先發送順序抵達時, TCP會重送最近一次發送的回覆序號. 此第二次傳輸相同的回覆被稱為“重複回覆”。下列哪些敘述是正確的 ?
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| (a) When the sending side sees a duplicate ACK, it knows that the other side must have received a packet out of order. 當傳送端收到重複回覆，它得知另一端一定是接收到非以原先發送順序抵達的封包 | |
| (b) When the sending side sees a duplicate ACK, it is also possible that the earlier packet has only been delayed rather than lost 當傳送端收到重複回覆，有可能先前傳送的封包發生延遲抵達而非遺失 | |
| (c) When the sending side sees a duplicate ACK, it knows that the other side must have received a packet out of order, and the packet was already lost. 當傳送端收到重複回覆，它得知另一端一定是接收到非以原先發送順序抵達的封包且未收到的封包已經遺失 | |
| (d) When the sending side sees a duplicate ACK, it is NOT possible that the earlier packet has only been delayed rather than lost 當傳送端收到重複回覆，表示之前傳送的封包不可能是延遲抵達，而是已經遺失 | |
| (e) When the sending side sees a duplicate ACK, it knows that the packet was already lost, and will retransmit the packet immediately. 當傳送端收到重複回覆，它得知該封包已經遺失，而會立即重送該封包 |
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8.15 In TCP fast retransmission mechanism, when a packet arrives out of order, the TCP resends the same acknowledgment it sent last time. This second transmission of the same acknowledgment is called a “duplicate ACK”. How many duplicate ACKs the TCP will wait before retransmitting the packet ?
在 TCP 快速重送機制中，當一個封包非以原先發送順序抵達時, TCP會重送最近一次發送的回覆序號. 此第二次傳輸相同的回覆被稱為“重複回覆”。TCP 在重送該封包前會等待幾個重複回覆 ?
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