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6.4 Which of the following statements are correct for “stop-and-wait” protocol ? |
| (a) After transmitting one frame, the sender waits for an acknowledgement before transmitting the next frame. 傳送端在傳送一個訊框後, 會等待一個肯定回覆, 才會再送出下一個訊框. | |
| (b) After transmitting one frame, the sender can still transmit one more frame before an acknowledgement is received. 傳送端在傳送一個訊框後, 在收到一個肯定回覆前, 依然可以傳送一個訊框 | |
| (c) If the acknowledgement does not arrive after a certain period of time, the sender times out and retransmits the original frame 傳送端若在經過一段時間後沒有收到肯定回覆, 會發生等待逾時, 且重傳該訊框 | |
| (d) The only reason the sender times out is that the acknowledgement is lost. 傳送端發生等待逾時的唯一原因是肯定回覆遺失. | |
| (e) The receiver may receive duplicate copies of a frame. 接收端可能收到許多個相同的訊框. |
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6.5. Which of the following cases may cause a sender to “timeout” in the “stop-and-wait” protocol ? |
| (a) The transmitted frame is lost. 已傳送的訊框遺失. | |
| (b) The transmitted frame is delayed. 已傳送的訊框延遲到達接收端 | |
| (c) The acknowledgement is delayed肯定回覆延遲到達傳送端 | |
| (d) The acknowledgement is lost. 肯定回覆遺失 | |
| (e) The transmitted frame is received with error. 接收到的訊框發生錯誤 |
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6.6 Which of the following statements are correct for using “stop-and-wait” protocol” with 1-bit sequence number of “0” and “1”? |
| (a) When a sender transmits frame 0, before receiving the ACK 0, the sender can transmit frame 1 to speedup the transmission. 為了加速傳送, 當傳送端送出編號 0 訊框後, 在接收到 ACK 0 之前, 傳送端可以傳送編號 1 訊框. | |
| (b) When a sender transmits frame 0, it will transmit frame 1 after the ACK 0 received. 當傳送端傳送編號 0 訊框,在收到 ACK 0 後,他會傳送編號 1 訊框. | |
| (c) When the sender retransmits frame 0, the receiver can determine that this is a second copy of frame 0 and therefore can ignore it. 當傳送端重傳編號 0 訊框, 接收端可以分辨出這是重複的編號 0 訊框, 因此可以忽略此訊框. | |
| (d) When the sender retransmits frame 1, the receiver can determine that this is a second copy of frame 1 and therefore can ignore it. 當傳送端重傳編號 1 訊框, 接收端可以分辨出這是重複的編號 1 訊框, 因此可以忽略此訊框. | |
| (e) When a second copy of frame is received, the receiver will discard the duplicated frame and therefore no need to send back an acknowledgement for this frame. 當接收端收到重複的訊框, 接收端會將之丟棄, 因此不需要再針對此訊框回傳一個肯定回覆. |
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6.7.In the “stop-and-wait” protocol, at most how many frames can be transmitted simultaneously on the link by the sender ? 在“停止與等待”協議中, 傳送端最多可以在鏈結上同時傳送幾個訊框 ? |
| (a) 1 | |
| (b) 2 | |
| (c) 3 | |
| (d) 4 | |
| (e) 5 |
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6.8 Consider a link of 2 Mbps with an RTT of 40 ms. Assume that the frame size is of 1 KBytes. What is the maximum sending rate (kbps) of the sender if the “stop-and-wait” protocol is used ? |
| ____?____(kbps) |
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6.9 Consider a link of 4 Mbps with an RTT of 20 ms. Assume that the frame size is of 2 KBytes. What is the maximum sending rate (kbps) of the sender if the “stop-and-wait” protocol is used ? |
| ____?___(kbps) |
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6.10 Consider a link of 2 Mbps with an RTT of 40 ms. Assume that the frame size is of 2 KBytes. To fully use the link, the sender should transmit up to ___?_____ frames before having to wait for an ACK ? |
| ____?_____ |
