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4.2 Assume a bridge receives a frame from port x, with destination MAC address D and source MAC address S. Let R = (address, port, timer) be a record in the Filtering database, where timer (in seconds) is the duration this record existed (initially, timer = 0). Which of the following statements about address learning are correct ? 假設橋接器由埠X收到了一個訊框，且該訊框的目的地MAC位址為D，來源MAC位址為S. 假設在過濾資料庫中的記錄R = (位址,埠,計時器) 其上的計時器記錄了該筆記錄存在的時間 (初始值為0).下列哪些關於位址學習的敘述是正確的? |
| (a) The bridge will add a new entry of R = (S,x,0) to the Filtering database if S is not found in the Filtering database. 該橋接器將會增加一筆記錄R = (S,x,0 到過濾資料庫中如果在過濾資料庫中找不到關於S的記錄. | |
| (b) The bridge will new entry of R = (D,x,0) to the Filtering database if D is not found in the Filtering database. 如果過濾資料庫中沒有D的記錄，則橋接器會將一筆記錄R = (D,x,0) 新增到過濾資料庫中. | |
| (c) If an entry R = (S, y, 20) already existed in the Filtering database, then the bridge will update the entry to (S, x, 0). 如果已經有一筆記錄R = (S, y, 20) 存在於過濾資料庫中，則橋接器會更新該筆記錄成 (S, x, 0). | |
| (d) If an entry R = (S, x, 20) already existed in the Filtering database, then the bridge will update the entry to (S, x, 0). 如果已經有一筆記錄R = (S, x, 20) 存在於過濾資料庫中，則該橋接器會更新該筆記錄成 (S, x, 0). | |
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4.3 Consider the following BLAN configuration. Initially, assume the Filtering databases are empty. Fill in each entry (an integer to present a port number) in the following table after the following five transmissions. Use integer “0” to indicate if a station is not learned in the corresponding filtering database. 考慮下列關於橋接器網路的設定。初始時，假設過濾資料庫為空。在下列五個訊息傳輸後，依據當下橋接器的狀況，填滿下方的表格。數字0代表該工作站的位址尚未被對應的過濾資料庫學習到。 (1) Station A transmits a frame to station B 工作站A傳輸了一個訊框到工作站B. (2) Station B transmits a frame to station C 工作站B傳輸了一個訊框到工作站C. (3) Station D transmits a frame to station A 工作站D傳輸了一個訊框到工作站A . (4) Station E transmits a frame to station D 工作站E傳輸了一個訊框到工作站D. (5) Station C transmits a frame to station B 工作站C傳輸了一個訊框到工作站B.
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