举两个网际网路的应用例子.ppt

WEEKLY QUIZ 3 (A) Computer Networks * 1. 舉兩個網際網路的應用例子，說明其應用架構具有P2P及主從式架構 ﹖ * Skype : centralized server: finding address of remote party: client-client connection: direct (not through server) Instant message: centralized service: client presence detection/location user registers its IP address with central server when it comes online user contacts central server to find IP addresses of buddies * 2. Explaination (1) API(2) Socket(3) RTT(4) Proprietary protocol * API Application programming interface the method by which an application program request services from libraries and/or operating systems ex. Java API, iPhone API * Socket 網路上資料進出的地方 位於應用層和傳輸層的介面 * RTT Round trip time 封包從發送開始到收到回應的時間 * Proprietary protocol communications protocol owned by a single organization or individual Example: Skype protocol * 3. 何謂Process ？ 如何決定一個網路上的Process ？ * Process : program in execution Addressing processes : IP and port number Examples : HTTP port 80, FTP port 21 * 4. Flow control與 Congestion control 有何不同 ﹖ * Flow control 調整sender端傳送資料的速率和receiver端處理速度相符，避免receiver 端buffer overflow Congestion control 控制sender端傳送資料的速率，避免網路中的上buffer overflow(packet loss) * 5. 舉例說明Non-persistent HTTP 與Persistent HTTP的不同 ﹖ * 假設一台伺服器上包含一份html檔和10份圖檔，共11個object： Non persistent Persistent 一次建立一條TCP連線，共建立11條 只建立一次TCP 連線 消耗頻寬資源 分為pipeline 與 without pipeline的方法 有閒置狀態產生 * Problems and Questions * 1. For a communication session between a pair of process, which process is the client and which is the server? * Client process: process that initiates communication Server process: process that waits to be contacted * 2. What information is used by a process running on one host to identify a process running on another host? * The IP address of the destination host and the port number of the destination socket. * 3. Suppose you want to do a transaction from remote client to a server as fast as possible. Would you use UDP or TCP ? Why? * You would use UDP. With UDP, the transaction can