1、第二章 作业 1. 2. 3. 4. 5. 6. 7. 8. Consider sending a packet of F bits over a path of Q links. Each link transmits at R bps. The network is lightly loaded so that there are no queuing delays. Propagation delay is negligible. a) Suppose the network is a packet-switched virtual circuit network. Denote the
2、 VC set-up time by ts seconds. Suppose the sending layers add a total of h bits of header to each packet. How long does it take to send the file from source to destination? (3 points) b) Suppose the network is a packet-switched datagram network and a connectionless service is used. Now suppose each
3、packet has 2h bits of header. How long does it take to send the file? c) Finally, suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is R bps. Assuming ts set- up time and h bits of header appended to the e
4、ntire file, how long does it take to send the file? 9. Consider the networks shown in the figure below. There are two user machines and in the network . Suppose the user at types in the URL into a browser to retrieve a 1Gbit (1000 Mbit) file from . 1） List the sequence of DNS and HTTP messages sent/
5、received from/by as well as any other messages that leave/enter the network that are not directly sent/received by from the point that the URL is entered into the browser until the file is completely received. Indicate the source and destination of each message. You can assume that every HTTP reques
6、t by is first directed to the HTTP cache in and that the cache is initially empty, and that all DNS requests are iterated queries. 2） Now assume that machine makes a request to exactly the same URL that made. List the sequence of DNS and HTTP messages sent/received from/by as well as any other messages that leave/enter the network that are not directly sent/received by from the point that the URL is entered into the browser until the file is completely received. Indicate the source and destination of each message. Hint: make sure you consider caching here
