Computer network Exercises

Computer network _ Fourth time operation

1. Consider an HTTP client that wants to get the Web text for a given URL . However , the IP address of the HTTP server at the beginning is unknown. There is an embedded GIF image in the web text of the URL that resides on the same server as the original text. In this case, what Transport layer and application layer protocols are required in addition to HTTP? and briefly describe the functions of each protocol in this task.

   Application layer Protocol:

   DNS: (Converts a person's easy-to-remember domain name to an IP address that is not easily remembered);

   HTTP: The transfer Protocol that transmits hypertext to the local browser from the WWW server. Ensure that your computer transmits hypertext documents correctly and quickly, determines which part of the document is transferred, and which content is displayed first (such as text before graphics), and so on.

Transport Layer Protocol:

UDP is responsible for the data transfer between client and DNS server in DNS query;

TCP provides a reliable delivery service for HTTP.

1. Suppose that in yourWebin the browser, you clicked on a link to get a Web page. Related toUrlof theIpThe address is not cached on your local host, so you need to perform aDnsquery to getIpaddress. Suppose that in your host fromDnsreceived aIpaddress, access theNaDnsserver; round trip time for continuous accessRTT (roundtrip time)to beRTT1、...、Rttn. Further assume that the link associated with theWebpage contains only one object, which is a smallHtmltext composition. InRTT0that represents the local host and the server that contains the object.Rtt. Assume that the object is transmitted at0, how much time has elapsed since you clicked the link until the client received the object?

   Time to get IP address:;

   After obtaining the IP, the TCP three handshake needs to be established; transmission time is 0;

   So altogether went through:

3. Reference Questions P7, suppose the HTML file references five very small objects on the same server. Ignore transfer time, how much time does each of the following three situations cost?
   1. Non-persistent HTTP with no parallel TCP connection;
   2. Non-persistent HTTP with parallel connection;
   3. Durable HTTP with pipelining.
5. consider a short link of ten meters long, a sender can pass it at 150bps rate two-way transmission. Assume that the grouping containing the data is 150kb long, and that only the groupings that contain controls (such as ACK or handshake) are 150b long. Suppose that N parallel connections each get 1/n link bandwidth. Now consider the HTTP protocol, and assume that each download object is 150kb long, and these initial download objects contain ten reference objects from the same sender. In this case , is it meaningful to parallel download of non-persistent HTTP parallel instances compared to non-parallel instances ? Now consider the persistent HTTP with pipelining , do you expect this to be much better than the non-durable situation? Evaluate and explain your answers and give a clear picture of how parallel instances will work.

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1. Read the textbook 2.6 section carefully. Consider distributing an F-bit file to N users using a peer- to architecture . It is assumed that a fluid model is used. For simplicity, the DMin is assumed to be large, so peer download bandwidth does not become a bottleneck.
   1. Assume U_s≤ (u_s+u_1++u_n)/n. Define a distribution scheme with f/u_s distribution time.
   2. Suppose u_s≥ (u_s+u_1+? +u_n)/N. Define a nf/(u_s+u_1+? +U_N) distribution plan for the delivery time.

The minimum distribution time is usually determined by Max. {f/u_s,nf/(u_s+u_1+? +u_n)} to determine the conclusion.

Computer network Exercises