# Protocol theory

Classified in Computers

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38. What are the steps that client and server take to deal with the webpages?
Steps a client (browser) takes to follow a hyperlink:   Determine the protocol (HTTP). Ask DNS for the IP address of server. Make a TCP connection to server. Send request for the page; server sends it back. Fetch other URLs as needed to display the page. Close idle TCP connections

Steps a server takes to serve pages:   Accept a TCP connection from client. Get page request and map it to a resource (e.G., file name). Get the resource (e.G., file from disk). Send contents of the resource to the client. Release idle TCP connections

39. What are the challenges in the P2P networking?

1. How do peers find each other?. 2. How do peers support rapid content. Downloads?.  3. How do peers encourage each other to upload?

40. Write down the steps to download using BitTorrent protocol

Steps to download a torrent:

1. Start with torrent description.      2. Contact tracker to join and get list of peers (with at least seed peer), Or, use DHT (Distributed Hash Tables) index for peers.            3. Trade pieces with different peers.       4. Favor peers that upload to you rapidly;  and “choke” peers that don’t by slowing your upload to them.

40. The distance from earth to a distant planet is approximately 9 × 10 10 m. What is the channel utilization if a stop-and-wait protocol is used for frame transmission on a 64 Mbps point-to-point link? Assume that the frame size is 32 KB and the speed of light is 3 × 10 8 m/s. (b) Now, based on the problem (a), suppose a sliding window protocol is used instead. For what send window size will the link utilization be 100%? You may ignore the protocol processing times at the sender and the receiver.

a.) delay (D) = (9 × 10^10 ) / (3 × 10^8 ) = 300 sec.      Bandwidth-delay product (BD) = 64 × 300 = 19,200 Mbit = 19.2 Gbit.    BD is equivalent to 75000 Frames.     then :    (1/(1+150000))*100% = 6.66 * 10^-4%

b.) For 100% utilization         (w/(1 + 2BD)) = 1  -->  w/(1 + 150,000) =1  --> w =150,001.  have 100% utilization of the channel, the window-size will need to be 150,001 frames.

41. For the following bit stream, draw: (a) Non-Return to Zero (NRZ), (b) NRZ-Invert (NRZI), (c) Manchester (with clock) and (d) Bipolar encoding