Dr. Chen Fal 2017 10/20/201 Question 4. (10 points) protocol, Go-Back N or Selec

Question

Dr. Chen Fal 2017 10/20/201 Question 4. (10 points) protocol, Go-Back N or Selective- Repeat, makes more efficient use of network bandwidth? Why QuestionS. (10 points) Assuming no DNS cache, illustrate how a typical iterated DNS query operates if requesting host (cis poly.edu) wants to get the IP address of gaia.cs.umass.edu. You may want to draw lines in the following figure to illustrate. local DNS server reqiesting ess.poly Question 6.(S points) Normally, people consider the fo lowing four elements when they design their applications: data loss, ut, timing and security. Among these four elements, which ones can be provided by the Internet (up to the transport layer)? Question 7. (10 points) What are the four techniques that have been used to achieve reliable data transfer over an unvreliable channel that may have bit errors and packet loss? Question 8. (10 points) Explain in the demultiplexing process, how does (i.e, what information is used to) the transport layer identify a TCP socket and a UPD socket, respectively. Page 2 of

Explanation / Answer

4)

If the error rate is high then more frames will be damaged.

Retransmitting all the frames that arrived after a damaged frame, waste the lots of bandwidth.

On the other hand, selective repeat protocol re-transmits only damaged frame hence,

minimum bandwidth is wasted in this case.

Hence selective repeat will efficiently use the bandwidth.

5)

1) Request will go from host to local dns server

2) local dns will give ip address of .edu root server as response.

3) Now host will send a request to root server for ip of TLD server.

4) Now Root server will send ip of umass.edu as a response to the host.

5) The host will send a request to TLD server for ip of the authoritative server(dns.cs.unam.edu).

6) Now TLD server will send the response (ip of dns.cs.unam.edu) to host.

7) The host will send a request to authoritative server for the ip of gaia.cs.unam.edu

8) Finally, the authoritative server will send the ip of gaia.cs.unam.edu as a response.

9) Using this ip host will establish a connection to gaia.cs.unam.edu.

6)

Transport Layer will guarantee retransmission of data packet when data loss occurs.

  Transport Layer set Maximum Segment Size (MSS) value, which is the Maximum

data that we can send at a time. Hence the throughput is provided by TL.

Transport Layer guarantee timely and orderly delivery of packets and hence

Transport Layer provides timing.

In Transport layer, we have TLS which is Transport Layer security hence

Transport layer provides security.

  

7)

Reliable data transfer will occur when we eliminate bit and packet errors,

1) checksum [ for Bit errors ]

2) stop and wait [ for packet errors ]

3) go back N [ for packet errors ]

4) selective repeat   [ for packet errors ]

8)

A TCP socket will be identified by 4 tuple SIP,DIP,SP,DP

which are Source IP , Destination IP , Source Port , Destination Port.

A UCP socket will be identified by 2 tuple DIP,DP

which are Destination IP , Destination Port

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