Analysis of Packets captured during a simple web request and differences between Signals and IP prot

Question 1

Question 1
For this question, you will analyse packets captured during a simple web request from a client PC in a home network to a www.google.com server. In a typical home broadband connection, the router provides a NAT translation service. Client-to-server packets captured by Wireshark on the ISP (WAN) side of the router will have already undergone NAT translation. The Wireshark trace file captured on the ISP side of the home router is called NAT_ISP_side.pcap while the trace file from the LAN interface is called NAT_home_side.pcap - the diagram below shows the Wireshark packet capture scenario used in this case:

 

Open the NAT_home_side file in Wireshark and answer the following questions. For some of the questions, you might find it useful to use a Wireshark filter. Whenever possible, when answering a question below, you should include a screen shot of the packet(s) within the trace that you used to answer the question asked. Also, if appropriate, annotate or highlight any packet data that helps explain your answer.

a) What is the IP address of the client PC? Is this a public or private IP address? 

 

b) Identify and explain the contents of the packets that relate to the DNS lookup that was done to find the IP Address of the www.google.com server. What IP addresses are returned by DNS for this domain name?

c) What is the actual (raw) sequence number and the TCP source port number of the TCP SYN segment that is used to initiate the connection between the PC and the www.google.com server? Fully explain any TCP Options present in the TCP SYN segment sent from the PC to the server.

 

d) What IP address is being used by the router on its ISP (WAN) interface? Is this a public or private IP address?

e) Identify the TCP segment that contains the initial HTTP GET request to the www.google.com server in both trace files. Which IP and TCP protocol header fields changed in this segment after it passed through the NAT router? Explain
the reason for each of these changes. 

Question 2
a) Compute the wavelength of a radio signal having a frequency of 600MHz. In what part of the electromagnetic spectrum does this signal belong i.e. would it correctly be described as UHF, Microwave or Infrared?

b) What are the key differences between a Digital Signal and an Analog Signal? Suppose we have a communications channel with 40MHz of bandwidth. How many bits/sec can be sent over one of these channels if 2048-level digital signals are used? Assume a noiseless channel.

a) DTT (Digital Terrestrial TV) channels are generally about 8MHz wide in terms of bandwidth. What is the minimum signal-to-noise ratio (in decibels) required to transmit a 120Mbps data stream through one of these channels?

 

Also, what minimum number of signal levels is required in the transmitted digital signal to achieve that data rate? 

Question 3
a) If the bit string 0111101111111111110 is “bit stuffed” for transmission using a bit-oriented data link protocol, what is the output bit string? What is the purpose of “bit stuffing” in this context?

b) Discuss the operation of a Sliding Windows protocol that could be used for data communications. In particular, show how such a protocol would recover from the typical error conditions that could occur e.g. lost or corrupted packets. What is the maximum possible window size for a sliding window protocol that uses a 4-bit sequence number?

c) Describe the main differences between the UDP and TCP transport layer protocols, use their header formats as the basis for the comparison. The maximum segment size of a TCP segment that traverses an Ethernet network is typically 1460 bytes. Explain fully how this number is calculated. How does the TCP protocol solve the potential efficiency problems caused by the    sending application delivering data to TCP one byte at a time or the receiving application reading data one byte at a time? 

Question 4
a) What are the main enhancements provided in IPv6 over IPv4? Why has the new protocol not included protocol header support for IP fragments? Explain fully, using an appropriate example, how IP fragmentation could happen.

b) Assume that you are working for a corporation that is using the IP address range 172.16.0.0/12 for its internal network. The company management wants to be able to accommodate 128 locations where each location has its own routed subnet with at least 8000 hosts per subnet. You are requested to design the network layout. Answer the following questions and fully explain the logic and the calculations behind each answer:
• What subnet mask will need to be used and how is this derived?

• What are the valid host addresses and what is the broadcast address for the first and second subnets?

• What other private IP ranges could the company use if needed? 

 

• When is it appropriate to use IP private addressing versus public addressing?