Exercise 4.1.
With reference to the DNS hierarchy shown in Figure 4.7, divide the domain ac.nz into zones so that the number of queries required for the name resolution of ocean.physics.auckland.ac.nz by a host external to the ac.nz domain is exactly 4 and the number of zones is the minimum possible.

Figure 4.7 Examples of domain names (Exercise 4.1).

Exercise 4.5.
With reference to Example 4.2, assuming that the local name server ns.math.auckland.ac.nz has a cache and that the records relating to the previous query for the host flower.deib.polimi.it are still in the cache, determine how many queries are needed to obtain the IP address of the host tree.deib.polimi.it with recursive resolution and with iterative resolution.

Exercise 4.7.
Represent graphically the exchange of messages that takes place between two MTAs using the SMTP protocol to transfer from the client ducato.com to the server fiorino.com an e-mail with the sender Andrea at the address andre@scudo.com and the receiver Mariangela at the address mari@guelfo.com. The message has as subject “Happy birthday” and contains the text lines “Happy birthday”, “from all of us”, “the cousins”.

Exercise 4.10.
Represent graphically the access of the user Linda to an FTP server. After authenticating with the “Hello” password, Linda asks to receive the file lastnews.pdf from the directory /home/news/updates. The server replies that the requested file is not in the indicated directory. So Linda asks for the file list in the directory and discovers that the file of interest to her is called last-updates.pdf. She therefore asks for its download which is carried out successfully and leaves the FTP connection open.

Exercise 4.12.
A client accesses a server through a backbone network which provides a dedicated channel with capacity C = 100 Mbit/s and the distance along the channel between the client and the server is d = 300 km. Determine the total download time T from the server of a 1000-byte HTML page containing 8 images of 25 kbytes each by adopting non-persistent or persistent connections. It is assumed that the size of the HTTP protocol control messages is negligible and that the closure of a TCP connection can be implemented in a negligible time.

Exercise 4.19.
In a peer-to-peer architecture of N peers with N power of 2 and upload capacity C_u less than the download capacity C_d identify the condition on the number of fragments k which determines a reduction by at least a factor F of the total distribution time of a file with size D bytes compared to the case of a nonfragmented file.