Discuss in detail about File Transfer Protocol (FTP). Explain at least five comm

Question

Discuss in detail about File Transfer Protocol (FTP). Explain at least five commands that are used by FTP. (20 Points) 2. Explain how emails are sent using Simple Mail Transfer Protocol (SMTP). Also explain how POP3 protocol is used to retrieve emails. (10 Points) 3. What is Domain Name System (DNS)? What are the services offered by DNS? What are the hierarchical servers in DNS? (15 Points) 4. A file of F = 1x109 bits is distributed to N peers. The server has an upload rate of us = 10x106 bps. Each peer has a download rate of di = 1x106 bps and an upload rate of u. For N = 10, 100, and 1,000 and u = 100,000 bps, 500,000 bps, and 1,000,000 bps, prepare a table giving the minimum distribution time for each of the combinations of N and u for both client-server distribution and P2P distribution. (20 Points) 5. Explain at least one P2P application (BitTorrent or DHT) in detail. (10 Points) 6. What does the transport layer do? Name at least two transport layer protocols? (5 Points) 7. What is multiplexing and demultiplexing? How and why it is done at the transport layer? (10 Points) 8. Explain connectionless demultiplexing and connection-oriented demultiplexing

Explanation / Answer

(There are multiple questions with sub-parts. Please post the remaining questions as seperate.)

Some of the FTP commands are as shown below:

i>Binary- It sets the file transfer mode to binary

ii>Cd- It is used to change the directory on the remote machine.

iii>Put- It is used to copy the file from local machine to the remote machine.

iv>Pwd- It is used to find the pathname of the current directory on the remote server

v>Bye- It is used to quit the FTP environment.

2 Simple Mail Transfer Protocol is a standard internet protocols which is used for transferring mail between two hosts electronically. A message is sent from one server by using the simplest TCP/IP protocols and some of the text commands. The command and data are sent and numeric responses are received from the other server. It can be simulated by using any telnet client using port 25 of the TCP/IP. EHLO command is used for initiating a communication from one server which is identified by the receiving machine and is ready to receive. The sending machine next provides the email address of the sender in proper format. Then the receiving address must be specified. After, the address has been specified the actual mail and data are sent. After the message is on the way , the connecting server sends another command to quit the session.

POP3 understands for POST OFFICE PROTOCOL 3. It is an application layer protocol and is used to retrieve emails from a remote server to a local server over TCP/IP connection. It deletes the mail on the server as soon as the user downloads it. It listens for the request on the sever and initializes the endpool, creates a thread pool for I/O packets and a socket pool from where a message is received.

3 DNS is the domain naming system that controls a domain name of a website or internet. Its simple use is to convert the user friendly domain like www.chegg.com” i nto an IP address like 10.0.0.1 and vice versa. All the electronic devices on internet uses an IP address to communicate from one host server to other. Thus it converts those IP address into a user friendly name. It has a pool of IP address mapped with some specific name.

The hierarchy of domain server includes a root at the top of the hierarchy. Next, we have keywords like com,in,edu,us,etc which further bifurcates to name of the website like chegg, Microsoft,etc. So, www.chegg.com has a root, com at second level and chegg at the third level.

5. BitTorrent is example of P2P (Peer to Peer) application and is used for transfer and downloading of large files with minimum bandwidth. Here, the downloading and uploading of data files takes place between each other without the need of any central server. It maximizes the transfer speed by downloading abd gathering bits of file from the user who has already downloaded it. A host joins the bit torrent pool by downloading a .torrent file into a client server. An inbuilt tracker is used to contact all the server who has downloaded the file by keeping a track of the IP address. After the connection, it downloads file into small pieces and gathers from all the connected hosts. So, the downloading and uploading of files takes place simultaneously. Also, this do not burdens any user and the transfer speed is also maximum for all. The tracker in .torrent file does not downloads or uploads by itself but helps in connecting of hosts.

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