Question

1.

(A) A Web server is identified by port number 25 while an email server process using the SMTP protocol is identified by port number 80.

True

False

(b) Both SMTP with HTTP are used to transfer files from one host to another.

True

False

(c) We are sending a 30 Mbit MP3 file from a source host to a destination host. All links in the path between source and destination have a transmission rate of 10 Mbps. Assume that the propagation speed is 2*10⁸ meters/sec, and the distance between source and destination is 10,000 km. Now suppose there is only one link between source and destination. Also suppose that the entire MP3 file is sent as one packet. How many bits will the source have transmitted when the first bit arrives at the destination?

	A.	30,000,000 bits
	B.	1 bit
	C.	500,000 bits
	D.	none of the above

(d) Suppose a client sends an HTTP request message with the "If-modified-since": header. Suppose the object in a server has not changed since the last time a client retrieved the object. Then the server will send a response message with the status code ____.

	A.	200 OK
	B.	404 Not Found
	C.	304 Not Modified
	D.	none of the above

(e) UDP provides a flow-control service to its applications to eliminate the possibility of the sender overflowing the receiver’s buffer.

True

False

(F)The TCP connection is not an end-to-end TDM or FDM circuit as in a packet-switched network.

True

False

Answer 1

a.) The correct answer is True because of the fact that the a Web server is identified by port number 80. A mailserver process (using the SMTP protocol) is identified by port number 25. A list of well-known and most used port numbers for all Internet based standard protocols can be found in directory of window netwrok manager.

b.) the correct option is True because for transmitting data from one host to another, all protocols are used: HTTP passes data (also called objects) from a Web server to a Web client (usually a browser); SMTP passes files (i.e. e-mail messages) from one mail server to another mail server.

c.) The correct option is C. 500,000 bits because it is given that the data travel as 2X10^8m/sec , which means 20,000km/sec and the distance in between is 10,000km , so we need 0.5 second to reach the first bit to destination and it is given that we have data transmission rate of 10Mbps , in 0.5 second , it will send 5 mb into the link , we means 500,000bits will sent into the link in 0.5seconds , which is time needed for first bit to reach destination.

d.) The correct option is option C. 304 Not Modified because of fact that the server will send a response message with this status code if the client is sending is a HTTP request message with the "If-modified-since": header and  that there is no need to retransmit the requested resources.