Q7: TCP, UDP Ports

Question 1

TCP or UDP?

a. used by TFTP
b. used by FTP
c. connection-oriented
d. connectionless
e. best-effort delivery
f. guaranteed delivery

A. TCP, UDP, TCP, UDP, UDP, TCP

B. UDP, TCP, TCP, UDP, UDP, TCP

C. TCP,UDP, TCP, UDP, UDP, TCP

D. UDP, TCP, UDP, TCP, TCP, UDP

Answer 1

Answer:
B) UDP, TCP, TCP, UDP, UDP, TCP

Explanation:

TCP = Connection-oriented, guaranteed delivery via acknowledgement
UDP = Connectionless, best-effort delivery with no acknowledgement
FTP is an acknowledged transfer where TFTP is best-effort transfer

Question 2

Which of the port numbers in the table below is not assoicated with the following protocols?

FTP (data)
DHCP (client)
SMTP
SSH
HTTPS
SNMP

A. 21
B. 68
C. 25
D. 161
E. 20

Answer 2

Answer:

A) 21

Question 3

How would a host know if the UDP datagram it sent was received by the far end host?

A. TCP ACK
B. UDP ACK
C.CRC
D. it wouldn't 
E. ICMP

Answer 3

Answer:
D) it wouldn’t

Explanation: UDP is connectionless and therefore a best-effort delivery. There is no acknowledgement sent so there is no way of confirming if everything got there.

Question 4

Why does it makes sense that voice packets in an ip phone session use UDP instead of TCP protocol?

Answer 4

Explanation:
Voice traffic is extremely sensitive to delay and packet loss. So two things come into play here. First, it takes time to acknowledge a TCP packet and voice does not have the time to spare. Second, it TCP were in use and detected that a packet in a voice stream of packets did not make it to the destination, sending the packet again would only cause more problems. The initial problem being that some part of the conversation will be chopped off- which is annoying. Then imagine if 20 seconds later that missing voice packet showed up- it would be in the wrong place at the wrong time and only cause more poor voice quality. So, with voice, you use best effort and then configure QoS in the network.