GATE IT 2004 | Question: 23

Question

Which one of the following statements is FALSE?

• A. TCP guarantees a minimum communication rate
• B. TCP ensures in-order delivery
• C. TCP reacts to congestion by reducing sender window size
• D. TCP employs retransmission to compensate for packet loss

Comments

@Bikram sir

why option a is wrong

---

TCP is the combination of SR and GBN flow control technique. By SR technique TCP can accept out of order packet and by GBN there is cumulative acknowledgement.

---

Excerpt from Kurose and Ross, 6th Ed.

We have already noted that TCP provides reliable end-to-end data transfer. And we also know that TCP can be easily enhanced at the application layer with SSL to provide security services.

But in our brief description of TCP and UDP, conspicuously missing was any mention of throughput or timing guarantees—services not provided by today’s Internet transport protocols.

Neither TCP nor UDP can give you any throughtput (communication rate) guaranatees.

Answer 1

Option B: "Sequence numbers allow receivers to discard duplicate packets and properly sequence reordered packets." 
Option C: "When congestion is detected, the transmitter decreases the transmission rate by a multiplicative factor; for example, cut the congestion window in half after loss." (Additive Increase/multiplicative decrease)
Option D: "Acknowledgments allow senders to determine when to retransmit lost packets."

So, (A) is answer. 

http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Error_detection

http://en.wikipedia.org/wiki/Additive_increase/multiplicative_decrease

Comments

What is the meaning of minimum communication rate ?

---

Sir, Please throw some lights on option A.  ?

---

@vijaycs i m not getting more onthis    see it may  help ... 

---

Thanks @saurabh  :)

Answer 2

I just solved this by elimination method as B C D are correct.

TCP ensures in order delivery as it ensures the reliable delivery of a packet to other TCP connection.

TCP uses AIMD and Slow start Exponencial Increase Algo for Congestion and if time out occurs then Threshold window is reduced by half so sender window is adjusted if congestion comes into picture.

There is a retransmission timer which starts when a packet is sent. and it is en-queued and if an acknowledgement is received then that packet is de-queued

Answer 3

)	TCP guarantees a minimum communication rate