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

can someone explain why B is not false as TCP supports out of order delivery?

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@priyanka understand what is the difference between "TCP ensures in-order delivery" and "TCP can accept out of order segments"
  1.first we consider  "TCP can accept out of order segments"  in this case receiver can accepts out of order segments and store into buffer .
2."TCP ensures in-order delivery" here it means deliver the segments to upper layer (like TCP to application layer) it insures in order delivery of segments to upper layer
I think u r confuse between 1 nd 2.

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thanku sir...yes i was confused as every where it is written tcp has out of order delivery but now all clear. Thank again

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@Bikram sir

why option a is wrong

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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.

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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.

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TCP does not guarantee a minimum communication rate because it is designed to ensure that data is delivered reliably and in the correct order, not to maintain a specific speed. It adjusts the sending rate based on network congestion and uses retransmissions to handle packet loss. UDP, on the other hand, does not guarantee reliability but can be faster because it doesn't have these controls.

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 ?

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Sir, Please throw some lights on option A.  ?

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

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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

From Kurose, Ross (might be useful)

Given the mechanism of adjusting the value of cwnd to control the sending rate, the critical question remains: How should a TCP sender determine the rate at which it should send? If TCP senders collectively send too fast, they can congest the net- work, leading to the type of congestion collapse that we saw in Figure 3.48. Indeed, the version of TCP that we’ll study shortly was developed in response to observed Internet congestion collapse [Jacobson 1988] under earlier versions of TCP. How- ever, if TCP senders are too cautious and send too slowly, they could under utilize the bandwidth in the network; that is, the TCP senders could send at a higher rate without congesting the network. How then do the TCP senders determine their send- ing rates such that they don’t congest the network but at the same time make use of all the available bandwidth? Are TCP senders explicitly coordinated, or is there a distributed approach in which the TCP senders can set their sending rates based only on local information? TCP answers these questions using TCP congestion-control algorithm

So option A is the answer

 

Answer 4

COMMENT BELOW IF YOU HAVE ANY DOUBT

Comments

Don't put AI panipuri photoshop answer.

Answer 5

)	TCP guarantees a minimum communication rate