CN-TCP

Question

In a TCP connection, the value of congestion window Cnwd = 2500 and the value of receiver window Rwnd = 4500.The host has sent 2000 bytes which has not been acknowledge. How many more bytes can be sent?

A) 2000

B) 500

C) 2500

D) none of these

Answer 1

Window Size = Min (Cnwd,Rwnd) = Min (2500,4500) = 2500

The host has sent 2000 bytes which has not been acknowledged.

Hence, Number of bytes that can be sent = 2500 - 2000 = 500 .

Answer B).

Comments

@Anu "they are in the way right i.e. not reached till receiver" or "ack is delayed" these are not only the reasons that sender didn't receive the acknowledgment of bytes. 
There is one more possible reason, until receiver's transport layer doesn't deliver the bytes to the receiver's application process, it keeps all the unacknowledged bytes in its buffer.
for your reference, from my own notes copied from Forouzan:

 

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sir what you know from congestion winodw.

congestion winodw: The congestion window is a sender imposed window that was implemented to avoid overrunning some routers in the middle of the network path.

I dont know why you think reciver cannot manage 2500 bytes. since it has sapce for that.

Since reviver said i have capacity to recieve 4500 byte , since 2000 byte not ack so 4500-2000 = 2500 can not accomodated more in reciver buffer. Hope you get my point and i made my point correctly.

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yes @anu i understood your point. 

"Since reviver said i have capacity to receive 4500 byte , since 2000 byte not ack so 4500-2000 = 2500 can not accommodated more in receiver buffer."

This assumption is not correct, when receiver advertises its window size that itself it subtracts those bytes which are unprocessed, it means rwnd = total receiver buffer size - number of unprocessed bytes.

If rwnd=4500 it means reciever is capable of accepting 4500 bytes apart from 2000 unprocessed bytes.

but the size of sender is set by the min(cwnd,rwnd) and in this case it's 2500 Bytes, and 2000 bytes are still in the buffer of sender, see how this system works:

 

by the way, can you show some reference to prove your point? May be you're correct, and i am not!

Answer 2

option b iscorrect one