Question

Select all True statements! Question 1 options: a) Host A is sending Host B a large file over a TCP connection. Assume Host B has no data to send Host A. Host B will not send acknowledgments to Host A because Host B cannot piggyback the acknowledgments on data. b) The size of the TCP rwnd never changes throughout the duration of the connection. c) Suppose Host A is sending Host B a large file over a TCP connection. The number of unacknowledged bytes that A sends cannot exceed the size of the receive buffer. d) Suppose Host A is sending a large file to Host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment will necessarily be m + 1. e) The TCP segment has a field in its header for rwnd. f) Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. The current value of TimeoutInterval for the connection will necessarily be ≥ 1 sec. g) Suppose Host A sends one segment with sequence number 38 and 4 bytes of data over a TCP connection to Host B. In this same segment the acknowledgment number is necessarily 42.

Answer 1

Solution:

a)   False. Piggyback is used only for efficiency. If there's no data packet to be piggybacked to, then B will just send the acknowledgement packet.

b)  False. It is the size of the receiver's buffer that's never changed. RcvWindow is the part of the receiver's buffer that's changing all the time depending on the processing capability at the receiver's side and the network traffic.

c)  The given statement is True.

 d) False. The sequence number of the subsequent segment depends on the number of 8-byte characters in the current segment.

e)  True. Every TCP segment has a current value of rwnd in the receive window.

f)  False. Next_RTT = alpha * last_estimated_RTT + (1-alpha)*newly_collected_RTT_sample. In this case even though the last sampleRTT which is the newly_collected_RTT_sample is 1sec, the next_RTT still depends on alpha and last_estimated_RTT. Therefore, the next_RTT is not necessarily greater than 1sec.

g) False. The acknowledgement number has nothing to do with the sequence number. The ack. number indicates the next sequence number A is expecting from B.