4. Consider transferring a very big file of L bytes from Host A to Host B. Assum

Question

4. Consider transferring a very big file of L bytes from Host A to Host B. Assume a MSS (Maximum Segment Size) of 1460 bytes.

a) What is the maximum value of L such that TCP sequence numbers (in total 2^32) are not exhausted?

b) For the L you obtain in part (a), find how long it takes to transmit the file. Assume that a total of 66 bytes of transport, network and data link header are added to each segment before the resulting packet is sent out over 10Mbps link. Ignore flow control and congestion control.

Explanation / Answer

a) There are 2^32 = 4,294,967,296 possible sequence numbers. The sequence number does not increment by one with each segment. Rather, it increments by the number of bytes of data sent. So the size of the MSS is irrelevant -- the maximum size file that can be sent from A to B is simply the number of bytes representable by 2^32 4.19 Gbytes.

b) ceil(2^32 / 536) = 8,012,999

The number of segments is. 66 bytes of header get added to each segment giving a total of 528,857,934 bytes of header. The total number of bytes transmitted is 2^32 + 528,857,934 = 4.824 × 10^9 bytes. Thus it would take 249 seconds to transmit the file over a 155~Mbps link.:

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