Question 4 Consider transferring an enormous file of L bytes from Host A to Host

Question

Question 4 Consider transferring an enormous file of L bytes from Host A to Host B. Assume an MSS of 1000 bytes. (I) If we want to send a file consisting of 500,000 bytes, how many segments are constructed by TCP? and what are the sequence numbers assigned to the first 5 Segments (II) What is the maximum value of L such that TCP sequence numbers are not exhausted? Recall that the TCP sequence number field has 4 bytes. (III) For the L you obtain in (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 a 155 Mbps link. Ignore flow control and congestion control so A can pump out the segments back to back and continuously.

Explanation / Answer

I)

the sequences constructed by the tcp to send 500,000 bytes will be 500,000/1000 = 500 sequences and the first 5 sequence will be from binary 1 to 5.

2)

In case of TCP there are 232 possible sequences which can exist. The sequce numbers does not increment by one by rather they are incremented by the number of bytes sent. So basically the size of the MSS is irrelevant here and the maximum value of L which can be sent will be 232 =4.29 GB

3)

The number of segements will be 232/1000 = 4294967 bytes. Now to each of these segements a 66 byte header is added so L = (1000+66) * S = 1066 * 4294967 = 4578434822. bytes. Now on the 155 mbps links time taken will be

= 4578434822*8/155*1,000,000 = 236 seconds approx.

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