Data file with 3 bytes long name, comprising 500 bytes needs to be transmitted.

Question

Data file with 3 bytes long name, comprising 500 bytes needs to be transmitted.

a) How many TFTP packets would be required?

b) For transmission each TFTP packet is handed to UDP, which adds its header to form a UDP segment, which is in turn handed to IP (assume IPv4 is used), which adds its header to for an IP datagram. What is the size of the IP datagram?

c) What is the total size (number of bytes) of the packets actually being transmitted?

d) What is the overhead percentage in this data transfer? Note: Refer to detailed description of the TFTP protocol. Recall that TFTP includes packets for initiating communication as well as acknowledgement. Also assume the Mode field in the TFTP WRQ packet is 2 bytes long.

Explanation / Answer

a) fixed length block size is 512 byte/block

So data file size is 500 bytes

So packets or blocks required is 500/512= 0.97 ~ 1 packet

b) size of TFTP packet is 500 bytes + 4 bytes(TFTP header)+ 8 bytes of UDP + 20 bytes(IP)=532bytes ( size of IP datagram)

c) total size is 500+4 bytes(TFTP header)=504 bytes

d)Initial write request is

write request message size=

(write request(2 bytes))+file name (3 bytes)+1 byte(0)+mode(2 bytes)+1 byte(0)

=9 bytes

Acknowledgement message size is 2 bytes(ack)+ 2 bytes(sequence number)

= 4 bytes

actual data message =500 bytes + 2 bytes(sequence number)=502 bytes

overhead=515 bytes-500 bytes/500*100=3%

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