GATE CS 2018 Q.23 (CS Q.13): OSI/TCP-IP Layering, Physical Layer and Switching

Match the following:

Field	Length in bits
P. UDP Header’s Port Number	I. 48
Q. Ethernet MAC Address	II. 8
R. IPv6 Next Header	III. 32
S. TCP Header’s Sequence Number	IV. 16

P-III, Q-IV, R-II, S-I

P-II, Q-I, R-IV, S-III

P-IV, Q-I, R-II, S-III

P-IV, Q-I, R-III, S-II

Official answer and solution

Solution

Recall standard networking protocol header specifications for each listed field.

Evaluate the bit length of each field:

P. UDP Header's Port Number: Both source and destination port numbers in UDP (and TCP) are 16 bits long $\implies$ IV.
Q. Ethernet MAC Address: Standard IEEE 802.3 MAC addresses are 6 bytes = 48 bits long $\implies$ I.
R. IPv6 Next Header: Identifies the type of header immediately following the IPv6 header; it is an 8-bit field (equivalent to IPv4's Protocol field) $\implies$ II.
S. TCP Header's Sequence Number: Tracks byte sequencing in the byte stream and is 32 bits long $\implies$ III.

This matches P-IV, Q-I, R-II, S-III, which corresponds to option C.

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

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