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Suppose an application layer entity wants to send an L-byte message to its
peer process, using an existing TCP connection. The TCP segment consists
of the message plus 20 bytes of header. The segment is encapsulated into
an IP packet that has an additional 20 bytes of header and trailer. What
percentage of the transmitted bits in the physical layer correspond to message
information, if L = 100 bytes, 500 bytes, 1000 bytes ?
(A) 67%, 89%, 94% (B) 63%, 90%, 95%
(C) 63%, 94%, 89% (D) 56%, 95%, 90%

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ANS is Option B

TCP/IP over Ethernet allows data frames with a payload size up to 1460 bytes.

Therefore, L = 100, 500 and 1000 bytes are within this limit.

The message overhead includes: •

TCP: 20 bytes of header •

IP: 20 bytes of header •

Ethernet: total 18 bytes of header and trailer.

Therefore L = 100 bytes, 100/158 = 63% efficiency.

L = 500 bytes, 500/558 = 90% efficiency.

L = 1000 bytes, 1000/1058 = 95% efficiency.

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