What does MSS stand for in TCP, and what is its primary purpose?

• A. Maximum Segment Size; it limits the payload per segment to avoid IP fragmentation and optimize transmission efficiency
• B. Maximum Service Size; it defines the maximum service payload for TCP processing
• C. Minimum Segment Size; it sets the smallest allowed TCP segment
• D. Message Segments Size; it controls how messages are segmented for TCP

Answer: (A)

The main idea tested here is understanding what MSS means in TCP and why it matters. MSS stands for Maximum Segment Size, and its primary purpose is to cap how much TCP data can be carried in a single segment. This value represents just the payload size of the TCP segment, meaning it does not include the IP or TCP headers.

During the TCP handshake, the two ends negotiate an MSS using the MSS option in the SYN packets. The chosen MSS is typically derived from the path MTU (maximum transmission unit) minus the header overhead, so segments stay within what the network path can carry without fragmentation. For example, on a common Ethernet network with a 1500-byte MTU, the typical MSS is about 1460 bytes. Keeping segments within this limit helps avoid IP fragmentation, which can degrade performance and reliability because fragmented packets are more likely to be dropped or reordered.

Keep in mind that MSS is not the same as MTU. MTU is the maximum size of an entire IP packet on a link, including headers, whereas MSS is specifically the maximum TCP data payload that a segment can carry. The other options don’t match TCP terminology: there isn’t a service size, minimum segment size, or message segment size in standard TCP usage.