Maximum Segment Size

What Does Maximum Segment Size Mean?

Maximum Segment Size (MSS) refers to the ceiling, or largest data segment, accommodated as an unfragmented piece by a computer or communications device.


The MSS does not include the size of the TCP and IP headers in computation. However, to achieve optimum communication, the number of bytes and headers are combined but must not exceed the number of bytes specified in the Maximum Transmission Unit (MTU). A lower MSS ensures that fragmentation is not present during the process, even though there is a decrease in data and header ration.

Techopedia Explains Maximum Segment Size

The MSS is typically established by the operating system (OS) when a TCP handshake occurs in a SYN packet. Each data flow direction may use a different MSS. The MSS is an important Internet connection component, especially when using a Web browser. When TCP is used in an Internet connection, the connected computers must establish a specific MTU size agreeable to all connected parties.

Internet data goes through several gateway routers. Data segments must pass through all of these routers without becoming fragmented. If the data is too large, the oversized segment is broken into smaller fragments, resulting in decreased Internet speed, which may be noticeable to users. However, this cannot be avoided if the gateway routers on the path set a smaller MTU size, or if the user’s computer has set a larger MSS value.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.