What is Maximum Segment Size?

Maximum segment size has to do with defining the largest amount of data that a computer system or other type of communications device can efficiently deal with without breaking the data into smaller components. Generally, the maximum segment size is calculated as the number of bytes that the device can handle at one time. Maximum segment size has a lot to do with the speed that web pages will load into a browser, as well as how quickly other online functions, such as connections and updates to online databases, can take place.

Referred to simply as MSS in most cases, maximum segment size plays a huge role in the speed and efficiency of web browsing. Whenever the connection is established between the end user and the Internet service provider, both the provider and the communications device at the end user level must mutually establish an acceptable speed of operation and the transference of data. This action is based on the capability of the systems at both ends of the connection. The process of evaluating and agreeing upon this rate of transfer is known as setting the MTU size.

The establishment of the MTU size is essential to determining the maximum segment size. Typically, a computer residing in a home environment and making use of a dial up connection would generate an MTU size of 1500 bytes or less. Headers generally are around 40 bytes long. By subtracting the header size from the MTU size, it is possible to determine the maximum segment size.

Assuming that the maximum segment size is sufficient to allow all segments of data to be transferred without fragmenting the segments, the web page is likely to fulfill relatively quickly. However, if the data segment is too large for the maximum segment size established between the ISP and the end user’s computer, then the segment will have to be broken down into smaller fragments that will pass through the routing process. The end result is that the web page will fulfill at a noticeably slower rate.