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A TCP segment consists of a segment "header" and a "data" section. The segment header contains 10 mandatory fields, and an optional extension field ("Options", pink background in table). The data section follows the header and is the payload data carried for the application. The length of the data section is not specified in the segment header; It can be calculated by subtracting the combined length of the segment header and IP header from the total IP datagram length specified in the IP header.