TCP Specification


A fundamental notion in the design is that every octet of data sent over a TCP connection has a sequence number.

Since every octet is sequenced, each of them can be
acknowledged.

The acknowledgment mechanism employed is cumulative so that an acknowledgment of sequence number X indicates that all octets up to but not including X have been received.

This mechanism allows for straight-forward duplicate detection in the presence of retransmission.

Numbering of octets within a segment is that the first data octet immediately following  the header is the lowest numbered, and the following octets are numbered consecutively.