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A TCP segment consists of a segment header and a data section.

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The TCP header contains ten mandatory fields and an optional extension field.

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The optional field is the options field, which is the last field seen on the slide.

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The TCP header includes a source port and destination port.

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Each 16 bits in length.

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The source port is the port on the originating machine that emitted the packet.

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The destination port indicates the port on the target machine the packet should be delivered to.

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The sequence number and an acknowledgement number allows TCP to track a series of packets to make sure

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they arrive reliably and pretty much in order.

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No, absolutely in order.

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If a packet is lost, TCP will retransmit it.

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If packets arrive out of order.

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TCP will adjust them to make sure that they are delivered to the destination services in the proper

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order.

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Data offset specifies the size of the TCP header in 32 bit words.

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The minimum size header is five words and the maximum is 15 words.

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There is also TCP control bit space, also known as flags, which are incredibly important for tracking

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the state of a given TCP connection.

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As you know, we've talked about them a few minutes ago.

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Of course, if you didn't take a break, it was a few minutes ago, but whatever you do, just don't

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spill on the keyboard.

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Now, TCP senders use a number called window size, which is in bytes by default.

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To regulate how much data they send to a receiver before requiring an acknowledgement in return.

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So if the window size becomes too small, network data transfer will be unnecessarily slow.

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While if the window size becomes too large, the network link can become saturated or the receiver may

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not be able to process incoming data quickly enough, also resulting in slow performance.

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When doing algorithms built into the protocol, dynamically calculate size values and use this field

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of the TCP headers to coordinate changes between senders and receivers.