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In this lesson, we're going to discuss

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the transmission control protocol.

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Now, the transmission control protocol or TCP,

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is a fundamental protocol within the internet protocol suite

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that consists of a set of rules

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that govern the exchange of data over the internet.

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The transmission control protocol is widely used

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due to its reliability in delivering packets of data

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across the network because it can ensure

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that all the data packets reach their intended destination,

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in the correct order and without corruption.

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Now, this is achieved through a process of error checking,

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data sequencing, and acknowledgement.

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TCP operates it through the transport layer of the OSI model

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which conceptualizes and standardizes the functions

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of a telecommunication or computing system

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into seven abstraction layers.

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At its core, TCP is responsible

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for ensuring the reliable transmission of data

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between a client and a server,

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by breaking down larger messages into smaller packets,

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setting them over the network,

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and reassembling them at the destination.

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This packetization makes the data transfer

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more efficient and more manageable.

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Now, when you think of TCP,

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you should immediately think of the three-way handshake

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that's going to be used to establish a connection

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between two different systems.

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This handshaking process will involve three steps,

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the SYN, or synchronize step,

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the SYN-ACK, or synchronize-acknowledge step,

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and the ACK or acknowledge step.

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Initially, the client is going to send a SYN packet

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to the server to initiate a communication session.

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Then, the server will respond back with a SYN-ACK packet

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to acknowledge receipt of the SYN packet,

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and to inform the client that the server is willing

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and able to establish a session.

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Finally, the client will send an ACK packet

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back to the server to confirm

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the establishment of that connection.

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This three-way handshaking process

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will ensure that both the sender and the receiver

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are ready for data transmission,

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and that the communication channel is reliable and secure.

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Another important feature of TCP,

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is its error checking and flow control mechanisms,

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that ensure the reliable deliverability

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of the data being transmitted,

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using the transmission control protocol.

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TCP will use a sequence number and acknowledgement messages

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to ensure the data is being received correctly

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and in the proper order.

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If a packet is lost or corrupted,

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the protocol will notice that,

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and it will require for it to be retransmitted

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by the sender.

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TCP also employs flow control to prevent the center

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from overwhelming the receiver with too much data at once.

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This flow control is achieved

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through a mechanism called, windowing.

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Windowing occurs by allowing the receiver

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to specify the amount of data it can handle at one time.

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And during the communication session,

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this window can continually be widened or narrowed,

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to allow more or less data to be sent

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during each transmission,

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based on the current network conditions

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being experienced by that client.

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When sending data over the network,

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the transmission control protocol will use ports

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as part of its communication process.

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Now, a port is a numerical identifier

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inside of the TCP/IP suite,

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and other networking protocols

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that helps distinguish between different services

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or applications running on the same physical computer.

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Each TCP connection is going to be identified

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by a pair of endpoint addresses,

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each consisting of an IP address and a port number.

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We call these, the source and destination IPs,

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and the source and destination ports.

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For example, when you access a secure website,

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your web browser will establish a TCP connection

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with the server over Port 443,

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which is a standard port for HTTPS,

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known as the Hyper Text Transfer Protocol Secure,

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and this traffic will then use SSL or TLS

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to encrypt any data being sent over this particular port.

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Now, ports are important in the communication process,

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because these ports allow for multiple network applications

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to coexist on the same physical server,

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while each application or service

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gets aside a unique port number to identify its function.

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So remember, the transmission control protocol

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is at the heart of internet communication

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by ensuring the reliability and order delivery

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of data between a client and a server.

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It's really important that you remember

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that TCP operates at the transport layer of the OSI model,

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and it uses a process of packetization,

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acknowledgement, and error checking,

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to ensure data integrity.

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The three-way handshake here

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is going to be crucial for establishing the connection,

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and TCP will use ports to allow

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for the logical differentiation of services

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on a single physical machine.