The Internet Protocol Suite, better known as TCP/IP, is a set of communications rules that allow two or more network devices to communicate.
TCP: creates the link that allows the devices to connect and determines how data is packaged into smaller packets before being transmitted, and then reassembled after transfer.
IP: addresses and routes the packets of data to make sure they reach the right destination and device within the network.
Based on the “end-to-end” and “client/server” communication models, TCP/IP features are separated based on functions into layers where one program or device (the client) can request a service from another program or device (the server). Once the server has completed the request from the client, the connection is dissolved. This frees up network paths for more requests since they are all considered unique connections and can be used continuously.
TCP and IP use the four-layer model that separates the protocols based on their functions.
Application Layer: standardizes the communication for data exchange between programs or devices and uses ports to pass data along to the transport layer. Protocols include: FTP, HTTP, IMAP, SMTP, SSH
Transport Layer: creates and delivers the data packets passed on from the application layer to the appropriate host devices by adding source and destination port numbers and maintaining the end-to-end network connections.
Protocols include: TCP, UDP DCCP, SCTP
Internet Layer: takes the network packets from the transport layer and sends them to the proper destinations based on their IP addresses.
Protocols include: IP, ICMP
Link Layer: separate from the other layers, this layer describes protocols that exist only through one link that a host is connected to.
Protocols include: Ethernet, DSL
Why is this important for FTP?
When an FTP client requests to connect to an FTP server, a TCP connection is being established using the application layer within TCP and ports 20 and 21. FTP uses and relies on TCP to ensure all the packets of data are sent correctly and to the proper destination.