Layer 4 is transport layer provides transportation of variable length data from any point to any other point. relies upon sending packets from any device to any other device builds abstratctoins that are useful to applications on tpo of layer 3 packets reliability: transmits data reliably, in order ports: provides multiple “addresses” per real IP address.
tcp: provides reliability and ports udp: provides ports, no reliability, faster performance
application layer: provides applications and services to users relies upon: transportation of variable length data from any point to any other point every online app is layer 7 web browsing online video games messaging services video calls
http request
http tcp ip ethernet wires
protocols application | web security secure transport | tls transport | tcp udp internet | ip link | arp physical | wpa
tcp: reliably send packets
reliability ensures that packets are received correctly ip is unreliable and only provides a best effort delivery service, which means packets may be lost packets may be corrupted packets may be delivered out of order