The top layer at which human interacts with several applications.
Some Application layer Protocols are
DNS: resolves the website name into server ip, TCP/UDP Port 53
http: transfer webpage files, TCP Port 80
SMTP: sends mail from application to MUA like outlook express, TCP Port 25
POP: receives mail to outlook express, UDP Port 110
These protocols works on two processes
MTA: sends mail to another server
MDA: sends mail to host
Telnet: connect to remote device, TCP Port 23
FTP: shares file, TCP port 20, 21 (21 connects to remote device, 20 sends data)
DHCP: dynamically get ip from a pool from an ISP.
SMB: file sharing protocol, for linux it’s samba
P2P: works on gnutella protocol to share files
It codes, compresses, and encrypt the application layer data
Initiate, maintain and terminates session between two hosts.