Suggest an editImprove this articleRefine the answer for “Which protocols belong to the application layer?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**Application layer** protocols are the ones **used directly by applications** to work over the network: browsers, email clients, messengers, APIs, and so on. **Key point:** if a protocol is needed by a program rather than by the network's internal plumbing, it belongs to the application layer.Shown above the full answer for quick recall.Answer (EN)Image**Application layer** protocols are the ones **used directly by applications** to work over the network: browsers, email clients, messengers, APIs, and so on. In simpler terms: **if a protocol is needed by a program rather than by the network's internal plumbing, it is application layer**. --- ## Main application layer protocols ### Web and APIs - **HTTP** - transferring web pages and API requests - **HTTPS** - the same, but encrypted - **WebSocket** - a persistent bidirectional connection (chats, online games) --- ### Email - **SMTP** - sending mail - **POP3** - receiving mail (downloads it, then deletes it from the server) - **IMAP** - receiving mail while keeping messages stored on the server --- ### File transfer - **FTP** - file transfer (unencrypted) - **FTPS** - FTP with encryption - **SFTP** - file transfer over SSH - **TFTP** - simplified file transfer (often used for network equipment) --- ### Utility network services - **DNS** - converts a domain name into an IP address - **DHCP** - automatically hands out IP addresses to devices - **NTP** - time synchronization --- ### Remote access and management - **SSH** - secure remote access to a server - **Telnet** - remote access without encryption (obsolete) - **SNMP** - monitoring and managing network devices --- ## An important point for interviews **An application layer protocol is not the same thing as a program** Examples: - a browser uses HTTP / HTTPS - an email client uses SMTP, IMAP, POP3 - `ping` is a **utility**, and ICMP **is not an application layer protocol**For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.