Numerous web protocols are used for communication, data exchange, and service interaction on the Internet. Below is an overview of the most commonly used web protocols, categorized by their primary purpose.

1. Transfer Protocols (Data Transfer)

• HTTP (Hypertext Transfer Protocol): The fundamental protocol for transferring web pages and other resources over the web.
  • Versions: HTTP/1.1, HTTP/2, and HTTP/3.
• HTTPS (HTTP Secure): An extension of HTTP that uses encryption (SSL/TLS) to secure communication.
• FTP (File Transfer Protocol): Used for transferring files between a client and a server over the internet.
• SFTP (Secure File Transfer Protocol): A secure version of FTP using SSH for encryption.
• TFTP (Trivial File Transfer Protocol): A simplified, lightweight version of FTP for transferring smaller amounts of data, typically in LAN environments.
• WebSocket: A protocol providing full-duplex communication channels over a single TCP connection, used for real-time web applications (e.g., chat, live updates).
• gRPC: A high-performance remote procedure call (RPC) framework that uses HTTP/2 for transport and Protocol Buffers for message serialization.

2. Email and Messaging Protocols

• SMTP (Simple Mail Transfer Protocol): Used for sending emails across the internet.
• IMAP (Internet Message Access Protocol): Allows clients to access and manipulate their email messages on a server in real time.
• POP3 (Post Office Protocol version 3): A protocol used to retrieve email from a mail server.
• XMPP (Extensible Messaging and Presence Protocol): Used for instant messaging, presence information, and real-time communication.
• MQTT (Message Queuing Telemetry Transport): A lightweight messaging protocol used in IoT (Internet of Things) for low-bandwidth, high-latency environments.
• AMQP (Advanced Message Queuing Protocol): A protocol for messaging middleware designed for reliability and interoperability in messaging systems.

3. Security Protocols

• SSL (Secure Sockets Layer) / TLS (Transport Layer Security): Protocols that encrypt data to secure communication over the internet (e.g., HTTPS).
• SSH (Secure Shell): Used to securely access and manage devices over a network.
• IPsec (Internet Protocol Security): A suite of protocols for securing Internet protocol (IP) communications through encryption and authentication.
• OAuth: An open standard for access delegation, often used as a way for internet users to grant websites access to their information without sharing passwords.
• OpenID Connect (OIDC): An identity layer built on top of OAuth 2.0 to authenticate users.

4. Service Protocols

• SOAP (Simple Object Access Protocol): A protocol for exchanging structured information in web services (typically XML-based).
• REST (Representational State Transfer): A style of web services typically using HTTP for communication, often in JSON or XML formats.
• XML-RPC (Remote Procedure Call): A protocol that allows data to be encoded in XML and transported via HTTP to invoke functions remotely.
• DNS (Domain Name System): Resolves domain names to IP addresses, acting as the internet's "phone book."

5. File Sharing and Peer-to-Peer (P2P) Protocols

• BitTorrent: A protocol for peer-to-peer file sharing that distributes data across multiple users.
• Gnutella: Another peer-to-peer protocol for decentralized file sharing.

6. Network and Communication Protocols

• TCP (Transmission Control Protocol): Ensures reliable, ordered, and error-checked delivery of data between applications.
• UDP (User Datagram Protocol): A simpler, connectionless alternative to TCP, used when speed is more important than reliability (e.g., live streaming, gaming).
• IP (Internet Protocol): The protocol responsible for addressing and routing packets between devices on a network.
• ICMP (Internet Control Message Protocol): Used for network diagnostics, including error messages like those generated by the ping command.

7. Real-Time Communication Protocols

• RTP (Real-Time Transport Protocol): Used for delivering audio and video over IP networks.
• RTSP (Real-Time Streaming Protocol): A protocol for controlling streaming media servers.
• SIP (Session Initiation Protocol): Used for initiating, maintaining, and terminating real-time sessions involving video, voice, messaging, and other communications.
• SRTP (Secure Real-Time Transport Protocol): Provides encryption, message authentication, and integrity for RTP streams.

8. IoT and Specialized Communication Protocols

• CoAP (Constrained Application Protocol): A specialized web transfer protocol designed for IoT devices that allows for simple interaction between devices with limited processing power.
• Zigbee: A wireless communication protocol designed for low-power devices in mesh networks, often used in home automation and IoT.
• Z-Wave: Another wireless protocol designed for smart homes and IoT devices.

9. Database Communication Protocols

• ODBC (Open Database Connectivity): A standard API for accessing database management systems (DBMS).
• JDBC (Java Database Connectivity): A Java API for connecting and executing queries on a database.
• LDAP (Lightweight Directory Access Protocol): Used to access and maintain distributed directory information services, such as Microsoft Active Directory.

How Many Web Protocols Are There?

It is difficult to provide a definitive number, as there are dozens to hundreds of web protocols depending on the level of specificity and application domains considered. Each serves specific purposes, and new protocols emerge to address evolving technological needs (e.g., WebAssembly, QUIC, and HTTP/3).