Layer 7 Protocols
Application Layer Protocols
Introduction to Layer 7 Protocols
1. HTTP (Hypertext Transfer Protocol)
The most widely used protocol on the web for request-response communication. Pattern: Synchronous request/response Transport: TCP Stateless: Yes Use Cases: Web APIs (REST), websites, microservices communication Protocols on top: REST, GraphQL, gRPC (over HTTP/2)2. WebSocket
A full-duplex communication protocol over a single, long-lived TCP connection. Pattern: Bidirectional streaming Transport: TCP (via HTTP handshake) Stateful: Yes Use Cases: Real-time apps like chat, gaming, live dashboards Compared to HTTP: Persistent and allows server push3. gRPC
A high-performance RPC framework using HTTP/2 and Protocol Buffers. Pattern: Client-server, supports streaming and unary calls Transport: HTTP/2 Efficient: Binary data (Protobuf) Use Cases: Internal service communication, mobile/backend APIs4. MQTT (Message Queuing Telemetry Transport)
A lightweight Pub/Sub protocol optimized for unreliable or low-bandwidth networks. Pattern: Publish-Subscribe Transport: TCP/IP Features: QoS levels, retained messages, last will Use Cases: IoT devices, telemetry, sensors5. AMQP (Advanced Message Queuing Protocol)
A binary, application-layer protocol for message-oriented middleware. Pattern: Supports both Point-to-Point and Pub/Sub Transport: TCP Features: Queues, topics, routing, transactions Used By: RabbitMQ, Apache Qpid6. SMTP (Simple Mail Transfer Protocol)
Protocol for sending email between servers. Pattern: Push (store-and-forward) Transport: TCP (port 25/587) Use Cases: Email services7. XMPP (Extensible Messaging and Presence Protocol)
An XML-based messaging protocol. Pattern: Publish-Subscribe, Chat Transport: TCP Use Cases: Instant messaging, presence systems (e.g., Jabber)Summary
| Protocol | Pattern | Transport | Default Port | Common Use Case |
|---|---|---|---|---|
| HTTP | Request/Response | TCP | 80/443 | Web, APIs |
| WebSocket | Full-duplex | TCP | 80/443 | Real-time apps |
| SMTP | Push | TCP | 25/587 | Sending email |
| IMAP | Pull | TCP | 143/993 | Reading email |
| POP3 | Pull (delete local) | TCP | 110/995 | Reading email |
| SSH | Remote shell | TCP | 22 | Secure remote access |
| FTP | File Transfer | TCP | 21 | File uploads/downloads |
| DNS | Lookup | UDP/TCP | 53 | Domain resolution |
| SNMP | Monitoring | UDP | 161 | Network management |
| Telnet | Remote shell | TCP | 23 | Legacy access |
| gRPC | RPC | HTTP/2 | 50051 | Microservices, APIs |
| MQTT | Pub/Sub | TCP | 1883/8883 | IoT messaging |
| AMQP | P2P + Pub/Sub | TCP | 5672/5671 | Enterprise messaging |
| XMPP | Messaging + Pub/Sub | TCP | 5222 | Chat systems |
| CoAP | REST + Pub/Sub | UDP | 5683 | Lightweight IoT |