TCP vs UDP

TCP (Transmission Control Protocol)
- Ensures reliable data transfer with error checking and retransmission.
- Guarantees ordered delivery of packets.
- Establishes a connection through a three-way handshake before data transfer.
- Commonly used for applications where reliability is crucial (e.g., web browsing, email).
UDP (User Datagram Protocol)
- Provides a faster but less reliable data transfer.
- No connection setup, and minimal error checking.
- Does not guarantee packet order or delivery.
- Suitable for applications where speed is essential and occasional data loss is acceptable (e.g., video streaming, online gaming).
  To summarize in a table,

Factor	TCP	UDP
Connection type	Requires an established connection before transmitting data	No connection is needed to start and end a data transfer
Data sequence	Can sequence data (send in a specific order)	Cannot sequence or arrange data
Data retransmission	Can retransmit data if packets fail to arrive	No data retransmitting. Lost data can’t be retrieved
Delivery	Delivery is guaranteed	Delivery is not guaranteed
Check for errors	Thorough error-checking guarantees data arrives in its intended state	Minimal error-checking covers the basics but may not prevent all errors
Broadcasting	Not supported	Supported
Speed	Slow, but complete data delivery	Fast, but at risk of incomplete data delivery

Connection Establishment (Three-way Handshake)
1. SYN: The client sends a SYN (synchronize) packet to the server, initiating the connection and specifying the initial sequence number.
2. SYN-ACK: The server responds with a SYN-ACK packet, acknowledging the client's SYN and providing its initial sequence number.
3. ACK: The client sends an ACK (acknowledgment) packet back to the server, completing the handshake and establishing the connection.
Data Transfer
- Once the connection is established, data can be sent between the client and server. TCP ensures data integrity through sequence numbers and acknowledgments.
Connection Termination
- To close the connection, a four-step process (FIN, FIN-ACK, ACK) is typically used, ensuring that both sides properly terminate the connection.

Flow Control: TCP uses flow control mechanisms like the sliding window protocol to manage the rate of data transmission between sender and receiver, preventing congestion.
Congestion Control: TCP also incorporates congestion control algorithms (e.g., slow start, congestion avoidance) to avoid network congestion.
UDP Use Cases: While UDP lacks the reliability of TCP, its low latency makes it ideal for real-time applications such as live broadcasts, and online gaming.
Security Considerations:
- TCP is more susceptible to certain types of attacks, such as SYN flooding, due to its connection-oriented nature.
- UDP can be more challenging to secure because it is connectionless and often used for broadcasting.

HTTP: Uses TCP as its underlying transport protocol.
- Relies on the reliable, ordered, and error-checked delivery of TCP.
- HTTP/1.1 introduced persistent connections, reducing the overhead of establishing a new TCP connection for each request.

HTTP/2: Also uses TCP but introduces significant improvements over HTTP/1.x.
- Multiplexing: Allows multiple requests and responses to be sent simultaneously over a single TCP connection, reducing latency.
- Header Compression: Compresses headers to reduce overhead and improve performance.
- Server Push: Enables servers to send resources to clients proactively, reducing load times.
- Binary Protocol: Uses a binary protocol instead of a text-based protocol, making parsing more efficient.

HTTP/3: Uses UDP instead of TCP, leveraging the QUIC (Quick UDP Internet Connections) protocol.
- QUIC: Developed by Google, QUIC aims to combine the reliability of TCP with the speed of UDP.
- Connection Establishment: Faster connection establishment compared to TCP's three-way handshake, improving latency.
- Multiplexing: Like HTTP/2, HTTP/3 supports multiplexing without the head-of-line blocking issue present in TCP.
- Improved Congestion Control: QUIC includes advanced congestion control mechanisms.
- Built-in Encryption: QUIC includes encryption by default, enhancing security.

Protocol	Transport Layer	Key Features
HTTP	TCP	Reliable, ordered, error-checked delivery. Persistent connections in HTTP/1.1.
HTTP/2	TCP	Multiplexing, header compression, server push, binary protocol.
HTTP/3	UDP (QUIC)	Faster connection establishment, multiplexing without head-of-line blocking, improved congestion control, built-in encryption.