3.8 Evolution of Transport Layer Functionality

Overview of Transport Layer Evolution

• TCP and UDP protocols have been in use for over 40 years.

• Proven to support a wide range of applications (email, FTP, web, streaming, VoIP, gaming).

Future Directions

• Specialization of TCP has led to multiple flavors for specific scenarios.

• Dominant TCP flavors continue to be the main choices despite recent developments.

Application Layer Services

• Real-time services and security are lacking in traditional transport layer protocols.

• These features are primarily added at the application layer (e.g., application layer protocols, CDNs).

Transition to HTTP/3 and QUIC

• HTTP/3 runs over UDP, introduces transport layer capabilities at the application layer.

• QUIC (Quick UDP Internet Connections) is a critical development for HTTP/3.

• QUIC is designed to enhance connection setup, reliability, and multiplexing features.

Connection Establishment in QUIC

• QUIC uses a single RTT for handshake compared to TCP’s two RTTs (for connection + security setup).

• Reliability, congestion control, and security states are established in one handshake.

Multiplexing in QUIC

• Multiple application streams can operate concurrently over a single QUIC connection.

• Unlike traditional HTTP, where requests are serial, QUIC allows concurrent retrieval of multiple objects.

• This reduces head-of-line blocking issues present in TCP, improving efficiency.