3.8 Evolution of Transport-layer Functionality

Future of Transport Layer Functionality

Overview of TCP and UDP Evolution

• The TCP and UDP protocols have been in use for over 40 years, demonstrating a simple yet sufficient set of services for various applications.

• These protocols support a wide range of applications, from early internet uses like email and FTP to modern services such as web streaming and gaming.

Development of TCP Variants

• Numerous specialized flavors of TCP have emerged over the past two decades, although traditional TCP remains dominant in deployments.

• The transport layer lacks support for real-time services or security, which are typically addressed at the application layer through specific protocols.

Introduction to HTTP/3 and QUIC

• HTTP has traditionally run over TCP; however, HTTP/3 is shifting towards utilizing transport layer capabilities directly at the application level via UDP.

• QUIC (Quick UDP Internet Connections) is an emerging application layer protocol designed to operate beneath HTTP and leverage UDP's advantages.

Technical Insights on QUIC

• QUIC incorporates reliability, congestion control, and connection management techniques similar to those found in TCP.

• Familiarity with TCP’s lost detection and congestion control will aid understanding QUIC's algorithms as they parallel established methods.

Connection Establishment in QUIC

• QUIC establishes connections using a handshake protocol that sets up sender-receiver states for reliability, congestion control, and security.

• Unlike traditional HTTP requiring two round-trip times (RTTs), QUIC achieves this setup in just one RTT by combining all necessary states into a single handshake.

Multiplexing Streams with QUIC

• QUIC allows multiple application-level streams to be multiplexed over one connection, enhancing efficiency compared to traditional HTTP where objects are retrieved serially.

• Each stream maintains its own reliability and security while being managed under a common congestion control protocol akin to that used by TCP.

Advantages Over Traditional Protocols

• In scenarios where errors occur during object retrieval (e.g., second object fails), traditional HTTP stalls subsequent requests until resolution occurs.