Overview
This lecture introduces the transport layer in Internet architecture, focusing on its principles, key protocols (UDP and TCP), and its distinction from the network layer.
Introduction to the Transport Layer
- The transport layer manages communication between processes over unreliable or lossy channels.
- Key challenges include ensuring reliable communication, handling message corruption or loss, and adjusting communication rates.
Transport Layer Principles
- Main principles: multiplexing/demultiplexing, reliable data transfer, flow control, and congestion control.
- Transport services are implemented with these principles in mind for effective communication.
Logical Communication & Layer Distinctions
- Logical communication refers to the abstraction that processes on different hosts are directly connected.
- The network layer delivers messages between hosts; the transport layer delivers messages between processes within those hosts.
- Analogy: the network layer is like a postal service; the transport layer is like distributing letters to the correct recipient in a house.
Transport Layer Actions
- Sender side: Application creates message → transport layer creates segment with headers → passes to network layer (IP).
- Receiver side: Transport layer receives segment from network layer → checks headers (e.g., for corruption) → delivers message to the correct application process.
Internet Transport Protocols: UDP and TCP
- TCP (Transmission Control Protocol): provides reliable, in-order delivery, congestion control, flow control, and requires connection setup and state at both ends.
- UDP (User Datagram Protocol): provides unreliable, best-effort delivery without guarantees on order or reliability and minimal setup.
- Internet transport protocols do not guarantee delivery time or bandwidth between sender/receiver.
Key Terms & Definitions
- Transport Layer — Layer responsible for process-to-process communication over a network.
- Multiplexing/Demultiplexing — Combining multiple messages into a single stream or directing incoming messages to the correct process.
- Reliable Data Transfer — Ensuring messages reach the destination uncorrupted and in order.
- Flow Control — Regulating data transmission rate between sender and receiver to avoid overwhelming the receiver.
- Congestion Control — Adjusting data flow to prevent overloading the network.
- TCP — Connection-oriented, reliable, congestion-controlled transport protocol.
- UDP — Connectionless, unreliable, best-effort transport protocol.
Action Items / Next Steps
- Review principles of multiplexing, reliable data transfer, flow, and congestion control.
- Prepare for deeper exploration of TCP and UDP in upcoming lessons.