Transport Layer Overview: Services and Protocols

Questions and Answers

What happens to delay as upstream capacity approaches R/2?

Delay decreases moderately

Delay remains constant

Delay decreases significantly

Delay increases (correct)

Which of the following causes a decrease in effective throughput?

Optimal link utilization

Increased transmission capacity

Low latency transmission

Packet duplication (correct)

What does the end-to-end congestion control approach primarily rely on?

Observed loss and delay (correct)

User-configured congestion policies

Automatic rate adjustment

Explicit feedback from routers

What is the role of the ECE bit in TCP?

To indicate congestion to the sender Signup and view all the answers

Under idealized assumptions, how should TCP sessions share bandwidth at a bottleneck of R?

Equally at R/K Signup and view all the answers

What happens to TCP throughput during a loss event?

It decreases by a factor of 2 Signup and view all the answers

What is the primary reason multimedia applications often use UDP instead of TCP?

Rate throttling is undesirable Signup and view all the answers

What is the function of explicit congestion notification (ECN) in TCP?

To indicate congestion to hosts through marked IP headers Signup and view all the answers

What does TCP fairness aim to achieve among K TCP sessions sharing a bottleneck link?

Average rate of R/K for each session Signup and view all the answers

How does application behavior impact TCP connections?

Multiple connections can lead to unequal bandwidth share Signup and view all the answers

Study Notes

Transport Layer Overview

Provides logical communication between application processes on different hosts.
Key transport protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Transport-layer Services

Enables communication between application processes through segmentation.
Sender breaks messages into segments and passes them to the network layer.
Receiver reassembles segments into messages for the application layer.

Multiplexing and Demultiplexing

Multiplexing at sender: combines data from multiple sockets, adding transport headers.
Demultiplexing at receiver: uses header info to deliver segments to the correct application socket.
Utilizes source and destination port numbers for correct data routing.

Connectionless Transport: UDP

Connectorless, unreliable, and unordered delivery method.
No guarantee for delivery, order, or connection establishment.
Designed for applications sensitive to speed and can tolerate data loss (e.g., streaming).
Usage in services like DNS, SNMP, and HTTP/3.

Connection-Oriented Transport: TCP

Reliable, in-order delivery using acknowledgments and sequence numbers.
Connection setup requires a handshake to initiate communication.
Implements flow control to prevent overwhelming the receiver.
Supports full duplex data flow and guarantees delivery.

Congestion Control Principles

Distinct from flow control, focusing on managing data rate from multiple senders.
Congestion leads to long delays and packet loss due to overloaded router buffers.
Techniques involve end-to-end feedback mechanisms and explicit congestion notification (ECN) from routers.

TCP Flow Control Management

Utilizes a receiver window to manage how much data can be sent before receiving an acknowledgment.
Adjusts transmission rates based on the receiver's ability to process incoming data without overflowing buffers.

TCP Connection Management

State management through connections: uses three-way handshake to establish state before data exchange.
Closing connections requires each party to send a FIN segment followed by an ACK.

TCP Sequence and Acknowledgment Management

Sequence numbers help track byte streams, allowing orderly and reliable data transfer.
Acknowledgments confirm receipt of data, and cumulative acknowledgments indicate the next byte expected.

TCP Retransmission Strategies

Handles lost data segments via timeouts or duplicate acknowledgments to ensure reliability.
Fast retransmit protocol responds to three duplicate ACKs, indicating potential lost segments.

Congestion Control Techniques

Employs a mixture of network-assisted and end-to-end approaches with an emphasis on fairness among multiple TCP sessions sharing bandwidth.
Fairness seeks to equate bandwidth usage among multiple sessions across network resources.

Evolution of Transport Layer Functionality

Ongoing adaptation to application requirements and network conditions.
Emphasis on enhancing congestion control mechanisms and reliability protocols to suit modern Internet demands.

Description

Explore the transport layer's key concepts including services, multiplexing, and protocols like TCP and UDP. This quiz covers principles of reliable data transfer, congestion control, and the evolution of transport-layer functionality in various network settings. Test your understanding of how these protocols enable communication between diverse application processes.