Transport Layer Review

A set of flashcards based on lecture notes covering key concepts of the transport layer, protocols, and data transfer principles.

What is the primary responsibility of the transport layer?

Creating logical communication between application processes running on different end systems.

What is the data unit used by the transport layer called?

Segment

Define logical communication in the context of the transport layer.

The illusion created by the transport layer that two application processes are directly connected, despite layers and routers separating them.

What protocol does the transport layer build reliable services on top of?

IP (Internet Protocol)

What is the primary function of UDP?

A fast, connectionless transport protocol that adds minimal error checking.

What does TCP stand for, and what is its purpose?

Transmission Control Protocol; it provides a reliable, in-order byte-stream delivery.

Define multiplexing in the context of the transport layer.

The sender's task of gathering data from multiple application sockets, encapsulating it with headers, and passing it to the network layer.

What is demultiplexing?

The receiver's task of delivering an incoming segment to the correct application socket by inspecting the header fields.

What is a port number?

A 16-bit number that identifies a specific application process running on a host.

What is the significance of a socket in network communication?

A software interface defined by the IP address and Port Number acting as an entry/exit point for data flow.

What does a UDP segment structure consist of?

An 8-byte header containing Source Port, Destination Port, Length, and Checksum.

What is the purpose of the UDP checksum?

Provides basic error detection but does not offer recovery from errors.

What does the Sequence Number in RDT protocols do?

Used to order packets and detect duplicates.

What does an Acknowledgment (ACK) packet signify?

It confirms the successful, error-free receipt of data.

What is the role of timers in reliable data transfer?

They signal when a presumed loss has occurred, triggering retransmission.

Describe the function of pipelining in RDT protocols.

Allows the sender to transmit multiple unacknowledged packets concurrently.

What happens in the Go-Back-N protocol?

The sender retransmits the lost packet and all subsequent packets that followed it.

How does the Selective Repeat protocol differ from Go-Back-N?

It retransmits only specific segments that are lost or timed out.

What is the purpose of the TCP three-way handshake?

To establish a connection and agree upon initial Sequence Numbers.

What does the TCP segment structure include?

A complex header containing Sequence Number, Acknowledgment Number, and various Flags.

What is the purpose of the congestion window (cwnd) in TCP?

It limits the amount of unacknowledged data the sender can inject into the network.

What does Slow Start refer to in TCP congestion control?

The initial phase where cwnd grows exponentially to quickly find a safe initial sending rate.

What does the term AIMD stand for and what does it signify?

Additive Increase, Multiplicative Decrease; it's the core control strategy for TCP's congestion management.

What role does QUIC play in modern transport protocols?

It runs over UDP and implements connection setup, reliability, and congestion control at the application layer.

What is BBR (Bottleneck Bandwidth & Round-trip propagation time?

An advanced congestion control algorithm that attempts to estimate congestion by measuring changes in RTT delay rather than relying solely on packet loss