Networking Protocols and Congestion Control: BBR, QUIC, Fairness, and TCP Dynamics

What is the purpose of BBR in networking?

BBR estimates the bandwidth-delay product (BDP) to set its sending rate instead of waiting for losses.

What does BDP stand for?

Bandwidth-Delay Product

How is BDP calculated?

BDP = bandwidth × propagation delay

What is a notable trait of BBR?

BBR completely ignores losses, which can lead to excessive retransmissions.

What is fairness in a networking context?

Fairness means each TCP connection sharing a bottleneck link should get an equal share of the bandwidth, ideally around R/K bps.

What is Jain's fairness index?

A value calculated to measure fairness among TCP connections sharing bandwidth.

Why is TCP Reno considered unfair to TCP Vegas?

TCP Reno is fair to itself but does not account for the different behaviors of other congestion control algorithms like TCP Vegas.

What is max-min fairness?

A flow can increase its rate as long as it does not decrease the throughput of any other flow.

Which flow obtains more bandwidth in TCP Reno, one with higher or lower RTT?

The flow with the lower RTT obtains more bandwidth because its congestion window (cwnd) is updated more frequently.

What happens to the cwnd in TCP after a loss event?

Both connections cut their cwnd in half after a loss event.

What is QUIC?

QUIC (Quick UDP Internet Connections) is an application-layer protocol that uses UDP for transport while implementing reliable data transfer and congestion control.

What are the benefits of using QUIC?

Application designers have more control and can implement faster update schedules than traditional transport-layer protocols.

What is a drawback of QUIC?

There is more potential for bugs due to its complexity compared to established protocols.

How does QUIC ensure secure connections?

QUIC is inherently secure as all packets are encrypted, unlike TCP which requires a separate TLS connection.

What is the difference between TCP and QUIC in terms of connection handling?

Both are connection-oriented, but QUIC allows multiple application-layer streams within a single connection.

What is the impact of multiple TCP connections from a single application on bandwidth allocation?

It can result in unfair allocation of bandwidth among applications sharing a bottleneck link.

What is the role of application-layer streams in QUIC?

Each stream in QUIC can transfer data independently, allowing for reliable in-order delivery without affecting other streams.

What congestion control algorithms does QUIC use?

QUIC uses similar congestion control algorithms to TCP, including NewReno and QUIC BBR.

What are the main features of QUIC?

QUIC is connection-oriented, secure, supports multiple application-layer streams, and provides reliable data transfer and congestion control.

What is the significance of the exam date mentioned in the notes?

The exam is scheduled for Monday, November 10, which is the last day of new content before the exam.

What is the purpose of the problem set mentioned in the notes?

Problem Set #2 is assigned to reinforce learning and is due on Monday, November 10 at 9:30.