TFRC Transmission Control Protocol friendly rate control

TFRC (Transmission Control Protocol Friendly Rate Control) is a congestion control algorithm designed for real-time multimedia applications that use UDP (User Datagram Protocol) for data transmission over IP networks. TFRC aims to achieve congestion control similar to that of TCP (Transmission Control Protocol) while providing a predictable and fair sharing of network resources.

Here is a detailed explanation of TFRC and its functioning:

1. Congestion Control: Congestion control is a mechanism used in computer networks to regulate the flow of data in order to prevent network congestion, which can degrade the performance of applications and lead to packet loss. TCP is a widely used protocol that employs congestion control algorithms, but its mechanisms are not suitable for real-time multimedia applications that typically use UDP for lower latency.
2. TCP Friendliness: TFRC is designed to be TCP-friendly, meaning it strives to achieve similar congestion control behavior as TCP. It aims to fairly share network bandwidth with TCP flows, ensuring that TCP traffic does not suffer due to TFRC flows and vice versa.
3. Rate Control: TFRC regulates the sending rate of data based on feedback received from the network. It adjusts the sending rate to achieve a target throughput without causing excessive congestion. Unlike TCP, which uses packet loss as a signal of congestion, TFRC estimates congestion levels based on round-trip time (RTT) variations.
4. Packet Loss-Based Feedback: TFRC uses receiver-based feedback to estimate congestion levels. The receiver periodically sends explicit feedback packets to the sender, including information about received packets and feedback on congestion levels. This feedback allows the sender to adjust its sending rate accordingly.
5. Equation-Based Control: TFRC employs an equation-based control mechanism to compute the sending rate. It uses the estimated RTT variations and loss event rate to calculate the appropriate sending rate that balances throughput and network congestion. The equation accounts for both the current and previous RTT variations to provide a smooth response to network conditions.
6. TCP-Like Behavior: TFRC aims to emulate the congestion control behavior of TCP. It seeks to achieve a stable and fair share of network resources without causing excessive congestion or starvation of other flows. TFRC adjusts its sending rate based on feedback information to maintain a congestion-controlled state.
7. Application-Layer Signaling: TFRC requires application-layer signaling between the sender and receiver to exchange information necessary for congestion control. This signaling can be achieved through out-of-band signaling protocols or by embedding the necessary information within the application's payload.
8. Applicability: TFRC is particularly suitable for real-time applications, such as video conferencing, voice-over-IP (VoIP), and multimedia streaming, that require low delay and smooth throughput. By providing TCP-friendly congestion control, TFRC helps maintain a stable and fair network environment for these applications.

In summary, TFRC (Transmission Control Protocol Friendly Rate Control) is a congestion control algorithm designed for real-time multimedia applications using UDP. It aims to achieve congestion control behavior similar to TCP while ensuring a fair and predictable sharing of network resources. TFRC adjusts the sending rate based on feedback received from the network, estimates congestion levels using RTT variations, and employs equation-based control to regulate the throughput. TFRC provides an effective congestion control mechanism for real-time applications without compromising their low-latency requirements.