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What is fast recovery in congestion control?

Fast Recovery is a technique that often allows the sender to avoid draining the pipe, and to move from cwnd to cwnd /2 in the space of a single RTT. TCP Reno is TCP Tahoe with the addition of Fast Recovery. The idea is to use the arriving dupACKs to pace retransmission.

How does TCP fast retransmit work?

Fast retransmit is a modification to the congestion avoidance algorithm. As in Jacobson’s fast retransmit algorithm, when the sender receives 3rd duplicate ACK, it assumes that the packet is lost and retransmit that packet without waiting for a retransmission timer to expire.

When fast recovery occurs in TCP Reno?

What is “fast recovery”? In TCP Reno, when TCP does fast re-transmit (see above question), instead of beginning a slow-start phase with cwind set to 1, it goes directly to congestion-avoidance phase, with cwind set to ½ its value when packet loss occurred. This is called fast recovery.

What is the advantage of fast retransmit?

The Fast Retransmit mechanism is able to efficiently recover from packet losses as long as no more than one packet is lost in the window. If more than one packet is lost, then usually the retransmit timer for the second or later expires, which triggers the more drastic step of resetting W back to one packet.

Why do we need fast recovery for TCP congestion control?

Fast Recovery is now the last improvement of TCP. With using only Fast Retransmit, the congestion window is dropped down to 1 each time network congestion is detected. Thus, it takes an amount of time to reach high link utilization as before.

Why does TCP use slow start?

Slow start is part of the congestion control strategy used by TCP in conjunction with other algorithms to avoid sending more data than the network is capable of forwarding, that is, to avoid causing network congestion. The algorithm is specified by RFC 5681.

Does TCP have congestion control?

To avoid congestive collapse, TCP uses multi-faceted congestion-control strategy. For each connection, TCP maintains a CWND, limiting the total number of unacknowledged packets that may be in transit end-to-end. This is somewhat analogous to TCP’s sliding window used for flow control.

How does TCP detect congestion?

TCP uses a congestion window in the sender side to do congestion avoidance. The congestion window indicates the maximum amount of data that can be sent out on a connection without being acknowledged. TCP detects congestion when it fails to receive an acknowledgement for a packet within the estimated timeout.

What is TCP Reno and Tahoe?

TCP Tahoe and Reno are two forms of handling TCP congestion controls specifically when it comes to receiving 3 duplicate acks. Tahoe: handles 3 duplicate acks similar (exactly?) to receiving a timeout. It first performs a fast retransmit.

What is fast retransmission in Wireshark?

TCP Fast Retransmission – Occurs when the sender retransmits a packet before the expiration of the acknowledgement timer. Senders receive some packets which sequence number are bigger than the acknowledged packets. Senders should Fast Retransmit upon receipt of 3 duplicate ACKs.

What is the difference between Fast Retransmit and fast recovery?

After the fast retransmit algorithm sends what appears to be the missing segment, the “fast recovery” algorithm governs the transmission of new data until a non-duplicate ACK arrives.

What is the disadvantage of i TCP?

The disadvantages of the TCP/IP model are It does not clearly separate the concepts of services, interfaces, and protocols. So, it is not suitable to describe new technologies in new networks. It does not distinguish between the data link and the physical layers, which has very different functionalities.

What is fast retransmit and recovery (FRR)?

In TCP/IP, fast retransmit and recovery (FRR) is a congestion control algorithm that makes it possible to quickly recover lost data packets. Without FRR, the TCP uses a timer that requires a retransmission timeout if a packet is lost. No new or duplicate packets can be sent during the timeout period. With FRR, if a receiver receives a data segment that is out of order, it immediately sends a duplicate acknowledgement to the sender.

What is TCP loss recovery?

TCP Loss Recovery Mode is a TCP algorithm that helps recover throughput efficiently after packet losses occur in the network. It also addresses performance problems caused by the loss of a single packet during a large transfer over long delay pipes. By default, loss recovery mode is set to the enhanced option. To disable the algorithm:

What is FAST TCP?

FAST TCP (also written FastTCP) is a TCP congestion avoidance algorithm especially targeted at long-distance, high latency links, developed at the Netlab, California Institute of Technology and now being commercialized by FastSoft. Sep 19 2019