tcp_dupack_fast_retransmit

[Plamen SIMEONOV]

Hello masters,

Would you explain me in details the meaning of NDD tunable parameter: tcp_dupack_fast_retransmit
(or suitable URLs)

Thank you in advance!
Plamen

[eran maor]

Hi

from what i know on this param - this a param that Unsupported tunables param

tcp_dupack_fast_retransmit
No. of ACKs needed to trigger a retransmit



The minimum is 0.
The maximum is 10.
The default is set to 3.

[Christopher Caldwell]

# of duplicate ACKs needed to invoke fast retransmit.
The number of consecutive duplicate ACKs that trigger the fast
retransmit, fast recovery algorithm

[Christopher Caldwell · Accepted solution]

[painful detail]
from
ftp://ftp.isi.edu/in-notes/rfc2581.txt

3.2 Fast Retransmit/Fast Recovery

A TCP receiver SHOULD send an immediate duplicate ACK when an out-
of-order segment arrives. The purpose of this ACK is to inform the
sender that a segment was received out-of-order and which sequence
number is expected. From the sender's perspective, duplicate ACKs
can be caused by a number of network problems. First, they can be
caused by dropped segments. In this case, all segments after the
dropped segment will trigger duplicate ACKs. Second, duplicate ACKs
can be caused by the re-ordering of data segments by the network (not
a rare event along some network paths [Pax97]). Finally, duplicate
ACKs can be caused by replication of ACK or data segments by the
network. In addition, a TCP receiver SHOULD send an immediate ACK
when the incoming segment fills in all or part of a gap in the
sequence space. This will generate more timely information for a
sender recovering from a loss through a retransmission timeout, a
fast retransmit, or an experimental loss recovery algorithm, such as
NewReno [FH98].

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