[ns] Why TCP doesn't react to three dup acks ?

[Buchholcz Gergo]

Hi!

Are you sure that you use TCP/Reno agent? I think the simple TCP agent
doesn't do fast retransmission and fast recovery, only slow start and
congestion control. (If you want more details about them, you should look
rfc2001)

Greg

On Mon, 22 Apr 2002, Cris Tomas wrote:

>
> Hello all,
>
> I am observing a phenomena simulating NS that I'm not
> able to understand. Let's consider a single TCP
> connection with a initial window of 4 over a sinple
> topology of two nodes. The first packet is dropped and
> as a result the TCP sender receives three dup acks. We
> expect the sender to retransmit inmediately the lost
> packet but it turns out he sends two new packets and
> eventually he will timeout.
>
> (after the first packet is send and ack received)
> d 0.100007 0 1 tcp 500 ------- 1 0.1 1.1 1 2
> r 0.150007 0 1 tcp 500 ------- 1 0.1 1.1 2 3
> r 0.150007 0 1 tcp 500 ------- 1 0.1 1.1 3 4
> r 0.150007 0 1 tcp 500 ------- 1 0.1 1.1 4 5
> r 0.20049 1 0 ack 40 ------- 1 1.1 0.1 0 6
> r 0.20091 1 0 ack 40 ------- 1 1.1 0.1 0 7
> r 0.20134 1 0 ack 40 ------- 1 1.1 0.1 0 8
> r 0.250138 0 1 tcp 500 ------- 1 0.1 1.1 5 9
> r 0.250138 0 1 tcp 500 ------- 1 0.1 1.1 6 10
> r 0.30176 1 0 ack 40 ------- 1 1.1 0.1 0 11
> r 0.30217 1 0 ack 40 ------- 1 1.1 0.1 0 12
> r 0.350179 0 1 tcp 500 ------- 1 0.1 1.1 7 13
> r 0.40218 1 0 ack 40 ------- 1 1.1 0.1 0 14
> + 1.100007 0 1 tcp 500 ---A--- 1 0.1 1.1 1 15
>
> I will appreciate if somebody can give some insight
> about what is going on.
>
> thanks in advance
> Cris
>
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