Re: [PATCH] SCTP: Fix DATA retransmit after fast retransmit

[Wei Yongjun <yjwei@cn.fujitsu.com>]

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Hi Vlad:

The test sequence is the same as yours. The data flow see the following. 
If you can receive attachment, see the tcpdump file in the attachment.

Endpoint A                       Endpoint B
DATA (TSN = 1)  ------------->
DATA (TSN = 2)  -- (lost)---->
DATA (TSN = 3)  ------------->
DATA (TSN = 4)  ------------->
               <-------------   SACK (CTSN = 1)
DATA (TSN = 5)  ------------->
               <-------------   SACK (CTSN = 1, GAP-START = 2, GAP-ENT = 2)
               <------------    SACK (CTSN = 1, GAP-START = 2, GAP-ENT = 3)
               <------------    SACK (CTSN = 1, GAP-START = 2, GAP-ENT = 4)
DATA (TSN = 2)  -(fast rtx)-->
               <---(lost)----   SACK (CTSN = 5)
NO DATA send   --(t3-rtx)----
HEARTBEAT      -(hb rtx1)-->
HEARTBEAT      -(hb rtx1)-->

I do not know what packet generater you used for test, maybe it send too 
fast, I think If you do same delay before send SACK (CTSN = 1, 
GAP=3,4,5), you can find this problem.

Wei Yongjun

Vlad Yasevich wrote:
> Hi Wei
>
> I am attempting to reproduce this scenario and trying to understand
> the packet sequence.
>
> I have tried the following simple scenario and it works correctly:
>
> Endpoint A                       Endpoint B
> DATA (TSN = 1)  ------------->
>                <-------------   SACK (CTSN = 1)
>
> DATA (TSN = 2)  -- (lost)---->
> DATA (TSN = 3)  ------------->
>                <-------------   SACK (CTSN = 1, GAP = 3)
>
> DATA (TSN = 4)  ------------->
>                <------------    SACK (CTSN = 1, GAP = 3,4)
>
> DATA (TSN = 5)  ------------->
>                <------------    SACK (CTSN = 1, GAP = 3,4,5)
>
> DATA (TSN = 2)  -(fast rtx)-->
>                <---(lost)----   SACK (CTSN = 5)
>
> DATA (TSN = 2)  -(t3 rtx) --->
>
> The T3_RTX retransmission happens because at the initial sending
> of TSN 2 (the one that was lost), the rtx timer was set and
> running.  It was never reset since not all outstanding chunks
> have been acknowledged.
>
> Can you describe the SACKs in your scenario with CTSN and GAP breakdowns
> so I can try to reproduce it.




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