Re: [multipathtcp] Multipath TCP FAST_CLOSE - abrupt closing

[Olivier Bonaventure <[e-mail]>]

Hi Yoshifumi,
> 
> This is an interesting proposal for the bis draft. But, I guess the
> receiver of FAST_CLOSE (will be clients in most cases) may need to
> wait longer time in some cases.
> 
> I am thinking that the main motivation of SO_LINGER with zero timeout
> approach is to avoid going into time_wait.

I totally agree

> I think MPTCP's FAST_CLOSE already takes care of this point to some
> extent and senders don't go into M_TIMEWAIT, although it requires at
> least 1 RTT.

This requires one RTT when there are no packet losses. Unfortunately, 
with mobile nodes, there is no guarantee that the ACK packet sent with 
the FAST_CLOSE option will reach the client. If this packet is lost, the 
server needs to wait for the expiration of its timer to retransmit the 
ACK with the FAST_CLOSE option. This ACK could again be lost as well...

> So, I am still not very sure if we should save this 1 RTT or should
> avoid unfortunate cases for long waiting.

The issue if when there is no reply to the ACK sent by the server. This 
forces the server to maintain state for a potentially long duration to 
retransmit the ACK with FAST_CLOSE. Francois' proposal avoids this and 
forces the client to retransmit a SYN later to verify that the 
connection does not exist anymore. When there are no packet losses, the 
client is informed immediately with the RST that includes FAST_CLOSE.


Olivier

-- 

------------------------------
DISCLAIMER.
This email and any files transmitted with it are confidential and intended 
solely for the use of the individual or entity to whom they are addressed. 
If you have received this email in error please notify the system manager. 
This message contains confidential information and is intended only for the 
individual named. If you are not the named addressee you should not 
disseminate, distribute or copy this e-mail. Please notify the sender 
immediately by e-mail if you have received this e-mail by mistake and 
delete this e-mail from your system. If you are not the intended recipient 
you are notified that disclosing, copying, distributing or taking any 
action in reliance on the contents of this information is strictly 
prohibited.