[e2e] [Fwd: ECN & PMTU]

[Neil Spring]

Arun,

the congenstion control analogue to fragmentation required is
called source quench.  these emails describe why it is not 
useful for congestion control.

ftp://ftp.ee.lbl.gov/email/sf.97nov20.txt
ftp://ftp.ee.lbl.gov/email/sf.98may7.txt

you may also find that this question has been asked before
on this mailing list (and probably on all the other ones
you sent this message to.)

http://www.postel.org/pipermail/end2end-interest/2001-February/000113.html

-neil


On Tue, Apr 09, 2002 at 11:09:57AM +0530, Arun Prasad wrote:
> 
> 
> --
> ****************************************************************
> V.Arun Prasad
> HCL Technologies Ltd.
> 51, Jawaharlal Nehru Road,
> Ekkattuthangal,
> Guindy Industrial Estate,
> Chennai - 600097.
> 
> Contact # : 9144 - 2334174
>             9144 - 2334181
>             extn : 233
> ****************************************************************
> 

> Date: Tue, 09 Apr 2002 10:09:47 +0530
> From: Arun Prasad <arun at netlab.hcltech.com>
> Subject: ECN & PMTU
> To: tsvwg <tsvwg at ietf.org>
> Cc: tcp-impl at grc.nasa.gov, sctp <sctpimp at netlab.hcltech.com>
> X-Mailer: Mozilla 4.72 [en] (WinNT; U)
> 
> Hi all,
>     Some doubts on the procedure followed for PMTU (Path mtu) discovery and
> ECN method.....
>     The doubt is not related to the procedure as such, but the relation between the
> two procedures stated above......
> Tcp and Sctp uses ICMP message to handle the PMTU discovery procedure....
> ie., the intermediate router will send an ICMP messge of "Message too Long"
> to the end point sending the data packet of size greater than the MTU size of some
> intermediate path to the destination.....
> 
> For ECN, the intermediate router should set the appropriate bits in the IP header
> (if it supports ECN ....) whenever there is congestion and risk of packet drops
> is high....... The endpoints then correct their Congestion window accordingly and
> help in reducing the Congestion in the intermediate router.....
> 
> Why, we adopt two different methods to carry out similar (in the sense, both are
> related to the Intermediate routers....)?????
>     Why cant we generalise this stuff.... ie.,  the need here is some way to
> communicate between the intermediate router and the endpoint.... Not sure
> which of the two ways is advantageous, but cant we use the same method for
> both..... ie.,
> As for the PMTU discovery, the intermediate router can send an ICMP message
> to the endpoint carrying a message "CONGESTION", by receiving this the
> endpoint will do all appropriate actions as it does when it receives the packet set
> with ECN-ECHO flag (as in present ECN procedure...)
> 
> or vice versa ( ie., adopt the method followed by ECN  for PMTU discovery aslo,
> that might be slighly tough, considering the Backward compatibility....)
> 
>     What we can achieve by this is the simplicity  in the router implementation,
> which doesnt need to do different procedure for different features of the Transport
> layer..... and by maintaining this uniformity, the future extentions which demands a
> similar requirement can use the same way......
> 
> I could have missed some points....
> 
> Any comments on this????
> 
> 
> Thanks
> -arun
> --
> ****************************************************************
> V.Arun Prasad
> HCL Technologies Ltd.
> 51, Jawaharlal Nehru Road,
> Ekkattuthangal,
> Guindy Industrial Estate,
> Chennai - 600097.
> 
> Contact # : 9144 - 2334174
>             9144 - 2334181
>             extn : 233
> ****************************************************************
>