Subject: Re: pilc minutes for IETF 48

From: Nitin H Vaidya <[email-masked]>
Date: Thu, 21 Sep 2000 13:22:51 -0500 (CDT)

Lloyd:

  >> From [email-masked] Thu Sep 21 12:05:17 2000
  >> 
  >> On Thu, 21 Sep 2000, Nitin H Vaidya wrote:
  >> 
  >> >   >> > If you have a reliable link layer protocol (ARQ) _and_ you tune the error
  >> >   >> > recovery persistency of that protocol to a high value like 64 seconds
  >> >   >> > (TCP's max. RTO), you pretty much eliminate losses but trade them for delay.
  >> >   >> >
  >> >   >> > ***However***, you have to ensure that the link layer does this _only_ for
  >> >   >> > the reliable flows such as the TCP-based flows.
  >> > 
  >> > Some folks seem to be arguing that we can solve the errored-link
  >> > problem at the link layer by doing ARQ-for-ever & differentiating
  >> > between TCP and UDP.
  >> 
  >> I'd _really_ like to know how you can differentiate between TCP and
  >> UDP given e.g. use of IPSec. (In a diffserv framework you cannot
  >> expect TCP and UDP to be marked separately, particularly if you're
  >> downstream. And, again, there's IPSec.)
  >> 
  >> Watching flow behaviour can tell you which flows are controlled and
  >> congestion-sensitive or uncontrolled and not, so that you can treat
  >> them differently and ensure fairness, but it won't tell you whether a
  >> flow is intended as reliable or unreliable by its application, or
  >> whether it's (gack) TCP or UDP.

Lest you get the wrong idea, the text I quoted (>> > ...) is
not mine - I believe it was from an e-mail from Reiner.

I do agree with you about the difficulties in distinguishing between TCP
and UDP (not to mention differentiating between TCP flows which
need to responsive, and UDPs which need to be reasonably reliable - this
was partly a point of my earlier e-mail. *If* we are going to have some
mechanism to convey information to the link layer, it needs to have a
greater resolution).

- nitin

  >> 
  >> L.
  >> 
  >> layeringabstractionlayeringabstractionlayeringabstraction.
  >> 
  >> <[email-masked]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>
  >> 
  >> 
  >> 
  >>

---

From: Reiner Ludwig <[email-masked]>
Date: Thu, 21 Sep 2000 23:15:34 +0200

At 13:22 21.09.00 -0500, Nitin H Vaidya wrote:
>need to responsive,

No matter how delay-sensitive the application ontop of TCP is (e.g. telnet 
vs. ftp), *all* those packets have to make it across the link. Thus, *for 
those packets* you can afford to be as persistent with ARQ at the link 
layer as TCP is at the transport layer.

>*If* we are going to have some

I agree with you here.

///Reiner

---

From: Lloyd Wood <[email-masked]>
Date: Fri, 22 Sep 2000 14:27:06 +0100 (BST)

On Thu, 21 Sep 2000, Reiner Ludwig wrote:

> vs. ftp), *all* those packets have to make it across the link. 

that's a fallacy.

a single copy of the data that the packets contain has to make it
across the link - eventually. You can afford to drop some packets.

L.

> Thus, *for