[e2e] What should e2e protocols know about lower layers?

[Anoop Ghanwani]

I agree with Ran's analysis.  Especially with things
like L2 VPNs over MPLS, there's no way to know how
far the traffic will be going, or what kind of path
it would take (routed, switched).

-Anoop

> -----Original Message-----
> From: RJ Atkinson [mailto:rja at inet.org]
> Sent: Wednesday, October 10, 2001 9:09 AM
> To: Tim Moors
> Cc: end2end-interest at postel.org
> Subject: Re: [e2e] What should e2e protocols know about lower layers?
> 
> 
> At 10:34 10/10/01, Tim Moors wrote:
> >One thread of the discussion questioned how an instance of an e2e 
> >protocol like TCP can determine whether its communicating peer is
> >"local".
> 
> I do not think "local" can be determined above layer-2.  I can't 
> even convince myself that it is always something that can be
> determined at layer-2.  Depending on what "local" means, even
> a single Ethernet might not be "local" (e.g. 1 GigE products
> often have 70-100 Km reach now a days; most shipping GigE 
> products also support MTUs larger than IEEE-standard size).
> 
> Even in the old days there were often mixed L2 technologies
> (e.g. FDDI & Ethernet, with different link speeds and different 
> MTUs) that were bridged together on a single subnet.  In later
> days, one might have had the wacky ATM LAN Emulation stuff bridged
> with real Ethernet.
> 
> As I also read the TSVWG list, I'll note that I think that congestion
> avoidance and control mechanisms should always be turned on.
> I disagree with folk disabling congestion avoidance and control
> just because a given link might be perceived to be "local"
> (particularly where "local" seems to have the de facto meaning
> of "on-subnet").
> 
> I'm not sure that followups belong on all the original lists,
> so I've trimmed this reply to just the E2E list.
> 
> Ran
> rja at inet.org
>