[e2e] Is a non-TCP solution dead?

[David P. Reed]

Hari - I wasn't attacking you - though I fear now that my remarks can be 
easily misinterpreted that way; sorry if they came out that way.  I'm 
familiar with your work, and I know you have explored these options.

What I meant to say is that your remarks may have been misleading (taken in 
the narrow context of this exchange).   Just as, it appears, my remarks may 
have been misleading. :-(

- David

At 08:24 PM 3/31/2003 -0500, Hari Balakrishnan wrote:

>David,
>
>I didn't say anything about how to run wireless (particularly multi-hop)
>networks at close to available capacity.  I do believe that integrated
>approaches are needed for that to work well.
>
>My comments were restricted to dealing with wireless bit errors induced by
>corruption.  Period.  I don't think having TCP deal with such link errors 
>is a
>useful optimization.
>
>I do agree that TCP doesn't do a great job of estimating available 
>capacity in
>many kinds of wireless networks, for some of the reasons you mention, and 
>also
>because wireless capacity in many networks is tied to the details of the MAC
>protocol and we don't deal well with that kind of thing in TCP.  Also, I do
>think one can integrate wireless routing better with link characteristics.
>
>My comments were not about general partitioning of functionality in wireless
>systems; they were about who should deal with bit corruption.  (I have been
>quite guilty of exploring end-to-end approaches to traditional lower-layer
>problems, including routing.)
>
>Hari
>
> > At 11:47 AM 3/31/2003 -0800, Mark Handley wrote:
> > >This raises a higher level issue: to what extent is a wireless link
> > >error a sign of congestion?
> >
> > Relating this to my other mail:  in the RF medium, any number of
> > communications can happen simultaneously.   Congestion of a sort (too many
> > signals impinging on a single receiver antenna) results in a link error,
> > but this depends significantly on the systems design of the receiver and
> > its assumptions about the kinds of signals that may concurrently be
> > transmitted.
> >
> > There are many more dimensions of adaptation in the RF medium to adapt to
> > variations in end-to-end bitrate demand.  These are extraordinarily
> > interesting dimensions, far more so than mere rate control.  Simple
> > examples include power control, rate adaptation, frequency adaptation,
> > antenna steering, reconfiguration of network repeaters into new 
> topologies,
> > etc.   Many of these are not mere "link level" adaptations, but can 
> involve
> > the whole wireless network topology.
> >
> > Given that the entire capacity of a wireless system varies tremendously
> > depending on demand, one cannot layer wireless networks in the traditional
> > way by assuming a set of independent fixed capacities at the physical 
> level
> > and then managing capacity above that layer as if the networks consist of
> > fixed capacity links.
> >
> > Thus Hari Balakrishnan's comment implying that partitioning wireless
> > networks into a link layer and an end-to-end layer are misleading.   I
> > personally suspect that end-to-end approaches are far more important for
> > managing latency, throughput, etc. than he'd suggest.   But those
> > end-to-end approaches will need to be worked out in a context that 
> includes
> > a better abstraction of the tradeoffs than has been traditionally used in
> > modeling wired networks.
> >