[e2e] Overly Overlay; Peer to peer is commonplace

[Nitin H Vaidya]

On Wed, 2 Jan 2002, J. Noel Chiappa wrote:

  >>    > 2. The abstraction being imposed (IP's addressing) is intended to apply
  >>    > to communications systems that are not graphs at all. For example,
  >>    > radio networks have topology, but in space, time, and frequency domain
  >>    > they are continuous manifolds, not graphs.
  >>
  >>True enough.
  >>
  >>But it's also true that one can represent the connectivity between the radio
  >>nodes by a graph, with arcs between all nodes that can directly communicate.
  >>One can further enhance that graph by adding attributes to the arcs, showing
  >>bandwidth, S/N (aka error rates), etc, etc. (Of course, it may be a very
  >>dense graph, but there are ways to deal with that which I'm going to gloss
  >>over for the moment.) The question then becomes "which is a more useful way
  >>to model the real world radio network".

I believe graphs are fine so far as modeling a radio network is concerned,
but a couple of issues must be addressed a bit more carefully:

 * Links in radio networks are not necessarily a "given" -- one can
   decide which links "exist" and which don't, by controlling parameters
   such as the transmit power.

 * I presume you mean bit rate, when you say bandwidth above: Bit rate of
   a link between a pair of nodes is not always an independent variable,
   since all the "links" terminating at a given node may share the channel
   with each other. Thus, bit rates of these links are correlated, not
   independent (generally, a link's bit rate is correlated with those
   links one or, possibly, more hops away).
   Also, the bit rate can be tweaked by changing parameters such as the
   modulation scheme.

Regards.

- nitin