sell shell accounts?

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From: Avi Freedman <freedman@netaxs.com>
Subject: Re: sell shell accounts?
To: vansax@atmnet.net (Jim Van Baalen)
Date: Fri, 19 Jul 1996 17:17:19 -0400 (EDT)
Cc: richards@netrex.com, agislist@interstice.com, nanog@merit.edu
  [...]
Nope, remember - there is no magic. Any mesh of PVCs that one makes
over a switched network must reflect the toplogy of that network, and
one can set up a matching set of active routing sessions and route
weights which will cause traffic to flow the same way.
  [...]

If I understand what you are asserting, I probably don't agree with it.

I assume that we are talking about using wide-area ATM networks, (or
more specifically, wide-area ATM services provided by, for example,
carriers).

Consider the following configuration

   ________ _______________________ ________

2

It's ATM day.

Consider the following configuration

   ________ _______________________ ________
  > Router | loop A | | loop C | Router |
  > A |=========| Wide-Area ATM Service |========| C |
  >________| |_______________________| |________|
                                 >
                                 > local loop B
                                 >
                             ________
                            > Router |
                            > B |
                            >________|

Consider the following configuration:

  Ra----fibrepath2----------RbRc------fibrepath2--------Rd

or the following:

  Ra---ll1---[IXCi]---ll2---RbRc---ll3---[IXCii]---ll4--Rd

I wonder what the distribution is, in terms of number of
backbones, of each of the three models.

(You may choose to imagine easy extensions like Ra and Rd
really being two routers, with physical connectivity between Ra' and Rd')

In terms of designing Internet backbones, do you see any
issues other than cost when choosing between your version
and either one of my versions?

Also, does this change when there are, say, twenty-odd
routers at each of the three locations?

  Sean.

3

It's still ATM day, 'cause something else just occurred to
me:

Consider the following configuration

   ________ _______________________ ________
  > Router | loop A | | loop C | Router |
  > A |=========| Wide-Area ATM Service |========| C |
  >________| |_______________________| |________|
                                 >
                                 > local loop B
                                 >
                             ________
                            > Router |
                            > B |
                            >________|

How is one doing bandwidth allocation in this scheme? Are
we assuming CBR (to be very conservative) (or VBR with V=0
for those that don't do CBR)?

If so, then local loop B is really two circuits, one of
BW X and the other of BW 1-X.

Moreover, continuing with the thought of CBR or the
equivalent, if one has a hundred routers in one's network,
how does one allocate a fixed bandwidth from B to each
router? Or does one overcommit and lean on UBR or ABR or
some other *BR?

These are serious questions I don't have an answer to, and
come a result of having remembered the paragraph below and
of remembering that a couple of our competitors have
very large (admittedly "Frame Relay") PVC meshes.

  Sean.