Re: ATM Wide-Area Networks

[salo () msc edu (Tim Salo)]

> From: Sean Doran <smd () icp net>
> To: pferguso () cisco com, salo () msc edu
> Subject: Re: sell shell accounts?
> Cc: nanog () merit edu
> Date:  Wed, 24 Jul 1996 01:43:30 +0100
>
> | o    Given that each link is rather expensive, it behooves the
> |      NSP to try to avoid needlessly moving a packet back and
> |      forth across a DS-3 local loop just because my ATM 
> |      provider can't provide me with any more PVCs.
> |      (Which was my major point, by the way.)
>
> Interestingly enough, the NSPs I observe moving large amounts
> of traffic around are set up in such a way that their routers
> are generally colocated with carrier transmission gear, and
> so there *is* no local loop to speak of, as an added cost to
> an outside supplier.
>       [...]

Hopefully, my thinking is clearer than my writing...

What I originally called "local loop B," now relabeled "This Thing Here,"
is probably comprised of:

o       a port on the ATM switch/service

o       a connection between the router and the switch, (usually a
        wide-area link, given that most wide-area ATM services 
        backhaul traffic to a few ATM switches)

o       a port on the router

A short-cut VC would avoid needlessly passing packets back and forth
across "This Thing Here."  That would seem to be a good thing in
most circumstances, inasmuch as some or all of the components of
"This Thing Here" cost something and may potentially become a bottleneck.

-tjs

|    ________           _______________________          ________
|   | Router | loop A  |                       | loop C | Router |
|   |   A    |=========| Wide-Area ATM Service |========|   C    |
|   |________|         |_______________________|        |________|
|                                  |
|                                  | <=== This Thing Here
|                                  |
|                              ________
|                             | Router |
|                             |   B    |
|                             |________|
- - - - - - - - - - - - - - - - -