The IP over ATM Mailing List Archive by date

[manfredi@engr05.comsys.rockwell.com (Albert E. Manfredi)]

> From:	curtis@ans.net    26-JAN-1996 19:42
> > > From:	asmith@baynetworks.com    25-JAN-1996 23:28
> > > 
> > > If you have such a deployment scenario then there is really no need for
> > > an internetwork layer any more - you don't really need IP or LISs at all,
> > > let alone 1577 and ATMARP! Roll on TULIP and TUNIC ...
> > 
> > Exactly. Need for internetwork remains for compatibility with legacy, 
> > non-ATM IP nets.
> 
> I think there was some sarcasm in the statement that you missed.  ;-)

Naw, not really. I didn't think it needed to be a sarcastic comment, 
though.

> The need for internetworking only remains if you are willing to be an
> island unconnected to the rest of the world or are willing to have a
> static default route to the rest of the world.

In a sense, this is a detail. Use the premise that 90 percent of the 
world is IP over ATM and the static routes between legacy IP-over-MAC 
systems and their router to the world is not such a big deal. I'm simply 
showing that a flat IP network for a huge number of hosts is not 
inconceivable AS LONG AS that huge network is IP over ATM, and as long as 
the remaining old style LANs are a small minority. (I'm not saying it
will happen anytime soon or at all, but I'm proposing that it's perfectly
conceivable to have very large LISs _en principe_.)

> > I'm not sure I follow. You don't need to set up circuits at 8 AM for the 
> > rest of the day, just as you don't need to dial up all your business 
> > contacts at 8 AM and keep those lines open all day long.
> 
> The first issue is the size of VCI space.  We long ago (May 1994 I
> think) measured 7,800 unique destination hosts on a 90 second IP
> sampling on one spot on the Internet (at just about 12 Mb/s.  A factor
> of 10 and there goes VCI space.  I haven't seen any idea on how to use
> VPI space to make up for it.

Should this be a hard problem to solve? Do these 7800 destinations in 90 
seconds each require a long-term VC? Would the "one spot in the Internet" 
still be "one spot" if the backbone were ATM, or would the calls be routed 
differently?

> The second issue is VC establishment time.  I think 8AM here was just
> a guess at when peak time might be (chance are it would be later in
> the day, but that's irrelevant).  Currently routers run in the 10s of
> kpps per interface per direction or up to 100-200 kpps per box.
> Estimates of flow duration (even when measured in terms of host pairs
> that don't go idle more than 60 seconds) are well under 100 packets.
> That would put current VC connect rate in the range already
> approaching 1000 new VC per second.  Connection load could easily be
> an issue.

Again, I don't think one can automatically assume that choke points 
created by the current router/dedicated link topology would exist in a 
large ATM mesh. The traffic would be routed differently, as it is for 
telephone calls.

> > It is entirely conceivable, for the sake of argument, to have 90 percent 
> > of all IP users in the world riding on a single IP "network," all over 
> > ATM. The remaining 10 percent, over their little Ethernets, would have to 
> > use different IP "networks" to be routable. Such a scheme would work 
> > because ATM can provide all the management and routing needed using its 
> > own mechanisms.
> 
> It just might work if all the connected networks were stubs, single
> homed to the ATM network.  That is if the VC issues can be solved.

Right. Or even n-homed as long as n is small. 
 
> The big flat ATM LIS is infeasible.  This has come up many times on
> this list.  If you don't think so you are welcome to try to build one.

It would be quite easy to build one if ATM in the WAN were ubiquitous. I 
mean, a public ATM in the WAN. Routing to/from legacy systems, I believe, 
becomes difficult when both legacy IP nets and ATM nets are big. If one or 
the other is small and isolated, then static routes would work fine.

Basically, small ATM LISs solve the problem of having packets from
legacy IP nets routed efficiently between the old net and the ATM host. 
But if we can accept circuitous paths to/from those legacy nets, it's not 
such a big problem, is it? (As it is, my IP stuff has to cross the country 
anyway, no matter where its destined, even though there's not a whiff of
ATM on our enterprise net.)

Bert
manfredi@engr05.comsys.rockwell.com