NAP Solutions

Fri Nov 14 21:12:56 UTC 1997

Gigabit ethernet just isn't really available yet.

	Brian

On Fri, 14 Nov 1997, Gregory Mirsky wrote:

> Brian Horvitz wrote:
> > 
> > Well, as we know WAN speeds have certainly outgrown LAN technologies.  The
> > is however no reason not to use WAN technologies in a local area
> > environment.  The scenario I had in mind was something like a Cisco 12000
> > as a concentrator (I have not done NEARLY enough research on that unit to
> > know if it's the right choice), and packet over sonet to either other
> > units in the same room or right onto someone's WAN if they can extend
> > their sonet in such a way.  The concentrator units could then be connected
> > onto a backbone sonet which everyone can talk across if they are not in
> > the same box.  This make a nice expandable solution.
> > 
> >         Brian
> > 
> Brian,
> why not to consider GigaEthernet as media of choice for NAP in
> combination with Fast Ethernet
> if needed?
> 
> 	Greg
> 
> > On Fri, 14 Nov 1997, Tim Salo wrote:
> > 
> > > > Date: Fri, 14 Nov 1997 10:57:39 -0500 (EST)
> > > > From: Brian Horvitz <horvitz at shore.net>
> > > > To: nanog at merit.edu
> > > > Subject: NAP Solutions
> > > >
> > > > Has anybody though about a packet over sonet solution for an exchange?
> > > > Seems like you could get a pretty effective answer out of a GSR with OC3
> > > > and OC12 interfaces...
> > >
> > > I think your question provides an interesting opportunity for comparing
> > > SONET solutions with, for example, ATM solutions.
> > >
> > > First, some thoughts on a local-area interconnect.
> > >
> > > If you want a fully-meshed interconnect, you will need n-1 SONET
> > > interfaces on each router, when "n" is the number of routers at the
> > > interconnect, [assuming one router per ISP].
> > >
> > > You might feel that this is an excessive number of router interfaces,
> > > (assuming n > 2), so you might consider creating a ring instead.
> > > In this case, each router would require only two interfaces.  However,
> > > most packets will need to be forwarded through several routers before
> > > reaching their final destination [within the interconnect].  As a result,
> > > a certain amount of the capacity of your router and your interfaces will
> > > be used to forward packets between your competitors.
> > >
> > > Obviously, there is a spectrum of configurations between a full mesh and a
> > > ring.  However, determining the best trade-off between the cost of
> > > additional interfaces, additional bandwidth used to forward packets
> > > between routers not directly connected, and additional routing
> > > capacity to forward packets within the interconnect is probably
> > > worthy of a Master's thesis.  (Of course, you might have to write
> > > another thesis every time you add another router to the interconnect.
> > > Creating a general solution might be worthy of a Doctoral dissertation.)
> > >
> > > [Note that this assumes that no router vendor integrates a SONET mux
> > > into the router.  As far as I know, no router vendor has an integrated
> > > SONET mux.]
> > >
> > > Using an ATM switch (or most any other switch, for that matter) has
> > > a number of advantages.  First, each router needs only one interface
> > > to the interconnect.  This interface should probably be as large as
> > > the router can support.  (This is the problem facing many of the
> > > existing interconnects, namely that the router can support more than
> > > 100 Mbps, but the interconnect media runs at only 100 Mbps.)
> > > Second, adding additional routers is fairly straight-forward, (e.g.,
> > > you don't have to add another SONET interface to every existing router,
> > > in the rather unlikely event that you have a full-mesh topology).
> > > Rather, you merely plug the new router into the switch.  Finally, adding
> > > additional capacity is probably a lot easier.  Each router [ATM] interface
> > > can be upgraded as that router requires additional capacity.  For example,
> > > an interconnect could simultaneously support both OC-3c and OC-12c
> > > connections.  In a similar fashion, the aggregate capacity of the
> > > interconnect can be increased by swapping in a new ATM switch,
> > > (rather than, for example, swapping out the FDDI interfaces on the
> > > routers for gigabit ethernet interfaces).
> > >
> > > Now, there is a certain price for using ATM rather than SONET, namely
> > > the overhead incurred by ATM.  However, as I have said before, the
> > > best decision criteria is an analysis of cost/performance, not
> > > merely looking at overheads.  In this case, you would need to compare
> > > the cost of the unnecessary SONET interfaces with the cost of the
> > > bandwidth used for ATM.
> > >
> > > So, it seems to me that SONET makes sense for a private interconnect
> > > between two parties, but that a switched technology, such as ATM or
> > > perhaps gigabit ethernet, makes sense when the number of parties is
> > > greater than two, (like three, for example).
> > >
> > > Now, this same analysis can be applied in the wide area.
> > >
> > > The next question is, if you have decide to use ATM, whether to
> > > create a local interconnect, (i.e., put the switch and all the routers
> > > in one room) or to create a distributed interconnect, (e.g., leave
> > > the routers distributed throughout a LATA or even throughout the country).
> > > I think there are a number of good arguments both ways.  Both local
> > > interconnects and intra-LATA interconnects have been tried.  I don't
> > > know of anyone who has created a nationwide interconnect, (although
> > > I think all of the original NAP proposals suggested nationwide NAPs).
> > >
> > > On the other hand, the question of SONET versus ATM in a wide-area
> > > environment is still being explored in, for example, the Internet2 efforts.
> > > I don't understand how wide-area SONET solutions are supposed to scale,
> > > but perhaps someone will figure it out.  Of course, another interesting
> > > question is why, with services like ATM with distance-insensitive
> > > pricing, one would build a regional wide-area interconnect (e.g., a
> > > regional, wide-area gigapop), rather than a nationwide interconnect.
> > > (Note that some claim that propagation delays are an issue in a
> > > nationwide interconnect, but I believe that, e.g., routing through the
> > > opposite coast to get to the adjacent city, would result from poor
> > > design or configuration, rather from any inherent defect in the
> > > concept of nationwide interconnects/gigapops).
> > >
> > > Wide-area SONET certainly has its place, depending on the relative price
> > > of SONET versus ATM services, the number of locations which need to be
> > > interconnected and the amount of bandwidth required.  For example, in
> > > a campus environment where private fiber is available, point-to-point
> > > SONET solutions are easier to justify than when you need to lease SONET
> > > links from a carrier.
> > >
> > > Hopefully, projects like Internet2 and NGI will explore both SONET and
> > > ATM wide-area interconnects so we can gain a better understanding
> > > of their advantages and capabilities.
> > >
> > > And finally, I don't know if I answered you question.  But, if you do
> > > decide to build a SONET interconnect, please let us know how it works.
> > >
> > > -tjs
> > >
> 