North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: NAP Solutions
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 <[email protected]> > > > To: [email protected] > > > 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 > >
|