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@shore.net> To: nanog@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