patrick@ianai.net wrote:

The Internet can be mission critical. (Well, not really, but it's =20 trying.) And for something mission critical, a single point, no =20 matter how well reinforced, is not good enough.

It may not be "mission critical" for any one particular client, but when you bundle all of the separate non critical applications on the net, the impact of downtime on the population becomes important enough to be seen as "critical". Think about airlines expecting passengers to check-in via the internet more and more so that they can reduce staff at airports.

The exchange point should _NOT_ be mission critical. As I explained =20 multiple times in the thread, if that is your only vector, your design =20= is broken. Period. Care to argue otherwise?

Fair enough. However, in a particular city, you may have difficulty finding multiple different transit providers whose fiber trunks are truly differently routed. It is bad enough that different transit providers may share the same dark fibre cable out of the city. Very large cities such as New York may make it much easier to find truly independant transit links. But for small, medium cities, it becomes harder (especially if geography limits the number of truly separate links). In the end, to form a truly redundant service, you probably need to have a presence in multiple cities, each with its own carrier hotel. And at that point, each carrier hotel need not be "mission critical" because you can continue service from another city. But even if you have backup, you still want the carrier hotels to be robust. And if you can't afford to have data centres/networks in different cities, you do want to have a robust interconnect to the internet. Consider the number of small/medium size ISPs whose infrastructrure is located at the carrier hotel where the local exchange resides. To them, the availability of services at that carrier hotel is mission critical because their bueiness depends on it, and they can't afford to be in multiple locations.