All true but it is becoming increasingly difficult to determine if a provider is using another providers infrastructure (all are at some level). For example, in the SIP world there are several national level carriers that are using Level 3s core SIP network and if you were not aware of that you could buy trunks from two of the largest SIP trunk providers in the US and actually be running on the same network. Carriers are also very often reliant on the ILEC for fiber and last mile access. Especially in non-metro areas getting diverse last mile access could be impossible or have huge construction costs. It is pretty complicated to ensure that your carriers are really diverse and much harder to ensure that they stay that way. I have many examples of carrier grooming their own primary and backup circuits onto the same L1 path and not realize they have done so.
Contractual diversity is a great idea that does not work since the carriers do not actually know what each other’s network looks like. So let’s say that Sprint and CenturyLink choose the same fiber carrier between areas, do you think they would notify each other of that fact? Do you think the fiber carrier would tell them what another customer’s network looks like? You can tell Sprint to not use CenturyLink but there is no way to get both of them not to use the same third party. I suppose you could contractually tell a carrier to avoid xxx cable but I would have little faith that they maintain that over time. I seriously doubt they review all existing contracts when re-grooming their networks. Steven Naslund Chicago IL >I'm of the opinion that, if you need resiliency, you should order explicitly >diverse circuits from a primary provider and then a secondary circuit from a >second vendor. > >Ultimately, If you want contractually-enforced physical diversity then the >best options will be single-vendor solutions: Obviously you also want to avoid >an unknown single-vendor single-point-of-failure, hence the >secondary >provider. Having two vendors is usually a less than optimal solution since >neither has visibility into the others' network to ensure the physical >diversity required for a truly resilient service: what happens if >an undersea >cable is cut, etc? > >The cost of such solutions is often unpleasant to justify, mind. > >~a
