Sean M. Doran <smd@clock.org> wrote:

PDH protection switching is slow and ugly, but it allows fall-back connectivity to be oversold or not provisioned in the first place. That is, you can sell people "cheapo" circuits which have no backup, and even more, circuits which will fail when an unrelated circuit used by a customer buying an expensive circuit fails.

Yep. I would say that telcos have rather strong incentive to keep PDH in place. It may actually be a good deal for IP people -- you can get more capacity at a lower price, and handle redundancy at level 3 (hey, interior re-routing is fast). Of course, to get advantage of that practice one may want to work closely with telco to understand their modes of failure, and write a language protecting topology of his network overlay.

If you have spare fibres in the ground, light them up to protect your primary SDH paths.

Nyah. Protection does not generate more sales, and so does not seem attractive to sales folks. The ones calling for protection are engineers inside telcos, and they are usually ignored.

You don't need an additional MUX, you don't need extra DAXCs, and you don't need to scurry around reprogramming lots of equipment when someone wrecks your fibre.

It's technical staff who's doing all the scurrying. Sales people already got their comission and are quite happy. My prediction is that redundancy of telco data services won't improve at all until they find a way to reconcile need for redundancy and desire to sell all the capacity they got. Native IP networks seem to have the ability to provide that. --vadim