JRH, "self-healing" is a service "option" which many ISPs elect to avoid due to what they feel is adequate robustness in their routing capabilities. Ah hem. Not all SONET routes are created equal, in this respect.
Also, many SONET routes which do employ self healing use a cheaper design [two-fiber, as opposed to four-fiber, and some other subtle differences] which relegates half of their overall capacity to back up or standby status. When this occurs, you could easily regard an OC-192 as actually one that could only support OC-96, OC-48 as only an OC-24, etc., for the purposes of self-healing and overall service assurance.
If a subscribing SP happens to be situated on the half of the system which is designated for "backup" channels (which operate just like regular production channels in the absence of an outage), and if they have elected to forego self healing, then they get "bumped," or preempted, during outages to make way for those who do pay. HTH.
Regards, Frank Coluccio |
