Reading the discussion here reminded me of the outage of AT&T's long-distance network back in 1991. After a bit of searching, I found an interesting-looking do

Reading the discussion here reminded me of the outage of AT&T's long-distance network back in 1991. After a bit of searching, I found an interesting-looking document at http://faqs.org/rfcs/rfc3439.html http://faqs.org/rfcs/rfc3439.html entitled "RFC 3439 - Some Internet Architectural Guidelines and Philosophy," which seems relevant here somehow. Though this document outlines considerations pertaining to complexity in Internet backbone architecture, perhaps the overall philosophical questions it poses and guidelines it offers could be instructive as regards the recent Skype meltdown. As regards the aforementioned 1991 failure of the AT&T long-distance system, which resulted in a service outage of about six hours, the document says: "The PSTN's SS7 control network provides an interesting example of what can go wrong with a tightly coupled complex system. Outages such as the well publicized 1991 outage of AT&T's SS7 demonstrates the phenomenon: the outage was caused by software bugs in the switches' crash recovery code. In this case, one switch crashed due to a hardware glitch. When this switch came back up, it (plus a reasonably probable timing event) caused its neighbors to crash When the neighboring switches came back up, they caused their neighbors to crash, and so on [NEUMANN] (the root cause turned out to be a misplaced 'break' statement; this is an excellent example of cross- layer coupling). This phenomenon is similar to the phase-locking of weakly coupled oscillators, in which random variations in sequence times plays an important role in system stability [THOMPSON]."