Arguing about which is more reliable misses the point. The only thing that matters is, is "it reliable _enough_". And does it offer enough other advantages (either in cost or services) to overcome any deficiancy in reliability?
For example, are cell phones as reliable as analog lines? No. But they certainly are reliable enough for their intended purpose and the additional features they have more than make up for their relative lack of reliability. So even though they are MORE expensive and less reliable, cell phones activations are going up while analog lines are going down. Is SIP trunking over the public internet as reliable as a dedicated PSTN connection? No (Actually, in my experience it is but lets just say "no" for the sake of argument). But it is more than reliable enough for 95% of the business users out there and it also offers more flexibility and lower cost (potentially much lower cost if you no longer have to install an on-site PBX or gateway). And back to reliability, PSTN service (both analog and PRI) has zero redundancy. It's a single wire connecting to a single piece of equipment (at both ends) that does not support any of the routing and switching redundancy and fail-over that an IP network enjoys. All of my clients with PRI connections (including myself) have had some kind of failure resulting in downtime. MTBF (mean time between failures) is only a meaningful measure if you assume that the system was immediately repaired which is why for networks we typically measure "uptime", not MTBF. When voice over internet is done correctly, it's very stable and reliable. The problem is, doing it correctly requires a lot of experience. A lot of people have done it wrong and it's going to take some time to convince people that it wasn't a deficiency of the technology, but a problem with the implementation. John
