It's more about lack of regulation than technology
The major issue with the move towards IP-based telecommunications systems is that the regulators are not requiring the telcos to ensure that there is 'always-up service.' Traditionally, most telephone exchanges (switches/central offices) had pretty huge battery back up and most telcos tended to have diesel generators at key sites too should the power go down.
These buildings were mostly designed in the days of crossbar and step-by-step switching after WWII and during the cold war. They were also designed to house technologies that didn't really allow for much distribution of switching. They would typically use longer lines and fewer central offices.
As technology improved, the idea of distributed switching starts to emerge. So, by the late 1970s when digital telephone exchanges were popping up, one of the major advantages of them was that you could install more, smaller nodes, closer to the customers. This meant less complicated wiring systems (i.e. shorter lines) and easier upgrades as demand increased.
So, from the 1980s onwards you started to see what's referred to over here as "RCUs" (Remote Concentrator Units). Here in Ireland, the switches would have mostly been Ericsson AXE or Alcatel E10 equipment. The typical layout from the 1980s onwards was a local exchange with quite a large number of RCUs in individual suburbs/towns/villages all managed from a central location. These were linked back by fibre (or in the earlier days microwave) to their local main node.
The downside, is that they're often tiny units, sometimes only a few outdoor, weather proof cabinets, and their battery back up is pretty limited.
Then you'd the growth of mobile networks in the 1980s too.
Cellular coverage requires lots of distributed technology too. As the number of users and the expectations of perfect coverage went up, the networks added more and more microcells and picocells to fill in gaps in coverage and increase capacity. These sites are usually just on the sides of buildings, hidden in fake trees and generally camouflaged into the environment. In hard to cover areas like streets with high buildings, campuses, shopping malls etc, metro systems, tunnels, etc they'll add picocells which are not much bigger than your home WiFi hub. They're just a little panel on the wall.
The smaller these things get the less likelihood of battery backup. So, when the power goes down, you can be left with just the major towers on air which results in poor coverage.
If you ever do lose power and your mobile coverage goes down, switch to 2G and stand outside to get a signal. It's likely that your network's major locations are still on air as they typically have significant battery backup.
With the move towards VoIP replacing POTS for landlines, there are a few ways of providing it.
You can keep the copper wiring in place and just convert the central offices to IP technology. That's happening in a lot of places. However, the speed at which people are adopting other technologies is making the business case for retaining POTS central offices very difficult to justify.
For example, our local telco here in Ireland originally planned to place POTS/ISDN cards into the FTTC cabinets that they provide VDSL from and close central offices. However, people don't seem to want POTS service anymore and residential users are quite happily switching over to using IP phones and ATAs to connect to VoIP services without any need for line cards. I'm sure that's the same in most other countries too.
What we're seeing is a mixture of managed IP telephony services using home gateways (i.e. the type of stuff you plug into the back of the box your cable TV company or ISP provides). These can provide end-to-end managed VoIP and ensure full quality of service.
The other part of the market that's growing quite quickly is "Over the Top" VoIP services which just use the public Internet and have nothing to do with the ISP or telco. For many people this is perfectly adequate and as broadband speeds and reliability increase, it's a very viable alternative to services from telcos and cable cos.
Then you've got a huge shift in the way businesses are connecting their telephone systems. In the past they generally (here in Europe anyway) tended to use ISDN to connect to their PBX (office system). This is what allowed all the direct-inward-dial extensions and all of those things. Now, that's largely being replaced by VoIP technology mostly using SIP trunks.
Many small businesses are moving towards using cloud-based hosted PBXs which require no equipment on site at all. You just connect every extension to the internet and the whole thing is hosted on a soft switch somewhere else.
So, basically the entire voice telephony market is being turned upside-down and inside out.
...
The other aspect is that the telcos have no option but to retire PSTN/POTS switching equipment as the manufactures are no longer supporting it. You're talking about 1970s/80s technology that's reaching the end of its life.
In the USA and Canada most local landline companies were using 5ESS switches built originally by Western Electric / Bell Labs (now part of Alcatel Lucent) for AT&T, DMS 100 switches made by Nortel (no longer exists) or in some cases Ericsson's AXE platform (major European system) which is still supported.
In Europe, you've a similar scenario:
Ericsson AXE - by far the biggest digital TDM switching platform in the world, is moving towards being a 'soft switch'. The old gear is still supported, but they're pushing people onto new IP-based systems.
Alcatel E10 and S12 - Alcatel Lucent is also moving everyone onto IP and consider these systems "End of Life"
Siemens EWSD - Huge platform that's used in many European countries, also 'end of life'. Nokia Networks now owns the technology and are pushing users onto IP too.
In Britain, there's an even more serious problem. British Telecom's digital network is largely made up of a UK system called "System X" which was originally a government-driven project in the 1970s/80s that was delivered by a consortium of British telecommunications equipment markers : GPT, Plessey and STC. It ended up as part of Marconi's stable of products, but it was quite late to market and it never achieved export sales. Basically it's is only used by BT in the UK. Marconi vanished a few years ago and various bits of the company ended up in Siemens and Ericsson. However, the System X switching system didn't. The result is that it's basically being managed as 'end of life' and I would assume that BT will want to find an alternative solution as soon as possible and I know some of those switches are being replaced by IP-based technology. However, they're possibly maintaining dial tones for now.
Basically, to cut a long story short, PSTN/POTS service will not be around for more than another decade at most. The technology's literally dying out.
In most scenarios, large chunks of the POTS network have already been replaced with soft switches and IP-based systems. They'll eventually get down to ripping out local exchanges and that'll be the end of 100+ years telephony delivered over an analogue interface to your home.
The major issue with the move towards IP-based telecommunications systems is that the regulators are not requiring the telcos to ensure that there is 'always-up service.' Traditionally, most telephone exchanges (switches/central offices) had pretty huge battery back up and most telcos tended to have diesel generators at key sites too should the power go down.
These buildings were mostly designed in the days of crossbar and step-by-step switching after WWII and during the cold war. They were also designed to house technologies that didn't really allow for much distribution of switching. They would typically use longer lines and fewer central offices.
As technology improved, the idea of distributed switching starts to emerge. So, by the late 1970s when digital telephone exchanges were popping up, one of the major advantages of them was that you could install more, smaller nodes, closer to the customers. This meant less complicated wiring systems (i.e. shorter lines) and easier upgrades as demand increased.
So, from the 1980s onwards you started to see what's referred to over here as "RCUs" (Remote Concentrator Units). Here in Ireland, the switches would have mostly been Ericsson AXE or Alcatel E10 equipment. The typical layout from the 1980s onwards was a local exchange with quite a large number of RCUs in individual suburbs/towns/villages all managed from a central location. These were linked back by fibre (or in the earlier days microwave) to their local main node.
The downside, is that they're often tiny units, sometimes only a few outdoor, weather proof cabinets, and their battery back up is pretty limited.
Then you'd the growth of mobile networks in the 1980s too.
Cellular coverage requires lots of distributed technology too. As the number of users and the expectations of perfect coverage went up, the networks added more and more microcells and picocells to fill in gaps in coverage and increase capacity. These sites are usually just on the sides of buildings, hidden in fake trees and generally camouflaged into the environment. In hard to cover areas like streets with high buildings, campuses, shopping malls etc, metro systems, tunnels, etc they'll add picocells which are not much bigger than your home WiFi hub. They're just a little panel on the wall.
The smaller these things get the less likelihood of battery backup. So, when the power goes down, you can be left with just the major towers on air which results in poor coverage.
If you ever do lose power and your mobile coverage goes down, switch to 2G and stand outside to get a signal. It's likely that your network's major locations are still on air as they typically have significant battery backup.
With the move towards VoIP replacing POTS for landlines, there are a few ways of providing it.
You can keep the copper wiring in place and just convert the central offices to IP technology. That's happening in a lot of places. However, the speed at which people are adopting other technologies is making the business case for retaining POTS central offices very difficult to justify.
For example, our local telco here in Ireland originally planned to place POTS/ISDN cards into the FTTC cabinets that they provide VDSL from and close central offices. However, people don't seem to want POTS service anymore and residential users are quite happily switching over to using IP phones and ATAs to connect to VoIP services without any need for line cards. I'm sure that's the same in most other countries too.
What we're seeing is a mixture of managed IP telephony services using home gateways (i.e. the type of stuff you plug into the back of the box your cable TV company or ISP provides). These can provide end-to-end managed VoIP and ensure full quality of service.
The other part of the market that's growing quite quickly is "Over the Top" VoIP services which just use the public Internet and have nothing to do with the ISP or telco. For many people this is perfectly adequate and as broadband speeds and reliability increase, it's a very viable alternative to services from telcos and cable cos.
Then you've got a huge shift in the way businesses are connecting their telephone systems. In the past they generally (here in Europe anyway) tended to use ISDN to connect to their PBX (office system). This is what allowed all the direct-inward-dial extensions and all of those things. Now, that's largely being replaced by VoIP technology mostly using SIP trunks.
Many small businesses are moving towards using cloud-based hosted PBXs which require no equipment on site at all. You just connect every extension to the internet and the whole thing is hosted on a soft switch somewhere else.
So, basically the entire voice telephony market is being turned upside-down and inside out.
...
The other aspect is that the telcos have no option but to retire PSTN/POTS switching equipment as the manufactures are no longer supporting it. You're talking about 1970s/80s technology that's reaching the end of its life.
In the USA and Canada most local landline companies were using 5ESS switches built originally by Western Electric / Bell Labs (now part of Alcatel Lucent) for AT&T, DMS 100 switches made by Nortel (no longer exists) or in some cases Ericsson's AXE platform (major European system) which is still supported.
In Europe, you've a similar scenario:
Ericsson AXE - by far the biggest digital TDM switching platform in the world, is moving towards being a 'soft switch'. The old gear is still supported, but they're pushing people onto new IP-based systems.
Alcatel E10 and S12 - Alcatel Lucent is also moving everyone onto IP and consider these systems "End of Life"
Siemens EWSD - Huge platform that's used in many European countries, also 'end of life'. Nokia Networks now owns the technology and are pushing users onto IP too.
In Britain, there's an even more serious problem. British Telecom's digital network is largely made up of a UK system called "System X" which was originally a government-driven project in the 1970s/80s that was delivered by a consortium of British telecommunications equipment markers : GPT, Plessey and STC. It ended up as part of Marconi's stable of products, but it was quite late to market and it never achieved export sales. Basically it's is only used by BT in the UK. Marconi vanished a few years ago and various bits of the company ended up in Siemens and Ericsson. However, the System X switching system didn't. The result is that it's basically being managed as 'end of life' and I would assume that BT will want to find an alternative solution as soon as possible and I know some of those switches are being replaced by IP-based technology. However, they're possibly maintaining dial tones for now.
Basically, to cut a long story short, PSTN/POTS service will not be around for more than another decade at most. The technology's literally dying out.
In most scenarios, large chunks of the POTS network have already been replaced with soft switches and IP-based systems. They'll eventually get down to ripping out local exchanges and that'll be the end of 100+ years telephony delivered over an analogue interface to your home.
