The Public Communications Network: What You Need To Know.

There has been a lot of on line chatter about how the public communications network (i.e., “the phone company”) fits into off grid ham radio and survival/prepping plans. After listening to endless anecdotes, half truths, misunderstandings, and in some cases amazing fiction, I will attempt to clear up a few things. My perspective comes from over 25 years of professional technical experience in the telecommunications industry.

I realize this topic does not neatly fit into the theme of Off Grid Ham, but it is worth drifting out of the format a little to bring clarity to a subject that effects how we prepared radio amateurs organize our stations and operating procedures. My goal is to impart a greater awareness of the public communications network and illustrate the importance of off grid ham radio capabilities for when the network is unavailable. Knowledge about other communications systems makes us more circumspect radio operators.

The breadth and width of this subject is way too large to comprehensively cover in one article, so I’ll hit only a few major points.

public communications


The Legend: Hardwired “landline” phones are reliable and simple.
This used to be a lot more true than it is now. The public switched telephone network (PSTN), colloquially referred to as Plain Old Telephone Service (POTS), was the workhorse of the old Bell System. As customer traffic grew, new technologies were developed to make better use of copper cables, or reduce the need for copper cables at all. Copper is very expensive to install and maintain, and until recently had very limited traffic capacity.

There is so much more to the time-tested POTS lines than a run of wire connected to a switch. If you live in a newer area, or are rural, your service probably terminates in a roadside cabinet (requiring a power source) called a remote terminal or RT, which serves a small geographical area such as a subdivision. There it is mixed (in telecom lingo, multiplexed or muxed) with all the other traffic from your area. It is then converted to an optical signal, or sometimes a copper-based T-carrier and sent to the central office. A similar setup in the central office reverses this process (demuxing), and passes it off to a phone switch.

A ground mounted telephone cross box. Note the graffiti and vandalism. PHOTO COURTESY OF SENSORCITIES.COM

A ground mounted telephone cross box. Note the graffiti and vandalism. PHOTO COURTESY OF SENSORCITIES.COM

In other applications, the copper from individual subscribers is fed into a cross box, or X-box. Cross boxes are passive devices that do not require external power and act as miniature switchboards between the main cable, known as the F1, and the wire to the customer premise, or F2. Cross boxes can be set on the ground or pole mounted. What’s important to the off grid ham is that cross boxes are deliberately placed for easy access by technicians. As such, they are vulnerable to vandalism, weather, and accidents.

The most desirable scenario for a prepper/survivalist is buried direct feed copper, meaning, a buried cable straight from your house to the central office  (not through an RT or cross box). This setup has the least exposure to common causes of breakdown. Unfortunately, buried direct feed copper is very, very rare. That 1970’s era rotary dial phone hanging in your kitchen may make you all feel all gushy & nostalgic, but it’s got all the same shortcomings and points of failure as anything else.

Switched and routed networks.
Switched networks were the standard since the dawn of the Bell System…but that is not true anymore. Switched networks operate like a light switch: A closed circuit is established between two fixed points. Communications is exchanged. When the two parties are done, the path is broken. The big disadvantage is that it’s very inefficient because most of the time network resources sit around doing nothing. Think of it as a road that only one car at a time is allowed to use. The phone company has to maintain that public communications network even when hardly anyone is using it.

Routed networks were a huge evolutionary leap forward.
The internet could never possibly function on a switched network. They had to come up with a better plan. Instead of a dedicated circuit between every point, routed network users share common paths. Bit addressing means multiple blocks of data going to the same destination do not necessarily get there via the same path; a dynamic routing protocol automatically detours data around network congestion in real time. The road can accommodate many cars.

The disadvantage is that a failure can effect many, many customers. This problem is mitigated with a principle called network diversity. Implementing diversity allows alternate paths between the same destinations so that failure in any one path does not completely cut off public communications. There are failures every day that customers never notice because the large telecoms have spent billions on diversity.

Routed networks were a huge leap in efficiency. More traffic can be processed faster with less resources, and expensive hardware does not sit around waiting for something to do. If you get your services from a cable company, AT&T uVerse, Verizon FiOS, a VOIP provider such as Ooma, or any type of wireless/cellular provider, then you are already on a routed system. This is the future of the public communications network.

public communications

Diagram of a Public Switched Telephone Network (PSTN). GRAPHIC COURTESY OF FLYLIB.COM

Switched networks, the FCC, and you.
The large telecoms have been wanting to retire switched networks for years because there is no business case for maintaining two totally separate systems. The only reason the telecom providers haven’t pulled the plug on switched public communications networks is due to state level regulators and the Federal Communications Commission (FCC) not allowing it. Yet, consumer and political attitudes are changing. The regulatory hurdles are slowly falling away and customers are rapidly being moved to software based routed networks. The potential cost savings is in the billions.

A few years ago AT&T announced Project 2020, which is an initiative to accelerate the phase out of switched networks. They are on track to have 75% of their entire network on virtualized/routed platforms by 2020. Verizon is looking to do the same. In the not too distant future you may be able to go to a swap meet and buy an entire Lucent 5ESS or Nortel PSTN switch for cheap! Bring a semi trailer and a forklift, and you better have one mutha of a power supply, too!

If your wired phone service currently terminates into a switch, sometime in next few years you will be moved to a pure routed network, probably without your knowledge.

The issue of government recalcitrance is becoming less relevant because fewer and fewer consumers have wired POTS lines anymore. Customer choice and attrition is doing the Big Telecom lobbyists’ job for them.

The ridiculous fantasy of “POTS lines are better”.
This biggest myth I see on amateur radio, survival, and prepping internet forums is that having a fixed POTS line running on copper is a huge advantage over a cell phone. This ridiculous fantasy comes from the once true but now outdated & incorrect belief that switched POTS lines are more reliable and less likely to break than routed services.

The hard truth is that the phone company does not want you to have that switched POTS line in the first place. They are doing the bare minimum to maintain it and are not going to bust their ass to fix it if it breaks. If the government is too slow in letting telecom providers get rid of switched networks, then the next best thing is to make life unpleasant for those who still use them and encourage customers to leave on their own.

I have heard the personal accounts about how someone had a POTS line for 30 years and it never broke once. That was then and this is now. If it fails in a SHTF incident, it may never get fixed.

Exhibit A: Hurricane Sandy vs. Verizon.
In the aftermath of hurricane Sandy on the east coast of the USA in the fall of 2012, Verizon did not want to be bothered restoring all the legacy copper facilities damaged by the storm. Instead, they wanted to place many of the effected customers on a wireless routed system and abandon the copper entirely. They later backed off that plan, but only because of public and legislative pressure, not technical considerations. Yet, the writing is on the wall: The telecomm providers very badly want to get out of copper-based switched public communications networks and are not going to cooperate with keeping them around.

In a disaster scenario, what makes more sense: Repairing individual wired phone lines one at a time, or restoring fiber optic routed services to cell towers that serve thousands of customers each? Many Verizon wireline PSTN customers were still out of service months after hurricane Sandy while the cell service was quickly back on line, in many cases within hours of the storm passing.

The Verizon-Sandy incident is illustrative of the backward thinking of legislative bodies and the FCC in particular: They pressure the telecoms to invest in advanced broadband routed technology while at the same time mandating they maintain decades-old, obsolete switched public communications networks that very few customers want anyway. It’s like missing a payment on the brand new car you drive every day because you spent all your money fixing the old junk that sits in the driveway most of the time but your spouse flatly refuses to let you get rid of.

Backup power for public communications networks.
Large telecomm facilities and most cell towers have stationary diesel generators with about 3-5 days of fuel is stored on site. Also, there are large battery banks that act as a UPS system to run the equipment for the time between when the commercial power fails and the generator comes on line. This is usually less than a minute or so, but the batteries can support the network for a few hours if the engine does not start.

Portable generators are trailered in to smaller facilities that do not have dedicated engines; in a perfect world this is done before the batteries go dead. Generators are stored in strategic places, but it’s easy to see the problems that would arise if there was no technician available to bring the generator or if the power outage was so widespread that there were not enough portable generators to go around.

Remote terminals are low on the priority list for portable generators but some have battery backup. Other RTs have no backup at all. In the event of a wide scale power outage, many RTs would go dark immediately, the rest within a few hours.

What to do if you live in an area with poor cell coverage.
If you live in an area with weak or no cell service and depend wholly on a wired line, the best option is to have a plan for when the wired line goes down.

Identify nearby places ahead of time where you can get a decent signal, preferably more than one location. You may have to drive to the top of a hill to make a phone call, but it’s better than being totally cut off. A second option is to have a distant ham radio operator do a phone patch for you. Phone patches via amateur radio are very rare these days, but the equipment is still available. If you do not have phone patch capability, consider adding it so you can assist other hams in times of need.

Lastly, some repeaters still have an autopatch function that allows operators to make phone calls over the radio. Again, it’s important to plan ahead. Do not wait for a tornado to level your town to find out that your local repeater does not have autopatch.

So why should amateur radio operators care about any of this?
Switched networks’ glory days have long past. They run over aging equipment and copper that is not being upgraded and is a very low priority for repairs. Still, many survivalists/preppers still cling to the laughable belief that the switched public communications network is inherently more stable than routed services.

I doubt anything I’ve said here will kill the “POTS lines are better” myth circulating in survivalist/prepper circles, but let me put it this way: I work in telecomm, mess with this stuff every day, and have deep insight as to what the industry priorities are. When SHTF, the telecomm providers will not so much as vaguely think about restoring PSTN services until all the routed services are back on line, and even then they will look for a way to squirm out of it. Routed networks will be the last to go down and the first to come back. Believe it.

Knowing how the public communications system works helps the radio amateur understand the consequences if it should go down. They can then apply their knowledge to preparing for those consequences by assembling a station that can communicate when nothing else is working.

Author’s note: This article was adapted from old internet forum posts I made on Survival Monkey,  Prepared Ham, and  I no longer have access to most of these posts, but I did update Prepared Ham to reference this article and prove that I did not plagiarize it. Those posts were subsequently circulated around other forums by other people and I have no control over that content. 

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