Just One Phone?

Many of us have just a mobile these days. Dismal Manor has not adopted that strategy for a number of reasons.

• Mobile phones are failure prone.
• Mobile phones and “land-line phones” are not equivalent.

So we have one of each. Just recently, T-Mobile was hard down in Norfolk Virginia. OOMA VoIP was fat, dumb, and happy but nether matches the 5-nines reliability of a plain old central office switched line. And neither is equivalent to a switched line.

References

Most of this article is based on my personal observations over 50+ years as a telephone service subscriber and electric power customer in New England and southeastern Virginia. I do have references for phone cost and cell size planning.

1. https://www.statista.com/statistics/619830/smartphone-average-price-in-the-us/
2. https://sites.google.com/site/lteencyclopedia/lte-radio-link-budgeting-and-rf-planning

Dismal Manor’s Phone Services

I have both fixed and mobile service here at home, an OOMA VoIP line (2 actually as I subscribe to OOMA Premier service) and a mobile line (2 actually as I use YouMail). I do this primarily to have redundant access to emergency services calling.

I had, for some years, given my mobile number to business callers. After all, the mobile number would ring both phones. As robocalling became pandemic, I have have switched my business callers, especially healthcare providers to my fixed number. When health care providers calls from their business line, caller id shows that it is a health care provider calling. It is almost 100 percent reliable about this. I don’t have to have the number in a white list for it to be properly identified.

I use the YouMail mobile number as my public mobile number. If a phone goes in the bay, I can quickly set up its replacement. No magic spells to cope with transfer of a mobile number belonging to a drowned device.

Did not answer mobile calls forward to my OOMA second number. There is distinctive ringing so I can recognize a forwarded mobile call. OOMA outages forward incoming OOMA calls to my mobile.

For my mobile to identify an individual mobile caller, the caller’s number must be in the phone’s contacts. This is true whether the caller is using a personal mobile, business mobile, or business terrestrial line.

It is very rare for both mobile service and terrestrial service to be interrupted simultaneously. This usually happens when Cox circuits are involved in the back haul of both. It also happens when a hurricane or ice storm power outage exceeds the duration of the carrier’s backup power systems. It is not uncommon for a weather outage to exhaust field network backup power sources.

Cox is my local Internet carrier for OOMA and Cox provides back haul to many cell tower operators too. A Cox fade can affect all of the cellular operators present in a cell or group of cells. This has happened at least once in 2021. If it is not a Cox circuit, it is most likely a Verizon circuit. They are the two common carriers that are everywhere.

Terrestrial Phone Service

Back in the old days, the regional telephone monopoly provided a dedicated pair to each residence in its service territory. You subscribed or you didn’t. The Federal Communications Commission regulated the regional carriers which were each part of the AT&T nationwide network. The carriers prided themselves on high reliability of the central switch but the subscriber lines between the central switch and the customer were at the mercy of backhoes, weather, and vehicles. In areas where the lines were below ground, water infiltration would cause them to snap, crackle, and pop like a bowl of Rice Krispies. Or a construction worker would break a line while digging.

In the beginnings of telephone service, subscriber lines would originate at a central office, run in a bundle to a neighborhood, and fan out to individual homes. More recently, in the 1980’s, a group of lines would leave the central office as a fiber optic circuit. At a group of service delivery points, a subscriber line interface would create individual copper lines for the devices to be served at that location. Today, many older locations have been updated to fiber to copper service.

Central office lines just worked unless damaged in the field. The central office used batteries to power the subscriber loops and a generator kept the batteries charged. The newer field multiplexing schemes require power out in the field. Commonly, the operator installs either a battery bank and inverter or a natural gas powered generator, battery bank, and inverter. The batteries appear to support operation for about 24 hours. The field generators are able to run continuously for several days but shut down on low oil level eventually. We saw this behavior here during Hurricane Isabel.

POTS characteristics

Over time, this service came to be known as POTS (plain old telephone service). It had the following characteristics.

• It was expensive
• It usually just worked, you always got a dial tone
• It was inflexible. The operating company provided equipment.
• The endpoint address was fixed and well known
• The phone company maintained and distributed directories of individual numbers and a pay to be listed business directory, the Yellow Pages.
• You could call 411 for directory information. Often you spoke to an operator familiar with your region.
• Area codes and direct distance dialing were introduced.
• Satellite and fiber optic circuits reduced long distance call cost. But out of service area calling was billed at a premium.

In the 1970’s Congress began the deregulation of the telephone carriers and broke AT&T up into regional carriers. With this change, the carriers could no longer require you to lease equipment from them and customers could provide their own certified equipment. Radio Shack and others began selling FCC certified customer equipment including handsets, desk sets, voice message recorders, and caller id loggers.

SPRINT and others began offering alternative long distance calling. You called SPRINT, entered your billing code, then dialed the regular 10 digit number to receive reduced cost service that was usually a bit noisier than that offered by the incumbent local carrier.

Universal Service

In exchange for monopoly status, the carrier had to agree to provide service to all residences and businesses in the service territory. Each line subscriber chipped in to a universal service fund mandated by Congress. The carrier used the proceeds of this fund to provide service to low income and rural subscribers who cost more to serve than they brought in.

The notion of universal service was carried over to mobile service. Each mobile subscriber pays a fee set aside to pay for “Obama phones” as a certain political party called devices provided under the provisions for universal service.

Mobile Phone Service

In the beginning, mobile phone service was pretty specialized and quite expensive. It relied on MF/HF AM radios and an operator was involved in each call. Very few individuals owned or operated a mobile phone. Usage was mostly for calling between larger vessels and shore support facilities.

In college, I owned an AM/FM/SW portable radio that covered the HF marine band. I recall listening in on several ship to shore calls between Electric Boat test officials and Electric Boat management discussing issues that had cut a submarine’s builders trials or acceptance trials short. Such usage was rare and usually happened when a ship was experiencing main-propulsion issues that required a tow. Before delivery, the builder provided the tow.

At the time, Dad was deputy director of Fitting Out and Test and received the fall-out from these calls. And he had a sea story or two to tell from riding trials.

A Better Mobile Service, Cellular Service

In the 1970s Motorola and Bell Labs were working in competition to develop cellular mobile telephone service. The service area is divided into line of sight cells. Towers in each cell and the surrounding cells are visible to stations operating in a cell. The idea was to allow computers to set up and manage the call. As the endpoint moved about the service area, the cell that the vehicle was exiting could hand the call off to a neighbor automatically. No operator or user action was required.

By moving the frequency way up into the UHF bands, more simultaneous calls could be accommodated. Automatic call provisioning allowed use of line of sight radio frequencies making calling much less subject to ionospheric effects and mutual interference.

Tower height determined cell size since propagation was strictly line of sight at these higher frequencies.

Since integrated circuit electronics and integrated circuit computers could be used, the cost of terminal equipment dropped rapidly from thousands of dollars to a few tens of dollars. By the mid-1990’s (about 20 years after introduction) most traveling business people could afford to own and operate a mobile phone.

Today’s phones have a median price in the $700 to $900 range but have greatly expanded functionality including media storage and play back, cameras and image management, and satellite navigation features in addition to voice communications. The camera hardware and software probably dominate the development cost of the modern mobile.

Many carriers have neglected their terrestrial networks to the point where service in low income urban areas is substandard. Carriers, Verizon in particular, are trying to retire terrestrial copper circuits.

As with terrestrial service, mobile service is considered essential as it allows emergency services communications. So there is a universal service fund and subsidized service is available to low income and rural customers.

Mobile Service Characteristics

Mobile service replaces the wired subscriber circuit with a two way (full-duplex) radio channel. This circuit has the following capabilities and limitations.

• The call requires both an outbound and an inbound communications channel (2 radio frequencies). In practice its a bit trickier as spread spectrum channels are used.
• Service is to a mobile device that can move about the service area. When a call moves into a new cell, there is no guarantee that it can be provisioned with radio channels in the new cell.
• Mobile service is mobile. The number is associated with you rather than your place of residence. Moving phone service to your new residence is as easy as driving to your new residence.
• Service is less robust. Weather, terrain, and structures can reduce or block the radio signals. In addition, the shared infrastructure is subject to power cuts and back-haul service fades.
• Calls appear to be perfect until they are not possible. Dropped packets present as static. When the drop rate gets high, the system will usually drop the call, often without indication to either party beyond silence.
• Individual cells are subject to call origination saturation. The handset requests but does not receive call setup service.
• Mobile call caller-id is less robust than that used by POTS calls. POTS provides the calling number and the subscriber name of record for the number. Mobile service provides the calling number and handset county or city.
• Mapping of a call’s geodetic coordinates to an address is approximate. The network will randomly map a device’s location to a side street or a back street rather than to the parcel’s canonical address. Apple’s Find My app shows this nicely.
• Although rare, problems affecting back-haul from the tower network to the terrestrial switching and routing system can cause city-scale outages. We had one here in late September.