Landline Phone Q: Why is the phone line plugged into modem-not wall?

  • Thread starter kyphysics
  • Start date
  • #1
kyphysics
426
362
In the old days, people plugged landline phones into house/apartment wall mounted phone jacks. This was standard.

Then, at some point, people started plugging their landline phone cords (via an adapter) into their internet modems.

Dumb question for a non-techie. Why is that? Also:

a.) How is it possible for modems to give you phone service when it's an internet connection service to residences? Is it because you can use your internet provider (I use Verizon) to also purchase residential landline phone service too?
b.) Even if the above is true and you use the same internet and landline phone service provider, how does the modem itself let you make calls through a landline phone? I thought there was something special about those old school wall mounted phone jacks that required you to use them for old school phone service.
c.) If your internet and landline provider are different, can you still plug a landline phone into modem? Or, in that case, would the phone cord have to go into a phone wall jack.
d.) If you plug a landline phone into your modem, does that make it susceptible to someone over the internet hacking your phone and/or listening into your call somehow?

Thanks for your feedback.
 

Answers and Replies

  • #2
phinds
Science Advisor
Insights Author
Gold Member
2022 Award
18,141
10,971
1669584745004.png
 
  • Like
  • Wow
Likes russ_watters and kyphysics
  • #3
berkeman
Mentor
64,139
15,352
I thought there was something special about those old school wall mounted phone jacks that required you to use them for old school phone service.
Yes, they are provided 48Vdc power from the Central Office (CO) and transmit audio band waveforms to/from the connected CO.

c.) If your internet and landline provider are different, can you still plug a landline phone into modem?
Doubtful.

d.) If you plug a landline phone into your modem
Can you provide an example of a 48V POTS (plain old telephone service) phone jack on a modern Internet modem? I've never seen that.
 
  • #4
hutchphd
Science Advisor
Homework Helper
2022 Award
5,348
4,515
My VOIP provider supplies a dedicated modem which connects to my LAN and allows connection of an otherwise unpowered old style "wall phone" which is part of my former interior phone service. So I assume it supplies the 48V. It in fact is connected to my two-wire house telephone wiring formerly used by AT@T with several connected phones.
 
  • Like
Likes russ_watters and kyphysics
  • #5
berkeman
Mentor
64,139
15,352
My VOIP provider supplies a dedicated modem which connects to my LAN and allows connection of an otherwise unpowered old style "wall phone" which is part of my former interior phone service. So I assume it supplies the 48V. It in fact is connected to my two-wire house telephone wiring formerly used by AT@T with several connected phones.
Interesting. But when you say your VOIP provider, what is the physical connection to their CO? Fiber, cable, or DSL twisted pair?

And can you still dial a number with your classic POTS phone by clicking the hang-up buttons? I wonder if they included that feature...

1669601387672.png


https://www.mgraves.org/wp-content/uploads/2010/08/vintage-phone1.jpg
 
  • #7
berkeman
Mentor
64,139
15,352
  • #8
hutchphd
Science Advisor
Homework Helper
2022 Award
5,348
4,515
And can you still dial a number with your classic POTS by clicking the hang-up buttons? I wonder if they included that feature...
Love it.
I think the phone as tone dialing. (No crank on the side either). But no other external power
My internet connection is cable and that feeds my Wi-Fi and Lan router. Phone modem attaches cat5 to one Lan port and to standard phone jack which connects to house wires and standard phones.
Truth be told I haven't had the wall phone on it for several years but the system hasn't changed. Service is VoipO.
 
  • #9
kyphysics
426
362
Can you provide an example of a 48V POTS (plain old telephone service) phone jack on a modern Internet modem? I've never seen that.
Sorry, I meant doing so through an adapter. You're right that this probably doesn't exist and needs an adapter.
 
  • #10
Tom.G
Science Advisor
Gold Member
4,691
3,444
And can you still dial a number with your classic POTS phone by clicking the hang-up buttons? I wonder if they included that feature...
I have phone service by Spectrum (Charter Cable) for VOIP. Their phone-internet modem accepts only tone dialing and also can not drive the Ringer (bells) on the old dial phones. Nominal phone ring voltage was 90V, ½Watt maximum, (about 5.5mA), 20Hz. You didn't want to be hanging on to those wires when a Ring signal came in!

Those phones with a dial presented a pulsed open circuit to the line, 2 pulses when dialing '2', 9 pulses when dialing '9', etc. With the unloaded line voltage being 48V, that sent 48V pulses back to the CO (Central Office) riding on an Off-Hook voltage of roughly 10Volts.

Although I haven't tried it, when I asked several years ago if the old style phone could be used just as an extension without dialing or ringing, they said 'Yes'.

Irrelevant footnote: The nominal audio signal impedance of the phone line was 600Ω.

[Rant]
The POTS phone system was much more reliable that the present VOIP system. It wasn't affected by power outages or Internet outages. If either one goes down here, I'm stuck with no landline service, averaged around 20 minutes a month last year; sometimes minutes, sometimes hours.
[/Rant]

Cheers,
Tom
 
Last edited:
  • Like
Likes russ_watters and berkeman
  • #11
Rive
Science Advisor
2,449
1,864
Then, at some point, people started plugging their landline phone cords (via an adapter) into their internet modems.
There are different solutions for the same problem. What I'm familiar with is the ADSL type mixed service.
It's about having the low frequency band for voice calls, while having two high frequency bands for high speed digital communication (upstream, downstream).
You get a 'splitter' which separates the bands (and that 48VDC which was mentioned before) for the (old style) phone and (on a different connector) for the modem.

Ps.: before the ADSL there was the 'old style modem' thing: that's the one where you get the voice phone through the modem, so it could switch over to use it for itself. For ADSL it's parallel. But, of course: I'm not familiar with all the relevant systems, so there may be other similar solutions.

Ps2.: well, out of curiosity I've checked and actually there are ADSL modems with inbuilt VOIP capability: so an old-style phone can be connected to the modem, while the modem doing the digital part of the communication through the internet. So that works too: reaslly depends on the choice of your provider.
Though I'm happy with the old solution: that works without the modem (during a power outage, for example) too.
 
Last edited:
  • #12
anorlunda
Staff Emeritus
Insights Author
11,192
8,589
If your internet and landline provider are different, can you still plug a landline phone into modem?
Oh no. Don't pay two phone bills. If you have VOIP via your Internet provider, you must cancel your landline subscription. Moving the plug will not stop the billing.
 
  • #13
russ_watters
Mentor
22,054
9,152
Oh no. Don't pay two phone bills. If you have VOIP via your Internet provider, you must cancel your landline subscription. Moving the plug will not stop the billing.
I think he's just asking about compatibility/capabilities.

[Edit - on second read I'm not sure which "modem" he's referring to, so this answer may not apply. Heck, the term "modem" is an anachronism in this context too.]
The answer is yes you can still have different phone and internet - and TV for that matter - providers. The connection to your house is the same regardless of what services you buy, bit who runs which wires where will be different.
 
Last edited:
  • #14
russ_watters
Mentor
22,054
9,152
No, not with that. The question is how the POTS phone gets the 48V power that it needs. Hutch seems to be saying that he has used such a modem, but I've never seen it, and it seems strange that Internet providers would provide that capability when VOIP phone sets are so inexpensive to produce and they can sell them to the users.

I have phone service by Spectrum (Charter Cable) for VOIP. Their phone-internet modem accepts only tone dialing and also can not drive the Ringer (bells) on the old dial phones.
[Rant]
The POTS phone system was much more reliable that the present VOIP system. It wasn't affected by power outages or Internet outages. If either one goes down here, I'm stuck with no landline service, averaged around 20 minutes a month last year; sometimes minutes, sometimes hours.
[/Rant]
@berkeman , this is driven by legal requirements for compatibility, availability and reliability(safety). It's the reason why the newer service requires a provider-provided UPS at the service entrance; so that you still keep phone service during a power outage. But in practice, it is less reliable.
 
  • #15
pbuk
Science Advisor
Homework Helper
Gold Member
4,031
2,367
It is probably worth mentioning that everything in this thread is only generally applicable in the USA.
 
  • Like
Likes russ_watters, phinds and berkeman
  • #16
anorlunda
Staff Emeritus
Insights Author
11,192
8,589
It is probably worth mentioning that everything in this thread is only generally applicable in the USA.
That's interesting. Here's an opportunity for others to educate Americans like me.

  • What do providers in other countries do about phone service during electric blackouts?
  • Do other countries still maintain independent Internet and landline phone networks? If yes, might a homeowner have both landline and VOIP ports available in their home?
  • Do they provide means for all people to make emergency calls even if they can't afford all-purpose phone service?
 
  • #17
StevieTNZ
1,876
853
@berkeman , this is driven by legal requirements for compatibility, availability and reliability(safety). It's the reason why the newer service requires a provider-provided UPS at the service entrance; so that you still keep phone service during a power outage. But in practice, it is less reliable.
If the router/modem that the household phone is plugged into doesn't have power, how do you expect the phone line to work? I guess I don't know what you mean by 'service entrance'.

Our landline is now via the router. However, if we lose power we cannot use the phone. In any case, even before then, because we have wireless handsets if the power went out and the line was plugged into the old wiring, the phone still wouldn't work.
 
  • #18
pbuk
Science Advisor
Homework Helper
Gold Member
4,031
2,367
That's interesting. Here's an opportunity for others to educate Americans like me.
Oh there's never a shortage of opportunities to educate Americans :wink:

What do providers in other countries do about phone service during electric blackouts?
Traditional landlines in the UK are similar to the US with 50-60V on the line.

Do other countries still maintain independent Internet and landline phone networks? If yes, might a homeowner have both landline and VOIP ports available in their home?
In the UK there are few dual-cabled domestic premises: this is generally only where there were cable TV networks that now provide TV/Broadband/Voice services alongside the former GPO cabling (some of which has been upgraded to fibre). There is much less demand for provision of IP-only services in the UK (so far), partly because most landline (and most mobile) packages include free calls to anywhere in the UK (although standing charges are high) so there is less demand, but also because rollout by the monopoly supplier is slow.

Do they provide means for all people to make emergency calls even if they can't afford all-purpose phone service?
No, however most broadband packages come with an all-purpose phone service included. For fully digital services I believe it is a requirement to provide 1-hour battery backup for vulnerable customers only, however all the informaton on the regulator Ofcom's site is over a decade old.

Summary: the situation in the UK is just as much of a mess as the US, just a different mess.
 
Last edited:
  • #19
Tom.G
Science Advisor
Gold Member
4,691
3,444
this is driven by legal requirements for compatibility, availability and reliability(safety). It's the reason why the newer service requires a provider-provided UPS at the service entrance; so that you still keep phone service during a power outage.

Does that vary by state or is it a Federal requirement? If Federal, could you supply a hint on where I could find it?

It sure would be a convenience here in California!

Cheers,
Tom
 
  • #20
russ_watters
Mentor
22,054
9,152
Does that vary by state or is it a Federal requirement? If Federal, could you supply a hint on where I could find it?
Federal. I found this: https://docs.fcc.gov/public/attachments/FCC-15-98A1.pdf

From the intro:
FCC said:
In this Report and Order, the Federal Communications Commission (FCC or
Commission) takes important steps to ensure continued public confidence in the availability of 911
service by providers of facilities-based fixed, residential voice services in the event of power outages.1
2. For over one hundred years, consumers have trusted that they will hear a dial tone in an
emergency even when the power is out. Now, as networks transition away from copper-based, linepowered
technology, many are aware of the innovation this transition has spurred in emergency services,
but many consumers, remain unaware that they must take action to ensure that dial tone’s availability in
the event of a commercial power outage. The Commission’s own consumer complaints portal reveals
frustration over the failure of service providers to adequately inform subscribers about how to selfprovision
backup power in order to access 911 services in a power outage. This period of transition has
the potential to create a widespread public safety issue if unaddressed.
3. Accordingly, we create new section 12.5 of our rules to place limited backup power
obligations on providers of facilities-based fixed, residential voice services that are not line-powered to
ensure that such service providers meet their obligation to provide access to 911 service during a power
outage, and to provide clarity for the role of consumers and their communities should they elect not to
purchase backup power.
Note, that's from 1998 though and may be obsolete. It also describes the battery backup as optional but with a duty to inform by the provider. For my service, the backup battery was not presented as an option to me, but is mandatory. Annoyingly, the unit is the same regardless of the service, and has a battery even though I don't have a phone line (internet and TV only). And it failed once and needed to be replaced.

Another source saying something similar:
https://www.dwt.com/insights/2015/1...equipment, especially in emergency situations.

Search terms: "voip backup battery"
 
Last edited:
  • #21
anorlunda
Staff Emeritus
Insights Author
11,192
8,589
Interesting. But the language of regulators is hard to understand. I was stumped by "providers of facilities-based fixed, residential voice services" A bit of search found this.

https://en.wikipedia.org/wiki/Managed_facilities-based_voice_network
today's MFVNs can include a combination of access network (last mile network of copper, coaxial cable, fiber optics, or cellular), battery-backed customer premises equipment (CPE), network switches and routers, network management systems, voice call servers, and gateways to the broader PSTN.

In the 90s, I learned the regulations in one US state. It required phone service to achieve 0.9999 availability, whereas the power grid in some places only provided 0.9 more or less.

So how is this maintained with the switch from copper to fiber? The answer appears to be that it is not maintained. The burden is shifted from the provider to the customer. Providers are required to accommodate customer backup and to inform customers of their option, but customers can not be required to achieve 0.9999 or any other specific number. Indeed, I expect that many or most residential customers will fail to provide and maintain backup power for their VOIP phones. Businesses and condominiums may perform better.

The whole issue is entangled with the shift to wireless. VOIP customers already think of their cell phones as the primary backup to VOIP phones, and backup power to the modems as secondary at best.

Few providers and few customers are motivated to make investments in landline or VOIP services when wireless appears to be the future. Some consumers are even doing most of their data consumption mobile and wirelessly. Starlink offers an attractive way to do all of my data and communications needs via satellite.

The larger problem is how do you gradually shift from a centralized, regulated utility service to decentralized customer-owned service without risking an instability that results in catastrophic collapse of the central service at some point? Collapse leaves the poorest customers stranded. I wrestled with the same question in the context of the power grid in this article. https://www.physicsforums.com/insights/renewable-energy-meets-power-grid-operations/
 

Suggested for: Landline Phone Q: Why is the phone line plugged into modem-not wall?

  • Last Post
Replies
10
Views
524
  • Last Post
Replies
26
Views
785
  • Last Post
2
Replies
46
Views
2K
Replies
8
Views
458
Replies
3
Views
567
Replies
11
Views
730
Replies
5
Views
508
Replies
10
Views
1K
  • Last Post
Replies
23
Views
2K
Replies
3
Views
978
Top