I want to theoretically understand the general relationship between the PSTN (public switched telephone network), cellular networks, and the Internet.

I understand that the PSTN provides the infrastructure that ISPs buy in order to offer provide internet subscribers with shared lines.

What about cellular networks and how Internet is accessed over a mobile phone? Are cellular networks, with all their stations and satellites, also ultimately connected underground with the PSTN? Is the PSTN therefore the lowest level of communication for all networks?

Or is it that cellular networks are independent of the underground telephone lines and exists fine even without it?

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PSTN == ancient circuit switched analog voice communication network. It has been increasingly converted to digital carrier over the decades. But, the "last mile" is still analog, and entirely digital everywhere else -- even transported by IP in many cases. It's only relation to "the internet" was by use of dialup modems. Today DSL rides on the same physical infrastructure, but is not part of the PSTN.

Cellular == in it's early days, basically a wireless version of the PSTN. Today it's a totally digital packet switched system. In this sense, data is data. Internet and voice are just streams of 1's and 0's.

The Internet is a global packet switched communication network crisscrossing a multitude of technologies, some wired (dialup modems, DSL, cable, fiber, etc) and some not (terrestrial microwave, laser, satellite, shortwave radio, IR, ultrasonic, etc)


PSTN is only used for dial up and DSL services. Other access technologies use cable, fiber, radio waves, etc. Typically, cellular network stations are connected using one of the latter.

There's no such thing as one lowest form of communication in terms of a specific type of carrier. Each one has its advantages and disadvantages when it comes to distance, price, capacity, etc. But you can be sure that most communication between networks isn't done on PSTN, it's mostly fiber.

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    Even if it is fiber, this is mostly all underground, right? And so - even cell towers eventually need to fetch Internet data transmitted from underground, is that right? Because I've learned that the PSTN provides most of the basic long-distance infrastructure of the Internet. – user961627 May 10 '15 at 9:01
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    Usually fibers are underground, yes. But it doesn't have to be fiber (it can also be radio, cable or DSL for example), and fiber does not have to be underground. I fail to understand your 'underground' fascination. Why is the location of the carrier so relevant for you? – Teun Vink May 10 '15 at 9:07
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    The PSTN doesn't provide the backbone infrastructure. That may have been true 15-20 years ago but no longer. The same companies may own the fiber or lease bandwidth, but it is not part of the network. – Ron Trunk May 10 '15 at 11:53
  • You're mixing up technologies here. DSL is a last mile technology. PSTN today means for all practical purposes E.164 addressing assignment. In other words, PSTN service is a higher layer service, independent of the type of last mile access whether copper, fiber, or cellular. – Ronnie Royston Jun 16 '15 at 21:01
  • I would disagree here. The PSTN is in a way the backbone of telephony. Despite shifts to VoIP and mobile, we will always have landlines and thus the PSTN. Calls to and from landlines must go through the PSTN. It is not only for DSL, Fax and Dial-up, voice converstions also use copper wire, at the very least in the last mile. Users who want high voice quality and need their phones to work in a power outage also need connections to the PSTN – InterLinked Jul 16 '16 at 12:24

Internet Protocol is currently the network that the vast majority of telecommunications services depend on. Even dial tone circuits (PSTN) are converted to IP on the carriers network. The PSTN provides dial tone, the Cell towers provide 3g/4g access, and ISPs provide Internet access.

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    You're mixing very different layers of the intenet protocol suite here. – Teun Vink May 10 '15 at 21:08
  • No, actually I'm not. – Ronnie Royston May 10 '15 at 21:54
  • We have seen a reversal in recent years, It used to be that IP networks were run on top of telco techologies (ATM, SONET, ISDN etc) but nowadays increasingly an IP network is used as the underlay for carrying telco services. – Peter Green Nov 16 '16 at 14:44

i think this is good link and explain relationship between the PSTN (public switched telephone network)


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    Link only answers are discouraged here, since the page you're referring to can change or be deleted in future. Please consider adding some information to your post. – Teun Vink May 11 '15 at 6:20

The cellular network towers have connections to fetch data from the Internet, but these connections can use many different technologies. In the early days of mobile communication these connections were mainly leased lines from the PSTN.

Now these lines can't provide sufficient capacity for the broadband data connectivity offered to the users. New technologies are used such as fiber optics, microwave lines or other depending on different factors (distance, price, capacity, location, legalization ...).

PSTN lines are still used but very rare on place where another alternative is difficult to be implemented. They remain for the GSM mobile networks. Fot UMTS and LTE networks the backhaul consists mainly of IP data network with fiber optics as physical media. An IP bases fiber backhaul can offer much more capacity for the mobile towers.

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