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Before IPv4 addresses there were phone numbers. Why did they switch to IPv4 addresses to address devices in the internet?

I thought one reason is you need addresses in the local LAN. But I could even imagine to reserve a country code (e.g. +99) for local LAN addresses.

Another reason may be that phone numbers don't have a fixed length. So you have to store them in a string and not int. But is this a problem? Also int64 can hold most phone numbers. They could have limited phone number lengths intended to be used in the internet to 64bit.

Phone numbers worked well. It was possible to establish a (phone/modem) connection between one person and another on the opposite site of the earth. The routing and everything else worked fine.

I also know phone connections were analog only. But why do we need new addresses when switching to digital?

I think IP addresses work better but I couldn't find that single big reason which makes phone numbers unusable for the internet. Making a switch to IP addresses obligatory.

I tried to google it but found nothing.

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    While phone numbers on the phone network(s) and IP addresses on computer network(s) are both good, why would you think they should have been united at some point in time? They serve, and served, different purposes.
    – Jon Custer
    Jun 12, 2023 at 12:29
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    https://BR-549♪2/? You might want to read up on the North American Numbering Plan for a better appreciation of a segment of the global telephone number space. And Internet Protocol version 4. How do you tell DNS names from addresses when some "numbers" are "SueThemAndWinBig"? Routing tables full of arbitrary strings? An address space that was already being exhausted? Party lines and multicasting? Extensions? Network and international access codes?
    – HABO
    Jun 12, 2023 at 12:56
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    @javanerd - and fax, and Telex, and Minitel, and ...
    – Jon Custer
    Jun 12, 2023 at 15:09
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    @javanerd, Re, "...two points on Earth." I remember a time before the internet when a phone number, and a little patience, and some help from the operator could get you a connection between two telephones in the U.S.A. Trying to get a phone connection between phones on opposite sides of an ocean, on the other hand, was a whole 'nother level of tribulation. The year I graduated high school, I spent a whole month an ocean away from my parents, and I don't recall ever even attempting to phone home. To do so for any reason other than a dire emergency just would not have made any sense. Jun 12, 2023 at 18:28
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    This question needs to clarify itself better. There are multiple different addressing systems. Its like asking why we don't use the Dewey Decimal System to mail a letter, or phone someone's mailing address. There was no switch to IP numbers from phone numbers. Are you asking why IP numbers were created for computers instead of using phone numbers for networking?
    – David S
    Jun 12, 2023 at 22:05

7 Answers 7

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Phone numbers are no more related to IP addresses than USPS ZIP Codes are. I believe you are conflating these two concepts:

  1. Phone numbers were, and still are, used to identify the endpoint of a telephone network connection.

  2. IP addresses are used to identify the endpoint of an IP-based network.

These are NOT the same thing. I believe you are confused about this due to the prior widespread use of modems on telephone networks to connect remote computer systems to other systems or to internet providers. In this case you may have IP operating over telephone but the modem does not ever have an IP of its own.

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    All good except, having a dial-up connection does not imply that "you have IP operating over telephone." That's just one of many ways in which a dial-up connection could be used. Computer-to-computer, dial-up connections were in wide-spread use for at least several years before IP was invented, and I would not be surprised if a few of those legacy applications still were in-use today. Jun 12, 2023 at 13:38
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    Not only that, it makes even more sense when you remember that, in the early days of dial-up access to the Internet, we weren't using PPP or SLIP and the machine connecting to the Internet via modem didn't have an IP address... it was just using a terminal emulator to access a shell on the machine with Internet access.
    – ssokolow
    Jun 12, 2023 at 19:32
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Before IPv4 addresses there were phone numbers. Why did they switch to IPv4 addresses to address devices in the internet?

They didn't.

Before the Internet there was the Arpanet. The initial protocol on the Arpanet used a 5-bit number to identify the destination host (so a total of 32 different computers could communicate). That was fine because the Arpanet was experimental and small.

Then it grew, the protocols changed, and IPv4 came along, and hosts were identified by 4 bytes, which people back then thought was plenty compared to 5 bits. (And because they thought so, they also lavishly assigned address spaces).

Then it grew more, and IPv6 came along, and hosts were identified by 16 bytes, which again people thought was plenty, so (guess what?) IPv6 also lavishly gives out some address spaces. (But maybe it is indeed plenty).

Anyhow, phone numbers never entered into the picture. And in the time of the Arpanet computers were often connected by fixed leased lines, and didn't need phone numbers in the first place.

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    "5-bit...512 different" Wait! What? Jun 12, 2023 at 12:42
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    @SolomonSlow I did 8+1 instead of 4+1. Corrected.
    – dirkt
    Jun 12, 2023 at 12:45
  • en.wikipedia.org/wiki/ARPANET — Shows a map of the Arpanet with 35 IMPs, and 24 TIPs, for a total of 59 network nodes, and as many as four hosts connected to some IMPs. It says that prior to 1976, each IMP had a six bit ID (doesn't say about the TIPs) and says that a host was addressed by its six-bit IMP number plus an additional two bits. Starting in 1976, host number was expanded to 8 bits, and IMP ID was expanded to 16 bits. Finally, it says that ARPANET switched over to the IPv4 protocol in 1983. Jun 12, 2023 at 13:31
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    @SolomonSlow yes, the version I linked to was the first version. It got changed several times before switching to IPv4, but I didn't want to write a complete history of the Arpanet. That's what the Wikipedia link is for.
    – dirkt
    Jun 12, 2023 at 13:42
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Before IPv4 addresses there were phone numbers.

Yes, there were also social security numbers, driver's license numbers and real estate plat numbers.

"But those are completely different things!" Hold that thought.

Why did they switch to IPv4 addresses to address devices in the internet?

They didn't switch at all. Phone numbers were never computer network identifiers.

Phone numbers are completely different things, like your vehicle's VIN.

Even in the days of dialup, you dialed the public phone number of a network gateway like AOL or Tymnet and their modem picked up - it had no idea what your phone number was. Their modem and yours whistled at each other a lot. No one ever addressed you by your phone number.

If you're thinking people in the 80s and 90s had their modems set to auto-answer the phone, so Amazon would call your house to send you an email, no... that kind of "peer to peer modeming" was not a thing. (Except for gaming between real world buddies).

Many applications were "store and forward". Many online applications could even connect, sync email and things of interest, and then disconnect. You did much of your work offline. Compuserve charged like 10 cents a minute, and that was real money back then! So 5 minutes to download email and 2 to upload replies was important to keeping costs sane.

You could even do "googling by email" - you could email a query to some search bots and they would email you back a digest of answers.

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TL;DR:

Phone and Internet are different different networks, each with their own structure, protocols and addressing. Phone still uses phone numbers while Internet uses IP-addresses.


A Possible Mixup?

Could it be that you're mixing up

  • Internet vs.
  • Access via phone connection (dial in) vs.
  • Use of internet based phone services?

Those are related but independent issues.

The Internet is a network based on IP protocol since the start. All connection on that level are done using IP addresses.

It was and still is possible to access the Internet using the phone network via a dial in point. To do so a _phone connection is dialled (usually by a modem). When done Internet Protocol is run atop that connection, using IP-Addresses for all further communication.

An existing internet connection can in turn be used to establish a voice connection using appropriate IP-services. Most commonly Voice over IP.

Bottom Line: Phone and Internet are independent but sometimes related services that may use each other.


The Question(s)

Before IPv4 addresses there were phone numbers.

And they still are.

Why did they switch to IPv4 addresses to address devices in the internet?

They never did. Phone and internet are different networks.

I thought one reason is you need addresses in the local LAN. But I could even imagine to reserve a country code (e.g. +99) for local LAN addresses.

Why? Beside that 99 is already subdivided for some Asian countries(*1), this leaves barely more than IPv4 Addresses (*2).

Another reason may be that phone numbers don't have a fixed length.

They do 15 usable dgits (*3)

So you have to store them in a string and not int.

They are (usually) stored as BCD - as there are, depending on PBX up to 16 values per digit. Considered an int that's exactly an int64 :))

Phone numbers worked well.

And they still do.

It was possible to establish a (phone/modem) connection between one person and another on the opposite site of the earth. The routing and everything else worked fine.

In that case it was a phone connection, not an internet connection. Even if that connection was used with a modem and having run IP on top.

I also know phone connections were analog only. But why do we need new addresses when switching to digital?

Digital phones systems are not the same as Internet. They are still phone connection and they use still their own signalling within their own network. Don't mix that up with Voice Over IP (VoIP). VoIP is an IP application, like HTTP or Telnet. It is not part of the phone network - but usually offers gateways to the public telephone network.

I tried to google it but found nothing.

Usually a good hint that there isn't anything to be found :))


*1 - But 999 is still available.

*2 - Originally (*4) Phone numbers can have up to 15 digits (E.164), so taking off 3 (999( for a country code leaves only 12

*3 - Phones and exchanges usually have a 16 digit buffer to hold as well one additional control code.

*4 - This was extended to 20 for 3GPP aka mobile phone networks.

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    footnote 1- 15 minus 2 is 13, but the answer is still correct, since some countries have 3 digits in the country code.
    – UncleBod
    Jun 12, 2023 at 14:03
  • @UncleBod you're right. Sorry. I was going by his assumption of 99 as 'country' code for the Internet.
    – Raffzahn
    Jun 12, 2023 at 23:36
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Before IPv4 addresses there were phone numbers. Why did they switch to IPv4 addresses to address devices in the internet?

IP needed to store the address in a computer-efficient way in the IP packet. They needed a fixed-length address in a known location to make the job of the routers easier. This is because the router knows the destination address is a certain number of bytes past the start of the packet and (was) always 4 bytes long, which makes it extremely easy to pick out of the data and then quickly match against a table of 32-bit numbers vs which port to use for that address.

As you say in your post, telephone numbers do not match this criterion. They vary in length and vary significantly in format as well. Some use words, like "cypress 2343". One could convert these to numerics (as happened), but they would still remain difficult to store. Furthermore, telephone numbers do not represent a single endpoint: even in the 1970s most homes had multiple phones that rang when the number was called, and business had PBXs with hundreds or thousands of invisible numbers. This roughly corresponds to the "port" in IP, but mapping public IP port numbers to private internal numbers took a couple of decades to figure out.

TLDR: Telephone numbers were designed for and worked well on the telephone network. IP numbers were designed for and worked well on IP networks. I wouldn't expect otherwise?

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  • The words in a telephone number were mnemonics. Before there was all-digit dialing callers would tell the telephone operators (always women, until AT&T was hit by a discrimination suit) the exchange they wanted, which was a word, and the number. When dialing without the operator, callers looked up the first two letters in CYpress on your telephone dial and dial those, followed by the five digits. Exchanges were now uniformly three digits long in the USA. Then, people felt the letters were an unnecessary complication. Finally,area codes became another part of a ten-digit number..
    – Davislor
    Jun 12, 2023 at 22:00
  • Hence the Boston radio jingle, which ran for years after the old system disappeared: “How many cookies did Andrew eat? Andrew ate eight thousand. How do you keep your carpet neat? Dial ANdrew 8-8000.” Adams & Swett carpet cleaners was at 268-8000 if you were dialing locally, or if you were dialing long-distance, 1-(617)-268-8000. It’s now dialed 617-268-8000.
    – Davislor
    Jun 12, 2023 at 22:04
  • The phone number of my grandfather's Canadian cottage was "194".
    – John Doty
    Jun 12, 2023 at 22:09
  • A friend's van broke down while in Australia. He called the operator and was told the number for the garage was six. Jun 13, 2023 at 12:44
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As others have mentioned, they have no relation whatsoever and phone numbers were never used to identify devices on networks

When there was no internet a phone number was enough to establish a connection between two points on earth. Later they added IP addresses

Who said that? Connections don't depend on phones, 2 devices can connect to each other via any medium like a direct coaxial cable, a pair of RF transceiver, supersonic transceiver, a mesh of networks, a virtual packet-forwarding channel... What phone number should they have? There's no reason someone assigns some phone numbers to them when they have absolutely nothing to do with phones. Therefore network protocols were simply designed from scratch to allow 2 or more devices to send/receive data to/from each other

Even more, a device can have and actually have multiple IP addresses because IPs are associated with interfaces and not devices. A computer can have multiple interfaces and each interface can have multiple IP addresses. There's no reasonable way to assign phone numbers to interfaces like that

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All the existing answers point out that the switch never happened, because "they" never used phone numbers to address computer (nodes), whoever "they" are (presumably the users and/or admins). All the answers are correct.

Nevertheless... the switch did INDEED happen, in a manner. Before Internet went public (very slightly before), the way to be online for the "common folk" was to connect to a BBS, with the lists of phone numbers circulating among the users (kind of a directory listing). Using a modem and a phone number as an address. The BBS were especially popular during the 1980s, and into the early 1990s, when this new fad called "Internet" started to eclipse the BBS. Then there was the FidoNet addon that used numeric addresses "on top of" the underlying network addressed by phone numbers (kind of similar to DNS vs. IP numbers) that remained very popular for some years, especially in Russia.

To sum it up, Internet predated (phone number addressed) BBS, but BBS was a kind of grass root environment that coexisted with the (academic) Internet and when commercial (home oriented) network providers appeared, they started to offer access to SMTP & USENET (thus IPv4) and BBS (thus phone numbers) waned in popularity, especially after the explosive growth of the WWW.

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