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I am currently studying the textbook Computer Networking -- A Top-Down Approach (7th Edition) by Kurose and Ross. In a chapter on Home Access: DSL, Cable, FTTH, Dial-Up, and Satellite, the authors describe dial-up as follows:

Dial-up access over traditional phone lines is based on the same model as DSL -- a home modem connects over a phone line to a modem in the ISP.

Does this mean that, on either side of the connection (the home network and the ISP), there is a modem involved? So the connection goes from a modem at the home network, through the telephone line, and connects to a modem at the ISP?

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    That description is a vast oversimplification. A dialup modem can dial any other modem in the world. A DSL modem is point-to-point connected to a specific service provider modem.
    – Ricky
    Feb 4 '20 at 15:47
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Does this mean that, on either side of the connection (the home network and the ISP), there is a modem involved? So the connection goes from a modem at the home network, through the telephone line, and connects to a modem at the ISP?

Yes, exactly that for dialup modems. This is actually no longer used by ISPs, but ISPs used to have rack-mounted banks of modems that were connected to the phone system. As customers dialed in, the phone system at the ISP would roll over to the next available modem, and the customer modem would connect with the ISP modem.

For xDSL, the ISPs now have neighborhood DSLAMs (Digital Subscriber Line Access Multiplexer) to which the customer "modems" connect. These will terminate the customer lines and multiplex the data on to the ISP central office over one or more other lines. This saves the ISP from having to run a line for every customer from the CO to the customer.

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  • Sadly, dialup is still a thing. (mostly outsourced to a small number of wholesale operators.)
    – Ricky
    Feb 4 '20 at 15:44
  • Well, I know it is no longer available anywhere close to me, but I'm in a huge Metro area where almost everyone has access to cable or xDSL lines. I did have someone who moved out to a nearby lake, and he researched all the ways to get connected, but the only thing available was a neighborhood Wi-Fi connection, and it was horrible.
    – Ron Maupin
    Feb 4 '20 at 15:49
  • If you can get an analog phone line (which is getting rarer by the day), you can access dialup -- might not be a local call, but it's there. ( support.earthlink.net/access-numbers/index.php -- a lot of their POPs are wholesale )
    – Ricky
    Feb 4 '20 at 16:02
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    Well, it looks to be all long-distance calls from that lake number. It is interesting that it has ISDN, too. I used to use that at one time because it is a cheap flat-rate service that basically gives you two phone lines (cheaper than two analog lines). The ISP connection would bond the ISDN lines, and my connection would drop a line for a phone call. The ISP I had many years ago had that, and it was inexpensive. The ISP got rid of all the analog and ISDN by jacking up the prices until it was no longer affordable.
    – Ron Maupin
    Feb 4 '20 at 16:12
  • Thanks for the answer. The textbook also mentions DSLAMs in its explanation of DSL. Feb 4 '20 at 18:00
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Dial-up access over traditional phone lines is based on the same model as DSL

Umm no.

Dial-up access operates over the phone network. Your modem dials a phone number that connects to the ISP.

In the early days ISPs would literally have racks of modems, one for each subscriber that could be dialed-in at a time. Later-on however as phone networks became digital these racks of modems went away. The ISP would have a multi-channel digital connection from the phone network (ISDN PRI or similar), which would be connected to equipment at the ISP that would simulate a bunch of modems.

DSL on the other hand only piggybacks on the local loop (or the distribution subloop for FTTC services). It is converted back to digital data by equipment at the telephone exchange (or the cabinet for FTTC services). This digital data may go directly to the ISP if they have a presense at the telephone exchange or it may be back-hauled over a telco-run back-end network (traditionally ATM, but increasingly moving to something Ethernet and/or IP based) if they don't. It doesn't really touch the phone network as such.

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