Broadband (Cable, DSL, Satellite, Fiber Optics)/Internet Technology


Dear Sir,
I'll be grateful to you if you answer the following question:

what is the difference between dial up, ISDN and DSL/cable and how the technology evolves from each other?

Many Thanks

Dial up consists of a modem connected to a computer (or a modem inside of a computer) that dials a phone line (not cell phone) AKA POTS line, to another computer.  That other computer can be a "mainframe" and the first computer can be a terminal, or the other computer can be a "modem server" connected to the Internet and run the PPP protocol over the phone line so as to deliver network traffic to the first computer.

Dial Up is considered obsolete and too slow for Web access to the Internet although it can be useful for email, and for people who absolutely cannot get any other way to connect to the Internet.

ISDN (Integrated Services Digital Network) is a digital phone line.  An ISDN BRI line is divided into 2 logical data channels and 1 control channel.  It runs at 128kbps.  It can run either data or voice.  In a voice application it runs 2 56kbps digital voice channels and in a data application it "bonds" 2 64k digital data channels into a 128k data channel.  It is run on Plain Old Telephone (POTS) lines.  An ISDN PRI line is run over T1 lines and has 24 channels of 64kbps.  It is used only in voice applications.

DSL (Digital Subscriber Line) is a POTS line that runs data on radio frequencies using the DMT or G.Lite protocol, it is distance limited to a max of 18,000 feet.  Speeds are up to 7Mbt for regular DSL and higher for VDSL.  Despite having an overall standard for data format, it can be considered proprietary to any given telephone company due to optioning differences between phone companies.

Cable is CATV cable setup to run data, it can run hundreds of megabits of data and is generally setup using the DOCSIS 2.0 or DOCSIS 3.0 standard.

Dialup was the first, invented by the Bell Telephone Company and speeds started out at 110 Baud, increasing to 300 Baud, then continued into higher speeds as a plethora of modem companies invented incompatible standards. Speeds went up to 9600bps which was the industry de-facto standard serial port speed for an ASCII terminal.  At that speed interest developed in running PPP over the modem links and transferring network data, so speeds continued to rise and continued to be incompatible, notable standards were Hays Express, US Robotics HST, and Telebit's high speed protocol.  

Eventually 2 major competing (56kbps) standards arose, US Robotics X2 and the ITU's K56flex, which was primarily pushed by Rockwell, Lucent & Motorola.  The ITU merged these standards to V.90 and most modem makers offered flash upgrades that made their modems compatible.

During this time the ISDN standard was developed by the telephone companies.  Most phone companies switched inter-station trunks over to ISDN (switch to switch) and their hope was to push ISDN out to subscriber telephone sets, to realize the dream of telephones with video.  Unfortunately they priced ISDN too high and it never developed into anything more than a niche connectivity product.  ISDN and 56k Dialup were the standard for end user connectivity during the decade of 1990-2000.  The Internet was de-regulated in 1995 and we saw the shift from dialup BBSes such as were popular in the mid 80's to the mid 90's, to Internet Service Providers.

What really spelled the end of the Dial Up era was the emergence of the Cable TV providers into the data scene in the early 2000's followed by the telephone companies with the DSL standard.  Cable and DSL was standard during the 2000s until the entrance of both Fiber optic to the home and Fiber Optic to the pole, then VDSL from the pole to the home, in the early 2010's.

Today the battle is between the cable TV providers and the telephone companies who have deployed fiber to their subscribers.  Both Cable and Fiber have the capability of so-called "gigabit to the home" although the fact is that the Internet Core simply does not have the bandwidth to allow a gigabit connection across the Internet for all subscribers at this time.  Instead, an increasing number of content providers are deploying proxy servers on the networks of large retail cable and fiber providers.

These connectivity products didn't really evolve from each other - they mostly were developed independently from each other.  What has mainly evolved is the increase in connectivity speed.  As one technology was developed to the point that it wasn't possible to squeeze any more bandwidth from it, another technology was developed to take it's place that was faster.

The increase in bandwidth speed has allowed for video applications to become commonplace.  Consider for example that it wasn't until around 10 years ago that you could place a camera at a remote location and get a realtime video feed.  This has made a huge difference in process control in industry.  Take for example a rock quarry.  15 years ago a rock quarry would have a single dispatcher who would issue receipts for trucks going in and out of the quarry.  If the quarry owner purchased a second quarry then they would have to hire a second dispatcher.  Today, they can buy a second quarry and the dispatcher that handles the first quarry can handle the second one at the same time, using a remote video feed over the Internet and a remote ticket printer and scale.

Broadband (Cable, DSL, Satellite, Fiber Optics)

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Ted Mittelstaedt


I will answer questions on the following kinds of High Speed Internet connectivity; ISDN, Frame Relay, dedicated T1, higher speeeds such as DS3/OC3, wireless such as 802.11 and DSL. No questions on dialup V90 or Cable access. I can also answer questions on many types of Cisco routers, and a number of other brands of business routers as well.


I am the technical manager of Internet Partners Inc. an ISP.

I've written a book titled "The FreeBSD Corporate Networker's Guide" published by Addison Wesley

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