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    ISDN is an abbreviation for Integrated Services Digital Network. This type of network is roughly the same as a old analog phone network except that its digital from end to end. The POTS (Plain Old Telephone System) is mostly digital, except that its still analog from your home to the switch, digital from there all the rest of the way throught to the destination (we're assuming for the internet world mainly because most good ISP's are digital all the way in now).

    The basic rate line is an ISDN user-to-network interface made up of three communications channels-two B channels (each capable of 64000 bits/sec) for voice, data, etc. and one D channel (16 kbps) for signaling, call setup (dialing) etc... ISDN most often uses existing copper wires, your home or office may not need to be rewired, but you will need a new wall jack. If you don't already have ISDN, the phone company will install the jack when your service is connected.

    Your ISP probably supports ISDN connections, (almost all good ones do). Some ISP's charge extra for dial in ISDN, some don't, some have special numbers to dial for dialing ISDN, some don't. That's all up to your ISP and how they are setup. A recent trend in the small to medium size offices has been to install ISDN, and then everybody on the local lan in the office would be able to get internet access through the ISDN connection. In most instances the ISP would loan/rent/sell you a router which you would connect to your firewall or hub (hopefully you have a firewall). Most offices use dedicated ISDN, which essentially means that you are always "dialed in" and thus have internet access all the time. With dedicated ISDN you probably get your own ip address which you always have so it is possible for you to have your own mailserver or webserver. I would strongly suggest take your ISP's advice and use a router for a dedicated connection. I've seen some small offices that like to use a TA (terminal adapter) which essentially is just a "pumped up modem". ISDN TA's don't tend to require init strings as much, mainly because of the nature of the digital network. There is one saying in the computer world, "You get what you pay for" and if you are using an ISDN TA instead of a real router, to save yourself some money, this usually holds true. I would suggest getting a real router like a Cisco 700 Series, Ascend Pipeline Series, Netopia ISDN Routers or another such router. If the telco ever drops the line even for a fraction of a second, these routers tend to come back up quicker, and they are full routers where you can make use of features like access lists, NAT translations, simple firewalls, etc.... In short, they are generally more reliable and reliability should be a very very high priority for a small office.

    Advantages of ISDN over conventional analog lines.

    - ISDN is more reliable so there is no such thing as a noisy or fuzzy line. (chances of getting dropped part way through your 19 meg download are drasticaly reduced to almost nill).

    - ISDN lines are faster then analogue phone lines with max out at 56kbps (and like everyone with a 56k modem knows, in reality you get 44-50 kbps), ISDN always runs at 64kbps.

    - You can bond multiple "B" channels to get speeds of 128kbps

    - Call Setup is very fast (dialing, handshake and authentication), usually under 2 seconds (compared with 15 seconds at least for most analog modems).

    - With ISDN, you can get 2 calls at the same phone number since both get their own channels (or one line for voice, and the other channel for your internet connection)



  • Cisco 800 Router Series
  • 3Com ISDN Support Page

  • Adtran ISDN (usually quite slow)

  • Alpha Telecom TA's

  • Alpha Telecom Routers

  • Arowana ISDN
  • Ascend (Lucent) Pipeline ISDN Router Series

  • Cisco 700 Router Series

  • Dynamode ISDN Page

  • Netopia ISDN Routers (discontinued product line)

  • Motorola Bitsurfer Pro TA (offline)

  • ZytXel ISDN Routers
  • Teles Ag

  • Tornado and Tron ISDN Modems

  • Xircom (now part of Intel)


  • ZyXel ISDN TA's