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Troubleshooting ISDN

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ISDN Basics

Definitions:

ISDN (Integrated Services Digital Networking) is a single or dual-channel digital transmission that operates over and ordinary telephone connection (copper wire). There are 2 levels of ISDN service: the Basic Rate Interface (BRI) for home or small office use, and the Primary Rate Interface (PRI) for larger corporate needs.

Each ISDN connection has 2 "B" (bearer) channels (actual voice data streams) and a "D" (delta) channel (a carrier for control and signaling information). A typical BRI has two 64kbps B channels and one 16 kbps D channel, theoretically garnering a 128kbps connection when aggregated or "bonded".

Since there are technical limits on the types of regular phone lines that use ISDN it is a good idea to set up the service with your local phone company before continuing the instructions. For help, see Intel's Guide: How to order ISDN.

To set up ISDN service you will need:

  1. An ISDN Modem or Router (also called a terminal adapter)
  2. SPID(s) (Service Profile Identifiers) from your telephone company
  3. to know switch or network type your phone company uses
  4. Computer with a current operating system
  5. Your Account Information from Junction Box

Setting it up

  1. Set up your ISDN Hardware

    according to your modem (adapter) manufacturer's instructions

  2. Open up the ISDN configuration application

    provided by the ISDN modem manufacturer. This varies wildly between vendors: some have user friendly wizards and others have no frills terminal sessions.

  3. Enter the SPIDs and Switch information

    provided by the telephone company. Switch manufacturers have varying SPID conventions, so while 95% will look like the phone number followed by some extra digits, it can be whatever the ttelephone companydecides upon. They are normally 14 digits long.

    SPID and network / switch information work in concert to synchronize the ISDN modem (adapter) to the service parameters of the ISDN package set up by the telephone company. Normally, the application for entering this information will verify it and assign a TEI (Terminal Endpoint Identifier) for each successfully configured SPID.

  4. Set up your Computer's Dialer.

    Setting up your dialer for ISDN modems is just like setting up a dialer for other types of modems see the dial up technical information page for details

  5. You're Done!

    Dial up and enjoy your ISDN.

Troubleshooting ISDN Problems

ISDN adapters condition the telephone signal to simulate a dial tone but it's 100% synthesized. If you plug a regular handset into a functioning ISDN wall jack you should hear a steady clicking sound or static white noise, NEVER a dial tone or silence. That is a great test for checking that a Signal is present on the line, but the telephone company must check that the ISDN line is provisioned (set up) correctly.

Windows & Macintosh "No Dial Tone" errors can mean:

  1. No telephone cord is plugged into the modem. Plug it in.
  2. The cord is bad. Swap it with another one.
  3. SPIDs or switch type are incorrect. Verify with the telephone company!
  4. The wrong modem is selected in Dial Up Networking (Remote Access). Check the modem setting.
  5. ISDN service is not present on the line. Verify with the telephone company.

Cable Connections:

Most ISDN modems connect directly to a standard 9 pin serial port on a PC. In many cases the slow speed of the serial port is a bottleneck and doesn't allow the highest possible speed to the ISDN modem.

ISDN modems with native USB connectors are becoming more popular with the wide release of the iMac and the substantially faster speeds they permit. However, many users put in a serial-to-usb adapter when upgrading; these adapters (Keyspan is the most popular) have an impressive failure rate and are often the cause of intermittent episodes of modem unresponsiveness

It's also common for users to try a high-speed serial card to try to get every once of bandwidth from their connection. These cards replace the UART chip standard in most serial ports with a faster version stuck to an add-on card. They come with a speed multiplier that when configured too aggressively can overwhelm the router by as much as 4x the error correction on the ISDN modem. That can lead to "pauses" in data transfer as error-correction buffers overflow with stacks of information to sort through. It's a good idea to plug the ISDN modem into a regular serial connection to troubleshoot that type of problem. Serial cable failures and configuration problems with high speed serial cards are very common.

If you have a modem that acts as if it is not even plugged in, get a new serial cable. If the modem is still not responding to requests to dial and data uploaded from SPID configuration software, it is a good idea to contact the manufacturer of your ISDN modem (adapter).

Additional ISDN Troubleshooting links:

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