The basics of ISDN testing - Technology Information

The speed and features of ISDN inevitably bring complexity to the job of the manager who has to keep ISDN connections up and running. With a good tester and a basic understanding of the testing process, it should not throw you.

The right test equipment should:

* Perform switch emulation so that you can verify your customer premise equipment (CPE);

* Check the provisioning of your B channels quickly and effectively;

* Automatically check all the B channels on a PRI to verify proper operation.

On installation, if all goes smoothly, you need to make only three checks.

First, check that you get Layers 1 and 2 to come up. This will verify that you can talk with the switch at the phone company.

If you have trouble getting Layer 1 or 2 to come up, the most common error is misconfiguring the customer premise equipment. Do you have the CPE set for the proper switch type? How about the TEI -- is it set to AUTO? Your service provider should give you this information.

Second, make a call. Once Layers 1 and 2 have been established, it is time for Layer 3. The easiest way to verify this is to make a call. If that does not work, first check the Service Profile Identifier (SPID) you should have received from your service provider. If this is entered incorrectly in your CPE, you may be able to get Layer 1 and 2, but be unable to make a call.

Third, verify service provision on all B channels. Each of your B channels can be individually configured to carry either voice, data, or voice and data. All too often, the switch is misconfigured and a B channel is programmed for only voice when it should have been configured for both voice and data.

With the right test gear, you should be able to perform a service check of all B channels and verify each one's provisioning quickly and effectively. If a B channel is incorrectly configured, call your service provider -- the provider needs to re-program your service.

After your ISDN service is up and running, you may run across some common problems. For instance, someone can make only voice calls on the phone but should be able to do data calls as well. Or someone cannot receive faxes.

The tests are pretty much the same as for installation. Just remember to pull things apart and test one thing at a time. If a portion works, add another piece of the puzzle and test again. Eventually you will locate (and solve) the problem. Here's what you can do: 1. Verify that the CPE is working correctly.

First check to see that your switch type setting is correct. If this is not right, nothing will work. Then check the SPID and TEI programmed into your CPE. Are they what the phone company told you they should be? The switch and CPE often will automatically select the TEI. If this is the case, the TEI setting will be "Automatic."

If all this matches, emulate the switch with your test equipment and see if your CPE can connect to it. If the CPE still does not come up, check with the manufacturer. You may have a broken piece of equipment.

If does come up, call the service provider to make sure that the information given you is correct -- you may have been given the wrong settings. 2. Verify that the service is provisioned correctly.

Now that the CPE is working, use your test equipment to connect with the switch. Can you get Layer 1 and Layer 2 to come up? If Layer 1 or 2 don't come up, you may have:

* A bad cable

* The wrong switch setting

* The wrong TEI setting

* The wrong SPID

* A defective switch

If you are dealing with Primary Rate ISDN, you need to know if the physical layer is working for the T1. The best way to check this is doing a Bit Error Rate Test (BERT). If you're taking bit errors, there may be physical problems on the line, or T1 configuration problems, such as using the wrong line coding.

Either way, you will more than likely need to get in touch with your service provider to solve the problem.

Next, check the provisioning. Can you make voice and data calls on the channels as they were supposed to be provisioned? This is a great job for your test set. It should be able to check all of the B channels quickly and give you the results.

If you can make only voice calls on a channel that you expect to be able to do both voice and data on, or other such provisioning problems, the switch has been provisioned incorrectly. 3. Verify interoperability.

Sometimes everything seems to be set up correctly, but nothing works. Try hooking your test set inline between the CPE and the switch in monitor mode. Watch for communication messages on the D channel. Are there messages that don't make sense?

Check your configuration on your CPE again; often the wrong switch type setting or other misconfigurations will cause improper communications.

COPYRIGHT 1997 Nelson Publishing
COPYRIGHT 2004 Gale Group