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TROUBLESHOOTING
Don't forget that you must do multiple tests. If you dial from A to B and the call fails, and then try dialing from B to A and it works, you have proved very little. However, if you find that 7 of 15 calls dialing from A to B fail, while 15 out of 15 calls from B to A succeed, then you have a very important clue.
Eliminate
the easy stuff first
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Test the line and equipment. If you are using ISDN, you have the ability to dial from one channel to the other. Do so on each end, using a mode that requires both B channels. It's fairly easy to eliminate both the codec and the line. Then do end-to end tests using the same mode used for the local test (your codec might have a problem specific to a certain mode).
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If the problem is on a POTS line, see if the same problem occurs on another line from the same CO switch. Also determine if the problem occurs dialing between two lines on the same switch (if so, it's not a network problem).
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Does the problem only occur when dialing in one of the two directions? If so, it's likely to be a network problem.
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If the problem is occurring only with long distance calls, try some local calls. Or, vice versa. If the problem is limited to only one of these types of calls, you probably have a network problem.
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If the problem happens only on long distance, try placing the problem calls with several 101xxx access codes. If the problem occurs only with a certain carrier contact them, explain the problem, and work with them to solve it (see below). Not all carriers can handle CSD calls, so we suggest the following for troubleshooting those calls: 1010222, 1010288, and 1010333.
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If the problem occurs only with in-bound long distance calls (from multiple sites), and changing the carrier used (at the far end) to place the calls makes no difference, then the problem is in the local network at the end with problems receiving calls. This would be a problem with the path between the Access Tandem and the CO.
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If the problem occurs only on out-bound long distance calls (to multiple sites), and changing the carrier used to place the calls makes no difference, then the problem is in the local network at the end placing the calls. This would be a problem with the path between the CO and the Access Tandem.
Working with the phone company to solve your problem
If you have followed our advice, you have already eliminated the local line, the equipment, and all sources of problems other than the network. And you have done many test calls, and noted one or all of the following attributes that indicate a network problem:
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Problem limited to local or long distance, but not both.
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Probability of the problem occurring varies significantly between incoming versus outgoing calls.
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Probability of the problem occurring varies significantly between CSD calls versus voice calls.
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Probability of the problem occurring varies significantly between CSD calls at 56 kbps vs. 64 kbps.
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Probability of the problem occurring varies significantly depending on the time of day.
Now it's time to contact the phone company (local dial tone provider or long distance company). Remember, "Everybody blames the phone company". The old adage that "you will catch more flies with honey than with vinegar" applies here. You will probably need to be quite insistent at some point in the process. But, being pleasant, and keeping a good sense of humor, will help keep the Telco interested in solving your problem.
If they try to close out the "trouble ticket" before the problem is solved, insist that they do a conference call with the manufacturer or manufacturer's representative before doing so.
Working with long Distance Carriers. Here your task is reasonably straightforward. Nearly all of their problems are network related, so they won't show as much disbelief in your claims as the local Telcos do. Generally, all you need to tell them is that: "the problem only occurs when I use your network. If I dial with 101xxxx I don't have this problem" and they will start investigating.
You will need to be prepared to place calls until the problem occurs. If the problem only occurs on inbound calls be sure to have someone standing by elsewhere who can work with you. The process is that the tester sets up a "trace" to capture information about calls from the originating number. They will want you to keep placing calls until the problem occurs. S/he will then examine the routing information for that call and then tell you to hang up and dial again. After 3-6 "bad" call s/he should be able to notice what is common about the failed calls. At that point, the next step is usually to "busy out" the trunk group in question, to prevent calls from using the effected trunks. At that point you should have no additional failures. Make sure to test this based on your previous investigation (e.g. if only 1 of 10 calls failed in your tests, then you'd better make 20 calls just to be sure. On the other hand, if 12 of 15 calls were failing then you only need to make 4 or 5 successful calls to know the problem is solved. Once the problem trunk group is found, they will leave it busied out and fix it later.
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