Some Inbound Calls Not Ringing Through After Port-In

  • Updated

Shortly after porting in a number, you may encounter an issue in which some calls correctly come into the gaining carrier while others still incorrectly come in to the losing carrier. This issue most commonly indicates a partial port, specifically when the losing carrier still has some work to do to complete the port.

1. What You Can Do

Below are a few steps you can take to evaluate the issue, in order of increasing involvement. For future cases, if you'd like to stay ahead of this type of issues, you don't have to wait for the first problem reports. You can begin reaching out to your losing carrier or testing as soon as we inform you the number is ported.

1.1. Wait 48 Hours

Carriers generally advise that translations can take 24-48 hours after port confirmation to remove stale translations. If you're fine with waiting, it may be simplest just to wait.

1.2. Contact the Losing Carrier

If you need the porting process expedited or the issue is still present after 48 hours, it is the responsibility of the number owner to work with the losing carrier to remove the stale translation(s). Ask for them to check for your ported-out number(s) in their translations tables. In some cases the losing carrier might not be able to find anything, but you can ask if they can find some record of these calls in their billing system. If you're still getting calls to the old line, that often means you are also still paying a monthly service fee + per minute charge for the old line. Your callers can often open tickets with the losing carrier as well. If an affected sender reaches out, ask which carrier they are with. If they're on the losing carrier, ask them to open a ticket on the issue.

1.3. Perform Additional Troubleshooting

You will likely need to involve your company's telecom expert for this step. In some cases you may need to collect additional information about the situation to prove there is an issue to the losing carrier. The objective of the tests below is to demonstrate to the losing carrier that they are still sending some calls to the old trunk. Proof of this is proof enough that the losing carrier needs to take some form of action to correct their routing tables: the losing carrier should have entirely "forgotten" how to get these calls to your old trunk! Even if other issues are present, this behavior will need to be rectified before to fully port the number.

1.3.1 Testing

We advise customers to test the following to narrow down the issue, noting in each case whether the call hits your T38Fax trunk, your old trunk with your previous carrier, or results in an error. As you troubleshoot, keep in mind that getting a fax tone is not always an indication that the call routed successfully. Therefore, be sure to double check whether the call is coming in through the gaining carrier trunk or the losing carrier trunk.

  1. Call the number from one or more devices on an unrelated third party carrier. You may use a cell phone. If this test fails, verify that you are connected to your T38Fax trunk and contact us if the issue persists.
  2. Call the number from an unaffiliated trunk on the losing carrier. This test should be performed from a system uninvolved with the port. If this test fails but the first test was a success, you have most likely encountered a partial port.
  3. Call the number from one of your desk phones still connected to the losing carrier. This test can only serve as a drop-in replacement for test#2 if you can clearly demonstrate that the call leaves your phone system through the losing carrier and comes right back in. If this is the only test that fails, you likely have an internal routing issue. Contact your phone system administrator to double check how this call is handled.

1.3.2 Documenting Complaints

If you get complaints, note:

  • Which carrier the caller is using.
  • The time the call occurred.
  • The caller ID number the caller uses. Many are mistaken about their fax machine's caller ID number! To double check, have the sending party "send a fax" to a cell phone. The number that shows up on the screen is that fax machine's actual caller ID number.
  • Whether you can find a record of the calls Fax endpoints will keep a record of calls in their fax logs. Carriers also usually have a record of call logs for your account. T38Fax has the Transactions section of the T38Fax Portal.

1.3.3 Using Troubleshooting Results

If, having worked through the above, you've found that problematic callers are isolated to the losing carrier, you've likely fallen victim to the typical partial port. The information should help you confidently assert something like the following to the losing carrier:

Calls from other carriers are succeeding. Our business partners are only having issues if they're on [LOSING_CARRIER]. The gaining carrier has asked that you all remove stale translations for the following numbers:

If you believe you've run into some other issue, please contact us on your porting ticket.

2. Why Does This Happen?

2.1. How Porting Influences Call Routing

There are two routing methods carriers use to deliver calls to you, and both will need to be updated for the port to complete:

2.1.1. The LNP System

For inter-carrier calling, carriers use the local number portability (LNP) system. The LNP system allows the originating carrier to look up what carrier owns a particular number and how to route to them. In the US, this database is administrated by a central authority called NPAC. When a number is ported out, the gaining carrier files FCC paperwork to take over ownership of the number. Once approved, NPAC will broadcast a change of ownership to the rest of the telephone network. It is not strictly required that the gaining carrier and the losing carrier coordinate to port a number. It is optional, though generally advisable, for the gaining carrier to inform the losing carrier that they have lost their number. Some carriers have implemented a PIN system so that they must be informed of a port-out taking place.

2.1.2. Translations Tables

Once a call reaches a carrier's network, carriers use the destination number to perform a lookup in a database they call their "translations table." Translations tables maintain records of what numbers the carrier owns and how to route calls for those numbers: these records are called translations. If there is a match, they can assume the number belongs to them so they do not perform an LNP lookup and instead route the call internally. If there is no match, they do an LNP lookup to find out where to route the call next. Therefore, translations are checked before LNP routing.

2.2. How Issues Can Occur

When your LNP port order clears, the translations tables of both carriers should correspondingly be updated as well: the losing carrier should remove their translations for the number(s) and the gaining carrier should add translations for your number(s). This does not always occur though. Most issues in the porting process occur when the losing carrier does not remove their translations. If the translations are not removed from the losing carrier, issues can potentially occur in the following two scenarios:

  1. One of the losing carrier's customers places a call to a ported number.
  2. The losing carrier doesn't originate the call, but serves as an intermediary carrier for the call to a ported number.

In both cases, the call crosses paths with the losing carrier's stale translations, which override your number's LNP routing. When this occurs, calls may route to your old system or not connect at all.

Stale translations may remain after your port clears for the following reasons:

  • Translations may take 24-48h to be removed after the number has been fully ported by LNP standards.
  • The losing carrier does not have an automated system to synchronize their LNP and translations databases.
  • The gaining carrier did not inform the losing carrier that the losing carrier has lost the number.
  • The losing carrier was notified of the port-out but processes translations manually and committed a clerical error.

3. FAQ

3.1. Will unplugging the old line resolve the issue?

In itself, unplugging the fax machine won't resolve the issue. If the fax machine stays plugged in, your callers won't have any way of knowing the fax went to the wrong destination because the fax will still go through. If you choose to unplug your fax machine from the losing carrier's line, the caller will likely get a fast busy signal. Doing this may prompt senders to contact you to say your fax machine is down, at which point you can tell them to open a ticket with their carrier; or maybe they will open a ticket with their carrier without saying anything. There is no "right answer" to how you should leave the old line to get help - it depends on your situation.

3.2. Are you able to work this issue for us?

As the gaining carrier, we're not able to verify the operation of the losing carrier, nor are we able to speak with the losing carrier on our customer's behalf. The losing carrier requires one of their customers' authorized contacts to open tickets with them. You will need to correspond directly with the calling party and the losing carrier to resolve these issues.

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