Inbound Calls from Sprint Poor Quality

I think this may be a question for some of the long-time telecommunications gurus. I have some phone numbers with Flowroute, and I’ve been using them for a while. However, we recently begun having problems with inbound calls to a few of our DiDs that seem to be in the same area code. People would call in, hear ringing for a long time, eventually make it through, only to hear garbled audio. Other people would call in and it would ring through just fine with crystal clear audio. One strange thing we noticed was that on the calls that wouldn’t work, we would notice multiple invites coming from Flowroute before we were able to answer the call.

I thought, maybe this could this be a problem with our trunk config. So I tried bypassing our server completely, and just forwarded the call from flowroute to an external number. Same problem.

Then we tried routing another number we have with flowroute to the server with a different area code, and that number rings through fine with good audio.

All this time, the problem with the original DiD wasn’t happening on every call, only to certain callers. So I decided to find the pattern. I checked the numbers that had difficulty calling in with a carrier lookup, and found that all of them are originating from Sprint, Google Voice (our numbers), or other Flowroute numbers. AT&T and Verizon both seem to work perfectly 100% of the time.

The number that is having issues is one we ported into Flowroute. This port happened a long time ago, and worked fine for a while until recently, but could this be a clue?

We’ve been in touch with Flowroute and they’ve sent the information to their peer. However, their peer is apparently not able to reproduce this problem. I plan on continuing to communicate with them to try to get this resolved, but I thought I would check here to see if any of you guys had suggestions for next steps. Obviously our client doesn’t want to switch numbers, so that’s out of the question. Should we contact Sprint and see if they can help us? If so, who should I ask for when calling to get someone who could actually look at the details of the call flow?

This seems like a crazy problem, and I thought it might interest you all. Let me know if you have any suggestions. Thank you.

You betcha. There could have been an internal port. Look up the problematic DID at https://apeiron.io/lrn . Who is the carrier? Does it show a ported_on_date much later than when you ported it in?

Look up both the LRN and the DID at https://www.telcodata.us/search-area-code-exchange-detail . What rate center(s) are shown? If they don’t match, that could be an issue.

Do you have Google Voice Enterprise? If so, you should get awesome support; call and tell them that you have trouble reaching a number that works fine from a landline.

Otherwise, do you have access to a phone on Sprint (or a Sprint MVNO) for testing?

Can you see the trouble calling the DID from your own Flowroute trunk?

Were the multiple invites from Flowroute SIP level retries (same Call-ID), or route level (INVITE was CANCELed and resubmitted with a different Call-ID header)?

First of all, it seems like the duplicate origination symptom is no longer appearing. I’m still having the poor quality audio issue, and longer (although not as long as before) ring time before hitting my system. Also, I think that the multiple invites may have stopped happened before and then come back later, so this seems like more of a problem than a good thing, because Flowroute is coming back to me saying they can’t reproduce the multiple invites anymore, but the other problems are still happening, but slightly less intense. Ugh.

To answer you questions:

The carrier seems to be “Flowroute LLC”
The ported_on_date matches the date I would expect, December of 2018

Rate centers do seem to be different. When I input the area code and prefix of my DID into telcodata.us it lists the ratecenter as the city I would expect, while the LRN rate center is different.

I hadn’t heard of Google Voice Enterprise, but I do have a gsuite account, so I think I do. I’ll check out that possibility.

Unfortunately I don’t have access to a Sprint phone. But I can still test with GV and Flowroute numbers.

I do see the problem when I call from another flowroute trunk/DID associated with my account. Is that what you were asking?

Like I mentioned, the invite problem doesn’t seem to be happening anymore, but I opened up a packet capture I have, and it seems like the problem is route level. Kinda. So each of the invites has a different Call-ID, but I don’t see the CANCEL part. I’m not great at interpreting packet captures, so I may just be missing the CANCELs.

Also, I forgot to mention this initially, but the Invites come in multiple seconds apart. In the packet capture I have, the second came 14 seconds after the first, and the third came a little less than 4 seconds after the second.

Do these “puzzle pieces” point to anything?

Should I bring up the rate center potential problem with Flowroute, or the fact that this seems to be a route level problem?

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