About two weeks ago, Barb wrote us asking for advice on how to overcome some problems she was having with her AT&T CallVantage service. She was running the VoIP service over a wireless router connected to a cable modem with a high-speed Internet connection offered by her local cable company. Several minutes into a conversation, Barb could (on multiple occasions) still hear the person on the other end, but they couldn't hear her. (By the way, we've heard similar complaints from subscribers to other VoIP public network service providers.)

Barb ran some tests from home using testyourvoip.com and discovered the following results:

MOS: 4.0
Codec: 0.57 57.9%
Latency: 0.00 0.0%
Packet Discards: 0.42 42.1
Packet Loss: 0.00 0.0%

At AT&T's suggestion, she asked her cable company to check her signal to noise levels. While her levels were within cable company's tolerance (at 37.9 dbmv) they were beyond AT&T's recommendation of 35 to 36 dbmv.

She contacted us in desperation to see if we could suggest any further course of action. Of the possible options, we thought she could have a) switched to Vonage to see if it was an AT&T-only problem or b) switch from cable to DSL to see if it was a facilities problem, but both solutions seemed a bit extreme. So we called our friends at AT&T to see what they could suggest to help Barb with her problem.

The story does have a happy ending - at least so far. AT&T dispatched a technician the day after our inquiry who spent several hours completing additional tests both in the home and in AT&T's back office. He even brought some of his own home office equipment to confirm that the onsite gear wasn't creating the problems.

In Barb's words, AT&T provided "FABULOUS" service. AT&T recommended she work with her cable provider to see how it could reduce its packet discard levels - the most likely culprit for her intermittent problems. Barb hasn't had any other problems but there is a degree of continued up and down, intermittent packet discard according to the tests, but at least she knows the most likely culprit.

Our thanks to AT&T for the prompt attention and for helping Barb out.

Next time, we'll take a look at another related problem and solutions for public network VoIP.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Larry Hettick is a principal analyst at Current Analysis.