Has anyone else noticed that sometimes the talk path is half duplex? One of the uses here was complaining that the other side didn't appear to hear her, assumed it was a prank call and hung up. She called back a few minutes later and things were fine.
I was trying to get a feel for how common half-duplex talk paths were and perhaps have someone propose a model for why they would happen. Embarrassing the SIP gatewaying service I was using wasn't my intention. Leaving out voip service provider names, the talk path looks like this:
They are only half-duplex when things are going badly. A second call a few minutes later might work fine.
A second observation is that sometimes the talk path is just slow to open. One can hear the other side, but it takes 5-10 seconds or so for the other side to start to hear you. Often the other side has decided it is a prank phone call and hung up, so it isn't clear if the bad calls would have eventually started working.
A "talk path" comes from old telephone jargon where one has two pairs of wires used to carry the conversation, one in each direction. Each direction is a "talk path". If one pair is broken one party can hear the other, but the other can't hear the first. With careful software design, this "feature" now appears to be available for VOIP too. ;-)