A-Z voice termination, explained without jargon
Carriers, routes, CLI tiers, and why wholesale termination is more boring (and reliable) than it sounds.
By Codus Nullus
“Termination” is one of those telecom words that sounds dramatic and means nothing of the sort. It is simply the last leg of a phone call - the bit where the operator on the receiving side actually rings someone’s phone.
This post unpacks what an A-Z termination provider does, what the quality tiers (Platinum, Gold, Silver) really mean in practice, and why we route traffic the way we do.
What “A-Z” means
A-Z = the destination set covers every country with an alphabet entry, from Afghanistan to Zimbabwe. A small provider can technically claim A-Z while leaning on a handful of partner carriers to fill the gaps - which works until one of those partners has a bad week. A real A-Z provider either has direct interconnects, or transparent fallback routes that have been load-tested to every destination on the list.
CLI: the difference that actually matters
CLI = Calling Line Identification. When a call rings on the destination phone, does it show your number, a different number, or no number at all?
- Platinum: the route guarantees CLI delivery. Required for retail traffic and almost any business-to-consumer call where the recipient is expected to call back.
- Gold: CLI is preserved where the destination carrier supports it, but not guaranteed all the way through. Good enough for outbound where the recipient is unlikely to dial the number on their screen.
- Silver: non-CLI by design. Cheap, fine for transactional outbound (delivery confirmations, two-factor codes) where the recipient does not need a number to dial back.
MOS and ASR: the boring metrics that matter
Two numbers tell you most of what you need to know about a route:
- MOS (Mean Opinion Score): voice-quality rating from 1 (unintelligible) to 5 (perfect). Routes below 3.8 get rotated out automatically.
- ASR (Answer-Seizure Ratio): of all calls dialled, how many were answered? An anomalously low ASR usually points to a CLI block or a dead route, not bad luck or shy customers.
Our monitoring tracks both per-route, per-hour, with thresholds that trip before customers start filing tickets. Bad routes get pulled before the dashboards even need a human to look at them.