Why the choice matters
The wholesale carrier you pick sets the ceiling for your own service quality. Post Dial Delay, Answer-Seizure Ratio, caller ID integrity and NOC responsiveness all flow straight through to your customers. This guide walks through the technical and commercial criteria that separate a reliable Tier-1 supplier from a cheap least-cost aggregator.
Technical criteria
- PDD (Post Dial Delay): target <4s international, <2s domestic on premium routes.
- ASR / ACD: ask for 30-day rolling stats per destination; premium CLI should hold ASR above industry norms with steady ACD.
- CLI integrity: confirm A-number is preserved end to end and answer supervision is honest — no false answer, no early media billed as connect.
- STIR/SHAKEN: in the US and Canada, ask about attestation level and whether the supplier signs on your behalf.
- DTMF and fax: RFC2833 and SIP-INFO for DTMF, T.38 for fax where you need it.
- Codecs and transcoding: G.711 and G.729 baseline, Opus/G.722 for HD voice where relevant.
- SBC redundancy: geo-distributed SBC clusters, BGP anchoring, and documented failover behavior.
Premium vs standard tiers
Premium routes cost more because the supplier is buying direct interconnects and enforcing SLAs. Standard routes are LCR-based and appropriate for price-sensitive, one-way, or non-business traffic. Most healthy wholesale carriers offer both and let you steer traffic by customer profile and destination.
Commercial and NOC checks
- Per-second billing from second 1, no artificial minimums.
- Transparent rate decks with advance notice on increases.
- Written NOC escalation path and 24/7 human-answered ticketing.
- Weekly or bi-weekly invoicing and clear prepay/postpay terms.
- Test window before commercial go-live, with sample CDRs shared both ways.
Frequently asked questions
What is a good Post Dial Delay (PDD) for wholesale voice?
For premium CLI routes, PDD should typically stay under 4 seconds internationally and under 2 seconds domestically. Anything consistently above 6 seconds points to poor routing, excessive transit hops, or an overloaded SBC on the supplier side.
What is the difference between CLI and non-CLI termination?
CLI (Caller Line Identification) routes preserve the original A-number end to end and are required for callback services, business calls, and any traffic that needs answer supervision and reliable caller ID. Non-CLI routes are cheaper but strip or replace the calling number; they are only appropriate for one-way announcement traffic where caller ID does not matter.
How do premium and standard quality tiers differ?
Premium tiers use direct interconnects or short Tier-1 chains with strict ASR/ACD SLAs, higher price, and STIR/SHAKEN attestation where applicable. Standard tiers use least-cost routing across multiple suppliers with looser SLAs and lower rates. Most carriers deploy both and route by destination and customer profile.
What commercial terms should I ask a wholesale carrier for?
Per-second billing from the first second, no minimum call duration, transparent rate decks with 7-day notification on increases, weekly or bi-weekly invoicing, and a written NOC escalation path with a 24/7 phone or ticket channel.