The only telecom routing classification that matters

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Why routes are defined by type × scope — and everything else is marketing noise

TL;DR: In outbound telecom there are three quality types — CLI (legit caller ID), NCLI (hidden/faked caller ID / refile), and FAS (fraud / fake answer supervision) — and two scope variants — Local/National or International/Cross-border. The real taxonomy is:

[Scope: Local / International] × [Quality: CLI / NCLI / FAS]

If someone sells you “semi-CLI,” “smart routes,” or “correct display,” treat it like marketing. Ask for proof of a genuine carrier-to-carrier SS7 handoff and preserved A-number — otherwise assume refile/NCLI.

1) The clean taxonomy: quality types and scope

Start simple, because the industry doesn’t.

Quality types (only three that matter)

  • CLI — A legitimate, carrier-verified Caller ID. Delivered in the native domestic signaling path, preserved end-to-end (A-number intact). High trust, predictable ASR.
  • NCLI — Non-legit or rewritten Caller ID. Often a sanitized or re-injected number (refile). Can look “local” but isn’t. Less trust, higher burn rate.
  • FAS (False Answer Supervision / Fraud) — The route signals an answer though no human was on the other end (ghost connects), or otherwise fabricates billing-relevant events. Wastes agent time and money.

Scope variants

  • Local / National — Traffic kept inside a country, using domestic carriers and formats. CLI is presented as a local number; termination is through domestic interconnects.
  • International / Cross-Border — Originates in one country, terminates in another via international signaling and gateway interconnects. Can still be CLI or NCLI depending on how the terminating side handles the A-number.

Put together: you judge a route by where it stays (scope) and how honest the ID is (quality).

2) The real classification (don’t overcomplicate it)

A useful shorthand:

  • Local × CLI — Ideal: local DID, carrier-verified, SS7 or native SIP handoff with preserved A-number. Best ASR, lowest burn.
  • Local × NCLI — Looks local but the ID was rewritten/sanitized before termination. Moderate performance, numbers still burn.
  • Local × FAS — Domestic fraud / fake connects. Avoid.
  • International × CLI — Good option when truly carrier-to-carrier international interconnects preserve CLI. Requires proof.
  • International × NCLI — Common in gray-routes: cross-border refile or CLI rewriting. Watch out.
  • International × FAS — Cross-border fraud; junk.

Everything else — “correct display,” “semi-CLI,” “smart route,” “local emulation” — is packaging for one of the above categories. Don’t buy a new label; buy evidence.

3) TDM vs. refile — the myth busted

“TDM” is used as a prestige sticker, but the reality in 2024–2025:

  • True TDM = a direct carrier SS7 interconnect with preserved A-number. Rare, provable, and expensive.
  • Most “TDM” you see = refile (grey). What happens: your SIP call is dumped into a gateway and re-originated on an SS7 leg (or into a local VoIP pool) with the CLI rewritten or sanitized so it looks local. That’s NCLI, not premium TDM. If a provider can’t prove a direct carrier-to-carrier SS7 handoff with transparent A-number preservation, treat their “TDM” as refile/NCLI.

How to test: insist on technical evidence — carrier identifiers on signaling, SS7 handoff records, or an independent capture showing A-number preservation. Without that, assume refile.

4) SIM box (GSM) routes — the bottom of the barrel

Short version: SIM box = NCLI refile over cellular. Here’s why they’re toxic:

  • What they are: GSM gateways stuffed with prepaid SIMs that re-originate VoIP calls as local mobile calls to avoid termination fees and hide origin.
  • Why they’re used: To bypass higher international tariffs and to try and appear local.
  • Why they fail: illegal or out-of-policy in most markets; SIMs get flagged and die in 24–72 hours; CLI is random or rewritten; carriers’ anti-fraud systems block them; ASR and audio quality suffer.
  • Result: Low ASR, erratic call quality, rapid number burn, and regulatory risk.

Label: SIM box = illegal/grey/NCLI, poor performance and compliance exposure.

5) Practical red flags & questions to ask vendors

When a vendor sells you routes, don’t take semantics — demand evidence.

Red flags

  • Vague claims: “we have TDM” with no technical proof.
  • “Semi-CLI”, “smart display”, “local emulation” — marketing euphemisms.
  • Very cheap price with implausibly high connect rates.
  • Refusal to provide signaling captures or carrier identifiers.
  • Rapid CLI burnout (numbers die in days).

Useful questions / proof you should require

  1. Can you show SS7/SIGTRAN signaling logs or traces proving A-number preservation? (or equivalent SIP headers showing unmodified P-Asserted-Identity/A-Number)
  2. Which domestic carrier is the termination handed to? (carrier name + peer ASN)
  3. Do you perform STIR/SHAKEN attestation on this route? If so, at what level?
  4. What is your FAS policy and how is FAS detected/blocked?
  5. CLI lifespan and rotation policy / reputation engine details.
  6. Can we run a paid side-by-side test and inspect CDR + signaling?

If they dodge these — assume NCLI/refile or worse.

6) What operators should do

  • Measure, don’t believe. Run side-by-side paid tests with signaling capture, CDR comparison, and human-verified ASR.
  • Demand carrier evidence. SS7 handoffs, signaling traces, carrier peer names and IPs.
  • Prefer transparent CLIs and carrier-verified DIDs. Local DIDs from carrier-verified pools beat anything that “looks local.”
  • Budget for quality. Price per minute is meaningless without connect rate and replacement costs factored in (cost per connected conversation is the metric that matters).
  • Protect your floor. Use DNC scrubbing, STIR/SHAKEN where applicable, and real-time fraud detection to keep numbers healthy.

7) Final word — cut through the noise

The telecom market loves new labels. Don’t fall for them. Routes are about where traffic moves (scope) and how honest the CLI is (quality). Everything else — “smart routing”, “correct display”, “semi-CLI” — is noise until you see technical proof.

If you’re buying routes, buy the technical evidence: signaling captures, carrier names, and a clean paid test that proves the route behaves like a true CLI route — or don’t buy it.