What it does

The outbound routing chain for Direct Routing: a voice routing policy holds an ordered list of PSTN usages, each usage holds voice routes, and each route pairs a regex number pattern with a set of SBCs. Dial plans sit in front of it, normalising what the user typed into E.164 before routing runs.

Key facts

• Build order: Set-CsOnlinePstnUsage -Identity Global -Usage @{Add="UK"}, then New-CsOnlineVoiceRoute -NumberPattern ... -OnlinePstnGatewayList ... -Priority n -OnlinePstnUsages "UK", then New-CsOnlineVoiceRoutingPolicy -OnlinePstnUsages ..., then Grant-CsOnlineVoiceRoutingPolicy.
• PSTN usages are evaluated in the order they appear in the policy. The first usage with a matching route wins and later usages are never looked at.
• Within a usage, routes are tried by Priority — lower number first.
• SBCs listed in a single route's OnlinePstnGatewayList are tried in random order, not list order. For ordered failover, use separate routes with different priorities.
• Number patterns match the base number only — ;ext= is ignored for matching.
• No matching route means the call fails, unless the user also has a Calling Plan, which acts as the final fallback.
• Setting the Global (Org-wide default) voice routing policy hits every voice-enabled user, including Calling Plan and Operator Connect users — whose calls can then go out of your SBC.
• Dial plans: the service country dial plan is Microsoft-managed; tenant dial plans (Global or user-scoped) add normalisation rules on top. Maximum 1,000 tenant dial plans. Cmdlets: New-CsTenantDialPlan, New-CsVoiceNormalizationRule, Grant-CsTenantDialPlan, Get-CsEffectiveTenantDialPlan, Test-CsEffectiveTenantDialPlan.
• Gateway translation rules (New-CsTeamsTranslationRule) are applied per SBC via InboundTeamsNumberTranslationRules, InboundPSTNNumberTranslationRules, OutboundTeamsNumberTranslationRules and OutboundPSTNNumberTranslationRules. Limit 400 rules per tenant. Rules run in the listed order.
• Direct Routing numbers can be 3–38 digits. Extensions use ;ext= with 1–12 digits.

When to use / skip

Every Direct Routing tenant needs at least one policy, usage and route. What varies is how far you go. A single-country estate with one SBC pair can live happily on one usage with a catch-all ^\+44 route and a couple of priority tiers. Multi-country estates, least-cost routing, or regulatory splits (some countries forbid toll bypass) are where the usage ordering earns its keep.

Dial plans are optional for most UK deployments now — users dial E.164 or national format and the service country plan handles it. You need a tenant dial plan for short extension dialling, access codes, or a client who insists on "9 for an outside line". Don't build dial plans to fix carrier formatting — that's what gateway translation rules are for.

Configuration decisions

• Leave the Global voice routing policy empty and assign named policies, or populate Global? In mixed tenants (any Calling Plan or Operator Connect users) leave it empty.
• Usage granularity: per-country, per-call-class (national, mobile, international, premium), or per-site. Call classes let you build restriction tiers by assembling usages into policies.
• Route priorities for failover between SBCs or regions — remember randomisation within a route.
• Where to translate numbers: tenant dial plan (user-facing, also affects call history and click-to-dial) vs gateway translation rules (per trunk, invisible to the user) vs the SBC itself.
• Whether premium-rate and international are blocked in Teams routing or at the carrier. Do both if fraud exposure matters.
• Group policy assignment vs direct user assignment for voice routing and dial plans.

Gotchas

• A greedy pattern in an early usage swallows everything. ^\+ in the first usage means your international-restricted users can dial anywhere.
• Changing usage order needs Set-CsOnlineVoiceRoutingPolicy -OnlinePstnUsages @{Replace=...} with the full list — an Add appends to the end.
• Two SBCs in one route is load-sharing, not primary/backup. People design it as primary/backup and then wonder why half the calls go to the DR site.
• The ingress-SBC exception: if the call came in via an SBC that's also a valid egress for the route, that SBC is preferred regardless of priority. Watch this in forwarding and simultaneous ring.
• Emergency dial strings for Direct Routing no longer arrive with a + from Teams clients. Route patterns that assume ^\+999 miss them — see the emergency calling doc.
• Normalisation rules apply to call history and links, so a sloppy rule shows up as broken redial, not just broken dialling.

Consultant notes

• Write the regex in a design table with test numbers for each route, then prove them with Test-CsEffectiveTenantDialPlan and the Direct Routing diagnostic.
• Anchor every pattern with ^ and $. Unanchored patterns match more than you think.
• Keep naming boring and consistent: UK-National, UK-Mobile, INTL. The person who inherits it will thank you.
• Script the whole lot. Rebuilding routing by hand in the admin center across a dozen sites is how typos get into production.

---

Revisit if Microsoft changes route-level SBC selection or how Teams clients format emergency dial strings