SIP Trunking
Enterprise and global SIP trunks that replace PRI and ISDN with elastic channels, encrypted signalling and media, and native integration with your PBX, Microsoft Teams or contact-centre platform.
110+
Countries served
99.99%
Trunk availability SLA
≤ 15 min
P1 NOC response
What is SIP Trunking?
Dollu SIP Trunking connects your on-premises PBX, cloud PBX, Microsoft Teams tenant or contact-centre platform to the public telephone network over IP. Where a legacy PRI gave you 30 channels per circuit and a change order for every expansion, a Dollu trunk gives you a channel count you scale from the portal, numbers in 110+ countries on the same trunk, and one bill for local, national and international calling.
Trunks are delivered from geo-redundant session border controllers at our London, Frankfurt, Amsterdam, Ashburn, Mumbai and Singapore PoPs. Signalling can run over TLS and media over SRTP end to end, and you can authenticate by IP, by SIP registration or both. Multi-site enterprises can share a pool of channels across locations, or split trunks by region to keep media local and latency low.
The service is engineered around the platforms enterprises actually run. We maintain tested configuration guides for major IP-PBX and UCaaS vendors, are a Direct Routing carrier for Microsoft Teams, and support the SIP header, codec and DTMF behaviours contact-centre platforms rely on. Emergency calling - E911 in the US, 999/112 in the UK and EU and equivalents elsewhere - is provisioned with location information where the country's rules require it.
Because the trunk sits on the same core as our wholesale voice business, international calls take the same direct routes we sell to carriers, at enterprise rates rather than incumbent list price. Fraud controls, per-trunk spend caps, real-time CDRs and 24×7 NOC support come as standard, and named account management is included for multi-site and multi-country deployments.
SIP trunk topology: from your PBX to the PSTN.
Why choose Dollu for sip trunking.
The advantages of buying from a carrier that owns its network, interconnects and operations - rather than a reseller.
Lower cost than legacy circuits
No per-circuit rentals, no truck rolls and international calling at carrier rates typically cut voice spend substantially against PRI or incumbent SIP offers.
Scale in minutes
Add channels for a seasonal peak or a new site and remove them afterwards; burst capacity handles the days you did not plan for.
Secure by default
TLS and SRTP, IP allow-listing, per-trunk credentials and real-time fraud detection protect your PBX from toll fraud and eavesdropping.
Works with what you run
Tested configurations for major PBX, UCaaS and contact-centre platforms, plus certified Teams Direct Routing, mean deployment is measured in days.
One global trunk estate
Bring numbers from every country your business operates in onto a single provider, contract and portal, with local emergency and compliance handled per country.
Resilience for voice-critical teams
Geo-redundant SBCs, dual trunks to separate PoPs and automatic failover to mobile or a secondary site keep customer lines open.
Capabilities in detail.
Everything included with SIP Trunking - the platform features, options and controls you get from day one.
- 01
Elastic channel model
Committed channels with configurable burst headroom, or fully usage-based trunks; per-trunk CPS and concurrent-call limits managed live from the portal or API.
- 02
Secure signalling and media
SIP over TLS 1.2+ with SRTP (SDES or DTLS-SRTP), IP allow-listing, digest registration, and per-trunk credential rotation; optional IPsec or private interconnect.
- 03
Platform integrations
Microsoft Teams Direct Routing carrier; tested guides for major on-premises and cloud PBXs, SBCs and contact-centre platforms, including header, codec and DTMF settings.
- 04
Numbers and porting
Geographic, national, mobile and toll-free numbers in 110+ countries provisioned to the trunk; managed porting with cutover scheduling and regulatory paperwork.
- 05
Emergency calling
E911 with dispatchable location in the US, 999/112 with address registration in the UK and EU, and equivalent arrangements in other countries where the number type mandates them.
- 06
Fraud and spend controls
Per-trunk daily and monthly spend caps, destination allow and block lists, velocity limits, out-of-hours rules and real-time alerts on anomalous patterns.
- 07
Failover and business continuity
Dual trunks to separate PoPs, inbound failover to secondary sites or mobile numbers, and announcement fallback when all endpoints are unreachable.
- 08
Reporting and CDRs
Portal dashboards for utilisation, quality and cost per site; near-real-time CDRs by API and SFTP; monthly statements broken down by site, department or cost centre.
- 09
International calling
Outbound to 230+ destinations on Dollu's direct A–Z routes with enterprise rate cards, CLI presentation controls and optional premium routing per country.
How it works.
From first conversation to live traffic - a tracked, engineer-led onboarding with a named owner at every step.
- Step 01
Design
We review your sites, platforms, number estate and call profile and propose trunk topology, channel counts, security options and a porting plan.
- Step 02
Provision
Trunks, credentials and test numbers are issued within one business day. Your platform team applies our tested configuration guide or works with our engineers on the SBC.
- Step 03
Test and port
Validate inbound, outbound, DTMF, fax and emergency behaviour with our test plan. Ports are scheduled per country and cut over site by site.
- Step 04
Operate
Scale channels, add numbers and adjust routing from the portal. The NOC monitors trunk health around the clock and your account manager reviews usage quarterly.
SIP trunk vs ISDN PRI.
What changes when you move a PBX, contact centre or Teams estate from ISDN circuits to SIP - and why most estates never go back.
| Dimension | SIP trunkDollu recommends | ISDN PRI |
|---|---|---|
| Capacity per unit | Elastic - channels are added in software; burst capacity on demand for peaks | Fixed - 30 B-channels per E1 (23 per T1); a new circuit for every step up |
| Provisioning time | Hours to days over any existing IP connectivity | Weeks - physical circuit delivery, PBX card and installation visit |
| Resilience | Registration to multiple Dollu PoPs, DNS SRV failover, geographic redundancy without extra circuits | A single physical path unless a second circuit is installed and paid for |
| Media security | TLS signalling and SRTP media end to end; SBC-fronted | Physically separate circuit; no encryption in the protocol itself |
| Number portability | Numbers from 110+ countries on one trunk - ported in or newly issued; not tied to a location | Numbers tied to the local exchange and the circuit’s address; moving means porting |
| Cost model | Per channel or per concurrent call plus per-second usage; no circuit rental or install charge | Circuit rental plus per-channel plus per-minute usage; install and engineer charges |
| Future-proofing | Native to Teams Direct Routing, cloud PBX, CCaaS and voice APIs; ready for the ISDN switch-off | Being withdrawn - PSTN and ISDN switch-off programmes are under way in the UK, EU and elsewhere |
Who uses this and why.
Typical deployments across carriers, enterprises, platforms and contact centres.
PRI and ISDN replacement
Retire circuits ahead of PSTN switch-off with SIP trunks to your existing PBX, keeping numbers and call flows unchanged.
Microsoft Teams calling
Direct Routing to Teams for PSTN calling in countries where Calling Plans are unavailable or uneconomic, with numbers in 110+ countries.
Contact-centre platforms
High-density trunks with burst capacity, header support and premium international routing for inbound and outbound centres.
Multi-country enterprises
One trunk estate spanning regional PoPs with local numbers, emergency compliance and centralised reporting per country.
Managed service providers
Wholesale SIP trunks with sub-accounts, white-label portal access and per-customer spend controls behind your own UC offer.
Technical & commercial specifications.
Key parameters at a glance. Ask us for the full service description and SLA document.
| Signalling | SIP (RFC 3261) over UDP/TCP/TLS 1.2+; IP or registration authentication |
|---|---|
| Media | RTP/SRTP; G.711a/u, G.729, G.722, Opus; DTMF RFC 2833/4733; T.38 |
| Channels | From 5 to 5,000+ per trunk; committed plus burst or fully usage-based |
| Numbers | Geographic, national, mobile, toll-free in 110+ countries; porting |
| Emergency | E911 (US), 999/112 (UK/EU) and local equivalents with location data |
| Platforms | Teams Direct Routing; major PBX, UCaaS, SBC and CCaaS platforms |
| PoPs | London, Frankfurt, Amsterdam, Ashburn, Mumbai, Singapore |
| Availability | 99.99% trunk availability SLA; geo-redundant SBCs |
| Controls | Spend caps, destination lists, velocity limits, CPS and channel caps |
| Support | 24×7 NOC; P1 response ≤ 15 min; named account manager |
How Voice & Wholesale is priced.
Wholesale voice is priced from an A–Z rate deck: a rate per destination and breakout for each quality tier, billed on connected seconds. There are no setup or port fees on SIP interconnects.
We publish the model, not a public rate card - actual rates depend on destination, route class, volume and regulatory cost. See how every Dollu service is priced.
- A–Z rate deck in USD, EUR, GBP or INR
- Premium (CLI), Standard and Wholesale tiers per destination
- 1/1 billing on most destinations; 60/60 flagged on the deck
- Volume tiers from 1M minutes a month; bilateral and swap for carriers
- Rate increases with at least 7 days’ notice; decreases immediate
- Billing
- Prepaid (online top-up, auto-recharge) or postpaid net-15/30 after credit review; per-second increments
- Commitment
- None - month-to-month usage; optional volume commitments unlock better tiers
230+ destinations, A–Z.
Every country on the rate deck, in Premium, Standard and Wholesale tiers where the market supports them - over 600 direct carrier interconnects and Tier-1 partners. Country guides cover the destinations with the most traffic.
SIP Trunking - your questions answered.
The questions customers and carriers ask us most often before they interconnect. If yours is not here, our team answers within one business day.
Still have a question?
Ask our solutions teamRelated services.
Services customers commonly combine with SIP Trunking.
Move off PRI without moving your PBX.
Share your sites, platforms and monthly call volumes and we will return a trunk design, channel recommendation and rate card within one business day.
