SIP Trunk Solutions and PSTN Gateway Development
A SIP trunk is a virtual telephone line connecting your PBX to the PSTN via internet instead of expensive ISDN/PRI lines. CelloIP builds SIP trunk provisioning platforms, PSTN gateways, carrier peering, and DID management with TLS/SRTP security and intelligent failover. SIP trunks save 50–70% vs ISDN.
How much cheaper is SIP trunking vs ISDN PRI?
ISDN PRI costs $300–500/month per line with 23–30 channels. SIP trunking delivers the same or more capacity at 50–70% lower cost with elastic scaling.
How do you secure SIP trunks?
Implement TLS for signaling encryption, SRTP for media encryption, IP whitelisting, digest authentication, rate limiting, and DDoS protection.
SIP Trunk Solutions &
PSTN Gateway Development
Replace expensive ISDN/PRI lines with carrier-grade SIP trunking infrastructure. We build intelligent routing, multi-carrier failover, encrypted signaling, and self-service DID provisioning — saving 50–70% on your telecom costs.
Technology Stack
SIP Trunking vs ISDN/PRI
Why every business is making the switch
| Attribute | ISDN / PRI (Legacy) | SIP Trunking ✦ |
|---|---|---|
| Cost per Channel | $10–20/channel/month | $1–3/channel/month |
| Capacity | Fixed 23–30 channels/line | Unlimited — scale on demand |
| Setup Time | Weeks (physical install) | Minutes (software provisioning) |
| Geographic Reach | Local carrier only | Global PSTN coverage |
| Failover | Manual, slow | Automatic, sub-second |
| Scalability | Requires new physical lines | Instant elastic scaling |
| Call Recording | Requires extra hardware | Built-in software recording |
| Number Portability | Complex, weeks | Fast LNP, days |
| Encryption | Not available | TLS/SRTP standard |
| Cost vs ISDN | Baseline | 50–70% lower |
What We Build for You
End-to-end SIP trunking infrastructure from carrier to endpoint
SIP Trunk Provisioning
Self-service portal for customers to order, configure, and scale SIP trunks — with API-driven automation and instant activation.
Carrier Peering
Multi-carrier interconnection with LCR (Least Cost Routing), quality-based failover, and volume-based rate negotiation.
DID Management
Provision, allocate, and route DID numbers globally. Number porting (LNP), virtual numbers, geo-number selection.
TLS / SRTP Security
Encrypted SIP signaling via TLS 1.3 and encrypted media via SRTP/DTLS. Mutual auth, IP whitelisting, and cert pinning.
Failover Routing
Automatic carrier failover in under 1 second. Quality-based routing monitors ASR, PDD, MOS, jitter, and packet loss.
Codec Negotiation
Multi-codec support: G.711, G.729, Opus, iLBC. Transcode between codecs transparently with RTPEngine media proxy.
Fraud & DDoS Protection
Real-time toll fraud detection, velocity-based blocking, SIP scanner defence, rate limiting, and geo-based ACLs.
Analytics & CDRs
Live traffic dashboards, per-trunk CDR reports, quality metrics (ASR/PDD/MOS), and carrier cost analysis.
Platform Feature Set
Carrier-grade capabilities built in by default
Intelligent Routing Architecture
Every call takes the optimal path — automatically
Least Cost Routing (LCR)
- Automatic carrier selection by lowest cost per destination
- Per-country, per-prefix rate comparison in real-time
- Volume commitments tracked per carrier
- Cost vs quality trade-off thresholds
- Detailed carrier cost analytics dashboard
Quality-Based Routing
- Real-time ASR, PDD, MOS, jitter monitoring
- Auto-failover when quality drops below threshold
- ML-based peak-hour quality prediction
- Per-carrier quality SLA tracking
- Customer-tier based routing priority
Geo-Redundant HA
- Multi-region Kamailio clusters with BGP Anycast
- Active-active with sub-second DNS failover
- Full DC failover without call drops
- Geographic proximity routing for low latency
- Disaster recovery RTO < 30 seconds
Implementation Process
From architecture to live carrier traffic in 6 phases
Architecture & Carrier Plan
Traffic projections, carrier selection, routing topology design, HA architecture, security model, and compliance requirements.
Core SIP Infrastructure
Kamailio/OpenSIPS cluster setup, RTPEngine media proxy, TLS certificate provisioning, load balancer, and monitoring stack.
Carrier Peering & LCR
Carrier SIP interconnection, rate table import, LCR engine configuration, quality thresholds, and failover testing.
DID Management & Provisioning
DID database, upstream carrier API integration, self-service portal, number porting workflow, and routing rules engine.
Security & Fraud Engine
TLS/SRTP enforcement, IP ACLs, toll fraud detection rules, DDoS mitigation, SIP scanner blocking, and alerting.
QA, Load Testing & Go-Live
End-to-end call flow testing, failover drills, 10× load test, CDR reconciliation, pilot carrier traffic, production cutover.
Why Choose CelloIP for SIP Trunking?
SIP trunking is critical infrastructure — when it fails, customers can't make or receive calls. CelloIP builds systems that don't fail. We've designed SIP platforms handling 100,000+ concurrent channels with 99.99% uptime, tested failover for every scenario, and maintained carrier relationships globally. Our 40+ carrier partnerships mean we can negotiate rates and route quality that smaller providers simply can't access.
Frequently Asked Questions
What is SIP trunking and how does it work?
SIP trunking replaces ISDN/PRI lines with internet-based connectivity. Your PBX sends and receives calls via SIP protocol over your internet connection. Inbound calls arrive at your DID numbers via the SIP trunk; outbound calls leave via the trunk to carrier networks. No physical phone lines needed — just an internet connection and a SIP-compatible PBX.
How much cheaper is SIP trunking vs ISDN PRI?
ISDN PRI costs $300–500/month per line with only 23–30 channels. SIP trunks deliver the same capacity for $50–100/month with elastic scaling. Most businesses switching from 4–5 PRI lines to SIP save $1,500–$2,500/month. The savings compound further with on-demand scaling — you only pay for capacity you actually use.
How many concurrent calls can a SIP trunk handle?
There's no fixed limit — SIP trunks scale elastically. You purchase a concurrent channel count (e.g. 50, 100, 500 channels) and can scale up instantly. Each call needs roughly 90Kbps bandwidth (G.711 codec), so 100 concurrent calls requires ~9Mbps. A typical business broadband connection handles dozens of calls; a dedicated line handles hundreds.
What security does your SIP trunk platform include?
TLS 1.3 for encrypted SIP signaling, SRTP/DTLS for encrypted voice media, IP whitelisting, digest authentication, mutual TLS cert verification, rate limiting per source IP, automated toll fraud detection with call blocking, SIP scanner defence, and DDoS mitigation. For regulated industries (healthcare, finance), we add FIPS 140-2 crypto and full audit logging.
How does carrier failover work?
We maintain connections to multiple carriers simultaneously. Our quality monitoring tracks ASR, PDD, MOS, jitter, and packet loss in real-time. When a carrier's quality drops below threshold or connectivity fails, our Kamailio routing engine automatically shifts traffic to the best available carrier — typically within under one second, transparent to callers.
Can you build a SIP trunking service we can resell to customers?
Yes — building white-label SIP trunk platforms for ITSPs and resellers is one of our specialties. We build the full stack: provisioning portal, billing integration, DID management, customer self-service portal, and API access. Your customers see your brand; you manage the underlying carrier relationships and infrastructure.
Related VoIP Services
Ready to Deploy SIP Trunk Infrastructure?
Whether you're replacing legacy ISDN or launching a reseller SIP trunk service — we'll build carrier-grade infrastructure that scales reliably.