A PRI line is a physical E1 circuit with a fixed 30 voice channels and a fixed monthly rental. A SIP trunk carries the same calls over your internet link, scales by changing a number in a portal, and on Edesy is billed per minute. If you rarely fill 30 channels, or need more than 30, SIP usually fits better.
Add a SIP trunk next to your PRI: Create a trunk on Edesy — KYC, a number and a trunk, all self-serve.
How each one works
PRI (Primary Rate Interface, E1 in India) is a dedicated digital circuit the operator runs to your office. It ends in a PRI card inside the PBX or in a media gateway. One E1 carries 32 timeslots: 30 for voice and 2 for framing and signalling. That gives you up to 30 simultaneous calls per line. Need 35? You order a second line.
A SIP trunk is a logical connection between your PBX and a provider's SIP server. Your PBX sends call setup messages (SIP) and audio (RTP) over the internet or a private link. There is no card and no cable from the operator. The limit on simultaneous calls is a setting on the trunk.
Side-by-side comparison
| PRI line (E1) | SIP trunk (Edesy) | |
|---|---|---|
| Physical delivery | Copper or fibre circuit to your office | Over your existing internet link |
| Channels | 30 per line, in fixed blocks | A max-concurrent-calls setting per trunk |
| PBX hardware | PRI card or media gateway | None beyond a SIP-capable PBX |
| Cost model | Fixed monthly rental plus call charges | Rs 0.50/min, 60-second pulse, unanswered calls free, plus number rental (excl. 18% GST) |
| Numbers | Pilot number and DID block from the operator | Mobile/92-series Rs 499/mo, landline Rs 449/mo, toll-free Rs 999/mo, Rs 0 setup |
| Setup time | Operator installation visit | Self-serve after KYC (review takes about 24 hours) |
| Moving offices | New circuit at the new address | Point the PBX at the same trunk from anywhere |
| Failure mode | Line cut or card failure | Internet outage or NAT/firewall misconfiguration |
| AI voice agents | Needs a separate SIP path | Same trunk works with LiveKit, Vapi, Retell, Bolna and other SIP platforms |
The honest trade-off: PRI depends on one physical circuit, SIP depends on your internet connection. Neither is automatically more reliable. A SIP trunk on a flaky broadband line will sound worse than a PRI. A SIP trunk on a stable business connection, with a backup link, removes the hardware single point of failure.
When PRI still makes sense
- Your site has poor or unstable internet and no realistic backup link.
- You have a recent PBX with a PRI card, a long-term PRI contract, and steady usage near 30 channels.
- An internal policy requires a dedicated operator circuit.
When SIP is the better choice
- You use well under 30 channels most of the day and pay for idle capacity.
- You need more than 30 simultaneous calls at peak and don't want a second line.
- You are moving to a cloud or virtual PBX, or running FreePBX in a data centre.
- You want to connect an AI voice agent or a contact-center tool to the same phone numbers.
- You have more than one office and want one trunk shared across them.
Not sure how many channels you actually need? Work it out from busy-hour traffic in how many SIP channels do I need.
Cost: what to compare
A PRI bill is mostly fixed: line rental, plus call charges. A per-minute SIP trunk is mostly variable. To compare them fairly:
- Pull three months of call records from your PBX.
- Add up billable outbound minutes per month. On Edesy, calls are billed in 60-second pulses and unanswered calls cost nothing.
- Multiply by Rs 0.50 and add number rental for each number you need.
- Add 18% GST to both sides.
- Compare against your PRI rental plus its call charges.
We don't publish PRI prices because they vary by operator, city and contract. Use your own bill.
Migration plan: PRI to SIP without downtime
- Check your internet. Confirm upload bandwidth for your peak calls (roughly 80 to 90 kbps per G.711 call each way) and, ideally, a second link.
- Complete KYC and buy a number on Edesy. Business types from individual to public limited are supported, with PAN and Aadhaar.
- Create a termination trunk in the portal. Each trunk gets its own SIP host, port 5070, UDP or TCP, and either digest credentials or an IP allowlist.
- Add the trunk to your PBX next to the PRI. For FreePBX, follow FreePBX SIP trunk setup for India.
- Move outbound first. Put the SIP trunk first in the outbound route trunk sequence and leave the PRI second as a fallback.
- Test audio both ways. If the far end can't hear you, it is almost always NAT. See fixing one-way audio, SIP ALG and NAT.
- Move inbound. Point callers at the new number, or forward the old PRI number to it while you decide what to do with the PRI.
- Run both for a few weeks, then cancel the PRI once you are confident.
What you get on the Edesy side
- A per-trunk SIP host, max concurrent calls setting, and password reveal or rotate.
- A test-call button on the trunk page to confirm the Edesy side works independently of your PBX.
- Prepaid INR wallet topped up with Razorpay, with GST invoices and GSTIN capture for input tax credit.
- The same numbers can be routed to IVR flows, AI agents or a contact center later.
Read more on the SIP trunking page, the FreePBX guide and the SIP trunking docs. If you plan to put an AI agent on the line, see SIP trunks for AI voice agents.
Bottom line
PRI gives you a fixed 30-channel circuit at a fixed price. SIP gives you channels as a setting and a bill that follows usage. For most Indian businesses with a SIP-capable PBX and a stable connection, running SIP alongside PRI for a few weeks, then switching over, is low-risk.
Create your SIP trunk or talk to us about your migration.