If your office still runs on PRI lines or a bunch of analog lines, a SIP trunk is the simplest way to cut call costs and add capacity. This guide explains what a SIP trunk is, how it works with your PBX, what Indian businesses should check, and how to switch without changing your numbers.
What is a SIP trunk?
A SIP trunk is a phone line delivered over a data connection instead of copper wires. Your telecom operator connects its network to your IP PBX using the SIP protocol, and each trunk carries as many simultaneous calls as you subscribe to. One SIP trunk can replace several PRI or analog lines.
SIP trunk vs PRI vs analog lines
| Analog lines | PRI E1 | SIP trunk | |
|---|---|---|---|
| Calls per line | 1 | 30 | As many channels as you subscribe to |
| Hardware in the PBX | FXO gateway port per line | E1 card | None, runs over the network |
| Adding capacity | New lines and cabling | Another E1 | Change the channel count with your operator |
| Numbers | One number per line | DID number series | DID number series, can move with you |
| Typical cost | High per call | Medium | Usually lowest per call |
Benefits for Indian businesses
- Lower call charges: SIP plans from Indian operators are usually cheaper than PRI for the same calls.
- No interface hardware: no E1 cards or gateways needed in the PBX.
- Scale quickly: add channels for a campaign or a new team without new cabling.
- DID numbers: give departments or staff direct numbers.
- Backup routing: keep one PRI or analog line as a fallback if the data link fails.
Which operators offer SIP trunks in India?
Airtel, Jio, Tata Communications, BSNL and Vodafone Idea all offer enterprise SIP trunking. Plans differ by channels, included minutes, number series and whether the trunk runs over a dedicated link or the internet. Ask each operator for a quote with the same channel count.
Rules and good practice in India
- Buy SIP trunks only from licensed telecom operators.
- Indian telecom rules restrict routing calls in ways that bypass licensed networks, so let your operator and PBX vendor configure call routing correctly.
- Use a dedicated link or quality broadband with enough bandwidth (roughly 100 kbps per concurrent call with G.711).
- Secure your PBX: strong passwords, TLS and SRTP encryption, and allow SIP traffic only from your operator’s IP addresses to prevent toll fraud.
How to switch to SIP without changing numbers
- Ask your operator whether your existing number series can be moved to SIP, or ordered as a new DID series.
- Confirm the channel count from your peak simultaneous calls.
- Set up the trunk on your IP PBX and test inbound and outbound calls.
- Move routes from PRI or analog to SIP, keeping one old line as a fallback.
- Retire the old lines once the SIP trunk has run smoothly for a few weeks.
SIP trunks with Voxdial IP PBX
Voxdial IP PBX by BitVoice has ready SIP trunk templates for Airtel, Jio, Tata, BSNL and Vodafone, and runs SIP, PRI E1 and analog lines together, so you can move at your own pace. It is TEC certified and supports TLS and SRTP encryption. BitVoice coordinates with your operator during the switch. Book a free survey.
FAQs
What is a SIP trunk in simple terms?
It is a phone line delivered over your data network. Your operator connects calls to your IP PBX using SIP, and one trunk carries many simultaneous calls.
Is a SIP trunk cheaper than a PRI line?
Usually yes. SIP plans from Indian operators generally cost less per call, and they need no E1 hardware in your PBX.
Can I keep my existing phone numbers on a SIP trunk?
Often yes. Ask your operator whether your number series can be moved to the SIP trunk; otherwise you can get a new DID series and keep the old line during the change.
How much internet bandwidth does a SIP trunk need?
Plan for roughly 100 kbps per concurrent call with the G.711 codec, less with compressed codecs such as G.729, on a stable dedicated link or business broadband.
Does Voxdial IP PBX support Jio and Airtel SIP trunks?
Yes. Voxdial has ready templates for Airtel, Jio, Tata, BSNL and Vodafone SIP trunks.
