Many Indian businesses still run on PRI lines: a physical E1 circuit with 30 voice channels, a fixed monthly rental and a card in the exchange. SIP trunks deliver the same calls over a data connection and are easier to scale. This guide explains how to move from PRI to SIP without downtime, using Voxdial IP PBX.
PRI vs SIP trunk at a glance
| PRI line | SIP trunk | |
|---|---|---|
| Delivery | Physical E1 circuit and PRI card | Data link to the operator |
| Channels | 30 per E1 | Set by your plan |
| Scaling | Add another E1 circuit | Change the channel count |
| Hardware | PRI card in the PBX | None beyond the network |
| Reliability | Dedicated circuit | Depends on the quality of the data link |
Read more in our SIP trunk guide for India.
Before you start
- Get the SIP trunk from a licensed telecom operator, with the same numbers ported or new DIDs.
- Check bandwidth and quality of the data link; a SIP trunk on a poor connection sounds worse than PRI.
- List every number on the PRI and where calls to it should go.
- Note your outbound patterns: local, mobile, STD, toll-free and emergency.
Step 1: Add the SIP trunk alongside PRI
Voxdial supports PRI cards, SIP trunks and analog lines at the same time, so both can run in parallel. Add the SIP trunk with the operator’s details or a provider template, set the outbound caller ID and the maximum channels. The status page shows each SIP trunk as online or offline, next to the PRI ports.
Step 2: Route a few numbers first
Map one or two DIDs from the SIP trunk to their destinations. Enter each number exactly as the operator presents it. Test inbound calls, caller ID and audio in both directions.
Step 3: Move outgoing calls with failover
Outbound routes use an ordered trunk sequence. Put the SIP trunk first and the PRI second, so if the SIP trunk is busy or down, calls continue over PRI automatically. Watch quality for a few weeks.
Step 4: Move the remaining numbers
Once SIP calls are stable, port or move the remaining numbers and update the incoming routes. Keep the PRI as a backup route until you are confident, then cancel it.
Common problems and fixes
- One-way audio: usually a wrong external address or blocked media (RTP) ports on the firewall.
- Trunk shows offline: registration details or a firewall blocking the operator.
- Wrong caller ID: check the trunk’s outbound caller ID and route caller ID.
- PRI in alarm after changes: framing, coding, signalling and switch type must exactly match the operator’s settings.
After the migration
- Review call statistics to compare call volumes and long outbound calls.
- Remove unused PRI routes to keep the configuration clean.
- Keep backups before and after the change.
BitVoice plans and carries out PRI to SIP migrations on Voxdial IP PBX. Talk to our engineers.
FAQs
Can I move from PRI to SIP without downtime?
Yes. Run the SIP trunk alongside the PRI, move numbers in stages and keep the PRI as a failover route until SIP is proven.
How many channels does a PRI line have?
An E1 PRI line in India carries 30 voice channels.
Can an IP PBX use PRI and SIP at the same time?
Yes. Voxdial supports PRI cards, SIP trunks and analog lines together, and outbound routes can fail over from one trunk to another.
Why is there one-way audio on my SIP trunk?
The most common causes are a wrong external address setting or media (RTP) ports blocked on the firewall.
