Comparison
SIP Trunk vs PRI: Cost, Capacity and Migration
A PRI is a physical E1 or T1 circuit with a fixed number of channels. A SIP trunk carries the same calls over IP with channels set in software. Here is how they compare on cost, capacity, quality and risk.
Short answer
Side by side
SIP trunk and PRI compared
| SIP trunk | PRI | |
|---|---|---|
| Medium | IP over your internet or private link | Dedicated copper or fibre circuit |
| Capacity | Set per account, raised on request | 30 channels (E1) or 23 (T1) per circuit |
| Adding capacity | Config change, same day | New circuit, often weeks |
| Pricing model | Per minute from prepaid balance | Monthly line rental plus call charges |
| Hardware | None beyond the PBX | PRI card or gateway per circuit |
| Destinations | International routes on one trunk | Usually priced by the local carrier |
| Failover | Multi-carrier, per call | Second circuit or ISDN backup |
| Call quality | Depends on your network, G.711 matches PRI | Fixed, predictable TDM quality |
| Fax | T.38 with G.711 fallback | Native, very reliable |
| Encryption | TLS and SRTP available | None on the wire |
Which one fits
When each option makes sense
Choose SIP trunk when
- Your PBX already supports SIP, which almost every system sold in the last decade does.
- You need more than 30 channels or your traffic changes month to month.
- You call many countries and want one set of rates and CDRs.
- You want to stop paying line rental for channels you rarely fill.
- You run more than one site and want them on the same trunk.
Choose PRI when
- The site has no reliable broadband or only a very small uplink.
- A regulator, insurer or alarm system still requires a TDM line.
- You depend on high-volume analogue fax and cannot test T.38.
- You run a legacy PBX with no SIP licence and no budget to replace it yet.
Cost
Illustrative monthly cost for 30 channels
Sample figures for a business making around 20,000 outbound minutes a month. Real prices depend on country and carrier.
| Item | SIP trunk | PRI (E1) |
|---|---|---|
| Line rental / channel fee | $0 | $400 – $650 |
| Hardware amortised | $0 | $30 – $60 |
| 20,000 domestic minutes | $140 – $200 | $200 – $400 |
| Adding 10 more channels | $0 | New circuit |
| Typical monthly total | $140 – $200 | $630 – $1,110 |
Sample figures only, not a quote. SIP minute rates on this page start from $0.007 per minute and are placeholders until current rates are published.
Moving over
Migrating from PRI to SIP without downtime
- 01
Measure
Pull peak concurrent calls, numbers in use, fax lines and alarm lines from the last three months. - 02
Run in parallel
Add the SIP trunk next to the PRI. Test outbound calls and one inbound test DID. - 03
Move outbound
Shift outbound routes to SIP by destination and keep the PRI as the failover route. - 04
Move numbers
Port or replace inbound numbers, watch CDRs for a full billing cycle, then cancel the PRI.
FAQ
Common questions
Further reading:
Is SIP call quality worse than PRI?
Not on a healthy network. With G.711 and less than 1% packet loss, a SIP call sounds the same as a PRI call. Problems come from congested uplinks, Wi-Fi and SIP ALG, all of which can be fixed or avoided.
How much bandwidth do I need to replace a 30-channel PRI?
About 87 kbps per G.711 call in each direction including overhead, so roughly 2.6 Mbps up and down for 30 calls. G.729 cuts that to about 32 kbps per call.
Can I keep my PRI numbers?
Often, yes. Porting depends on the country and the losing carrier. Send sales the numbers and we confirm whether they can be ported or whether new DIDs are faster.
What happens if my internet goes down?
Inbound calls can be forwarded to a mobile or another site, and outbound calls fail over to a second connection or a 4G/5G router. Plan this before you cancel the PRI.
Do I need a new PBX?
Usually not. Most PBXs from the last decade support SIP trunks with a licence or a config change. Older systems can use a SIP-to-PRI gateway as a bridge.