Connecting legacy hardware pbx to asterisk pbx over pri


We currently have an older Inter-Tel PBX in service with one PRI card that connects to a T1 serviced by the local telco. As our contract with them is about to expire, I have been asked to look into the possibility of switching to Voice over IP for our connection to the PSTN to reduce costs. Our current system as it is now doesn’t seem to support any IP functionality so I was thinking of setting up an Asterisk server that would act as a ‘SIP Gateway’ and connect it to the old system over a point to point PRI connection. In this scenario, anyone making a call from the old system to the PSTN would be sent to the Asterisk system which would in turn translate the voice traffic into SIP/RTP packets that would be routed over the internet. I understand that there are dedicated hardware devices that are specifically designed to handle such a conversion but I would rather have a full blown Asterisk system in place to make it easier to completely phase out the Inter-Tel system when the time comes.

Is something like this possible using asterisk? Are there any pitfalls I should know about before taking on such a project?

Thanks in advance.

I think you can do this successfully, connecting the Asterisk to a pbx through a PRI line generally works well, don’t know nothing about Inter-Tel, so can’t tell you more.


Marco Bruni

If you are planing to replace your legacy PBX; you need to consider this like a new install and keep the following consideration

  1. TDM endpoints (will help you to calculate Number of slots in Channel bank to connect with asterisk server )
  2. IP end points
  3. Codec G711,G729 etc… (Compression would consume more cpu usage)
  4. Numbering Plan
  5. Traffic on peak time

All these would help you in deciding the suitable Hardware now itself. later on you can migrate to full blown asterisk with out any major changes in hardware