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Australian Telco

Call routing in LNP

How call routing including Donor Routing works in LNP.

Before we get started there’s a few key concepts we’ve got to be familiar with:

  • PLNR
  • Donor Carrier
  • Losing CSP
  • Gaining CSP
  • Donor Transit Routing
  • Third Party Ports

If you’re not familiar with some of these concepts go back to the LNP FAQ and Anatomy of Local Number Portability in Australia posts which explain them.

Before Porting

In the beginning ACA created the heavens and the earth? Wait, no, the Numbering Plan for Australia.

The numbering system lists all the phone numbers in Australia and the carrier they’re assigned to (Donor Carrier when ported).

This means each carrier downloads this data from what is now ACMA (but was at the time ACA) and for each outgoing call look the number up in that data set and route to the correct carrier.

This routing is used when a number has not been ported – The CSP it’s allocated to by ACMA is the CSP to route calls to.

During Porting – Donor & Losing CSP the Same

At the time the number is ported the Losing CSP provides Donor Transit Routing – In practice this is nothing more than a fancy redirection/ forward to the new carrier.

Once the port is completed (and the Emergency Porting Return period has expired) the Losing CSP (who in this case is also the donor CSP) updates their PLNR file, to include the number that’s just been ported out and the new carrier’s code.

During Porting – Donor & Losing CSP Different (3rd Party Porting)

At the time the number is ported the Losing CSP provides Donor Transit Routing – In practice this is nothing more than a fancy redirection/ forward to the new carrier.

Once the port is completed (and the Emergency Porting Return period has expired) the Donor CSP updates their PLNR file, to update the record for the ported number, which previously showed the code of the Losing CSP and now must show the new CSP code.

After Porting – PLNR Update

After the PLNR has been updated by the Donor CPSs, other CPS that participate in porting must update their routing records to ensure they route directly to the Gaining CSP and not to the Donor CSP and rely on Donor Routing.

Donor Routing is only required to be in place for a short time, meaning carriers that don’t update their routes will find the ported destination unreachable once donor transit routing has been stopped.

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