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Reserving Voice Call Capacity within the NBN

The two voice ports on the subscriber NTU allow the connection of fixed line phones, and the SIP Profile needed to setup and receive calls. For these calls to work, sufficient NBN data capacity must be reserved for them.

Subscribers access the NBN via an “Access Virtual Circuit” or AVC (click here for more detail on NBN AVCs). The default NBN subscriber interface comprises two Access VCs, one for data, one for voice services. The voice AVC has a bi-directional 150 kbps reserved to support voice calls.

Additional Requirements for Voice Service Support

The NBN provides voice ports and capacity for voice traffic. The Retail Voice Service Provider (or Access Seeker) is responsible for the remaining voice service components. These include:

  • subscriber number management (e.g. transferring telephone numbers from previous services)
  • call termination
  • billing
  • service assurance

Current retail VOIP service providers provide similar functions to the ones above.


The NBN replaces the fixed line voice network, and hence must allow the existing fixed line voice services to be replicated. The NBN does this by providing analog voice ports in the subscriber Network Terminal Unit (NTU) and reserving network capacity for voice calls. Retail voice service providers will be responsible for the other voice service components.

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