1 PSN Services Service Descriptions - Government Procurement ...

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Line Appearances provide access to a host of advanced PBX style features from a desktop IP
instrument without the need for the provision of a PBX. The service is rented on a per line
appearance basis and can be enhanced by a range of network and user features. Call traffic
between the customer's sites is routed over the customer's IP data network. The service also
provides inbound direct dialling in (DDI) facilities and PSTN breakout.
IPT Trunks provide a VPN service which allows existing suitably configured PBXs to continue
to handle on-site calls, while traffic between the customer's sites is routed over the customer's
IP data network. Signalling and network protocol converters (Voice Gateways) may be required
depending on the PBX configuration and signalling type. The service can also offer inbound
direct dialling in (DDI) facilities and PSTN breakout.
Whilst there are differences in how each system supports a given feature, they both
provide the following capabilities:
o On-net (IP Phone to IP Phone) calling
o On-net (IP) calls can be made to other Hosted IPT Service users within the customers
network. These calls are zero-tariff, and can be made by dialling the on net number (as
described in “dial-plans”).
o Off-net (IP Phone to PSTN) calling
Full PSTN break-in and breakout is available as part of the service.