# PSTN overflow routing

The PSTN overflow automatically routes calls via the public network if there are no more voice channels available via the IP network.

Using the PSN overflow routing, you can in AIN, for instance, define the audio channels and bandwidths on the IP networks for a medium traffic load and relay part of the calls via the PSTN during peak periods. This makes for a rapid configuration of call routing.

## Using PSTN overflow routing

PSTN overflow routing is suitable for routing peak loads between AIN nodes via the PSTN, and for routing fax connections in the AIN (as an alternative to FoIP).

PSTN overflow routing is supported for the following direct connections:

- internal to internal

- internal to external

- external to internal

## Restrictions

PSTN overflow routing is not suitable for routing all call connections in an AIN via the PSTN as a matter of principle. Please take good note of the following restrictions:

- The break-in and break-out of the PSTN overflow is supported via ISDN network interfaces (BRI-T and PRI).

- If a satellite is connected with the Master via QSIG, the break-in and break-out of the PSTN overflow is also supported via the QSIG interfaces. This, however, only if the AIN has one satellite.

- A call that has already been answered via PSTN overflow cannot be forwarded via PSTN overflow.

- Calls to or from IP and SIP phones are always routed via the IP network.

- PSTN overflow is available only for point-to-point connections. The function is not available for conference, call waiting, intrusion and announcements.

- With calls to a user group whose members are spread over several satellites, only members of the first satellite are called via the PSTN overflow. Members at the other nodes are called only if the connection can be set up via the IP network. This also applies if the other satellites are connected to the Master via the PSTN.

- Throughout the AIN a maximum of 30 calls can be routed via the PSTN simultaneously using PSTN overflow.

## Configuration

Table 1. PSTN overflow
Parameter | Remarks
Enable PSTN overflow in AIN | PSTN overflow routing is enabled in AIN. PSTN overflow routing is locked in AIN.
Enable PSTN overflow in PISN | PSTN overflow routing is enabled in PISN. PSTN overflow routing is locked in PISN.

Table 2. AIN node
Parameter | Remarks
AIN node | Node number in the AIN
Break-out route | Route for routing outgoing overflow connection
Break-in call number | Break-in takes place via this call number. The call number must be defined on the node as DDI number and be linked with the break-in call distribution element. Enter the full call number without access prefix. Complete the country code if the node is in another country.
Allowed break-out connections | You can limit here the number of break-out connections on this node.

Table 3. Call distribution elements
Parameter | Remarks
Call distribution element | ID of the call distribution element
Name | Name of the call distribution element
Stored call number | Call number of the call distribution element
Enable PSTN overflow | This setting is relevant if in a call distribution element a terminal is defined as destination on another node. It can also be implemented in the configuration of the call distribution element: For connections, which lead to a terminal on another node through this call distribution element, the PSTN overflow routing can be used. For connections, which lead to a terminal on another node through this call distribution element, the PSTN overflow routing cannot be used.

Table 4. Terminals
Parameter | Remarks
Terminal ID | Terminal ID
Description | Cleint-specific description of the terminal
Node | Name of the node to which the terminal is connected.
Port | Port of the terminal on the communication server.
Enable PSTN overflow | No: PSTN overflow routing cannot be used tor connections in which this terminal is involved. If necessary: PSTN overflow routing can be used from the view of this terminal if the regular connection path is not available over the IP network. Permanently: PSTN overflow routing should always be used tor connections in which this terminal is involved (e.g. for fax connections).

To set up PSTN overflow, first specify the authorisations then create the break-in and break-out configuration:

## Specifying authorisations

1. Enable PSTN overflow routing in general for the entire AIN (authorise PSTN overflow in AIN).

   Nodes connected via QSIG can be separately enabled for PSTN overflow (Enable PSTN overflow on PISN).

2. Disable PSTN overflow routing for all phones and terminals to be barred from this feature (Terminal stable, Setting Enable PSTN overflow = No).

3. In the call distribution elements, disable PSTN overflow for phones on the DDI numbers to be barred from this feature (Call distribution table table, setting Enable PSTN overflow = ).

4. Enable PSTN overflow for all phones and terminals whose calls are to be routed via the PSTN only if the connection cannot be set up via the IP network (e.g. for all fax machines if FoIP is to be used for the fax connections in normal operation (Terminals table, setting PSTN overflow = If necessary).

5. Force PSTN overflow for all phones and terminals whose calls are always to be routed via the PSTN and never via the IP network, e.g. for all fax machines (Terminals table, setting Terminals = Always).

## Creating the break-in configuration

1. For the entire AIN open only one call distribution element for break-in. For this, open a new call distribution element and define for all switching positions the destination PSTN overflow. Leave the remaining CDE settings on their default values.

2. For each node define a DDI number for break-in and link it with the break-in call distribution element that has just been opened.

## Creating the break-out configuration

1. Define the break-out route for each node (Table AIN node, setting Route).

2. Specify for each node how many calls from each node can be rerouted via the public network (Table AIN node, setting Enabled break-out connections).

The PSTN overflow is now set up.

See also...

## Focus topics:

"General information about Mitel Advanced Intelligent Network (AIN)"
Parent topic: AIN
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