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This article describes how the SIP trunking feature can be used to connect a PBX to an extension in VoipNow and how the concurrent call limits set up within the interface will be reflected in your VoipNow licensing. 

Enable an extension for SIP trunking

When enabled at extension level, this VoipNow feature allows you to connect a PBX to a phone terminal extension (when a DID assigned to that extension is called, it is passed further to the PBX in the SIP:To header) and thus provide SIP trunking services to your customers.

 To enable an extension for SIP Trunking, please go to the extension's Provisioning and SIP preferences. Under SIP Preferences, you will find a field called A". Select the Enable for SIP trunking service option available. Then go to the Phone does not register, is located on IP field and enter the IP address of the PBX that will be connecting to the VoipNow server. 

Set the limit of concurrent calls 

To set the number of concurrent calls that a PBX is allowed to make, go to the User level of the associated extension, under Roles and Phone Numbers. There, you will find a field called Maximum public concurrent calls. The value you enter here will be the number of concurrent calls you allow the connected PBX to make through the VoipNow system. 

You can set a number of Maximum public concurrent calls on each of the following tenancy levels: User, Organization, Service Provider.

VoipNow's overselling feature

The overselling feature available in VoipNow allows you to set a higher limit on a lower tenancy level (e.g. user) and at the same time it makes sure that only a certain number of concurrent can take place for a given organization, service provider, or server-wide. 


A service provider can set a limit of 100 concurrent calls on five individual users to allow the PBXs connected to the VoipNow system to make up to 100 concurrent calls each.

However, the service provider has also set a limit of 200 concurrent calls on the Service Provider level, meaning that only 200 concurrent calls can take place through the VoipNow server.

What this means is that each connected PBX could reach a maximum of 100 concurrent calls, but once the VoipNow server reaches a total of 200 concurrent calls, no other calls will be initiated.

SIP trunking channel licensing

The billing for the SIP trunking channels is processed at the end of each month and it takes into account the limits of SIP trunking channels (concurrent calls) you have set on your server. The limit set on the highest tenancy level is the one that will be invoiced.

In the example above, the service provider will be invoiced for 200 SIP trunking channels, as this is the limit on the highest tenancy level (namely the Service Provider level).

If the service provider would have set a limit of 100 concurrent calls on each user level for all five users, yet no limit on the service provider level, then at the end of the month he would have been billed for 500 concurrent calls. 

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