FRITZ!Box models from AVM Telephone Systems that have VoIP (Voice over IP = Internet telephony) integrated as a fixed component in the system. These are good solutions for home use, but for business customers, more than four telephones together with special functions such as system telephones or individual waiting music are often needed. Almost all larger telephone systems do not support VoIP directly, however. This problem can be solved by connecting an existing or newly acquired telephone system to the AVM FRITZ!Box 5050/7050 (and all future models that have an internal S0 bus; in the diagram we use a FRITZ!Box 7050 as an example). This system connection allows all telephones to make calls on the main telephone system via the fixed network as well as via VoIP.

Basics

The FRITZ!Box is a DSL router and telephone system in one device.

The FRITZ!Box is connected to the DSL connection on the splitter, and the computer to the FRITZ!Box via LAN, USB or WLAN. In this manner, the FRITZ!Box functions as a router, and provides Internet access to all computers. In addition, your VoIP numbers are configured in the FRITZ!Box, which registers your VoIP numbers when the Internet connection to your VoIP provider is being established and handles Internet calls via the existing DSL Internet connection. To ensure that you are always contactable telephonically via VoIP, the FRITZ!Box can be configured in such a manner that you keep the Internet connection active permanently.

Note: Under normal circumstances, the FRITZ!Box replaces an existing DSL router. However, if you wish to continue using the existing DSL router (e.g. because VPN connections are set up on the router) it is possible to connect the FRITZ!Box to the existing router as an alternative. In this case, the FRITZ!Box does not set up the Internet connections, but rather exclusively handles the Internet telephony via the existing router.

The FRITZ!Box has three analogue extensions and an internal S0 bus for connecting an ISDN telephone. All terminal devices connected to these extensions can make calls over the Internet. In addition, the FRITZ!Box is connected to the analogue telephone connection or the NTBA of the ISDN telephone connection, and consequently permits all connected terminal devices to make calls not only via the Internet but also via the fixed network. Where this number of extensions is insufficient, an existing or additionally procured ISDN telephone system can be "connected" to the FRITZ!Box, so that calls via the fixed network or Internet are possible from all telephones in the system. The type of system connection differs, depending on whether you use a single or multiple ISDN connections, and whether these are set up as multiple devices or system connections. As an alternative to these recommended system connections, it is also possible to operate the FRITZ!Box as a sub-system.

System connection to an ISDN multi-device connection

The FRITZ!Box is connected as described under Basics. The external S0 bus of an ISDN telephone system (the connection that was previously linked to the NTBA) can be connected to the internal FRITZ!Box S0 bus (Fon S0) instead of an ISDN telephone.

The external S0 of the telecomms system is connected to the internal S0 of the Box. The external S0 of the Box is connected to the NTBA. All calls run over the Box. The configuration decides whether the calls are to be set up via VoIP or the fixed network.

The behaviour of the FRITZ!Box is completely transparent to the subscriber. You dial the number without a special area code or key code, as before. The FRITZ!Box decides whether the call is to be routed via the Internet or the fixed network, based on the configuration. Incoming calls from the Internet or fixed network are simply routed to the telecomms system by the FRITZ!Box. Here, the configuration of the telecomms system decides which extension is to respond. The FRITZ!Box Fon decides whether the call is to be routed via the fixed network or the Internet, based on the existing number. The rule is simple: If the outgoing MSN is an Internet or VoIP-capable fixed network number, the call is set up via the Internet. All other calls are routed via the fixed network. A main number (fixed network or Internet) can be stored in the Box for devices without an outgoing number.

Tip: To ensure orderly operation, you should ensure that all subscribers to a telecomms system have a valid number configured, and that all fixed network numbers are entered in the FRITZ!Box Fon.

Where the device has the outgoing MSN 9876, the call will be carried via the Internet.

Where 1234 is used for outgoing calls, the call will also be carried via the Internet, as VoIP is used in preference.

Devices with the outgoing MSN 5678 use the fixed network for calls, by contrast.

Devices without an outgoing MSN make calls via the main number, in this case via the Internet using the number 1234.

When configured in this manner, all telephones on the system can make calls on both the Internet and via the fixed network.

As described above, the FRITZ!Box decides whether the call is to be routed via the Internet or the fixed network based on the outgoing number set in the telephone system.

Dialling rules for instances that deviate from this setting can be set up in the FRITZ!Box. In this manner, all service and emergency numbers are carried via the fixed network in principle, for example. However, you have the option to specify that all calls to mobile phones are routed via the fixed network rather than the Internet, and then optionally also via any call-by-call provider.

Where a call is occasionally to be routed explicitly via the fixed network or using a particular call number, this can be selected for the call by entering a key code on the telephone.

In this configuration, a maximum of two calls can be carried simultaneously (Internet or fixed network).

Where your ISDN telephone system has an additional S0 bus (or an internal S0 bus that has not been used up till now and that can be externally connected), you can also connect the telephone system to the NTBA.

An telephone system's external S0 is connected to the FRITZ!Box Fon S0. The S0 in the telecomms system must be prioritised, so that the first two calls are carried via VoIP. The telephone system's second external S0 bus is connected to the NTBA. This enables four simultaneous calls (two via the fixed network and two via VoIP).

System connection with more than one ISDN multi-device connection

The FRITZ!Box is connected and configured in the same manner as for operation with one ISDN connection. The first system's first external S0 bus is connected to the FRITZ!Box Fon 0 and the FRITZ!Box ISDN connection is connected to the NTBA of the first ISDN connection.

The telephone system's second external S0 bus remains connected to the NTBA of the second ISDN connection.

The first external S0 in the telecomms system must be prioritised, so that the first two calls are carried via VoIP.  This enables two calls via VoIP and two via the fixed network simultaneously. Where your ISDN telephone system has an additional external S0 bus (or an internal S0 bus that has not been used up till now and that can be externally connected), you can also connect this bus to the FRITZ!Box on the NTBA of the first ISDN connection.  This then enables a total of six simultaneous calls (2 via the Internet and four via the fixed network).

System connection with an ISDN system connection

When connecting a system, the FRITZ!Box Fon cannot be connected directly to the fixed network, as the FRITZ!Box "Analogue/ISDN" connection can only be used on ISDN multi-device connections and not on an ISDN system connection. For a system connection of a FRITZ!Box to an ISDN system connection, the telephone system must have a free external and a free internal S0 bus, and the system must support mixed operation of systems and multi-device connections.

Note: Where your existing telephone system does not have a free external and internal S0 bus, you can select the FRITZ!Box system connection as a sub-system as an alternative.

The telephone system remains connected to the NTBA (or the NTBAs in the case of multiple ISDN connections), as before. In addition, a telephone system's additional external S0 bus is connected to the FRITZ!Box Fon S0 internal S0 bus. This external S0 bus is prioritised in the telephone system, so that outgoing calls can be carried on this S0 bus and thereby on VoIP. In the case of an outgoing call, the telephone system now requests an "Internet exchange" via the FRITZ!Box and the call is routed via VoIP. A maximum of two simultaneous calls are possible in this case. If two calls are already being carried via VoIP, a third outgoing call from the telephone system via the fixed network can automatically be carried via the fixed network. If an outgoing call is being carried via the FRITZ!Box and thereby via VoIP and the number dialled  is not available via VoIP (e.g. for service or emergency numbers), the dialling rules become effective and the FRITZ!Box attempts to carry the call on the fixed network via its "Analogue/ISDN" connection.

To ensure that this is successful, the FRITZ!Box "Analogue/ISDN" connection is connected to a telephone system's free internal S0 bus. An extension for the FRITZ!Box is set up in the configuration of the telephone system on the internal S0 bus, for which the system's external S0 buses are set up exclusively as exchange line seizure, and are connected directly to the NTBA. This extension must be set to spontaneous exchange line seizure in the system. Where one of the telephones dials a number via FRITZ!Box that is not available via VoIP, the FRITZ!Box will automatically seize a fixed network exchange via the telephone system's internal S0 bus and route the call via the fixed network.

Alternative: Use as a sub-system

The FRITZ!Box is used as a "main system" in descriptions up till now. This is the preferred connection method, as it is the only method that provides the full functionality of the FRITZ!Box. The system should only be used as a sub-system when it is impossible to operate as a "main system" for technical reasons. Use as a sub-system can be useful or recommended in the following cases:

• The FRITZ!Box cannot be operated between a telecomms system and a fixed network (e.g. S2M connection)
• When connecting the system no free external S0 bus is available on the telephone system
• The configuration of the telecomms system cannot be modified
• VoIP should only be used for individual subscribers (e.g. for communication between extensions)

If the FRITZ!Box is connected to an existing telecomms system as an extension, it  is considered to be a sub-system. A telecomms system can be extended for VoIP without changing the system configuration.

The local loop of the FRITZ!Box is connected to an extension of the telecomms system (internal S0 or analogue). The FRITZ!Box with its local loop is connected to the telecomms system as an extension. A call coming into this extension appears to the Box as an incoming external call. The direct dialling function must be activated to ensure that the caller can continue to phone via the Internet. The "System connection" function is used to ensure maximum convenience for direct dialling. In this, the subscriber receives a dialling tone immediately after selecting the extension to which the FRITZ!Box Fon is connected, and can then simply dial the target number.

Direct dial or system connection is configured in the "Call diversion" menu item. The expert view must be activated in order to perform the configuration.

In this example the FRITZ!Box "listens" to the telecomms system on call number 10. If subscribers dial extension number 10, they will receive a dialling tone from the FRITZ!Box and can continue dialling. The connection is then set up via the Internet using call number 1234. Incoming calls from the Internet are routed to the telecomms system to call number 15. Phones connected to the FRITZ!Box extensions can make calls to the fixed network via the telecomms system. Spontaneous exchange line seizure is activated for this purpose.

In contrast to use as a main system, the following must be noted when using the system as a sub-system:

• Subscribers can only use VoIP after dialling the area code of the extension to which the FRITZ!Box Fon is connected.
• Only one call over VoIP is possible using the direct dial function. This also applies if the Box is connected to an internal S0 bus.
• When using direct dialling, the call number of the VoIP accounts used is always transmitted.

The major advantage of this mode of operation is that no changes need to be made to the existing telecomms system. Almost any system can be extended to use VoIP.