DFNFernsprechen

Send a request for contract documents to DFNFernsprechen@dfn.de. That consists of:

• A framework agreement that only needs to be signed once for all DFN services.
• A service agreement for DFNFernsprechen.
• A statement of work for DFNFernsprechen.
• A summary of all costs and fees.
• An order form for the transfer, deployment, and change of connections.

For further inquiries, please contact the DFNFernsprechen team:

The connection will be complete no later than 6 weeks after signing the contract other than for the following reasons:

• When transferring carrier connections (other than DTAG), porting can only take place after releasing the connection.
• In the case of VoIP connections, you may need to allow for additional time to test the telephone system.

You will receive invoices for all the services provided through DFNFernsprechen. These invoices are independent of what form the voice and video service was used. By request, we can provide an itemized invoice. Mobile network connections are not added to the DFN invoice, but paid to the respective provider directly. In the case of SMS-GW access, members can decide whether to pay separately or through an active account number. In the case of usage-based billing, every location will receive an invoice.

Yes. We do not offer a flat rate, but you can choose the “constant” billing model instead of the usage-based model. When choosing the constant model, you will be charged a standard monthly rate that can be paid either monthly or years. This rate will include all connection, activation, and subscription fees. DFN will base the monthly cost for the constant model based on your usage over the previous 12 months. DFN can change the price of the constant model at the beginning of any calendar year.

Your telephony system must be able to be connected to the network through VoIP. By request we can provide a detailed specifications list for all necessary technical requirements.

You can get VoIP-based connections on the research network. If you do not want to operate your own phone system, the “VoIP Centrix connection” is also available. If you intend to operate your own phone system in the future, the “VoIP connection” is available.

For special application and DSL-connectivity, so-called “substitute connections” are also available.

Yes, but it is necessary to operate a corresponding gateway that is VoIP-capable.

Analog devices can still be connected to the DFNFernsprechen service if they contain a gateway that is VoIP capable. List the corresponding connections and indicate if they are individual connections with their own number or direct-dial connections that go to a common number.

You must operate a VoIP-capable phone system or have one operated by a third party, or sign up for the VoIP-Centrex service. A local phone system must meet the specified technical requirements.

A location access model is the connection (a line) of a member of the telephone network. This was formerly called a “trunk line.” (Example: A VoIP connection with the number 1234-0).

A location consists of all location access that are combined under one number (the number 1234-0, for example).

Likely. In order to profit from a distributed telephone infrastructure, the individual locations need to be connected in such a way that the individual components can share data among themselves. It is recommended that every location operate an individual (redundant) connection to the research network.

Of course. You can reach anyone around the globe connected to a telecommunications network.

The simplest way is to sign up for a free, non-binding trial of VoIP-Centrex for 4 weeks. You can also order your own device and get a number assigned to it so you can evaluate it internally.

Yes. We also make sure that all requirements for correct emergency calls are always fulfilled.

As a general rule, one VoIP connection for all locations should be sufficient. Each location will then be configured as a so-called “peer.”

No. These connections work with different connection technologies that must be commissioned separately from one another.

We recommend that you separate voice data from other data in your internal network (through the appropriate VLAN, for example), and then prioritize the voice data higher at X-WiN transfer point. Incoming voice data will be given the higher priority in your overall connection.

Due to the regular performance improvements to the DFNInternet service, it is likely that your service will receive bandwidth increases.

No, with VoIP there is no meter pulse. These features are usually tracked through the telephone system itself. For internal billing, we suggest using the functions on the telephone system or the provided billing portal.

No, a normal IP-NAT is not supported by VoIP-connections.

However, you can use your SBC as a B2B user agent and configure a form of SIP-NAT. As a result, not only will all IP addresses change, but also the corresponding IP addresses in the complete SIP-Header so that the SBC is no longer visible on the other side of the architecture. This is also called “topology hiding” and in the realm of trunking, the purpose of an SBC. With this method, you can use internally private address spaces or even use IPv6 and outwardly appear in a public IPv4 in the direction of a VoIP-platform.

You can find information about receiving your certificate here:

With VoIP connections from DFNFernsprechen (SIP-Trunk and VoIP-Centrex) there are no parallel connections. The technical limit of your connection is the bandwidth to your X-WiN access and the given limitations of your telephone system.

Throttling measures have been implemented for security purposes (in order to minimize toll abuse, DoS attacks, or system compromises). However, these security measures have no performance effect on regular connections.

System limitations of your connection (with local telephones) can be caused by so-called loops. Loops arise when your telephone system sends incoming “INVITE” connections back to the C.SIP.G VoIP platform. The connection volume increases such that no more capacity is available and then your system can no longer establish new connections.

That means that an INVITE sent by C.SIP.G to the participant may under no circumstances be sent back.