Häufige Fragen zu Internettelefonie, VoIP und Cloud-Telefonie

FAQ on Internet telephony, VoIP and cloud telephony: a compact summary of DUStel, setup and technology at dus.net.

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General questions about Internet telephony

The terms Internet telephony and Voice over IP describe the same thing. This is about making calls via your Internet access using the specially developed SIP protocol. This way of making calls makes the old analog or ISDN technology completely superfluous and is also much more powerful.Cloud telephony also describes the fact that a classic telephone system is no longer required on site, or that the „cloud“ replaces it because a virtual telephone system is located there. This is particularly interesting for entrepreneurs, as traditional PBX systems can be very costly.Having a telephone system in the cloud or cloud telephony does not, however, mean that this service is always linked to a dedicated system, such as a server at the cloud provider on which the telephone system then runs. At dus.net, the customer center is already the virtual telephone system and therefore already a cloud-based telecommunications system.

Yes, in principle you can. All you need for Internet telephony is Internet-only access. Unfortunately, it is still not possible to order just an Internet connection from all Internet providers in Germany. As a customer, you are almost always forced to book a telephony connection at the same time. Internet and telephone are therefore usually linked together here.Since these telephone connections are usually only very rudimentarily equipped, you can always use a dus.net telephone connection in parallel or in addition.

No, you can use any Internet connection with us, so a connection with dus.net is provider-independent. Only the bandwidth of the Internet connection is important. However, so little is required here that it is possible with almost all Internet connections, even with DSL-light connections. With low bandwidths, however, it is a great advantage that sufficient telephony is available. End devices such as the FritzBox, for example, regulate this completely automatically.

In addition to an Internet connection, you will of course also need a SIP end device that can handle the SIP protocol. The most well-known device is probably the Fritz!Box, although this is much more than a pure SIP end device, such as an IP telephone. However, softphones that can be installed as software on a PC or as an app on a smartphone are also SIP end devices and are fully usable.

A clear yes, and in a positive sense. Internet telephony not only offers far more functions and options, but also enormous flexibility. It also offers the same ISDN voice quality and even HD telephony.

Questions about the SIP connection

A SIP connection is a virtual telephony or fax connection. Every SIP end device requires access data to be able to log in (register) with a SIP provider such as dus.net on the SIP server.

SIP connections are available in conjunction with a tariff and in varying numbers depending on the tariff. With dus.net, it is necessary to use a separate SIP connection for each SIP end device. A SIP connection may not be used by several SIP end devices at the same time.The SIP connections can be found in the customer center or additional SIP connections can be created there at any time until the quota corresponding to the tariff is exhausted.

With a SIP connection, your SIP end device registers with our SIP server and remains registered there for a certain period of time. Upon registration, we receive an IP address and a port from the end device. Now we know how and where to find your end device if we need to send it an incoming call. If several end devices were to share a SIP connection, only the end device that registered last would ring.

The time for which a SIP connection or the SIP end device with this connection remains registered on our SIP server depends on the end device itself. This is because the end device tells our system when it will re-register the next time. With a FritzBox, for example, this is always every 30 minutes, i.e. the box registers a connection at 13:32, for example. Shortly before 14:02, the box reports back to the server and renews the register for another half hour.

As described in the answer to question „How long does a SIP connection remain registered?“, your end device itself determines the time until the next registration, i.e. with the first registration your end device informs our server when it will register again. In the time between these two points in time, your end device is considered „online“ by our system, even if it may have been switched off in the meantime. Only when the device no longer responds at the second point in time is it considered „offline“ for us.

The „online“ „offline“ display in the customer center is therefore not a real-time display.

Wrong user data
There can be a variety of reasons for this. Usually it is something quite trivial, such as incorrect access data. It often happens that passwords are simply mixed up or a number has been forgotten in the user name. If you can rule out the possibility that everything has been entered correctly on your site, it may also be that your device's attempt to register has not even reached us due to network problems.

If everything else is excluded, it is also possible that your IP address has ended up on our blacklist. This usually only happens if your end device has tried to register too often with incorrect user data. The block is automatically lifted again after a certain period of time. If not or if it takes too long, you can write to us by email and have your IP address reactivated.

No real IPv4
You may no longer have a real IPv4 address on your Internet connection. Some Internet providers no longer assign real IPv4 addresses to their customers' connections (scarcity), but only internal IPv4 addresses. The problem is that internal IP addresses cannot be reached from outside. The provider therefore converts these internal IPv4 addresses to external IPv4 addresses. However, as savings have to be made on the IP addresses, many customers now receive identical IPv4 addresses externally, which are only differentiated via the ports.

You should therefore try to use not „proxy.dus.net“ but „proxy3.dus.net“ (DS-lite) or „proxyv6.dus.net (pure IPv6 connection) as the registrar. In the FritzBox, however, you must then also allow the connection via IPv6 in the access data, which is actually already the default setting.

Questions about the SIP call

Dropouts during the call indicate that RTP packets are being lost. This usually happens regularly and does not really matter. However, if there are too many packets that do not find their destination, this becomes noticeable with dropouts.
The reasons for this are manifold and can be caused in your own network or on the part of your Internet provider or routing. The latter is the path of the packets through the Internet, whereby there are other providers between your Internet provider and dus.net via which the traffic also runs. There are therefore many possible causes of errors that you can try to identify with the help of programs on your PC. These free utilities determine the individual „hops“, i.e. stations via which the packets run in the network and may show where these packets „get stuck“. The information can allow conclusions to be drawn, but cannot always be used as a cause.

If you or the other party cannot hear any audio after a call has been set up, this sounds like a firewall problem. The setup of a call and the call itself take place on different levels. The SIP packets are responsible for setting up and breaking down the call, the call itself then runs as an RTP stream via other IP addresses or servers. If the firewall blocks the other IPs, it also blocks the stream and therefore the audio.

As a rule, the firewall does not need to be configured because mechanisms allow nothing to be blocked here. However, if you have deliberately made your firewall „stricter“, it is best to unblock the dus.net IP network as a whole.

FritzBox behind router
If, for example, a FritzBox is not operated directly on a DSL connection, but behind another router/modem or a provider that works with wireless technology, for example, incoming calls may simply be disconnected after approx. 30 seconds. This has to do with the firewall of your upstream router or that of the provider. In such an environment, the FritzBox does not register with us using its standard port 5060 because the box is in an internal network. The FritzBox must therefore be configured so that it behaves like a client in the internal network. You must therefore set up Internet access on the FritzBox as a connection to an external modem or router (or with a cable provider as a connection to a cable modem).

IPv4 address only "shared" (carrier-grade NAT)
You may no longer have a real IPv4 address on your Internet connection. Some Internet providers no longer assign real IPv4 addresses to their customers' connections (scarcity), but only internal IPv4 addresses. The problem is that internal IP addresses cannot be reached from outside. The provider therefore converts these internal IPv4 addresses to external IPv4 addresses. However, as savings have to be made on the IP addresses, many customers now receive identical IPv4 addresses externally, which are only differentiated via the ports.

You should therefore try to use not „proxy.dus.net“ but „proxy3.dus.net“ (DS-lite) or „proxyv6.dus.net (pure IPv6 connection) as the registrar. In the FritzBox, however, you must then also allow the connection via IPv6 in the access data, which is actually already the default setting.

Questions about the tariff

The DUStel trunk tariff is no longer available in its old form. Instead, we offer you an excellent alternative with the DUStel business flex tariff.

We have integrated the DUStel 60 tariff into the DUStel starter. With the starter, you can now choose whether you want seconds or minutes billing.

Only the DUStel complete is now available from EUR 7.90/month with a minimum contract term of 12 months. It already includes a flat rate to the German landline network for one line. An additional line can be booked as well as flat rates for the German mobile network. The DUStel one is completely omitted.