„Voice over IP“ – everything you need to know about converting to VoIP, installing VoIP and using VoIP


The way we make phone calls now is very different to how we made them in the past: Today, you can simply communicate via the Internet using Voice over IP (VoIP), which enables you to make phone calls via your Internet connection. That means you can enjoy the benefits of digitalised voice transmission.

Deutsche Telekom is the only body to have already converted almost all connections to VoIP*. And by 2022 at the latest, other providers will have done away with obsolete ISDN connections and converted to Internet telephony throughout Germany as part of the all-IP conversion process.

You can already benefit from this new technology: Phone calls and other services such as mobile communications, TV or fax are received through IP telephony via a single network. This means you can dispense with conventional analogue ISDN telephone connections, which will save you money. We have come up with a summary of all you need to know to make the replacement of your telephone connection as smooth and convenient as possible.

* 85% of business clients, 90% of private connections – according to Klaus Müller, Head of Strategic Development and Transformation, Telekom Deutschland Business Clients (as of May 2018).

What is VoIP?

Voice over IP is often referred to as IP telephony or Internet telephony. It is a technological system that, in contrast to the conventional ISDN variant, uses IP connections to connect to broadband. This paves the way for voice communication via the Internet. "IP" stands for Internet Protocol – the network protocol that forms the basis for connections made via the Internet. Each Internet-enabled device has its own IP address. Data can be sent back and forth between end devices via this IP address.

Everything you need to know at a glance

What is VoIP?
  • "Voice over IP" (VoIP) is a technology that allows you to make phone calls via the Internet
  • VoIP allows you to save money on telephone calls and to take advantage of many other functions, such as video conferencing or instant messaging.
  • You can use VoIP with your smartphone, PC, analogue device or IP phone.

How does VoIP work?

VoIP does not use the conventional phone network. Instead, telephones connect to broadband via a DSL router or VoIP-enabled cable modem. The process that is taking place in the background can be divided into three steps:

How does VoIP work?
  1. Voice is converted
    Your VoIP application digitalises the audio signal.
  2. Data is transmitted
    The numerous data packets that make up a phone call are transmitted via the Internet.
  3. Data is decrypted
    Once the data arrives at the target destination, it is converted back into voice.

Using SIP to connect and disconnect

To establish a connection, you will need the Session Initiation Protocol (SIP). This is responsible for managing the communication connections between two or more participants. Each VoIP user has its own SIP address, which is structured in a similar way to an email address. This allows you to be identified online and to make a phone call from any SIP-enabled end device, regardless of where you are.

Voice transfer

The acoustic signals that are recorded by the microphone are firstly converted into electrical signals so that voice information can be transmitted in the form of digital data packets. These signals are then digitised and divided into small packages. The method of encoding is called Codec, and is crucial for transmitting the data packets. It determines the voice quality. The better the voice quality, the higher the required transmission rate.

Jitter and voice quality

The term "jitter" refers to variability in latency, and it is one of the factors that is crucial to good voice quality. Once the data packets have been sent from the sender to the receiver, they are decrypted again. The "jitter buffer" ensures that the phone call does not break up if there are delays to the data transmission process. The buffer temporarily stores the data packets that have been received and transmits them without any variability in latency, or with only minimal variability. A large jitter buffer compensates for more extreme variability in latency.

Conversion to IP telephony

Conversion to IP telephony

The transition from conventional ISDN telephony to VoIP is simple and straightforward. In most cases, you don't even need a new device. It's as simple as this:

Internet connection

IP telephony requires an Internet connection with sufficient bandwidth. You can achieve excellent voice quality at approximately 100 Kbit/s. However, as your Internet connection is normally used for a variety of applications, we recommend that you use a higher bandwidth.

Compatible hardware

You need a suitable device in order to use VoIP. In most cases, however, it is not necessary to purchase new hardware. You can normally use your PC, laptop or smartphone to make phone calls via VoIP.

VoIP providers

Here is what you should take into account when choosing the right provider:

  • Data protection
    Please ensure that your provider complies with the European Data Protection Directive and encrypts your data within the system.
  • Reliability
    Your provider should offer a high level of availability and reliability. An availability of 99% should be in place for businesses in particular.
  • Range of functions
    VoIP provides numerous options – for private clients and businesses. Find out which features are included and which you will need to pay extra for.

How do I use VoIP with my hardware?

VoIP generally works wherever there is a good Internet connection. You also need the right hardware. We will show you how to use IP telephony with your usual hardware:

Via your PC
Via your PC

Via your PC

Simply use your PC or laptop for VoIP. You will need a broadband connection and a suitable programme known as a softphone. Your computer should also be equipped with a microphone and speaker. If you make a lot of phone calls, a headset will give y0u added convenience.

Via your IP phone
Via your IP phone

Via your IP phone

Many phones on the market already support data transmission via the Internet. Connect your IP phone to a free LAN port on your router and connect it to the Internet. We have compiled an overview of all VoIP phones available from Gigaset.

Via your analogue phone
Via your analogue phone

Via your analogue phone

You can also use your old phone to take advantage of the new technology. An analogue telephone adapter (ATA) or an ISDN telephone adapter (ITA) allows you to connect to a DSL modem. The adapters convert the analogue telephone signals into digital data packets and then decrypt them again. This gives you the convenience of using VoIP on your usual phone.

Via your smartphone
Via your smartphone

Via your smartphone

Like your computer, your smartphone is also able to use mobile VoIP. Some devices already come with a pre-installed client for IP telephony. You can enable this by going to "Call Settings" -> "Internet Call Settings" -> "Internet Calling (SIP) Accounts". You can download a suitable app (SIP softphone) from the App Store or Google Play Store. You will need a stable WiFi connection or at least a 3G connection to achieve excellent voice quality via mobile VoIP. Note that mobile VoIP significantly increases the amount of power consumed by your mobile phone.

What businesses need to know when converting hardware

When converting to VoIP, it is particularly important for businesses to ensure communication is permanently available. If you are already using the Internet Protocol for voice transmission, you will not usually need any new end devices. If your business is communicating via an ISDN system, you might also be able to keep this system.

Converting the ISDN system

If you do not want to invest money in new devices, you can easily convert your ISDN telephone system to IP telephony. To do this, you will need either a SIP telecom system connection or you can use the services of a cloud telephone system.

SIP trunking using a SIP telecom system connection

If your ISDN system is Internet-ready, simply connect it to the IP network via the SIP telecom system connection. A SIP trunk bundles all telephone connections that are running in parallel and enables these connections to be established simultaneously. SIP trunking is the appropriate transitional solution when converting to VoIP. But in the long term, it is worth using a cloud telephone system to enjoy all the benefits of the new technology.

Cloud telephone system

Flexibility, functionality and convenience – use a virtual telephone system to discover new possibilities in communications. A cloud telephone system means you are no longer tied to to one location. Each of your end devices can access the system – even from abroad. Manage your phone numbers yourself at any time. You can also benefit from your provider's service offering: It will usually take care of maintenance, repairs and updates.

VoIP – the future of telephony


Advantages of VoIP
  • Lower costs, more options
    Use one provider for services such as telephony, Internet and mobile communications. Having the complete range of all services allows you to reduce costs considerably and, at the same time, enjoy all the possibilities that the new technology offers.
  • Clear sound
    Enjoy excellent voice quality thanks to HD voice technology.
  • Faster Internet
    The all-IP conversion process will free up frequency ranges that until now have been taken up by ISDN and analogue telephony. This will enable larger amounts of data to be transmitted while opening up greater bandwidths.
  • Forward-looking technology
    Most VoIP providers offer more than 150 telephone functions, which are constantly evolving.
  • Unlimited flexibility
    With many VoIP providers, you can take advantage of very short minimum contract periods. And cancellation periods are usually just one month, meaning you are not taking any risks.
  • Work effectively
    VoIP provides for optimal communication among all employees, even from abroad or from the home office. Video conferencing, file sharing or instant messaging improve collaboration among employees and with your clients.
  • More parallel calls
    An IP connection allows you to hold a number of phone calls at the same time.
  • Calls – any time, anywhere
    VoIP allows you to make phone calls from anywhere. All you need is access to the Internet, and you will be available for calls on your mobile or office number when you are on the go.
  • Simple configuration
    All you need to set up your VoIP hardware is a router. All other settings can be easily configured via the web interface of any Internet connection.


Disadvantages of VoIP
  • Internet connection is essential
    You will need sufficient bandwidth and a stable network for excellent voice transmission via VoIP. A broadband connection with guaranteed availability (e.g.: SDSL) reduces the risk of intermittent crashes and interrupted conversations.
  • Problems in the event of a power failure
    You will not be able to make a phone call if there is no power to the router. However in extreme cases, you can also use VoIP with a back-up battery (UPS) or your smartphone.
  • Cost of buying new systems
    Telephone systems bought more than five years ago will usually need to be replaced.
  • Interference from other equipment
    Fax machines, credit card machines and alarm systems are often connected to the telephone network too. Check with your VoIP provider or the device manufacturer about potential complications when converting to IP telephony.

Is my data safe?

VoIP Security

Complex encryption protocols such as TLS (Transport Layer Security) or Secure Real-Time Transport Protocol (SRTP) secure SIP trunking, i.e. the IP connection that is responsible for connecting and disconnecting the phone call. Your data is almost 100% secure during internal network calls. Once a phone call leaves the private network, complete security cannot be guaranteed as your encryption only protects half the connection.

Risk of voice phishing

If data packets are transmitted via the network, attacks from other computer programs can never be completely ruled out. This means data may be captured and converted into audio files as part of an Internet scam (voice phishing). It is very difficult to completely encrypt VoIP as this would compromise voice quality. Nevertheless, you can take security precautions.

VoIP for your business

VoIP for your business

Seamless communication and smooth collaboration are important to your business. With VoIP, you can access the latest technology and benefit from constantly up-to-date features. This means you will save money and will be able to respond to developments in your day-to-day work at any time.

  • Internal calls from VoIP to VoIP are free of charge – even international calls.
  • Make your office mobile. Use your smartphone to make calls from your office number while you are on the go.
  • It is possible to make cost-effective external phone calls (mobile or landline).
  • It is easy to incorporate other functions, such as video telephony, at an affordable price

Glossary – an overview of the key terms

VoIP "Voice over IP" – making phone calls via the Internet
IP "Internet Protocol" – the network protocol that forms the basis for the Internet.
Jitter variability in latency in the data transmission process
SIP the "Session Initiation Protocol" is responsible for managing communication connections between two or more participants.
SIP-Trunking SIP trunking bundles multiple phone lines together.


VoIP Summary

VoIP is in vogue and it is set to become the new standard of telephony. Voice communication via the Internet offers private clients and businesses numerous advantages. Making the change is quite simple: All you need is an Internet connection with sufficient bandwidth, appropriate hardware and a VoIP provider.


  • What is DECT?

    Everything about DECT

    What does dect stand for and how does it work? You can get all answers and information about DECT in our guide.


  • Comfortable and secure senior phones

    The phones of the Gigaset life series impresses with its functional technology, high-quality design and easy to use – perfect companions even in old age.


  • Import telephone contacts

    With the Gigaset ContactsPush app for Android and Apple you are easily able to transfer smartphone contacts to your landline telephone.


  • Cleaning your smartphone

    Extend the life of your smartphone. Regular cleaning prevents damage. And it’s so easy with these five tips.