Retirees can start a SIP

How to make calls over the Internet with VoIP

What is VoIP

Fixed line telephony is retiring. As early as 2015, more telephone connections were using the Internet as a transport medium than an ISDN or analog line and that is, in short, VoIP: Internet telephony.

Telephony as a service on the Internet

It is not possible to make direct calls over the Internet because the network does not transmit an analog data stream, but only digital data packed in IP packets. An analysis of the abbreviation VoIP reveals which trick VoIP uses so that you can still make calls over the Internet.

What does VoIP mean exactly?

VoIP is a technology-centric abbreviation typical of Internet jargon. The small o in the middle stands for “over”, in German “über”. On the left, an abbreviation for the type of data stream being transmitted and, on the right, an external transport medium in which the transmission takes place. With VoIP it is analog voice data that is digitized, fragmented and then sent packaged in data packets, the form of which is defined by the Internet Protocol (IP). This makes it possible to transport an analog data stream over a medium that can only transmit digital data packets. This also makes telephony one of the numerous services on the Internet, such as HTTP for transporting websites, SMTP for e-mail or FTP for file transfer. The advantage is obvious, only one data connection to the provider is necessary.

How to make calls over the Internet with VoIP

Voice over IP transmits voice in digitized form and signals for setting up, disconnecting and changing connections. The service uses two different channels for this purpose, such as ISDN with the B and D channels. VoIP does not require a special solution for the data connection, as existing protocols such as RTP / RTCP can be used. Several solutions have been developed for signaling, and ultimately this has turned out to be Session Initiation Protocol SIP enforced, the current version of which is specified in the Internet RFC 3261.

What is SIP

The Session Initiation Protocol SIP is used exclusively for signaling, i.e. the transmission of control information that is required to set up new connections (sessions) and to change and clear existing connections. SIP is not a dedicated VoIP protocol, but is also designed to manage sessions for multimedia applications with one or more participants, such as unified communications and video conferencing. Without session management, you cannot make calls over the Internet, which is why the abbreviation SIP often appears in connection with IP telephony, such as in the combinations SIP gateway, SIP client (telephone software) or SIP trunking. These are discussed in more detail in the Voice over IP telephone system section.

What changes with the telephone number through VoIP

SIP data telegrams contain information about the participants in a connection. These can be encoded in a form specific to IP telephony that is similar to an email address. For compatibility with conventional telephony (PSTN), a supplement to the Internet Domain Name Service (DNS) was developed, which can be assigned to conventional telephone numbers in accordance with ITU-T recommendation E.164 domain names. Such an assignment does not happen automatically, but has to be entered in the DNS by a registrar. However, it is only of interest if a connection is to be established directly between a conventional telephone and a VoIP device or if the same telephone number is to be assigned to different Internet services. If telephone software or a Voice over IP telephone system is connected via a SIP provider, then this provider generally also handles the conversion between PSTN and VoIP.

What should you watch out for when faxing via VoIP?

While Internet services such as HTTP (websites) or SMTP (e-mail) are based on the connection-oriented protocol TCP, which guarantees the orderly and complete transmission of data packets, those from The protocols used by VoIP also use connectionless UDP. This has the advantage of lower latency, but data loss can occur. Brief interruptions are hardly a problem when transmitting voice or a video conference, while low latency is a clear advantage. However, if you want to transmit a fax via VoIP, data loss often leads to connection interruptions. Internet-compatible fax machines allow faxes to be sent via a real-time connection in accordance with ITU T.38. However, this standard must be supported by both devices, sender and receiver.

Further differences between VoIP and classic telephony (PSTN)

An advantage of VoIP that has already been mentioned is the use of the Internet connection instead of a dedicated line. However, this has not only advantages. Telephoning over the Internet is easier to tap than a telephone call on a separate line. Furthermore, analog and ISDN terminal devices can be supplied with power by the telephone network, at least to a limited extent, so that telephoning is possible without power even in an emergency. A telephone as a software solution and a telephone server, on the other hand, are paralyzed in the event of a power failure if you do not install an emergency power supply.

What happens to the telephone system when switching to Voice over IP?

If you want to replace an existing ISDN connection with VoIP in your company, you have three options for adapting your existing internal telephone network to the age of the Internet. It looks similar for a completely new setup, but the weighting is different. The key words are:

Option 1: Continue to use your ISDN telephone system with VoIP

The first variant, also called SIP trunking, causes the with existing ISDN system connections lowest retrofitting effort. If your system is already VoIP-capable, connect it directly to the Internet, otherwise you simply set a gateway between your Internet connection and your telephone system, which converts the incoming VoIP traffic to ISDN and vice versa. Since you do not have to exchange the system, you do not need to change anything on the end devices in your company. If Voice over IP is supported by the telephone system for connecting the end devices, this enables a gradual transition to the new technology. You can then gradually convert your internal telephony hardware to VoIP devices and, if necessary, SIP clients. The latter is a kind of VoIP telephone in software that you can use on both dedicated and universal hardware, such as a PC.

Variant 1b: New installation of a Voice over IP telephone system on-premises

The installation of a VoIP-capable hardware telephone system is a suitable option, especially for a new connection, if you want to operate your own telephone system. This solution has the advantage that you have the hardware fully under your own control. The investment costs and the maintenance effort are disadvantageous. Like the VoIP telephone, a Voice over IP telephone system can also be implemented as software. Hence, you can possibly reduce the cost of the system by setting up a telephone server, that means installing the system software on a PC hardware.

Variant 2: Virtual telephone system - the hosted telephone server

With the “virtual VoIP telephone system” option, you save yourself the effort of installing, maintaining and operating your own telephone system hardware. In the case of the virtual telephone system, the telephone server is hosted in a data center. You need yourself only take care of the software and the configuration of the system. If necessary, prepared telephone server images are available for this. The advantages of the virtual telephone server solution are guaranteed availability and scalability. The lack of special hardware interfaces may be disadvantageous. For example, you cannot connect any analog end devices directly, but require separate ATA converters.

Variant 3: Move your telephone system to the cloud

The cloud solution of the Voice over IP telephone system also relieves you of the worry of updating and installing security updates on your telephone server. You can make phone calls over the Internet practically immediately as soon as your SIP provider has activated your access. This option is particularly interesting for small companies and startups and is characterized by the greatest possible flexibility and scalability, especially if you also use software-based solutions for end devices such as the telephone. A headset on the workstation computer and telephone software installed on it saves you the costs and space for the telephone hardware and telephoning over the Internet is fully integrated into the workflow.