What is the difference between VoIP and SIP?

When it comes to internet telephony, there is no getting around certain technical terms. Again and again, the words SIP and VoIP, which sound so similar, but have some parallels, come up. What is the difference between VoIP and SIP?

It’s about the connection and data transfer

Strictly speaking, both terms are protocols used in telephony via the internet. SIP is the abbreviation for Session Initiation Protocol and VoIP is the abbreviation for Voice over Internet Protocol. From these terms, it can be deduced what the main function of the protocols consists of and what the differences are.

SIP is responsible for the ”Session Initiation”. In a nutshell, this means that this does the connection request - as it were, dialing up. Responsible for this is a SIP trunk, which acts as a kind of central interface and makes it possible to use several phone numbers in a company with a user account from the SIP provider, as well as being able to receive calls from the outside. The intermediate device uses SIP trunking and SIP protocol to establish and terminate a call.

Once the call has been established, a further protocol is required in order for voice transmission to work at all during internet telephony. Data packets are transmitted on the internet. This is where VoIP is used. As soon as the connection is established and communicated, it takes over the data transfer. VoIP (Voice over IP) uses computer networks, a broadband internet connection and the provider’s servers to convert, forward, reassemble and render voice data. The basis for this is an IP telephone system, whereby softphones (PC) can also be used for telephoning.

VoIP and SIP: related terms, advanced technology

Although these are basically two steps and components of a system, the terms VoIP and SIP are often used as synonyms. For example, a VoIP telephone is also marketed by the provider as a SIP telephone. In return, the SIP provider can be referred to as a VoIP provider. It is theoretically possible to use Voice over IP without using a SIP protocol. In this case, protocol H.323 of the International Telecommunication Union serves as a mediator. It handles signaling, connection control, data flow control, status information exchange and terminal functions exchange. SIP, on the other hand, is only used to establish and control the connection. Which protocol should be used depends on the respective circumstances, such as the type of Internet connection (e.g. VDSL connection) and the systems and devices. VoIP with SIP has gained acceptance in Germany, most particularly in the business world.

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