What is a SIP trunk?

If VoIP is used for business purposes, you may want to manage and use multiple numbers. SIP trunking is the ideal solution for this purpose. What does the useful SIP trunk offer?

One account, multiple phone numbers

If you set up a user account with the SIP provider and want to have access to internet-based telephony with several numbers, then you cannot avoid a SIP trunk. There is an alternative, but this is a bit more complicated and not always desirable: In the regular SIP procedure, you would have to create your own account in order to connect a terminal with a telephone number to the network. This means an account with a username and password for each device or number - this can quickly lead to confusion, especially in large companies with many employees and intensive SIP use. If you rely on SIP trunking, on the other hand, you create one central account that allows direct dial-in – the Direct Dial In – for a large number of end devices, each equipped with its own phone number and accessible from outside. Additional phone numbers with separate extensions can be created quickly and easily and assigned to a terminal device. It is also easy to reduce the number range, because phone number blocks can also be booked from the provider. In this manner, VoIP telephony with SIP trunking offers a high degree of flexibility.

How VoIP works with SIP trunk

When the technology was even less sophisticated, people had to work with normal telephone systems and an intermediate device in order to use IP-based voice telephony. Modern IP phone systems, on the other hand, make this interconnection of a media gateway superfluous. You can rely on an SIP-DDI protocol that makes IP telephony systems dialable. This automatically means less configuration. Basically, the SIP trunk makes it possible to make calls with the outside world instead of just using the LAN (local network). This is advantageous for virtual collaboration with teams abroad or conversations with business travelers and freelance employees.

The SIP trunk is usually supplied by the SIP provider and can then be closed between the internet and the IP telephony system - a connection to phones or mobile phones is also possible. The number of services is also booked with the provider, in most cases up to 30 pieces. Another advantage is the money saving, because for VoIP with SIP trunk you pay less than for other connections. An important prerequisite (for IP telephony in general) is that the broadband internet connection has a sufficiently high speed to achieve clear voice quality. Conventional trunks are compatible with all SIP-capable telephone systems. If the telephone connection is not yet SIP-capable, the above-mentioned media gateway is used in combination with the trunk.

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