SIP Trunk for Your Telephone System

VoIP telephony and SIP trunking Blog

VoIP telephony and SIP trunking explained in an understandable way.

With SIP trunking, you can continue to use your conventional telephone system and benefit from the advantages of modern VoIP telephony. SIP trunking offers you the chance to benefit from numerous advantages of modern VoIP telephony without having to do without your current telephone system. Simply connect your system via SIP trunk to the virtual telephone system of inopla. The terminals connected to your telephone system can continue to be used without any problems. Your employees use them as usual and do not have to change. SIP trunking opens up many new possibilities for your company. You gain significant flexibility and freedom. At the same time, costs can be reduced. We will explain in detail what a SIP trunk is, how it works, what advantages a SIP trunk offers you, and everything else you need to know about SIP trunking.

What does SIP mean and what is a SIP trunk?

For a better understanding of the technology and functionality of SIP trunking, we will first explain the basic terms SIP and SIP trunk. The abbreviation SIP stands for Session Initiation Protocol. It is a standard based on the Internet Protocol (IP) that can be used to establish and terminate communication connections over IP networks such as the Internet. SIP is suitable for telephone calls, video conferencing and other communication services. One of the most commonly used applications is telephony via VoIP (Voice over IP). In this environment, SIP controls the establishment and termination of telephone connections between two or more subscribers. If a telephone is SIP-capable, it no longer requires a conventional analog or digital telephone connection. It can be connected to an IP network and establishes connections to other subscribers via the Internet. To do this, it registers its phone number with the selected VoIP provider. As telephone providers around the world replace their conventional analog or digital ISDN telephone networks with VoIP technology, SIP is becoming more and more important. Today, it is virtually the standard protocol for VoIP-based telephony.

However, not only a single telephone can establish a connection via SIP. Complete telephone systems, also known as PBXs (Private Branch Exchanges), with their many extensions can be connected to an IP-based telephone network or a cloud-based telephone system of a provider via Session Initiation Protocol. This is where the SIP trunk comes into play. The SIP trunk is a bundle of many individual SIP connections and uses a data line to exchange information. It replaces, for example, the primary multiplex PBX connection used in an ISDN telephone network with its maximum of 30 simultaneous connections. However, the maximum number of simultaneous connections possible with a SIP trunk is not limited. In principle, the number of parallel connections depends only on the available bandwidth of the data connection. To address the many extensions, the provider assigns a number block to the telephone system connected via SIP trunk.

How does SIP trunking work?

Basically, SIP trunking uses a data line and the TCP/IP protocol stack (Transmission Control Protocol/Internet Protocol). The line does not have to be reserved exclusively for SIP trunking, but can transmit other data in parallel in addition to the telephony data. Many companies use the broadband Internet connection of their IT systems simultaneously for SIP trunking. As already mentioned, the Session Initiation Protocol is used to control the establishment and termination of connections.

How many simultaneous connections can be realized with a SIP trunk and your PBX depends on several factors. For example, the capacity of the PBX or the parallel calls supported by the telephony provider limit the number of possible connections. With regard to the capacity of the data connection, it should be noted that a bandwidth of at least 100 kbit/s in downstream and upstream is required for each voice channel. With asymmetric DSL connections, as are often used for Internet connections, the smaller upload bandwidth is the limiting factor for the number of simultaneous calls. If other data is transmitted via the SIP trunk in addition to the voice data, prioritization of the voice data prevents disruptions to the telephone connections due to excessive data traffic.

A SIP trunk is usually assigned a block of telephone numbers by the telephone provider. The provider ensures that all incoming calls from the telephone network with destination numbers from this block are routed to the trunk. The configuration of your telephone system is responsible for local routing to the individual terminals.

In principle, any SIP-capable telephone system can be connected via SIP trunk. For non-SIP-compatible systems, there are corresponding solutions such as gateways. They equip a PBX with SIP capability. Many systems support both SIP trunking and conventional ISDN system connections and allow mixed operation of both technologies.

What are the basic advantages of a SIP trunk compared to conventional system connections?

A SIP trunk offers numerous advantages over conventional system connections. Your company is much more flexible and independent with a SIP trunk. The number of channels is not limited. It scales almost arbitrarily according to the bandwidth of your Internet connection. If new channels are to be added, no hardware or cabling work is necessary. Additional channels can be booked with the provider within a short time if the available bandwidth is sufficient. If the telephone volume decreases, scaling down is possible and the costs for the connection to the telephone network are reduced.

For dynamically growing companies with different locations, SIP trunking offers many opportunities. In principle, a SIP trunk is location-independent. If a location is relocated or other location-dependent changes are pending, the previous telephone numbers remain usable. Concepts for cross-location communication can be easily implemented with SIP trunking. If the provider is to be changed, you can take your existing numbers with you to the new provider (porting).

In addition to these classic advantages compared to conventional system connections, SIP trunking offers you further benefits. Despite the use of the public Internet, high security requirements can be met. By using virtual private networks (VPNs) and encryption techniques such as TLS (Transport Layer Security) or SRTP (Secure Real-Time Transport Protocol), both the SIP connection data and the transmitted voice information are reliably protected from being read or tapped by unauthorized persons. Many classic analog or digital telephone environments lack such modern protection mechanisms. Other advantages of SIP trunking include automatic backup mechanisms, convenient configuration options for the SIP trunk via user-friendly web interfaces, and extensive analysis and statistics functions.
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