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[Write to us](/gb/request-information "Write to us") ### SIP-Trunk [What is SIP Trunking?](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-3) [What is SIP Trunking used for?](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-4) [How does SIP Trunking work?](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-5) [Is SIP Trunking secure?](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-6) [The 5 most important advantages of SIP Trunking](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-7) [What is the best way to upgrade to SIP trunking?](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-8) [Option 1: Implementing SIP trunking into your existing PBX](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-9) [Option 2: SIP trunking with your existing IP-PBX](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk#section-10) # SIP-Trunk SIP stands for **Session Initiation Protocol.** [SIP](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/sip) is the universal standard for [Voice-over-IP](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/voice-over-ip) (VoIP) solutions because it allows telephone calls to be made over the Internet. The voice functionality enabled by SIP is the same as analogue phone calls. It allows us to make, receive, reject, hold or forward calls over the Internet. Using SIP, VoIP users can identify themselves online and forward calls to each other. ### What is SIP Trunking? SIP trunking bundles various telephone lines like branches held together by a single trunk. Originally, trunks were used to connect a telephone system ([PBX, Private Branch Exchange](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/private-branch-exchange-pbx)) to the telephone provider's network via the [Public Switched Telephone Network](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/pstn/) (PSTN). SIP trunking does almost the same thing, except that in this case the PBX is connected to the provider network via the internet instead of the PSTN. ### What is SIP Trunking used for? SIP trunking allows companies to upgrade their existing PBX infrastructure to use VoIP functionalities. This is all the more interesting because major changes are soon coming to the telecommunications market that will make it inevitable for many companies to switch to VoIP telephony. More precisely, [ISDN (Integrated Services Digital Network)](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/isdn), the standard that enables telephone calls over the PSTN, will soon be switched off in favour of VoIP. This means that many companies whose PBX infrastructure is based on analogue or ISDN technology will have to switch to VoIP systems. In these cases, SIP trunking is recommended as a perfect stepping stone from the ISDN to the VoIP world. Specifically, it allows companies to maintain their existing infrastructure and still benefit from all the advantages that VoIP telephony has to offer. ### sip ![](https://a.storyblok.com/f/290788/efa903ddf4/sip_trunk.png) ### How does SIP Trunking work? SIP trunking allows an existing PBX hardware to be converted to VoIP. How this works in detail depends on your PBX. There are **3 common PBX models** that can be converted with SIP. These are: 1. **Older, non-IP-capable PBX systems:** PBX systems older than five years are based on a primary rate interface (PRI, sometimes called T1). To connect these PBXs to a SIP trunk, an integrated access device (IAD) or similar hardware is needed to convert voice signals and signalling protocols into digital signals. An IAD can be used to extend the life of older hardware at an affordable cost. 2. **More up-to-date, non-IP-enabled PBX systems:** Many non-IP PBXs that have come onto the market in the last five years can be upgraded to provide SIP trunking interfaces. Depending on the manufacturer, the steps that need to be taken to provide SIP connectivity vary - from a simple software upgrade to extensive hardware and software purchases. Typically, these newer PBXs can be connected directly to a SIP trunk. 3. **IP PBX systems:** As the latest generation of PBXs, IP PBXs have inherent interfaces that allow direct connection to the SIP trunk, using straightforward configuration tools. This makes it quick and easy to connect IP PBX systems with VoIP systems, such as the NFON [Cloud Telephone System](t3://page?uid=16). NFON works with the leading IP PBX manufacturers and certifies the relevant equipment to ensure interoperability and ease of set-up. However, some devices may require additional equipment to connect to NFON, depending on the manufacturer. ### Is SIP Trunking secure? Yes, SIP trunking is secure, but only if the responsible provider takes the necessary security measures. NFON, for example, offers a SIP trunk that is hosted in **secure, geo-redundant data centres in Germany**. Our servers are subject to **EU regulations** regarding electronic communications and meet the highest requirements for data security and fail-safety etc. In the event of a technical problem, such as a power failure, NFON SIP trunk is still available. NFON data centres are certified according to **ISO/IEC 27001 - Information Security Management**. The voice quality of the NFON Cloud Telephone System has also been assessed and **certified by TÜV Saarland**, a globally recognised German certification body. ### ­ ![](https://a.storyblok.com/f/290788/60b3c2c224/image_2_sip_trunk.jpg) ### The 5 most important advantages of SIP Trunking 1. **Low call charges** SIP trunking allows telephone calls to be made over the Internet. The most efficient route is chosen and there is no need to set up a dedicated line over the PSTN for the duration of the call. Compared to traditional telephony, this approach saves resources and significantly reduces call charges. 2. **Quick and easy implementation of VoIP** SIP trunks are easy to install and configure. Companies can benefit from VoIP advantages such as flexibility and cost savings - without restrictions or cuts to their business processes. 3. **Maximum investment protection of the existing infrastructure** SIP trunking allows businesses to use their existing non-IP infrastructure - including PBX equipment - for as long as possible and maximise their investment. 4. **Lower in-house infrastructure requirements and costs.** SIP trunking makes it possible to move to cloud-based PBXs, such as the NFON Cloud PBX. This reduces in-house hardware, software and support requirements. Up-to-date upgrades are carried out by NFON, further reducing the cost and hassle for your business. 5. **Future-proof telephony** With SIP trunking, the ISDN switch-off can't hurt businesses because they have the option to upgrade their infrastructure from ISDN-dependent PBXs to VoIP-enabled systems. By making your telephone system fit for VoIP today, you can ensure that you will be able to maintain your usual work processes even after ISDN is switched off. ### What is the best way to upgrade to SIP trunking? There are basically two ways to provide SIP trunking - the one that suits you depends on your existing infrastructure and your requirements. The following two options describe the optional path for any business: ### Option 1: Implementing SIP trunking into your existing PBX With this option you can benefit from lower call charges and at the same time making your PBX fit for the future despite the switch-off of ISDN. However, the costs for hosting and operating the in-house PBX remain. In addition, not all VoIP functionalities provided by the provider can be used. ### Option 2: SIP trunking with your existing IP-PBX With this option you can reduce your call charges and still use a whole range of VoIP functionalities. However, you will still need to run your IP-PBX in-house and may need to employ specialist staff to do this. You may also need to invest in additional hardware to add SIP functionality to your IP-PBX. Switch now! **For more information on SIP trunking** and how NFON can help you make your existing infrastructure VoIP-ready or switch to a cloud-based PBX, see the following articles: [VoIP](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/voice-over-ip) [Phone line](https://www.nfon.com/en/service/knowledge-base/knowledge-base-detail/analogue-telephone-lines) Or discover NFON and take advantage of our 30-day free trial package, where you can test all the features and find out what suits your business! ### Related Articles ### Internet telephony **What is Internet Telephony?** Internet Telephony refers to all types of telephony services (including phone calls, fax, voicemail, video calls and other forms of communication) where calls and data are sent digitally over the Internet using the [Internet Protocol (IP)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/ip-address), rather than being transmitted over traditional analogue landlines. An example of an Internet Telephony service is [Cloudya, the Cloud Telephone System from NFON.](https://web-production.nfon.com/gb/products/cloudya) [Internet telephony](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/internet-telephony) ### Cloud The term “cloud” or “cloud computing” refers to a technology that allows applications and services to be accessed over a network such as the Internet as opposed to being run locally. Services made available by means of this technology are computing capacity, data storage space or applications such as [cloud telephone systems](https://web-production.nfon.com/gb/products/cloudya). The respective services are accessed via defined network protocols or interfaces. Many applications can be run directly from a browser. The actual IT resources for the services offered are located on a server or at a server farm **connected to the network.** [Cloud](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/cloud) ### Session Initiation Protocol (SIP) The acronym SIP stands for Session Initiation Protocol and refers to a TCP/IP-based network protocol which can be used to establish and control communication connections of several subscribers. SIP is often used in [Voice-over-IP telephony](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/voice-over-ip) to establish the connection for telephone calls. The key features of Session Initiation Protocol are specified in RFC3261. Since Session Initiation Protocol is an open standard, the protocol is widely used worldwide. Almost all IP-based [telephone systems](https://web-production.nfon.com/gb/products/cloudya) have SIP. 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