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[+44 330 383 8000](tel:+443303838000 "+44 330 383 8000") ![](/images/getstarted-writetous-navbar-int_ZY7MOf.webp) ### Write to us Fill out our request form. Our experts will respond as soon as possible. [Write to us](/gb/request-information "Write to us") ### XCAPI # XCAPI **History:** CAPI was an Application Programming Interface that allowed for the remote use of an [ISDN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn) device (e.g. [fax](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/virtual-fax-machine) server). The company TE-Systems designed a drop-in replacement for programs to still use the CAPI but instead of using an ISDN device the [XCAPI](https://www.nfon.com/en/service/documentation/leaflets/software/leaflet-xcapi-setup/a-process-for-integrating-xcapi) uses SIP. **Description:** In the NFON PBX XCAPI describes a [SIP trunk](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip) with registration (the SIP account (K…)) in the SIP From: header and the extension number (e.g. 306) in the To: header. Contrary to "normal" SIP trunks the device on the other end of the XCAPI trunk needs some [PBX](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/private-branch-exchange-pbx) intelligence to be able to route the incoming calls accordingly. CAPI was an API to use ISDN features over a computer network, i.e. a single ISDN connection could be used by various devices over a computer network (typically Ethernet and IP, but previously also other protocols such as IPX). XCAPI is a product from te-systems to offer a virtual CAPI connection, i.e. even without being able to use the ISDN features as a drop-in replacement without an ISDN connection. This is often used for fax servers that have previously used an ISDN router to send faxes and have placed them on the CAPI interface. The product can now speak in the direction of the "CAPI" network and in the direction of PSTN ISDN, H.323 and SIP. If we (NFON) speak of XCAPI connection, we are "the [PSTN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/pstn)" from the view of the end device. Conversely, this means that the XCAPI device on the other end registers with us as an end device (namely at our registrars). The device is therefore not a simple end device, but from our point of view a small, independent PBX. It must be able to route numbers with it. The extension to be called is the P-asserted-identity header. Are you looking for more information? Here you can find our instruction [manuals](https://www.nfon.com/en/service/documentation/leaflets/software/leaflet-xcapi-setup/a-process-for-integrating-xcapi) ! ### Related Articles ### Private Branch Exchange (PBX) Private Branch Exchange (PBX) is another term for a telephone system or an interphone network. It refers to a system connecting a specific number of communication devices such as phones or fax machines with each other and the [Public Switched Telephone Network (PSTN)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/pstn). One or several parallel lines can be used to connect to the telephone network. [Private Branch Exchange (PBX)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/private-branch-exchange-pbx) ### 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. [Session Initiation Protocol (SIP)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip) ### Virtual fax machine With [Cloudya](https://web-production.nfon.com/gb/products/cloudya), you can send and receive faxes. • Reach each employee directly via a personal fax number • Share virtual fax machines with a user group • Receive faxes in PDF format by email • T.38 fax protocol supported • Connect analogue fax devices via auto-provisioned analogue adapter Want to know more? [Check our leaflets](https://www.nfon.com/en/service/documentation/manuals/fax)! [Virtual fax machine](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/virtual-fax-machine) ### 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. [SIP-Trunk](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/sip-trunk) ### Calling Line Identification Presentation (CLIP) Using the feature Calling Line Identification Presentation (CLIP) it is possible for the call recipient to display the telephone number of the caller. Whilst CLIP was originally only available for use with digital [ISDN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn) telephony, this feature is now also supported and utilised in analogue telephony. CLIP is also available with all other variants of digital telephony, for example [Voice over IP (VoIP)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/voice-over-ip). With digital telephony, the transfer of the caller's telephone number or caller ID takes place via a separate signalling channel, which is independent of the voice transfer. In contrast, with analogue telephony special modulated audio signals are transferred to the recipient telephone as caller ID information whilst the telephone rings to signal the call. In order to display the caller ID the process must be supported by the recipient telephone. A prerequisite for using CLIP is that the caller ID is not suppressed by the caller. If all the prerequisites for Calling Line Identification Presentation are met then the caller's ID will be shown on the telephone display of the call recipient whilst the telephone rings to signal the call. It is also possible to display the name of the caller, if the recipient telephone is equipped with its own configurable address book. Legal regulations state that sales and advertising callers must activate the CLIP feature, so that the telephone number of the caller is always shown with these calls. 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