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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") ### ISDN private branch exchange line group [Private branch exchange line group as a feature of telephone systems](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn-private-branch-exchange-line-group#section-3) [Private branch exchange line group in modern cloud telephone systems](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn-private-branch-exchange-line-group#section-4) # ISDN private branch exchange line group An [ISDN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/isdn) private branch exchange line group is activated by the telephone network provider at the telephone switch and allows several ISDN point-to-multipoint connections to be reached under a single telephone number. The ISDN connections are technically interconnected to a single virtual connection. Combining three point-to-multipoint connections, for example, the subscriber has up to six B-channels for parallel calls. Depending on the connection and telephone network, incoming calls are indicated alternating or simultaneously. The availability of convenience features may be limited with this type of connection. ### Private branch exchange line group as a feature of telephone systems By setting up an private branch exchange line group on a telephone system, several extensions can be reached under a single telephone number. The [telephone system](t3://page?uid=16) can route incoming calls to free extensions. The type of private branch exchange line group being used determines how calls are routed. One option is cyclical routing, where incoming calls are routed equally among all extensions. A hierarchic routing will route the call to the first free extension. The "Block private branch exchange line group" feature allows individual extensions to connect or disconnect from calls through the online service. ### Private branch exchange line group in modern cloud telephone systems The private branch exchange line group function has also made its way into Voice-over-IP telephony and network-based cloud telephone systems. Many systems allow the user to sign into an online service or a premium service number with queue right from their phone. This can be done regardless of the actual location and only requires an internet connection. The connection can be static or mobile. Call logs will then show if calls are e.g. coming from an private branch exchange line group or a queue. ### Related Articles ### Voice over Internet Protocol (VoIP) **What is VoIP?** The **Voice over Internet Protocol,** also called IP telephony, is a method of communication for making calls over a broadband Internet connection as an alternative to regular calls made over an analogue phone using the [PSTN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/pstn). These VoIP calls can happen entirely over the Internet but where required, gateways also link to the PSTN. This means that VoIP users can still connect to anyone with a telephone number including local, mobile, and international numbers. VoIP services can be accessed from a computer with a so-called [softphone,](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/softphones) from an IP phone, from a smartphone or from a conventional landline phone that is connected to a VoIP adapter. 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