{"id":6434,"date":"2026-10-12T13:04:19","date_gmt":"2026-10-12T11:04:19","guid":{"rendered":"https:\/\/eu.klytic.com\/voip-sip-ip-pbx-ucaas\/"},"modified":"2026-10-12T13:34:44","modified_gmt":"2026-10-12T11:34:44","slug":"voip-sip-ip-pbx-ucaas","status":"publish","type":"page","link":"https:\/\/eu.klytic.com\/en\/voip-sip-ip-pbx-ucaas\/","title":{"rendered":"VoIP, SIP, IP PBX and UCaaS: which architecture"},"content":{"rendered":"\t\t
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Home<\/a>\u203a<\/span>Guides<\/a>\u203a<\/span>Telephony<\/a><\/p>

Telephony \u00b7 Understand<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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VoIP, SIP, IP PBX and UCaaS: which architecture<\/h1>\t\t\t\t<\/div>\n\t\t\t\t
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VoIP is a way of transporting voice, SIP a protocol, an IP PBX a phone system, UCaaS a service. These terms cannot be compared with one another. The real decision involves three points: who operates the phone system, whether it is shared with other customers, and how it stays reachable when a site or a link goes down.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Updated October 2026<\/b><\/span>7 min<\/b><\/span>Official sources cited<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Four terms, four levels<\/h2>

VoIP<\/strong> (Voice over IP): the voice is split into packets and carried over an IP network, the Internet or a private network, instead of a traditional phone line. It is a means of transport, not a product.<\/p><\/div>

SIP<\/strong> (Session Initiation Protocol): the protocol standardized by the IETF in RFC 3261 for establishing, modifying and terminating sessions, including calls. It is a signaling protocol: it organizes the call. The voice itself generally travels over another protocol, RTP, or its secure version SRTP.<\/p><\/div>

IP PBX<\/strong>: the company\u2019s phone system, in its IP version. It manages extensions, direct numbers, groups, the auto attendant, call queues and forwarding. It can run on your premises or at a third party.<\/p><\/div>

UCaaS<\/strong> (Unified Communications as a Service): a suite hosted and operated by a third party, often combining voice, presence, instant messaging and video conferencing.<\/p><\/div>

Two more terms complete the buying vocabulary. A SIP trunk<\/strong> is the connection of your phone system to the public telephone network, provided by a carrier. A cloud PBX<\/strong>, or hosted IP Centrex, is a hosted phone system shared among several customers, each seeing only its own part.<\/p>

Remember one rule: an IP PBX can be on your premises or at a third party; UCaaS is always a service operated by a third party. Many UCaaS offerings are in fact built on an IP PBX, plus a set of applications around it.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Shared cloud PBX or dedicated IP PBX<\/h2>

Both are hosted. They do not answer three questions in the same way.<\/p>

Question<\/th>Shared cloud PBX<\/th>Hosted dedicated IP PBX<\/th>On-premises IP PBX<\/th><\/tr><\/thead>
Who administers it<\/td>The provider; you configure your part<\/td>The provider or you, depending on the contract<\/td>You or your installer<\/td><\/tr>
Neighbors on the machine<\/td>Other customers<\/td>None<\/td>None<\/td><\/tr>
Power outage at the office<\/td>The phone system remains reachable<\/td>The phone system remains reachable<\/td>The phone system stops, unless there is a UPS<\/td><\/tr>
Updates<\/td>Provider, at the platform\u2019s pace<\/td>Provider, can be scheduled for you<\/td>You or your installer<\/td><\/tr>
Exit<\/td>Export as provided for by the platform<\/td>Isolated configuration and data, easier to extract<\/td>Everything is on your premises<\/td><\/tr><\/tbody><\/table><\/div>

A dedicated system isolates the organization: a configuration error or an overload at another customer does not affect it, and data is not mixed. It does not change the question of who the operator is. A dedicated server is still operated by someone, who can restore it and can therefore access it.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Should you host your IP PBX yourself<\/h2>

Hosting the phone system on your premises gives you control over the hardware, the network and the timing of updates. That comes at a price, which must be read in full.<\/p>