> For the complete documentation index, see [llms.txt](https://kb.hostednetwork.com.au/support/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kb.hostednetwork.com.au/support/services/voice-over-ip-voip/general/3cx-guides/3cx-sbc-guide.md). # 3CX SBC Guide #### Understanding 3CX SBCs 3CX runs in the cloud. If your client has physical desk phones in their office, a Session Border Controller (SBC) is required to securely connect those phones to the cloud 3CX system and help avoid network-related issues. #### What is an SBC? An SBC is a small device (or a phone with an SBC built in) located at the client's site. It securely connects the office desk phones to the cloud phone system and helps prevent issues such as dropped calls, no audio, or phones not ringing properly. Think of it as a security guard for the phone system, it connects desk phones to the cloud without needing to open up the firewall, while helping prevent call quality issues. #### When do you need one? If the client has desk phones in the office, that site will need an SBC. If staff are only using the 3CX mobile or desktop app, with no physical desk phones, no SBC is needed, they connect directly to the cloud. #### What are the options? Choose the right option based on how many desk phones are at the site: | Site Size | Use This | What It Is | | ------------------------------ | ------------- | -------------------------------------------------------------------- | | 1-10 desk phones | Router Phone | A normal desk phone with the SBC built in, no extra hardware needed. | | 10-20 desk phones | SBC appliance | A small box, e.g. a Raspberry Pi or mini PC. | | 20+ phones / multiple networks | Server / VM | Runs as software on an on-site server or VM. | | Mobile / remote workers | 3CX app only | No SBC needed, connects straight to the cloud. | #### Limitations to keep in mind * A Router Phone only covers up to 10 phones, larger sites need a dedicated SBC. * One SBC per site, it can't cover multiple office locations. * A decent internet connection is still required, a poor connection means poor call quality regardless of the SBC. If you have any questions please contact our support team via email at or via phone at 1300-781-148 --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://kb.hostednetwork.com.au/support/services/voice-over-ip-voip/general/3cx-guides/3cx-sbc-guide.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.