How it works
A SIP proxy examines a signalling request, selects the next hop and may enforce access or load-distribution policies. It does not necessarily carry RTP audio: the media path can be completely separate. Some deployments route a request through several proxies.
Business example
Company softphones send outbound calls through a provider’s SIP proxy, which selects the next signalling destination.
What to consider
A proxy is not automatically a PBX or media gateway. Troubleshoot SIP routing and media transport separately, and review whether the proxy is stateful or stateless.