9ne.pl — knowledge base https://9ne.pl/en/knowledge/ Practical guides to VoIP, SIP, WebRTC, Linux, deployments and diagnostics. en Fri, 07 Aug 2026 08:00:00 +0000 WebRTC, ICE, STUN and TURN explained https://9ne.pl/en/knowledge/webrtc-ice-stun-turn/ https://9ne.pl/en/knowledge/webrtc-ice-stun-turn/ Fri, 07 Aug 2026 08:00:00 +0000 WebRTC and media How the browser chooses a media path, why a public candidate is not always enough and when TURN is necessary for a reliable connection. Technical incident RCA — from symptom to lasting correction https://9ne.pl/en/knowledge/technical-incident-root-cause-analysis/ https://9ne.pl/en/knowledge/technical-incident-root-cause-analysis/ Fri, 07 Aug 2026 08:00:00 +0000 Diagnostics A good RCA does not seek someone to blame or merely recount events. It connects evidence, the failure mechanism, impact, correction and actions that prevent recurrence. How to plan a PBX migration without uncontrolled downtime https://9ne.pl/en/knowledge/pbx-migration-without-disruption/ https://9ne.pl/en/knowledge/pbx-migration-without-disruption/ Fri, 07 Aug 2026 08:00:00 +0000 VoIP and SIP A telephony platform migration needs parallel plans for configuration, registrations, routing, media, numbering, carriers and user behaviour. One-way audio in VoIP — NAT, RTP, SDP and firewalls https://9ne.pl/en/knowledge/one-way-audio-voip/ https://9ne.pl/en/knowledge/one-way-audio-voip/ Fri, 07 Aug 2026 08:00:00 +0000 VoIP and SIP One-way audio is not a single problem. It is a class of failures involving signalling, address translation, media routing, ACLs and device behaviour. How to read a SIP trace and identify why a call fails https://9ne.pl/en/knowledge/how-to-read-a-sip-trace/ https://9ne.pl/en/knowledge/how-to-read-a-sip-trace/ Fri, 07 Aug 2026 08:00:00 +0000 VoIP and SIP A practical method for analysing SIP signalling: from Call-ID and transactions, through routing and headers, to SDP, media and a precise RCA. Docker behind Nginx — TLS, health checks and predictable rollback https://9ne.pl/en/knowledge/docker-nginx-tls-healthcheck-rollback/ https://9ne.pl/en/knowledge/docker-nginx-tls-healthcheck-rollback/ Fri, 07 Aug 2026 08:00:00 +0000 Linux and infrastructure A lightweight production architecture for a web application: a locally accessible container, host Nginx, a certificate, readiness, versioned images and automatic rollback. A safe production server migration, step by step https://9ne.pl/en/knowledge/safe-production-server-migration/ https://9ne.pl/en/knowledge/safe-production-server-migration/ Fri, 07 Aug 2026 08:00:00 +0000 Linux and infrastructure Migration does not start with copying files. It starts with an inventory, dependencies, acceptance criteria and a practical way back.