Network Troubleshooting
Definition
Network faults are usually diagnosed layer by layer, starting from the physical link. The first checks are the port link light, the condition of the cable and the power to the switch. Addressing comes next: the devices must share a subnet with the correct mask, and no IP address may be duplicated. Reachability follows, since a ping confirms that a device answers and gaps in a continuous ping point to an intermittent fault. The last step is the quality of the link, measured as packet loss and delay variation.
The guide
Packet loss often comes from congestion, when a link or a switch buffer receives more traffic than it can forward. Delay variation, commonly called jitter and defined in RFC 3393 as IP packet delay variation, comes from packets waiting in queues for varying times. Real-time receivers absorb it with a fixed buffer, such as the latency setting in Dante, and a packet that arrives after that buffer has played out is lost even though the network delivered it. Jitter can therefore disrupt media while every device still answers a ping.
The method is structured isolation. The configuration is checked, connectivity is tested end to end, and the path is then split in halves, by swapping a cable, bypassing a switch or moving a device, until the faulty element is isolated. Swapping parts at random uses time that a show schedule rarely has.
File transfers run over TCP, which retransmits lost data, so a small amount of packet loss only slows them down. Live audio and video streams run over UDP, usually with RTP, and a packet that is lost or late cannot be sent again in time, so each loss becomes an audible click or a damaged frame.
The rule
On a show network, a lost packet reaches the audience as a click or a damaged frame.
Glossary terms
Sources
- IETF RFC 3393 (2002) : IP Packet Delay Variation ; le terme jitter est ambigu · datatracker.ietf.org
- IETF RFC 9293 (2022, STD 7) : TCP, transport fiable avec retransmission ; remplace la RFC 793 · datatracker.ietf.org
- IETF RFC 3550 (2003) : RTP, transport temps réel sur UDP · datatracker.ietf.org
- Audinate, Dante Controller User Guide, Latency : 1 ms par défaut, suffisant jusqu'à 10 sauts avec un cœur gigabit, valeurs plus basses sur les petits réseaux gigabit, jusqu'à 150 µs sur les appareils les plus rapides · dev.audinate.com