Bandwidth vs Throughput
Definition
Bandwidth is the nominal capacity of a link, such as 1 Gbps for Gigabit Ethernet, while throughput is the rate of useful data delivered. Throughput is lower because of protocol overhead (Ethernet framing and inter-frame gap, then IP, UDP and RTP headers), retransmissions and competing traffic. The share taken by overhead depends on packet size: small packets sent at short intervals, as in audio over IP, carry proportionally more header bytes than the large packets of a file transfer. The load an audio or video flow places on a link therefore depends on its packet rate as well as on its payload.
In the field
Network designs keep a margin below the nominal link rate, so that bursts and retransmissions do not fill the switch queues. A common rule of thumb limits planned sustained traffic to about 70% of the link, for example 700 Mbps on a 1 Gbps link carrying Dante, NDI, sACN and control together. The actual load of each port can be read from the switch port statistics during rehearsals.
Related lessons
Sources
- Ethernet frame (Wikipedia, pointeur secondaire), IEEE 802.3 : préambule, en-tête, FCS et intervalle entre trames · en.wikipedia.org
- RFC 3550 : en-tête RTP de 12 octets · rfc-editor.org
- Network throughput (Wikipedia, pointeur secondaire) : distinction entre débit nominal et débit utile, surcharge protocolaire · en.wikipedia.org
- Audinate FAQ, How hard can I push a Dante network link? Utilisation totale d'un lien à ne pas dépasser 70 % de sa capacité · support.getdante.com