NEC UNIVERGE SV9100 Manual page 16

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3.3 Layer 3 QoS
QoS is most commonly implemented at Layer 3. This allows the VoIP packets to be prioritised by
routers, before they are forwarded to their next hop.
Layer 3 QoS uses the Type of Service (ToS) field of the IP packet. This is an 8 bit field in the header
of the IP packet. The field can be used by Diffserv or IP Precedence. Although these are two different
standards, the actual field in the IP packet is the same - it is just the value that differs.
Please note that by QoS will not function just by utilizing the ToS field (i.e. Marking the VoIP
packets). It is an end-to-end process and requires configuration on all networking devices. Packet