Networking

VoIP QoS: Prioritizing Voice with DSCP and LLQ

Network Design diagram · made in Skemio

Network diagram illustrating an IP phone tagging voice to VLAN 20 with DSCP EF, passing untagged PC data through to VLAN 10 for priority queuing.
Network diagram illustrating an IP phone tagging voice to VLAN 20 with DSCP EF, passing untagged PC data through to VLAN 10 for priority queuing.
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What it shows

  • Voice VLAN isolates real-time packets from bursty desktop data traffic.
  • DSCP EF (Expedited Forwarding / 46) flags RTP voice packets for priority queues.
  • Low Latency Queuing (LLQ) forwards voice packets ahead of best-effort data.

The takeaway

Voice VLANs combined with DSCP EF tagging prevent packet jitter and dropped calls under heavy link loads.

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