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voip guide

DSCP And QoS For VoIP

QoS markings help network equipment identify traffic that should be prioritized. For voice, the most common marking is EF, which is DSCP decimal 46.

Common Voice Marking

  • EF usually maps to DSCP 46.
  • 802.1p CoS 5 is commonly used for voice on VLAN-tagged Ethernet.
  • Signaling is often marked differently from RTP media.

Where Markings Can Be Lost

  • At WAN edges that rewrite DSCP.
  • Across VPN tunnels without QoS preservation.
  • On unmanaged switches or consumer routers.
  • At provider boundaries that do not honor customer markings.

What QoS Cannot Fix

QoS can prioritize traffic during congestion, but it cannot fix a broken route, a blocked RTP path, a codec mismatch, or packet loss caused by a failing circuit.