350-801 · Question #345
Which DSCP value and PHB equivalent are the default for audio calls?
The correct answer is A. 46 and EF. DSCP 46 maps to the Expedited Forwarding (EF) Per-Hop Behavior, and this is the universally accepted standard marking for VoIP/audio traffic. EF is defined in RFC 3246 and guarantees low-latency, low-jitter, low-loss forwarding - exactly the characteristics required for…
Question
Which DSCP value and PHB equivalent are the default for audio calls?
Options
- A46 and EF
- B34 and AF41
- C32 and AF41
- D32 and CS4
How the community answered
(27 responses)- A93% (25)
- B4% (1)
- D4% (1)
Explanation
DSCP 46 maps to the Expedited Forwarding (EF) Per-Hop Behavior, and this is the universally accepted standard marking for VoIP/audio traffic. EF is defined in RFC 3246 and guarantees low-latency, low-jitter, low-loss forwarding - exactly the characteristics required for real-time voice. In binary, DSCP 46 = 101110, which sets the three Precedence bits to 5 (Critical) and the DTCP bits accordingly. Cisco devices mark voice RTP packets as DSCP EF (46) by default. DSCP 34 and 32 both map to the AF41 PHB (Assured Forwarding class 4, drop precedence 1 and 2 respectively) and are used for interactive video, not audio. CS4 (DSCP 32) is used for call signaling in some models, not voice bearer traffic.
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