Tools / Diagnostic / Vol I

DSCP / DiffServ Class Lookup

Enter a DSCP value, a PHB name, or a raw DS field byte and get every other representation back — decimal, hex, binary, the legacy ToS-byte view, the recommended 802.1p PCP mapping per RFC 8325, and the role this value typically plays in a VoIP network (voice bearer, video, signaling, OAM, scavenger).

Input

Accepts: 46 (decimal 0–63), 0x2E (hex), 101110 (6-bit binary), 0xB8 (DS field byte with ECN), or a PHB name like EF, AF41, CS3, BE.

ECN bits (DS-byte low 2)

Result

EF
Expedited Forwarding
DSCP 46 · 101110

Encodings

Classification

Layer 2 (802.1p PCP, RFC 8325)

Typical use

Common VoIP DSCP values

The DSCPs you'll see most often on a VoIP network. The row matching the currently-decoded value is highlighted.

PHB DSCP Hex Binary Recommended PCP Typical use

Reading the DS field

The DS byte

The 8-bit field is the ToS byte in IPv4 and the Traffic Class in IPv6 — same idea, same offset, same meaning. The upper 6 bits are DSCP (0–63, the marking); the lower 2 bits are ECN per RFC 3168. The tool shows the full DS-byte hex on the right so you can match what a packet capture displays in the IP header.

CS = legacy IP Precedence

Class Selector codepoints (CS0–CS7) are backward-compatible with the old IPv4 IP Precedence field — the top 3 DSCP bits map directly to IP Precedence 0–7, with the low 3 bits set to zero. CS3 = IP precedence 3 = Flash; CS6 = Internetwork Control; CS7 = Network Control.

AF = class × drop precedence

AFxy encodes two things at once: x (1–4) is the AF class — independent queues a router serves separately — and y (1–3) is the drop precedence inside that class. y=1 = lowest drop, kept in congestion; y=3 = highest drop, shed first. So AF41 is "high-priority video class, keep last"; AF43 is "high-priority video class, drop first."

EF = strict priority

Expedited Forwarding (DSCP 46) is the marking RFC 3246 specifies for low-loss, low-latency, low-jitter traffic — voice bearer in practice. EF queues are served with strict priority by routers and policed against an aggregate rate to keep them from starving everything else.

Voice-Admit (DSCP 44)

RFC 5865 carves DSCP 44 out as Voice-Admit — same scheduling as EF, but signals that the flow has passed explicit admission control (e.g. CAC / RSVP). Networks that admit voice without CAC stay on plain EF; if you see VA marking in a trace, something on the call path enforced admission.

Typical VoIP marking

Cisco's enterprise QoS baseline (and most SBC defaults) mark EF (46) for RTP voice, AF41 (34) for interactive video, CS3 (24) for SIP signaling, and CS6 (48) for network control. CS5 (40) also shows up for signaling in older designs.

Layer-2 mapping (RFC 8325)

On an 802.1Q trunk, DSCP doesn't carry — only the 3-bit PCP (802.1p) field does. RFC 8325 §4.3 publishes the recommended DSCP → PCP mapping; the tool reports the PCP that best preserves the QoS intent across an L2 hop. Voice (EF) → PCP 5; video / interactive (AF4x / CS4) → PCP 4; signaling (CS3) → PCP 3; network control (CS6/CS7) → PCP 7; best-effort (DF) → PCP 0.

ECN ≠ DSCP

The bottom 2 bits of the DS byte are ECN, not part of the DSCP marking. 00 Not-ECT = ECN not in use; 01/10 ECT(0)/ECT(1) = endpoint negotiated ECN; 11 CE = a router on the path marked the packet as congested instead of dropping it. Selecting an ECN value above only changes the DS-byte readout; the DSCP, PHB, and recommended PCP stay the same.