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QoS DSCP Reference

Networking

Showing all 22 DSCP entries

NameDSCPBinary (6-bit)PHBTraffic ClassDropToS (dec)ToS (hex)ToS (binary)

Default Forwarding (DF / BE)

0

000000

Default

Best Effort

—

0

0x00

00000000

CS1

8

001000

CS1

Background

—

32

0x20

00100000

AF11

10

001010

Assured Forwarding

AF Class 1

Low

40

0x28

00101000

AF12

12

001100

Assured Forwarding

AF Class 1

Medium

48

0x30

00110000

AF13

14

001110

Assured Forwarding

AF Class 1

High

56

0x38

00111000

CS2

16

010000

CS2

Standard

—

64

0x40

01000000

AF21

18

010010

Assured Forwarding

AF Class 2

Low

72

0x48

01001000

AF22

20

010100

Assured Forwarding

AF Class 2

Medium

80

0x50

01010000

AF23

22

010110

Assured Forwarding

AF Class 2

High

88

0x58

01011000

CS3

24

011000

CS3

Broadcast Video

—

96

0x60

01100000

AF31

26

011010

Assured Forwarding

AF Class 3

Low

104

0x68

01101000

AF32

28

011100

Assured Forwarding

AF Class 3

Medium

112

0x70

01110000

AF33

30

011110

Assured Forwarding

AF Class 3

High

120

0x78

01111000

CS4

32

100000

CS4

Real-Time Interactive

—

128

0x80

10000000

AF41

34

100010

Assured Forwarding

AF Class 4

Low

136

0x88

10001000

AF42

36

100100

Assured Forwarding

AF Class 4

Medium

144

0x90

10010000

AF43

38

100110

Assured Forwarding

AF Class 4

High

152

0x98

10011000

CS5

40

101000

CS5

Signaling

—

160

0xA0

10100000

VOICE-ADMIT

44

101100

Voice Admit

Telephony

—

176

0xB0

10110000

EF

46

101110

Expedited Forwarding

Telephony / VoIP

—

184

0xB8

10111000

CS6

48

110000

CS6

Network Control

—

192

0xC0

11000000

CS7

56

111000

CS7

Network Control

—

224

0xE0

11100000

ToS byte calculation: ToS byte = DSCP value × 4. For example, EF (DSCP 46) = 46 × 4 = 184 decimal = 0xB8 hex. The lower 2 bits of the ToS byte are the ECN field (set to 00 for standard marking).

About This Tool

QoS DSCP Reference – DSCP Values, PHB Markings, and ToS Byte Mappings

Quality of Service (QoS) in IP networks relies on a 6-bit field called the Differentiated Services Code Point (DSCP), defined in RFC 2474. Routers and switches read this field to determine forwarding priority — ensuring voice calls stay clear, video streams stay smooth, and routine data transfers don't starve critical applications. This reference tool provides a searchable, filterable table of every standard DSCP value with its binary encoding, Per-Hop Behaviour (PHB), traffic class, drop precedence, and the corresponding ToS (Type of Service) byte in decimal, hex, and binary.

The DS Byte: From ToS to DSCP

The original IPv4 header contained an 8-bit ToS field (RFC 791) with a 3-bit IP Precedence subfield. RFC 2474 redefined this byte as the Differentiated Services (DS) byte: the upper 6 bits became the DSCP field, and the lower 2 bits became the ECN (Explicit Congestion Notification) field (RFC 3168). Backward compatibility is preserved — the 8 original IP Precedence levels map to DSCP values 0, 8, 16, 24, 32, 40, 48, and 56 (the Class Selector series).

Converting between DSCP and ToS byte is straightforward: ToS byte = DSCP × 4. Left-shifting by 2 bits places the 6-bit DSCP value in the upper bits of the byte and leaves the two ECN bits as zero. For example, EF (DSCP 46) produces ToS byte 184 (decimal) or 0xB8 (hex).

Per-Hop Behaviour (PHB) Classes

DSCP values are grouped into PHB classes that define how routers treat packets:

  • Default Forwarding (DF / BE) — DSCP 0. Standard best-effort delivery with no priority guarantees. Used for ordinary internet traffic.
  • Class Selector (CS1–CS7) — DSCP values 8, 16, 24, 32, 40, 48, 56. Direct equivalents of legacy IP Precedence. CS6 and CS7 are reserved for routing protocol traffic (OSPF, BGP, EIGRP).
  • Assured Forwarding (AF11–AF43) — Four classes (AF1x through AF4x), each with three drop precedences (low, medium, high). RFC 2597 defines these for traffic that should be delivered under normal conditions but may be dropped during congestion, with higher drop numbers dropped first.
  • Expedited Forwarding (EF) — DSCP 46. The highest-priority PHB, designed for low-latency, low-jitter, low-loss traffic such as VoIP bearer streams. EF traffic is typically placed in a strict-priority queue.
  • Voice Admit (VA) — DSCP 44. Defined in RFC 5865 for capacity-admitted voice traffic; provides similar forwarding guarantees to EF but indicates admission control has been applied.

Recommended DSCP Markings by Application

RFC 4594 provides the definitive guidance for DSCP markings across application types. The most common enterprise assignments are:

  • VoIP bearer (RTP audio) — EF (DSCP 46)
  • VoIP signalling (SIP, H.323) — CS3 (DSCP 24) or CS5 (DSCP 40)
  • Interactive video conferencing — AF41 (DSCP 34)
  • Multimedia streaming — AF31 (DSCP 26)
  • Transactional data / ERP — AF21 (DSCP 18)
  • Bulk / backup data — CS1 (DSCP 8)
  • Routing protocols — CS6 (DSCP 48)

DSCP in Practice: Marking, Trusting, and Re-marking

Endpoints (phones, video endpoints, servers) ideally mark their own traffic at the source. At network boundaries, routers apply trust boundaries — traffic from untrusted hosts is re-marked to a lower class to prevent abuse. Most enterprise switches trust DSCP markings from managed IP phones but re-mark PC traffic entering the same port.

Wireless networks add complexity: Wi-Fi uses its own priority scheme (WMM/802.11e) with four Access Categories (AC_VO, AC_VI, AC_BE, AC_BK). Mapping DSCP to WMM is performed at the access point based on the upstream DSCP marking, so correct DSCP values on the wired side flow through to wireless clients.

Using This Reference Tool

Type any keyword in the search box — a DSCP name (such as EF or AF41), a decimal value (46), a hex ToS byte (0xB8), a PHB name, or a traffic class description. The table filters in real time. Use the binary columns to verify markings when reading packet captures in tools like Wireshark, where the DS byte is displayed as a raw hex value. Clear the search to restore the full table of all 22 standard DSCP codepoints.

Frequently Asked Questions

Is the QoS DSCP Reference free?

Yes, QoS DSCP Reference is totally free :)

Can I use the QoS DSCP Reference offline?

Yes, you can install the webapp as PWA.

Is it safe to use QoS DSCP Reference?

Yes, any data related to QoS DSCP Reference only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

How does this QoS DSCP Reference tool work?

The tool displays a searchable table of all standard DSCP (Differentiated Services Code Point) values defined in RFC 2474 and RFC 4594. Each row shows the DSCP name, decimal value, 6-bit binary encoding, PHB (Per-Hop Behaviour), traffic class, drop precedence, and the corresponding ToS (Type of Service) byte in decimal, hex, and binary. Use the search box to filter by name, DSCP value, PHB, or ToS byte.

What is DSCP and how does it relate to QoS?

DSCP (Differentiated Services Code Point) is a 6-bit field in the IP header's DS (Differentiated Services) byte — the reuse of the older ToS byte defined in RFC 791. Routers and switches read the DSCP value to determine how to treat each packet: high-priority classes such as EF (Expedited Forwarding) get low-latency guaranteed treatment, while lower classes may be subject to congestion-based dropping. DSCP is the primary mechanism for IP-layer QoS in enterprise and service-provider networks.

What is the difference between DSCP and ToS?

ToS (Type of Service) was the original 8-bit field in IPv4 headers, defined in RFC 791. It included a 3-bit Precedence subfield and several flag bits. RFC 2474 redefined this byte as the DS byte: the upper 6 bits became the DSCP field and the lower 2 bits became the ECN (Explicit Congestion Notification) field. DSCP values map to ToS bytes by left-shifting the DSCP value by 2 bits, so DSCP 46 (EF) becomes ToS byte 184 (0xB8).

What are PHB classes — Default, CS, AF, and EF?

PHB stands for Per-Hop Behaviour, the forwarding treatment a router applies to a class of traffic. Default PHB (DSCP 0) is best-effort. CS (Class Selector) PHBs (CS1–CS7) use multiples of 8 for backward compatibility with IP Precedence. AF (Assured Forwarding) PHBs provide four classes (AF1x–AF4x), each with three drop precedences (low/medium/high). EF (Expedited Forwarding, DSCP 46) guarantees low latency and low loss, making it ideal for VoIP.

Which DSCP value should I use for VoIP and video conferencing?

For VoIP bearer (RTP audio) use EF (DSCP 46 / 0xB8). For VoIP signalling (SIP, H.323) use CS3 (DSCP 24) or CS5 (DSCP 40). For interactive video conferencing use AF41 (DSCP 34). For streaming video use AF31 (DSCP 26) or AF32 (DSCP 28). These mappings follow the Cisco/RFC 4594 enterprise QoS model and are widely used in Unified Communications deployments.

How do I calculate the ToS byte from a DSCP value?

Multiply the DSCP decimal value by 4 (or equivalently, left-shift by 2 bits) to get the ToS byte. For example, EF has DSCP 46: 46 × 4 = 184 (decimal) = 0xB8 (hex). The lower 2 bits of the ToS byte are the ECN bits, which are left as 00 in standard DSCP marking. This tool's table shows the pre-computed ToS byte for every DSCP value.