QoS Priority Mapping

Service-Class

Service-class refers to the internal service class of packets. Eight service-class values are available: class selector 7 (CS7), CS6, expedited forwarding (EF), assured forwarding 4 (AF4), AF3, AF2, AF1, and best effort (BE). Service-class determines the type of queues to which packets belong.

The priority of queues with a specific service-class is calculated based on scheduling algorithms.

If queues with eight service-class all use priority queuing (PQ) scheduling, the queues are displayed in descending order of priorities: CS7 > CS6 > EF > AF4 > AF3 > AF2 > AF1 > BE.
If the BE queue uses PQ scheduling (rarely on live networks) but all the other seven queues use weighted fair queuing (WFQ) scheduling, the BE queue is of the highest priority.
If queues with eight service-class all use WFQ scheduling, the priority is irrelevant to WFQ scheduling.

More details about queue scheduling are provided later in this document.

Color

Color, referring to the drop precedence of packets on a device, determines the order in which packets in one queue are dropped when traffic congestion occurs. As defined by the Institute of Electrical and Electronics Engineers (IEEE), the color of a packet can be green, yellow, or red. In the DSCP value XXX YY0, YY indicates the drop precedence.

Drop precedences are compared based on the configured parameters. For example, if a maximum of 50% of the buffer area is configured to store packets colored Green, whereas a maximum of 100% of the buffer area is configured to store packets colored Red, the drop precedence of packets colored Green is higher than that of packets colored Red.

Trusting the Priority of Received Packets

As described in section Traffic Classifiers and Traffic Behaviors, after packets are classified on the DiffServ domain edge, internal nodes provide differentiated services for the packets that are classified. A downstream node can resume the classification result calculated on an upstream node or perform another traffic classification based on its own criteria. If the downstream node resumes the classification result calculated on an upstream node, the downstream node trusts the QoS priority (DSCP, IP precedence, 802.1p, or EXP) of packets that the interface connecting to the upstream node receives. This is called the mode of trusting the interface.

A NetEngine 8000 F does not trust the interface by default. After receiving a packet, a NetEngine 8000 F re-marks the service-class of the packet as BE and the color of the packet as Green, regardless of what QoS priority the packet carries.

DS Domain and Priority Mapping Table

An NetEngine 8000 F can perform QoS priority mapping based on the priority mapping table. Different DiffServ (DS) domains can have their own mapping tables. Administrators of a device can define DS domains and specify differentiated mappings for the DS domains.

An NetEngine 8000 F allows administrators to define a DS domain and has predefined the following domains:

Default domain: describes the default mappings between the external priority, service-class, and color of IP, VLAN, and MPLS packets.
5p3d domain: describes the mappings between the 802.1p value, service-class, and color of VLAN packets. This domain applies to the 802.1ad-compliant local area network (LAN) that supports five scheduling precedence and three drop precedences.

IETF defines eight PHBs (CS7, CS6, EF, AF4, AF3, AF2, AF1, and BE) and further defines four PHBs for three drop precedences. Therefore, the total number of PHBs is 16 (4 + 4 x 3 = 16).

There are 64 DSCP values, allowing each PHB to correspond to a DSCP value. However, there are only eight 802.1p values, causing some PHBs not to have corresponding 802.1p values. Generally the eight 802.1p values correspond to the eight scheduling precedence. IEEE 802.1ad defines STAG and CTAG formats, with the STAG supporting Drop Eligible Indicator (DEI) whereas the CTAG does not. IEEE 802.1ad provides a 3-bit Priority Code Point (PCP) field that applies to both the CTAG and STAG to specify the scheduling and drop precedence. PCP allows an 802.1p value to indicate both the scheduling and drop precedences, and also brings the concepts of 8p0d, 7p1d, 6p2d, and 5p3d. The letter p indicates the scheduling precedence, and the letter d indicates the drop precedence. For example, 5p3d supports five scheduling precedences and three drop precedences.

The default and 5p3d domains exist by default and cannot be deleted, and only the default domain can be modified.

Priority Mapping Table for the Default Domain

The mapping between the external priority, service-class, and color on a NetEngine 8000 F is described as follows:

**Table 1** Default mapping from the DSCP value to the service-class and color
DSCP	Service	Color	DSCP	Service	Color
0~7	BE	Green	28	AF3	Yellow
8	AF1		29	BE	Green
9	BE		30	AF3	Red
10	AF1		31	BE	Green
11	BE		32	AF4
12	AF1	Yellow	33	BE
13	BE	Green	34	AF4
14	AF1	Red	35	BE
15	BE	Green	36	AF4	Yellow
16	AF2		37	BE	Green
17	BE		38	AF4	Red
18	AF2		39	BE	Green
19	BE		40	EF
20	AF2	Yellow	41~45	BE
21	BE	Green	46	EF
22	AF2	Red	47	BE
23	BE	Green	48	CS6
24	AF3		49~55	BE
25	BE		56	CS7
26	AF3		57~63	BE
27	BE		57~63	BE

**Table 2** Default mapping from the service-class and color to the DSCP value
Service	Color	DSCP
BE	Green	0
AF1	Green	10
AF1	Yellow	12
AF1	Red	14
AF2	Green	18
AF2	Yellow	20
AF2	Red	22
AF3	Green	26
AF3	Yellow	28
AF3	Red	30
AF4	Green	34
AF4	Yellow	36
AF4	Red	38
EF	Green	46
CS6	Green	48
CS7	Green	56

**Table 3** Default mapping from the IP Precedence/MPLS EXP/802.1p to the service-class and color
IP Precedence/MPLS EXP/802.1p	Service	Color
0	BE	Green
1	AF1	Green
2	AF2	Green
3	AF3	Green
4	AF4	Green
5	EF	Green
6	CS6	Green
7	CS7	Green

**Table 4** Default mapping from the service-class and color to IP Precedence/MPLS EXP/802.1p
Service	Color	IP Precedence/MPLS EXP/802.1p
BE	Green, Yellow, Red	0
AF1	Green, Yellow, Red	1
AF2	Green, Yellow, Red	2
AF3	Green, Yellow, Red	3
AF4	Green, Yellow, Red	4
EF	Green, Yellow, Red	5
CS6	Green, Yellow, Red	6
CS7	Green, Yellow, Red	7

Priority Mapping Table for the 5p3d Domain

IEEE 802.1ad provided the PCP definition, as shown in the following figure.

Figure 2 PCP encoding/decoding
Click to enlarge

As shown in Figure 2, the number that ranges from 0 to 7 indicates the 802.1p priority. The value in the format of number x+letter DE indicates that the 802.1p priority is x and the drop_eligible value is true. If the drop_eligible value is false, the drop precedence cannot be set. If the drop_eligible value is true, the drop precedence can be set.

The 5p3d domain on a NetEngine 8000 F uses an IEEE 802.1ad-compliant priority mapping table by default. Table 5 shows the mapping table that is designed to match the IEEE 802.1ad.

**Table 5** IEEE 802.1ad-compliant mapping table for the 5p3d domain
802.1p Value to Color		Color to 802.1p Value
Drop_eligible defined in IEEE 802.1ad	Color defined in a NetEngine 8000 F	Color defined in a NetEngine 8000 F	Drop_eligible defined in IEEE 802.1ad
false	Green	Green	false
true	Yellow	Yellow, Red	true

The default mapping between the 802.1p value, service-class, and color for the 5p3d domain on a NetEngine 8000 F is shown in Table 6 and Table 7.

**Table 6** Mapping from the 802.1p value to the service-class and color
802.1p	Service	Color
0	BE	Yellow
1	BE	Green
2	AF2	Yellow
3	AF2	Green
4	AF4	Yellow
5	AF4	Green
6	CS6	Green
7	CS7	Green

The mapping from the 802.1p value to the service-class may apply to an inbound interface that belongs to a non-5p3d domain, leading to eight 802.1p values in Table 6. The outbound interface belongs to a 5p3d domain, leading to five service-classes in Table 6: BE, AF2, AF4, CS6, and CS7.

The mapping from the service-class and color to the 802.1p value may apply to an inbound interface that uses a 5p3d domain or DSCP, EXP, or IP precedence as a basis for mapping, leading to eight service-classes in Table 7. The outbound interface may belong to a non-5p3d domain, leading to eight 802.1p values in Table 7.

**Table 7** Mapping from the service-class and color to the 802.1p value
Service	Color	802.1p
BE	Green	1
BE	Yellow	0
BE	Red	0
AF1	Green	1
AF1	Yellow	0
AF1	Red	0
AF2	Green	3
AF2	Yellow	2
AF2	Red	2
AF3	Green	3
AF3	Yellow	2
AF3	Red	2
AF4	Green	5
AF4	Yellow	4
AF4	Red	4
EF	Green	5
EF	Yellow	4
EF	Red	4
CS6	Green, Yellow, Red	6
CS7	Green, Yellow, Red	7

IETF Recommendation

IETF standards classify services into 12 types (Table 8) based on service attributes and service quality requirements and provide recommendation on DSCP mappings (Table 9).

**Table 8** Recommendation for service classification
Service Category	Service Characteristics	QoS Counters
Service Category	Service Characteristics	Delay Tolerance	Jitter Tolerance	Packet Loss Rate Tolerance
Network Control	Network control plane service flow, such as a routing protocol, VRRP, and RSVP-TE	Low	Low	Yes
Telephony	VoIP services (such as G.711 and G.729)	Very Low	Very Low	Very Low
Signaling	VoIP and video service signaling, such as SIP, SIP-T, H.323, and H.248	Low	Low	Yes
Multimedia Conferencing	Desktop multimedia conference (including only voice and video. Data is classified as Low-Latency Data)	Low - Medium	Very Low	Low
Real-Time Interactive	Video conference (including only voice and video. Data is classified as Low-Latency Data), HD video, interactive game (using RTP/UDP)	Low	Very Low	Low
Multimedia Streaming	VoD	Low - Medium	Medium	Yes
Broadcast Video	Broadcast television, real-time video surveillance service	Very Low	Medium	Low
Low-Latency Data	Interactive important data services requiring quick response, such as VCX IP messaging, ERP, CRM, and DB.	Low	Low - Medium	Yes
OAM	Network O&M, maintenance, and management services, such as SNMP, Syslog, and SSH	Low	Medium	Yes
High-Throughput Data	Non-interactive background service, not requiring quick response, such as E-mail and FTP	Low	Medium - High	Yes
Standard	Default Internet services (best effort services). Services that are not marked with priorities can be classified into this category.	Not Specified
Low-Priority Data	Non-real-time elastic services, such as entertainment video traffic. If network congestion occurs, services of this category are dropped first.	High	High	Yes

**Table 9** Mappings from service types to DSCP values
Service Type	DSCP Name	DSCP Value	Application Examples
Network Control	CS6	110000(48)	Network routing
Telephony	EF	101110(46)	IP Telephony bearer
Signaling	CS5	101000(40)	IP Telephony signaling
Multimedia Conferencing	AF41 AF42 AF43	100010(34) 100100(36) 100110(38)	H.323/V2 video conferencing (adaptive)
Real-Time Interactive	CS4	100000(32)	Video conferencing and Interactive gaming
Multimedia Streaming	AF31 AF32 AF33	011010(26) 011100(28) 011110(30)	Streaming video and audio on demand
Broadcast Video	CS3	011000(24)	Broadcast TV & live events
Low-Latency Data	AF21 AF22 AF23	010010(18) 010100(20) 010110(22)	Client/server transactions Web-based ordering
OAM	CS2	010000(16)	OAM & P
High-Throughput Data	AF11 AF12 AF13	001010(10) 001100(12) 001110(14)	Store and forward applications
Standard	CS0	000000(0)	Undifferentiated applications
Low-Priority Data	CS1	001000(8)	Any flow that has no BW assurance

Traffic Classification Recommendations from the 3GPP

As defined in TS23.203 by the 3GPP, wireless services are classified as nine classes with specific QoS class identifiers (QCIs). Each QCI indicates the QoS requirements of one class, including the resource type, priority, delay, and packet loss rate. QCIs standardize the QoS requirements. The EPS controls QoS based on QCIs. QCIs are transmitted between NEs so that QoS parameters do not have to be negotiated or transmitted. QCIs are applied only to wireless NEs but are invisible at the bearer layer.

3GPP recommendations

**Table 10** Traffic classification recommendations from the 3GPP (Table 6.1.7 in 3GPP TS23.203)
QCI	Resource Type	Priority	Data Packet Delay	Packet Error Rate and Loss Rate	Typical Service
1	GBR	2	100 ms	10^-2	Conversational voice
2		4	150 ms	10^-3	Conversational video (real-time)
3		3	50 ms	10^-3	Online games
4		5	300 ms	10^-6	Non-conversational video (buffered streaming media)
5	Non-GBR	1	100 ms	10^-6	IMS signaling
6		6	300 ms	10^-6	Video (buffered streaming) and TCP-based applications such as WWW, emails, chat, FTP, P2P file sharing, and progressive scanning video
7		7	100 ms	10^-3	Voice, video (live streaming), and interactive game
8		8	300 ms	10^-6	Video (buffered streaming) and TCP-based applications such as the WWW Internet access, email, chat, FTP, P2P file sharing, progressive scanning video
9		9	300 ms	10^-6

The 3GPP does not provide any recommendations on mappings between QCIs and DSCP values. For Huawei's recommendation, see Table 11.

**Table 11** Recommended priority mappings for LTE services
Service Type	QCI	Resource Type	Typical Service	DSCP	802.1p/MPLS EXP	PHB
User Plane	1	GBR	Conversational voice	0x2E(46)	5	EF
	2		Conversational video	0x1A(26)	3	AF31
	3		Online games	0x22(34)	4	AF41
	4		Non-conversational video	0x1A(26)	3	AF31
	5	non-GBR	IMS signaling	0x30(48)	5	EF
	6		Video (buffered streaming) and TCP-based applications such as WWW, emails, chat, FTP, P2P file sharing, and progressive scanning video	0x12(18)	2	AF21
	7		Voice, video (live streaming), and interactive game	0x12(18)	2	AF21
	8		Video (buffered streaming) and TCP-based applications such as WWW, emails, chat, FTP, P2P file sharing, and progressive scanning video	0x0A(10)	1	AF11
	9			0x00(00)	0	BE
Control Plane	-	-	SCTP	0x2E(46)	5	EF
OM	-	-	Man-machine language (MML)	0x2E(46)	5	EF
OM	-	-	FTP	0x0E(14)	1	AF11
IP Clock	-	-	-	0x2E(46)	5	EF

Traffic Classification Recommendations from the GSMA

The GSMA classifies traffic as four types: conversational, streaming, interactive, and background traffic. The GSMA recommends that the four traffic types be mapped to six DSCP values recommended by the IETF. For details, see Table 12 and Table 13.

**Table 12** Mappings between traffic types and DSCP values (Table 6 in GSMA IR34)
Traffic Type	QoS Information
Traffic Type	THP(Traffic Handing Priority)	PHB	DSCP
Conversational	N/A	EF	101110 (46)
Streaming media	N/A	AF41	100010 (34)
Interactive	1	AF31	011010 (26)
	2	AF21	010010 (18)
	3	AF11	001010 (10)
Background	N/A	BE	000000 (0)

**Table 13** Mappings between service applications and DSCP values (Table 7 in GSMA IR34)
Service Application	Diffserv PHB	Traffic Type
Video sharing	EF	Conversational
VoIP	EF	Conversational
Push-to-Talk	AF4	Streaming media
Video streaming	AF4	Streaming media
GTP traffic that cannot be identified	AF3	Interactive
DNS	AF3	Interactive
Online games	AF3	Interactive
Web page browsing	AF2	Interactive
Instant messaging (IM)	AF1	Interactive
Remote connection	AF1	Interactive
Email, MMS	BE	Background

Traffic Classification Recommendations from the IEEE 802.1

As defined in the IEEE 802.1 standard (including the 802.1D, 802.1Q, and 802.1ad), services are classified as eight classes based on the PCP field (3 bits) in the VLAN tag.

**Table 14** Traffic classification recommendations from the IEEE 802.1
Traffic Type	Priority	Example Protocol	Service Characteristics
Network Control	7	BGP, PIM, SNMP	Network maintenance and management packets that must be transmitted in a reliable manner, with a low packet loss rate
Internet Work Control	6	STP, OSPF, RIP	Network protocol control packets that are differentiated from common packets on large-scale networks
Voice	5	SIP, MGCP	Voice services that generally require delay of less than 10 ms
Video	4	RTP	Video services that generally require delay of less than 100 ms
Critical Applications	3	NFS, SMB, RPC	Services that require the minimum bandwidth to be guaranteed
Excellent Effort	2	SQL	Used for an information organization to send messages to the most important customers.
Best Effort	0(default)	HTTP, IM, X11	Default service types, requiring only best-effort service quality
Background	1	FTP, SMTP	Batch transmission services that do not affect users or key applications

Traffic Classification Recommendations from the MEF

The MEF 23.1 standard classifies services as high-priority (H), medium-priority (M), and low-priority (L) services and uses CoS labels and drop eligibility identifiers (DEIs). For details, see Table 15.

The MEF 23.1 standard also provides recommended mappings between CoS labels and DSCP values. For details, see Table 16 and Table 17.

**Table 15** Service prioritizing (Table 36 in MEF 23.1)
Service Type	COS Label
VoIP	H
VoIP & videoconf signaling	M
Videoconf data	M
IPTV data	M
IPTV control	M
Streaming media	L
Interactive gaming	H/M
SANs synch replication	M
SANs asynch replication	M
Network attached storage	L
Text & graphics terminals	L
T.38 fax over IP	M
Database hot standby	M
Database WAN replication	M
Database client/server	L
Financial/Trading	H
CCTV	H
Telepresence	H
Circuit Emulation	H
Mobile BH H	H
Mobile BH M	M
Mobile BH L	L

**Table 16** Color IDs when the CoS ID type is only EVC or OVC EP (Table 3 in MEF 23.1)
CoS Label	CoS ID Type	Color ID
		C-Tag PCP		PHB (DSCP)
		Color Green	Color Yellow	Color Green	Color Yellow
H	EVC or OVC EP	5, 3 or 1	N/S in Phase 2	EF or AF (10, 26 or 46)	N/S in Phase 2
M	EVC or OVC EP	5, 3 or 1	2 or 0	EF or AF (10, 26 or 46)	AF (0, 12, 14, 28 or 30)
L	EVC or OVC EP	5, 3 or 1	2 or 0	EF or AF (10, 26 or 46)	AF (0, 12, 14, 28 or 30)

**Table 17** CoS and Color ID (Table 4 in MEF 23.1)
CoS Label	CoS and Color ID
	C-Tag PCP		PHB (DSCP)		S-Tag PCP (DEI not supported)		S-Tag PCP
	Color Green	Color Yellow	Color Green	Color Yellow	Color Green	Color Yellow	DEI supported
H	5	N/S in phase 2	EF(46)	N/S in phase 2	5	N/S in phase 2	5
M	3	2	AF31(26)	AF32(28)	3	2	3
M	3	2	AF31(26)	AF33(30)	3	2	3
L	1	0	AF11(10)	AF12(12)	1	0	1
				AF13(14)
				DF(0)

Recommendations from the ITU-T

As defined in Y.1541 by the ITU-T, services can be classified as six classes numbered 0 to 5 (see Table 18) based on the four parameters: IPTD, IPDV, IPLR, and IPER. For details about IP QoS guidance, see Table 19.

**Table 18** IP network QoS type definitions and network performance counters (Table 1 in ITU-T Y.1541)
Network Performance Parameter	Network Performance Target	QoS Type
Network Performance Parameter	Network Performance Target	Class 0	Class 1	Class 2	Class 3	Class 4	Class 5 Unspecified
IPTD	Upper limit for the average IPTD	100 ms	400 ms	100 ms	400 ms	1s	Not required
IPDV	Minimum value of IPTD x (1 - 10^-3) - IPTD	50 ms	50 ms	Not required	Not required	Not required	Not required
IPLR	Upper limit for IPLR	1 × 10^–3	1 × 10^–3	1 × 10^–3	1 × 10^–3	1 × 10^–3	Not required
IPER	Upper limit for IPER	1 × 10^–4					Not required

**Table 19** IP QoS classification guide (Table 2 in ITU-T Y.1541)
QoS Class	Application	Network Node Mechanism	Technology
0	Real-time, jitter-sensitive, and highly interactive services, such as VoIP and VTC	Independent queues, high service priority, and traffic grooming	Restrictions
1	Real-time, jitter-sensitive, and highly interactive services, such as VoIP and VTC		Constraint route and distance
2	The transaction (handling) data, and highly interactive services (such as the signaling)	Independent queues, and low packet loss rate	Constraint route and distance
3	Transaction data and interactive service	Independent queues, and low packet loss rate	Constraint route and distance
4	Services that require only low packet loss rates, such as short transaction data, batch data, and video streams	Long queue, low packet loss rate	Any route/path
5	Default traditional applications on IP networks	Independent queue (lowest service priority)	Any route/path

MPLS DiffSev

On an MPLS network, EXP values are used to identify a maximum of eight service priorities. If there are more than eight types of services, multiple types must be aggregated to one PHB.

Standards reclassify services as four types and provide recommended DSCP and EXP values. For details, see Table 20.

**Table 20** "Treatment Aggregate and MPLS EXP Field Usage"
Service Type	PHB	DSCP	Four-Type	QoS Counter			Exp
Service Type	PHB	Binary (Decimal Notation)	Four-Type	Delay Tolerance	Jitter Tolerance	Packet Loss Rate Tolerance	Binary (Decimal Notation)
Network Control	CS6	110000(48)	Network Control	Low	Low	Yes	110(6)
Telephony	EF	101110(46)	Real-Time	Very Low	Very Low	Very Low	100(4)
	CS5	101000(40)
	AF41	100010(34)
Signaling	AF42	100100(36)
Multimedia Conferencing	AF43	100110(38)
Real-Time Interactive	CS4	100000(32)
Broadcast Video	CS3	011000(24)
Multimedia Streaming	CS2	010000(16)	Assured Elastic	Low	Low – Medium	Yes	010(2)
	AF31	011010(26)
	AF21	010010(18)
Low-Latency Data	AF11	001010(10)
OAM	AF32	011100(28)					011(3)
	AF22	010100(20)
	AF12	001100(12)
	AF33	011110(30)
	AF23	010110(22)
High-Throughput Data	AF13	010110(14)
Standard	Default (CS0)	000000(0)	Elastic	Not Specified			000(0)
Low-Priority Data	CS1	001000(8)	Elastic	Not Specified			001(1)