Foundation Summary

The "Foundation Summary" is a collection of tables and figures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary can help you recall a few details. For those of you who just read this chapter, this review can help solidify some key facts. For any of you doing your final preparation before the exam, these tables and figures are a convenient way to review the day before the exam.

A single voice packet consists of the voice payload, an RTP header, a UDP header, an IP header, and a Layer 2 header, as shown in Figure 10-7.

Figure 10-7. Voice Packet

Layer 2	IP	UDP	RTP	Voice Payload
Variable Size Based on Layer 2 Protocol	20 Bytes	8 Bytes	12 Bytes	Variable Size Based on Codec Selection and the ms of Speech Included

Table 10-21 lists the common G.711 and G.729 rates without including Layer 2 overhead.

Table 10-21. Codec Selection

Codec	Speech Samples Per Packet	Voice Payload	Packets Per Second	Total Bandwidth Per Call
G.711	20 ms	160 bytes	50 pps	80 kbps
G.711	30 ms	240 bytes	33 pps	74 kbps
G.729	20 ms	20 bytes	50 pps	24 kbps
G.729	30 ms	30 bytes	33 pps	19 kbps

Table 10-22 lists the common G.711 and G.729 rates including Layer 2 overhead.

Table 10-22. Layer 2 Headers

Codec	802.1Q Ethernet (32 Bytes @ Layer 2)	MLP (13 Bytes @ Layer 2)	Frame Relay (8 Bytes @ Layer 2)	ATM (Variable Bytes @ Layer 2 Due to Cell Padding)
G.711 @ 50 pps	93 kbps	86 kbps	84 kbps	106 kbps
G.711 @ 33 pps	83 kbps	78 kbps	77 kbps	84 kbps
G729a @ 50 pps	37 kbps	30 kbps	28 kbps	43 kbps
G729a @ 33 pps	27 kbps	22 kbps	21 kbps	28 kbps

Table 10-23 lists the delay, jitter, and packet-loss requirements for transporting voice traffic.

Table 10-23. Voice Delay, Jitter, and Packet Loss

Delay	< or = 150 ms
Jitter	< or = 30 ms
Packet Loss	< 1 percent

Table 10-24 compares the QoS requirements of voice traffic with other types of traffic.

Table 10-24. Voice Traffic Requirements

	Voice	Video	Mission-Critical/Transactional Data	Bulk Data/Best-Effort Data
Bandwidth Requirements	Low to Moderate	Moderate	Low to Moderate	Moderate to High
Drop Sensitivity	High	High	Moderate to High	Low
Delay Sensitivity	High	High	Low to Moderate	Low
Jitter Sensitivity	High	High	Low to Moderate	Low
Smooth or Bursty	Smooth	Bursty	Both	Both
Benign or Greedy	Benign	Greedy	Both	Both

Table 10-25 lists the delay, jitter, and packet-loss requirements for transporting video traffic.

Table 10-25. Video Delay, Jitter, and Packet Loss

Delay	< or = 150 ms
Jitter	< or = 30 ms
Packet Loss	< 1 percent
Bandwidth Fluctuation	20 percent

Table 10-26 lists the Cisco best practices for classification and marking of DSCP and CoS values for each traffic type.

Table 10-26. Classification and Marking Best Practices

Application or Protocol	DSCP Marking	DSCP Decimal Value	CoS Value
Voice traffic	EF	46	5
Bulk transfer traffic Web traffic, FTP traffic, large data-transfer applications, and so on	AF11 AF12 AF13	10	1
Transactional applications Database access, interactive traffic, and so on	AF21 AF22 AF23	18	2
Mission-critical applications Core business traffic	AF31 AF32 AF33	25	3
Interactive video traffic	AF41 AF42 AF43	34	4
IP routing BGP, OSPF, and so on	Class 6 (CS6)	48	6
Streaming video	Class 4 (CS4)	32	4
Voice and video signaling traffic SIP, H.323, and so on	AF31/Class 3 (CS3)	26/24	3
Network management traffic SNMP	Class 2 (CS2)	16	2
Scavenger traffic	Class 1 (CS1)	8	1
Unspecified or unclassified traffic	Best Effort or class 0 (CSO)	0	0

Table 10-27 lists the congestion management best practices. Remember that the percentage of bandwidth allocated depends upon the applications on your network. In many cases, all the listed classes will not be needed. This allows for the bandwidth assigned to the unnecessary class to be allocated to necessary classes.

Table 10-27. Congestion Management Best Practices

Application or Protocol	DSCP Marking	Queue Used	Percentage of Queue
Voice traffic	EF	LLQ	The combination of voice and video traffic in LLQ should not use more than 33 percent of the total available link bandwidth (e.g., 20 percent of total bandwidth).
Bulk transfer traffic Web traffic, FTP traffic, large data-transfer applications, and so on	AF11 AF12 AF13	CBWFQ	This class will receive a moderate amount of the remaining bandwidth after LLQ has beenserviced (e.g., 15 percent of remaining bandwidth).
Transactional applications Database access, interactive traffic, and so on	AF21 AF22 AF23	CBWFQ	This class will receive a small amount of the remaining bandwidth after LLQ has been serviced (e.g., 5 percent of remaining bandwidth).
Mission-critical applications Core business traffic	AF31 AF32 AF33	CBWFQ	This class will receive more of the remaining bandwidth after LLQ has been serviced (e.g., 25 percent of remaining bandwidth).
Interactive video traffic	AF41 AF42 AF43	LLQ	The combination of voice and video traffic in LLQ should not use more than 33 percent of the total available link bandwidth).
IP routing BGP, OSPF, and so on	Class 6 (CS6)	CBWFQ	This class will receive a moderate amount of the remaining bandwidth after LLQ has been serviced (e.g., 10 percent of remaining bandwidth).
Streaming video	Class 4 (CS4)	CBWFQ	This class will receive a moderate amount of the remaining bandwidth after LLQ has been serviced (e.g., 10 percent of remaining bandwidth).
Voice and video signaling traffic SIP, H.323, and so on	AF31/Class 3 (CS3)	CBWFQ	This class will receive a small amount of the remaining bandwidth after LLQ has been serviced (e.g., 5 percent of remaining bandwidth).
Network management traffic SNMP	Class 2 (CS2)	CBWFQ	This class will receive a small amount of the remaining bandwidth after LLQ has been serviced (e.g., 5 percent of remaining bandwidth).
Scavenger traffic	Class 1 (CS1)	CBWFQ	If used, this class will receive less than besteffort treatment. Packets in this class will be transmitted only if there are no other packets to transmit.
Unspecified or unclassified traffic	Best Effort or class 0 (CS0)	CBWFQ	This class will receive no guarantees. Some percentage of bandwidth can be specified that will be used by this class if all other classes have been transmitted (e.g., 5 percent of remaining bandwidth).

Table 10-28 lists the best practices for congestion avoidance.

Table 10-28. Congestion Avoidance Best Practices

Application or Protocol	DSCP Marking	WRED Policy
Voice traffic	EF	WRED not applied.
Bulk transfer traffic Web traffic, FTP traffic, large data-transfer applications, and so on	AF11 AF12 AF13	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.
Transactional applications Database access, interactive traffic, and so on	AF21 AF22 AF23	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.
Mission-critical applications Core business traffic	AF31 AF32 AF33	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.
Interactive video traffic	AF41 AF42 AF43	DSCP-based The default minimum and maximum thresholds will be used for AF42 and AF43 if WRED is enabled. Interactive video, marked AF41, should use LLQ, and, therefore, WRED should not be applied.
IP routing BGP, OSPF, and so on	Class 6 (CS6)	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic.
Streaming video	Class 4 (CS4)	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.
Voice and video signaling traffic SIP, H.323, and so on	AF31/Class 3 (CS3)	DSCP-based A high minimum threshold should be set for this class of traffic if WRED is enabled.
Network management traffic SNMP	Class 2 (CS2)	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.
Scavenger traffic	Class 1 (CS1)	DSCP-based A low minimum threshold should be set for this class of traffic if WRED is enabled.
Unspecified or unclassified traffic	Best Effort or class 0 (CS0)	DSCP-based The default minimum and maximum thresholds will be used for this class of traffic if WRED is enabled.

Table 10-29 lists the QoS components that need to be configured in the access layer and distribution layer of the campus LAN.

Table 10-29. QoS Components of the Access and Distribution Layers

QoS Component	Component Function
Trust boundaries	Determines the devices to be trusted. Establishes the trust boundary as close to the source as possible. Access layer function.
Classification and marking	Identifies and marks traffic with desired DSCP/CoS values. Performs as close to the source as possible. Modifies CoS-to-DSCP map. Access layer function.
Congestion management	Schedules each class of traffic with the desired CoS. Access and distribution layer function.
Policing	Limits unwanted or excessive traffic. Access and distribution layer function.

Table 10-30 lists the QoS components required on the CE router.

Table 10-30. QoS Components of the CE Router

QoS Component	Component Function Managed Enterprise WAN Edge	Component Function Unmanaged Enterprise WAN Edge
SLA	Defines the supported classes of traffic and the level of service each class will receive. Enforced on the CE router	Defines the supported classes of traffic and the level of service each class will receive. Enforced on the PE router.
Trust boundaries	Established on the CE router by the service provider. The service provider can then trust packets received from the CE, which removes the need for an inbound policy on the PE router.	Established on the CE router by the enterprise administrator. The service provider may not trust packets received from the CE and may remark traffic at the PE based upon the SLA.
Classification and marking	Traffic will be reclassified and marked on the CE based upon the classes offered in the SLA. The service provider can then trust markings received from the CE, which removes the need for an inbound policy on the PE router.	Traffic may be reclassified and marked on the CE based upon the classes offered in the SLA. The service provider may not trust packets received from the CE and may remark traffic at the PE based upon the SLA.
Congestion management	LLQ/CBWFQ queuing will be configured on the CE in accordance with the SLA. Traffic shaping, LFI, and cRTP may be configured depending upon the link type and speed.	LLQ/CBWFQ queuing will be configured on the CE in accordance with the SLA. Traffic shaping, LFI, and cRTP may be configured depending upon the link type and speed.
Congestion avoidance	WRED may be used to randomly drop best-effort traffic.	WRED may be used to randomly drop besteffort traffic.
Policing	Policing may be required on the CE router. The service provider can then trust the traffic rate received from the CE, which removes the need for an inbound policy on the PE router.	Policing will be required on the PE router. The service provider will reclassify or drop traffic that exceeds the limit specified in the SLA.

Table 10-31 lists the QoS components required on the PE router.

Table 10-31. QoS Components of the PE Router

QoS Component	Component Function Managed Enterprise WAN Edge	Component Function Unmanaged Enterprise WAN Edge
SLA	Defines the supported classes of traffic and the level of service each class will receive. Enforced on the CE router	Defines the supported classes of traffic and the level of service each class will receive. Enforced on the PE router.
Trust boundaries	Established on the CE router by the service provider. The service provider can then trust packets received from the CE router, which removes the need for an inbound policy on the PE router.	The service provider may not trust packets received from the CE router and may remark traffic at the PE based upon the SLA.
Classification and marking	Traffic will be reclassified and remarked on the CE router based upon the classes offered in the SLA. The service provider can then trust markings received from the CE router, which removes the need for an inbound policy on the PE router.	Traffic may be reclassified and remarked on the PE based upon the classes offered in the SLA.
Congestion management	LLQ/CBWFQ queuing will be configured in accordance with the SLA. Traffic shaping, LFI, and cRTP may be configured depending upon the link type and speed.	LLQ/CBWFQ queuing will be configured in accordance with the SLA. Traffic shaping, LFI, and cRTP may be configured depending upon the link type and speed.
Congestion avoidance	WRED may be used to randomly drop best-effort traffic.	WRED may be used to randomly drop besteffort traffic.
Policing	Policing may be required on the CE router. The service provider can then trust the traffic rate received from the CE, which removes the need for an inbound policy on the PE router.	Policing will be required on the PE router. The service provider will reclassify or drop traffic that exceeds the limit specified in the SLA.

For Further Reading

This book attempts to cover the breadth and depth of QoS as covered on the QOS exam (643-642); however, you might want to read more about topics in this chapter.

For more on the topics in this chapter:

• QoS Classification best practices (http://www.cisco.com/en/US/support/index.html. Then follow this link path: Technology Support > QoS (Quality of Service) > Classification & Marking > View All Documents))

• "Implementing DiffServ for End-to-End Quality of Service Overview" (http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt7/qcfdfsrv.pdf)

For design-related guidance:

• "Cisco AVVID Network Infrastructure Enterprise Quality of Service Design" (http://cisco.com/application/pdf/en/us/guest/netsol/ns17/c649/ccmigration_09186a00800d67ed.pdf)