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 could help you recall a few details. For those of you who just read this chapter, this review will help solidify some key facts. For any of you doing your final prep before the exam, these tables and figures will be a convenient way to review the day before the exam.

Table 1-27 outlines some of the behaviors seen when no QoS is applied in a network.

Table 1-27. Traffic Behavior with No QoS

Type of Traffic	Behavior Without QoS
Voice	Voice is hard to understand.
	Voice breaks up, sounds choppy.
	Delays make interacting difficult; callers do not know when other party has finished talking.
	Calls are disconnected.
Video	Picture displays erratically; jerky movements.
	Audio not in sync with video.
	Movement slows down.
Data	Data arrives after it is no longer useful.
	Customer waiting for customer care agent, who waits for a screen to display.
	Erratic response times frustrate users, who may give up or try later.

As shown in Figure 1-36, with compression, if a ratio of 2:1 is achieved, the 80-kbps flow will only require 40 kbps in order to be sent across the linkeffectively doubling the bandwidth capacity of the link.

Figure 1-37 shows a two-queue system where the first queue gets 25 percent of the bandwidth on the link, and the second queue gets 75 percent of the bandwidth.

Figure 1-38 shows two contrasting examples of serialization and propagation delay.

Figure 1-39 lists the queuing, serialization, and propagation delays experienced by data, voice, and video traffic.

Figure 1-40 depicts LFI operation.

Figure 1-41 shows the jitter experienced by three packets as part of a voice call between phones at extension 301 and 201.

Figure 1-42 outlines the format of an IP packet using RTP.

Table 1-28 lists the bandwidth requirements when using one of two codecs, with varying types of data link protocols.

Table 1-28. Updated Bandwidth Requirements for Various Types of Voice Calls

Bandwidth Consumption, Including L2 Overhead	Layer 3 Bandwidth Consumption[*]	802.1Q Ethernet (32 Bytes of L2 Overhead)	PPP (9 Bytes of L2 Overhead)	MLP (13 Bytes of L2 Overhead)	Frame-Relay (8 Bytes of L2 Overhead)	ATM (Variable Bytes of L2 Overhead, Depending on Cell-Padding Requirements)
G.711 at 50 pps	80 kbps	93 kbps	84 kbps	86 kbps	84 kbps	106 kbps
G.711 at 33 pps	75 kbps	83 kbps	77 kbps	78 kbps	77 kbps	84 kbps
G.729A at 50 pps	24 kbps	37 kbps	28 kbps	30 kbps	28 kbps	43 kbps
G.729A at 33 pps	19 kbps	27 kbps	21 kbps	22 kbps	21 kbps	28 kbps

^[*] Layer 3 bandwidth consumption refers to the amount of bandwidth consumed by the Layer 3 header through the data (payload) portion of the packet.

Figure 1-43 shows an example of delay concepts, with sample delay values shown. When the delay is negligible, the delay is just listed as zero.

Table 1-29 outlines the suggested delay budgets.

Table 1-29. One-Way Delay Budget Guidelines

1-Way Delay (in ms)	Description
0150	ITU G.114 recommended acceptable range
0200	Cisco's recommended acceptable range
150400	ITU G.114's recommended range for degraded service
400+	ITU G.114's range of unacceptable delay in all cases

All the delay components for a voice call are summarized in the example in Figure 1-44.

Table 1-30 lists the different delay components and whether they are variable.

Table 1-30. Delay Components, Variable and Fixed

Delay Component	Fixed or Variable	Comments	QoS Tools That Can Help
Codec	Fixed	Varies slightly based on codec and processing load; considered fixed in course books (and probably on exams). Typically around 10 ms.	None.
Packetization	Fixed	Some codecs require a 30-ms payload, but packetization delay does not vary for a single codec. Typically 20 ms, including when using G.711 and G.729.	None.
Propagation	Variable	Varies based on length of circuit. About 5 ms/100 km	Move your facilities to the same town.
Queuing	Variable	This is the most controllable delay component for packet voice	Queuing features, particularly those with a priority-queuing feature.
Serialization	Fixed	It is fixed for voice packets, because all voice packets are of equal length. It is variable based on packet size for all packets.	Fragmentation and compression.
Network	Variable	Least controllable variable component.	Shaping, fragmentation, designs mindful of reducing delay.
De-jitter buffer (initial playout delay)	Variable	This component is variable because it can be configured for a different value. However, that value, once configured, remains fixed for all calls until another value is configured. In other words, the initial playout delay does not dynamically vary.	Configurable playout delay in IOS gateways; not configurable in IP Phones.

Table 1-31 summarizes the QoS requirements of data, in comparison to voice and video.

Table 1-31. Comparing Voice, Video, and Data QoS Requirements

	Bandwidth	Delay	Jitter	Loss
Voice Payload	Low to Medium	Low	Low	Low
Video Payload Interactive (2Way)	Medium	Low	Low	Low
Video Payload Streaming (1Way)	Medium to High	High	High	Low
Video Signaling	Low	Low	Medium	Medium
Voice Signaling	Low	Low	Medium	Medium
Data: Interactive, Mission Critical	Low to Medium	Low to Medium	Low to Medium	Medium to high
Data: Not Interactive, Mission Critical	Variable, typically high	High	High	Medium
Data: Interactive, Not Critical	Variable, typical medium	High	High	Medium
Data: Not Interactive, Not Critical	Variable, typically high	High	High	High