With over 10 years of deployment history, VoIP is the primary voice solution for just about every company in existence - large, medium, or small. But even with all that history, recent research from TRAC shows that VoIP is still the number one IT initiative impacting network performance. And with the growth of 802.11 and Wi-Fi enabled smart phones, the use of voice over Wi-Fi (VoFi) promises to increase the volume of VoIP traffic even more. Analyzing VoIP traffic alone is not enough. VoIP analysis must be part of your overall network performance analysis. After all, VoIP is just another data type on your network, and according to TRAC, it is impacting your network performance, so you must monitor and analyze the network as a whole, including voice and video over IP. Join us to see how easy it is to capture and analyze voice, video, and data traffic simultaneously, allowing you to pinpoint the impact of each data type on your overall network performance.

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VoIP – Still Top of Mind in
Network Performance Monitoring

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TRAC NPM Research
Demographics
Sep 2013
406 participants
Company type:
 70% - Enterprise
 28% - Service
Providers
Company size:
 41% - Large organizations
 38% - Medium
 21% - Small
Geography
 56% - North America
 24% - EMEA
 14% - APAC

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Key IT Initiatives Impacting
Network Performance
48%
54%
59%
65%
66%
69%
72%
BYOD
Public Cloud services
Video conferencing
Virtual desktops
Enterprise Mobility
Big Data
VoIP

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36%
40%
41%
59%
64%
Ability to improve performance for home
office users
Managing recreational traffic
Increase in number of IP flows to be managed
Managing bandwidth consumption per
user/subscriber
Managing real-time applications (VoIP, video,
etc.)
Key Challenges for
Managing Network Traffic

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Key Challenges for
Managing UC Performance
24%
31%
38%
44%
44%
52%
Time spent on extracting session details
Inability to correlate multiple network layers
Visibility into bandwidth utilization
Visibility into the quality of user experience
Visibility into each session for UC technologies
Visibility into the impact of UC deployments on
other applications on the network

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And It’s Not Just VoIP …
• Percentage of all forms of video (TV, VoD, Internet,
and P2P) will be approximately 90 percent of global
consumer traffic by 2015
• Internet video to TVs will increase 17-fold by 2015
http://www.cisco.com/en/US/solutions/collateral/ns341/n
s525/ns537/ns705/ns827/white_paper_c11-481360.pdf

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VoIP/Video Is Just Different!

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VoIP/Video Is Just Different!
• Packet delivery not guaranteed
• Small and consistent packet
sizes
• Highly regular packet spacing
• Reliable packet delivery
• Large and variable packet
sizes
• Widely varying packet
spacing
VoIP Data

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Key RTP (VoIP/VoFi/Video) Issues
CAMP IT Pinpointing the Problem 9
Packet
Loss
JitterLatency

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Latency
Queue Latency &
Decision Latency
Network
Propagation
Delay
Encoding / Decoding
Compression / Decompression
Jitter Buffer Latency
0 ms
100 ms
200 ms
300 ms
400 ms
500 ms
600 ms
700 ms
800
ms
The ITU
recommends a
maximum one-
way delay of
150 ms for
VoIP

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Latency's Effects
• Talkover
‒ Occurs when excessive latency delays audio
– Conversation cadence is not natural or comfortable
– Callers feel as if they must “push to talk” or say “over” to control the
conversation
• Echo
‒ The speaker’s voice feeds back into the listener’s microphone
‒ The speaker then hears his own voice returning from the listener’s end,
but delayed due to latency
‒ Most callers find it difficult to maintain normal speech when echo delay
is prolonged
‒ Some VoIP systems attempt to cancel echo, but are not always
successful
High latency may also cause additional troubles such as loss of
synchronization between audio and video for multimedia sessions.

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Jitter
• Jitter is the variance in packet delivery intervals to the listener
• Jitter buffer adds additional delay to voice reaching the ear piece in
case other packets need to catch up
• Packets delayed too long in the network are not allowed to enter the
jitter buffer
Packets delayed more than the buffer delay
(100 ms as an example) are dropped
. . .. .. . . ........
......
Packets are buffered and
delayed at the Receiver
The “jitter” buffer releases
a G.711 packet every 20 ms
A G.711 packet sent
every 20 ms
Packet jitter and drops
31
2
4

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Jitter's Effects
• Jitter causes weird “sound effects” that vary with
jitter severity and environmental factors
• Examples include:
‒ Static
‒ Stuttering or uneven audio – abnormal speech rhythm
‒ For multimedia systems, video may be “jerky” or irregular
• If jitter levels are high, packet loss can result
‒ In some cases, severe jitter may sound similar to packet loss,
even if no packets are actually dropped

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Packet Loss
• Packet dropped due to physical layer corruption
• Congestion without adequate QoS provisions
• Jitter buffer discards due to excessive latency

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Packet Loss Effects
• Causes missing sounds, syllables, words, or phrases
‒ DSP algorithms may compensate for up to 30 ms of missing data
‒ More than 30 ms of missing audio is noticeable by listeners
• An average person speaks at a rate of about 200 words per
minute
‒ That’s 3.33 words/sec = 300 ms per word
‒ For G.711, we would need to lose 15 consecutive RTP packets to lose
a whole word
‒ Dropping 15 packets/sec for G.711 would be a loss rate of 30%
• But losing only a few packets can still be very noticeable
‒ Loss of more than 2 consecutive packets will be heard
‒ Loss rates ≥ 2% will have a strong impact on quality
‒ Losses of 5 – 10% make calls all but intolerable
‒ Bursty periods of packet loss are worse than more dispersed loss

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Measuring Key RTP Metrics

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Making Sense of the Metrics
• A single value to reflect the user’s QoE (quality of experience)
• Mean Opinion Score (MOS) – several flavors
‒ Algorithmic simulation of subjective audio assessment
‒ Most commonly used varieties are MOS-LQ (listening quality) and
MOS-CQ (conversational quality)
‒ Possible range of 1 (poor) to 5 (excellent)
‒ Maximum possible MOS = 4.4 with G.711
‒ Typical range in most networks is 3.5 – 4.2
• R-Factor – several flavors
‒ Based on latency, jitter, packet loss, bit rate, and signal-to-noise ratio,
codec effects (for low bit-rate codecs)
• The ITU algorithms consider about 20 quality inputs
‒ Possible range of 0 (poor) to 100 (excellent)
‒ Provides LQ, CQ, and other score variants

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Key Metrics So Far
• Latency
• Jitter
• Packet Loss
• MOS
• R-Factor

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Measuring MOS and R-Factor

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Can RTP and TCP Coexist?

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Coexistence Is Possible, But Challenging
• While traditional network applications are very tolerant of jitter,
latency, and even to some degree packet loss, VoIP/Video/VoFi
is not
• Tolerable levels of jitter, latency, and packet for TCP are
devastating for RTP
• Pre- and post-deployment network assessments are critical
‒ Pre-deployment: understanding your network’s ability to accommodate
VoIP
• Current latency, jitter, and packet loss
• QoS capabilities
• Current bandwidth utilization (is there any room for VoIP)
• Mix of RTP vs. TCP
• Is all RTP traffic equal?
‒ Post-deployment: maintain a constant vigil after deployment to watch
for imminent troubles

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Network Traffic: Qualitative Analysis
• The quality of your network traffic is potentially more
important than its quantity when it comes to VoIP
• Understanding the character of network traffic is key
‒ “Bursty” traffic - rapid, recurring traffic spikes that can occur over
long periods of time
‒ Prolonged, slow rises in utilization may decrease the number of
calls that can occur simultaneously over the course of a day
‒ Sharp spikes can cause very noticeable quality issues with
ongoing calls
• Your baseline monitoring should consider not only
averages and long-term trends, but also the short-
term peaks and dips that characterize your traffic
flow

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Network Traffic: Quantitative Analysis
• Most network engineers are concerned about the
amount of traffic on their networks
‒ Utilization (percentage of bandwidth)
‒ Throughput (bits or bytes per second)
• You also need to be concerned about individual
utilization components
‒ How much bandwidth and throughput can be attributed to each
application or process?
• Clarifies which application traffic may need to be tuned or
controlled
‒ How well or poorly will the baseline (trended) behavior of each
application interact with VoIP
• Don’t forget to also consider the reverse case – VoIP’s impact on
existing applications

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The Impact of "Just One More Call"
• Although a network link may be able to support a
number of concurrent calls, one additional call is
often enough to cause quality problems …
x1113
x2111
x1112
x1111
1st Call
2nd Call
3rd Call
x2112
x2113
Example: The WAN can support 2 simultaneous calls.
What happens when a third call is attempted???
Call #3 Causes Poor Quality for ALL Calls

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Quality Score Trending
• Isolated scores are useful for validating single call
complaints, but overall VoIP health is best seen by
graphing long-term trends
Overlaying VoIP trends
with network utilization,
errors, or other metrics
may reveal previously
unseen performance
relationships!

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Data Impacts on VoIP

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Got QoS?
• One of the most potent weapons for fighting VoIP
troubles is to provision Quality of Service (QoS)
• QoS enables network devices to prioritize and give
preference to packet streams that are sensitive to delay,
packet loss, jitter, and other performance inhibitors
• Standards-based QoS methods include:
‒ IP Differentiated Services (DiffServ)
‒ MAC Layer QoS with IEEE 802.1p
‒ VLANs
• QoS may be obtained or supplemented via proprietary
means, such as traffic shaping via various flow
processing algorithms
• Watch for too much differentiated traffic!

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Ready for QoS?
• QoS provisions are based on the “weakest link”
concept
‒ If any device in a data path does not support QoS, then media
streams will not be afforded the preference they require for good
performance
• Pre-deployment assessment must ensure that ALL
devices can recognize and respond to QoS
parameters in packet headers
‒ Switches, routers, firewalls, proxies, and any other devices that
touch RTP packets must be “VoIP-friendly”

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Monitoring QoS Configuration

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Unique Challenges of VoFi

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Quantitative Interference Impacts on VoFi
Source: Farpoint Group

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Quantitative Interference Impacts on VidFi
Source: Farpoint Group

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Packet-by-Packet
VoFi Call
Wired VoIP Call

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Troubleshooting RTP Issues

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VoIP Dashboard View

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Calls View

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Media View

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Down To The Details …

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Call Data Record (CDR)
Provides comprehensive, real-time
statistical and quality report for base-
lining, and 100% visibility into calls

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Identifying Unauthorized RTP Traffic
• Look for bandwidth hogs
• Use filters and alarms

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