Download Sales Meeting - Draware A/S | Tlf. (+45) 45 76 20 21 | Vi

Network Instruments
VoIP Analysis
VoIP Basics
 What is VoIP?
 Packetized voice traffic sent over an IP network
 Competes with other traffic on the network
 A new technology that needs real-time, consistent monitoring
 Sensitive to delay
 Understanding VoIP Begins with Understanding Delay
 Normal (not sensitive to delay)
example: FTP, HTTP, e-mail, etc.
 Tolerant (sensitive to delay, loss tolerant, buffered
by receiver)
example: streaming video, Internet radio, etc.
 Real-time (delay and loss sensitive)
example: VoIP
Common VoIP Troubleshooting Myths
Myth #1
Running VoIP without Quality of Service is acceptable
Myth #2
No VoIP Site Survey is necessary
Myth #3
Voice conversations are secure
VoIP Monitoring and Analysis Challenges





Current, competing tools were designed for lab use
No method of quickly determining status and health
No mechanism for understanding aggregate call quality
VoIP dependencies are not implemented properly
Separate tools increase learning curve, reduce ROI
Observer
Other VoIP tools
VoIP Terms





Jitter
R-Factor / MOS
QoS / TOS / Precedence
Burstiness / Gap / Gap Duration
Compression Techniques (Codecs)
Jitter
 What is it?
 Jitter is the variation in the time between packets transmitted
and received.
 For example, if a packet stream leaves a device with 30 ms packet
spacing and arrives with 50 ms packet spacing, the
jitter is 20 ms.
 Adjusting jitter buffers can help at the expense of increased latency
and thus, clipping. Jitter buffer overflow will introduce dropped
packets.
 Why measure it?
 Understanding jitter gives you the hard facts to help improve call
quality
Observer’s Jitter Measurement
In aggregate…
and per call…
Call Quality Scoring

What is it?
 R-factor
 Identify call quality using a single source of visibility (actual live calls)
 Based on E-Model
 Scale: 1-100, with the theoretical maximum being 93.2 after
typical degradation
 MOS

 Determine user satisfaction level with a call
 Takes into account a number of different factors
(handset quality, ambient noise, network performance)
 Scale: 1-5, with 4.0 and higher considered satisfied,
4.5 and higher is extremely satisfied
 When using a simulated call, traffic can be captured at the destination and
compared to the original sent data to identify degradation.
Why measure Call Quality Scoring?
 Provides objective and subjective scores to evaluate
existing conditions and to compare with historical conditions.
Observer’s Call Quality Scoring
In aggregate…
per call…
and Expert…
Burstiness and Burst Density
 What is it?
 A burst is a period of time characterized by high rates of packet loss.
 Burst Percentage is the % of time bursts are occurring.
 Burst Density is the rate of VoIP data packets lost during a burst
period.
 Why measure it?
 Higher rates affect call quality, especially when coupled with long
Average Burst Duration times.
 Possible reason for packet loss include network congestion, media
failure, and link failure.
Gap Density and Duration
 What is it?
 Bursts are periods characterized by high rates of packet loss.
 Gaps are the periods between bursts.
 A gap is a period of time characterized by lower levels of
packet loss than the burst periods that bound it.
 Gap Density is the percent rate of packet loss during the gaps.
 Average Gap Duration is measured in time.
 Why measure it?
 Knowing the gap helps define the burst.
 In most cases, packet loss during gaps is rendered insignificant
by packet loss concealment techniques built into the VoIP
infrastructure.
Observer’s Burst and Gap Density
In aggregate…
and per call…
Settings for QoS / Precedence



Support for multiple definitions of Quality of Service (QoS)
Also known as Precedence
Also known as Type Of Service (TOS)

What is it?
 QoS is a bit setting used by routers and switches to prioritize
packet flow.
Why measure it?
 Incorrectly set QoS can lead to
contention of VoIP and other
data on a network.
 Contention will lead to delays
in packet delivery, and thus
reduce call quality.

Observer’s QoS/TOS/Precedence
In aggregate…
per call…
and Decode…
Compression Techniques
 Codec is a term for Coder/Decoder
 Different compression techniques (codecs)
 G.711: 64kbps (no compression)
 G.729: 8kbps
 G.723: 6.3kbps, 5.3kbps
 Higher compression reduces R-Factor and MOS but also
reduces potential contention
Observer’s Codecs Used Display
In aggregate…
per call…
and Decode…
Thank you