Transcript 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…