Modern enterprises are adopting VoIP throughout branch offices, but don’t have great tools for pre-deployment testing, capacity planning and troubleshooting when voice performance issues arise. Software Engineer Joao Antunes demos the ThousandEyes VoIP network test.

1. VoIP Performance Management
Joao Antunes
Software Engineer

2. 2
Corporate
Network A
Corporate
Network B
VoIP Performance Management
RTP
SIP
SIP
SIP
Internet
SIP gateway SIP gateway

3. 3
Corporate
Network A
Corporate
Network B
VoIP Performance Management
Internet
Agent
RTP
Agent

4. 4
VoIP Performance Management
• Key use cases
– Planning VoIP deployment (capacity, scaling, traffic management)
– Troubleshooting existing infrastructure
• Each test measures metrics in a single direction
– Displays loss, latency, discards, packet delay and QoS metrics
– To simulate a voice call, a test in each direction is desirable
• VoIP requires an agent on both ends (UDP+RTP-based)
– At least one agent must be an Enterprise Agent
– Enterprise Agents ideally located in branch offices

5. 5
VoIP Performance Management
Quality of Service requested
(IP layer)
Audio codec used
MOS Score (1-5)
Packets dropped by the
network
Packets dropped by the de-jitter
buffer
Average of packet delays
99.9th percentile of packet
delay variation

6. 6
VoIP Performance Management
Quality of Service obtained
Quality of Service requested
(IP layer)
Audio codec used
MOS Score (1-5)
Packets dropped by the
network
Packets dropped by the de-jitter
buffer
Average of packet delays
99.9th percentile of packet
delay variation

7. 7
VoIP Performance Management
Jump to…
• Path Visualization
• BGB Route Visualization

8. According to the equipment impairment factor method, the fundamental principle of the E-model on a concept given in the description of the OPINE model (see [b-ITU-T P-Sup.3]).
Psychological factors on the psychological scale are additive.
result of any calculation with the E-model in a first step is a transmission rating factor R, combines all transmission parameters relevant for the considered connection. This rating factor composed of:
R = Ro − Is − Id − Ie-eff + A represents in principle the basic signal-to-noise ratio, including noise sources such as and room noise. Factor Is is a combination of all impairments which occur more or simultaneously with the voice signal. Factor Id represents the impairments caused by delay and effective equipment impairment factor Ie-eff represents impairments caused by low bit-rate codecs.
includes impairment due to randomly distributed pack losses. The advantage factor A compensation of impairment factors when the user benefits from other types of access The term Ro and the Is and Id values are subdivided into further specific impairment values.
following clauses give the equations used in the E-model.
8
Calculation of the transmission rating factor, R
VoIP Performance Management
• Mean Opinion Score (MOS)
E-Model (ITU-T Recommendation G.107, 1998-2014)
Based on a mathematical model in which the individual transmission parameters are
transformed into different individual "impairment factors” such as codec characteristics,
delay, loss ratio, discard ratio, etc., to obtain a quality metric called R factor:
Basic signal-to-
noise ratio
Delay
impairment
Equipment
impairment
Advantage
factor
(expectation)
• Network latency
• De-jitter buffer size
• Ie (codec)
• Packet loss robustness (codec)
• Packet loss probability
Simultaneous
impairment
• Network latency

9. It’s time to see the entire picture.

10. 10
VoIP Performance Management
• Audio codec
– Generated traffic vs audio compression/quality
• DSCP
– Traffic shaping, firewall and LB configuration
• De-jitter buffer
– Network jitter vs call latency
• Network
– Capacity, latency, loss, etc.