This paper describes an implementation for monitoring the QoS and expecting the QoE of a voice communication in a Real-time Transport Protocol (RTP) based telecommunication environment. The resulting QoS parameters are evaluated; the QoE is determined with the E-Model and processed for graphical presentation. With the use of some open-source programming libraries, the presented prototype can be a helpful alternative for expensive measurement devices and is ready to be deployed in a widespread telecom environment at low cost. Presented at NGMAST 2011 in Cardiff, UK.

1. Open-­‐‑Source Based Prototype for QoS
Monitoring and QoE Estimation in
Telecommunication Environments
Sebastian Schumann
Slovak University of Technology
Bratislava, Slovakia
Cardiff, UK – 15. September 2011

2. Introduction
• Implementation for Quality of Service (QoS) and
Experience (QoE) monitoring
• Works in Real-time Transport Protocol (RTP) based
telecommunication environments
• Analysis
o QoS parameters are evaluated
o QoE is determined with the E-Model
• Output
o R-Factor, one-way delay, packet-loss probability
o Graphical representation

3. Environment
• Usage of Voice over IP (VoIP) increased over the last
years
• It is not always possible to enforce QoS, esp. in
unmanaged networks
• Size of measured network does not matter
• Measurement system
o Measurement points (probes) are distributed
o Central reporting unit collects and evaluates the data
• Focus on widespread networks, not system
components

4. Motivation
• ngnlab.eu targets distributed VoIP environments
and open-source based solutions
• Commercial solutions are expensive, only for
operators
• Main goals
o Easy but flexible measurement design
o A non-intrusive online monitoring
o Informative results
o Ability to determine the geographical and technical
source of degradations

5. “Competition”

6. Theory
• E-model used to determine QoE (calculated acc.
several network parameters)
• Objective (i.e., calculated) value can be mapped
to the subjective Mean Opinion Score (MOS)
• Impacts on speech quality are
o One-way delay
o Packet-loss probability
o Packet-loss distribution
o Speech codec
• Measurement and evaluation of values allow
calculation of QoS/QoE during the call

7. Correlation between MOS
value and R-­‐‑Factor

8. Measured Impairments I
• One-way delay
• Measured by halving
the Round-Trip-Time
(RTT) value of the voice
packets (estimation)
• Both directions possible
• RTT determination using
measured values
o Time-stamp in PCAP
o Time-stamp in RTCP
• RTT1=A2-A1-D2
• RTT2=A3-A2-D3
DLSR .. delay sender report
A1 .. 1st SR passes ME
A2 .. following SR
D2 .. DL btw reception of SR1 and transmission of SR2

9. Measured Impairments II
• Packet loss probability
• Determined by recording the sequence number of
each RTP packet that passes the ME
• The loss probability is updated after every 100 RTP
packets
o The time distance is a good balance between the applied
load on the ME, the network load, and the actuality of the
measurement results on the EE

10. Measured Impairments III
• Packet loss distribution calculated acc. the patent
of McGowan
o Overall packet loss probability (Ppl)
o Average length of all loss sequences
• Speech codec is determined by parsing the Session
Description Protocol (SDP) during the session
establishment procedure
• Knowledge is important in relation to the used
compression method and its robustness against
packet loss (packet loss robustness factor)

11. Network setup

12. Application
• Measurement probes
o PCAP library captures packet for analysis
o Perl script extracts required information from each packet
o HTTP is used to exchange measured parameters
• Central reporting unit
o Java application
o Real-time monitoring with three detail levels (monitoring
unit, call, details)
o Adjustable color indication when pre-set thresholds are
reached

13. GUI

14. Measurement setup

15. Results I
• Non-degraded
measurement
• Normal values
• Delay in path 2+4 high
due to public network

16. Results II
• Degraded
measurement
• One-way delay on the
Internet higher (20x) in
paths 2+4
• R-Factor decreased as
well
• Knowing network and
taking packet loss into
account, low upload on
office B is determined

17. Summary
• QoS and QoE can be measured using the designed
prototype
• Implementation is scalable to smaller or larger Telco
networks (probes can be distributed accordingly)
• Implementation can compete with professional
equipment to a certain extent
• Extensions open but easily possible
o Alarms
o Visual network status display in real-time
o Follow-up calls for neg. quality calls
o Recording of call samples possible as well

18. Thank you!
Sebastian Schumann
seb.schumann@gmail.com
@s_schumann