Transcript 20040721-Satellite-Calyam

Video and Voice over IP
performance over a Satellite link
Bob Dixon, Ohio State University/OARnet
Prasad Calyam, OARnet
Joint Techs Workshops, Columbus, OH, July 21st, 2004
1
Overview
Terminology
E-Model
Delay, Jitter, Loss
H.323 Beacon
Demo
Demo Setup
Network Performance Bounds
H.323 Beacon Server-to-Server Test Module
Conclusion
2
Evaluating Audiovisual Quality
Two approaches
Subjective Measurements
Involve human participants to rate audiovisual
quality Can you hear me now?
Mean Opinion Score (MOS) Ranking technique
(ITU-T P.800) Not just “Good”!
Objective Measurements
Automated techniques to rate audiovisual quality
Perceptual Assessment of Speech Quality (PESQ)
[ITU-T P.862]
“E-Model” [ITU-T G.107]
3
MOS Rankings
4
E-Model
A computational model that uses
transmission parameters to predict user
perceived voice quality
Uses a psycho-acoustic R-scale (0-100)
that can be mapped to MOS rankings (1-5)
E-Model Components
R = Ro – Is – Id – Ie + A ≈ 94 – Id –Ie
5
E-Model Components
Ro → Effects of noise and loudness
Is → Simultaneous Impairment Factor
Impairments occurring simultaneously with the speech
signal
Id → Delay Impairment Factor
Impairments that are delayed with respect to the speech
signal
Ie → Equipment Impairment Factor
Impairments caused by transmission equipment
A → Advantage Factor
Used to compensate for the allowance users make for poor
quality in return for the ease of access; e.g. cell phone or
satellite phone
6
Understanding Delay…
Delay is the amount of time that a packet takes to travel from
the sender’s application to reach the receiver’s destination
application
Caused by codecs, router queuing delays, …
One-way delay requirement is stringent for H.323
Videoconferencing to maintain good interaction between both
ends
7
Understanding Jitter…
Jitter is the variation in delay of the packets arriving
at the receiving end
Caused by congestion, insufficient bandwidth, varying
packet sizes in the network, out of order packets, …
Excessive jitter may cause packet loss in the
receiver jitter buffers thus affecting the playback of
the audio and video streams
8
Understanding Loss…
Packet Loss is the packets discarded
deliberately (RED, TTL=0) or non-deliberately
by intermediate links, nodes and end-systems
along a given transmission path
Caused by line properties (Layer 1), full buffers
(Layer 3) or late arrivals (at the application)
9
Network Performance Bounds
for MOS Grades
Delay (Least Problematic)
Good (0ms - 150ms)
Acceptable (150ms - 300ms)
Poor (> 300ms)
Jitter (Most problematic)
Good (0ms - 20ms)
Acceptable (20ms - 50ms)
Poor (> 50ms)
Loss
Good (0% - 0.5%)
Acceptable (0.5% - 1.5%)
Poor (> 1.5%)
http://www.cl.cam.ac.uk/Research/SRG/netos/pam2004/papers/222.pdf
10
H.323 Traffic performance
characterization Testing Sites
More than 500 one-on-one subjective quality
assessments from Videoconferencing end-users
and corresponding traffic traces were obtained
from the Testing!!!
11
H.323 Beacon
http://www.itecohio.org/beacon
An H.323 application related end-to-end
performance troubleshooting tool
Can be used to obtain H.323-protocol
specific evidence and other network
information necessary for troubleshooting
Latest Version 1.4 released on
Sourceforge.net
Developed by OARnet and supported by
Internet2 and Ohio Board of Regents
12
Demo Setup
13
Questions?
14