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Jenifer Murillo, Jose Saldana, Julian Fernandez-Navajas, Jose Ruiz-Mas, Eduardo Viruete, Jose I. Aznar, "Improving Quality in a Distributed IP Telephony System by the use of Multiplexing Techniques" .Proc. International Symposium on Performance Evaluation of Computer and Telecommunication Systems SPECTS 2011, pp.54-61, The Hague, Netherlands, June 2011. ISBN: 978-161-782-309-1
Citation preview
Presentación
Jenifer Murillo
Jose Saldana
Julián Fernández Navajas
José Ruiz Mas
José I. Aznar
Eduardo Viruete Navarro
O M U N I C A C I O N E S
TRUPO DE
CECNOLOGÍAS
GDE LAS
CPS - University of Zaragoza, Spain
<>
SPECTS 2011
June 27-30, 2011, The Hague, Netherlands
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
4
Introduction
- VoIP is replacing traditional telephony systems.
- Objective: Cost saving, taking advantage of Internet connections.
- Decentralized resources: each office is independent.
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
5
Introduction
- Making a global management of the resources, we can save costs and increase admission probability
Country 1
Country 2
Country 3
Country 4
Country 5
Zone 1
Zone 2
Zone 3
IP network
PSTN
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
6
Introduction
- Software-based solutions allow a simple PC to assume the role of the PBX, making it possible to
- Build a central-managed system
- Sharing gateways of different offices
PSTN
IP networkOffice 1 Office 2
GatewayGateway
IP call Local call
Country 1 Country 2
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
7
Introduction
- VoIP is a real-time service which has to work in a best-effort network.
- Users demand a QoS similar to the one they used to have with traditional telephony.
- Solutions for adding QoS:
- CAC: Call Access Control
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
8
R-factor - Defined by ITU G.107 (E-Model)
- Ranges from 0 (bad quality) to 100 (good)
- Acceptable for R > 70
- Dependence on delay and packet loss
- Widely accepted quality estimator for VoIP services
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
9
Introduction - In a business with many offices, each one
with many users, a number of conferences can be established between the same pair of offices.
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
10
Introduction - In a business with many offices, each one
with many users, a number of conferences can be established between the same pair of offices.
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
11
Introduction - Advantage of grouping traffic:
- Overhead reduction
- Disadvantage:
- Added delays
RTP TCRTP RTP
MUX/DEMUX MUX/DEMUX
IP network
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
12
Introduction - We will study the advantages of adding a
multiplexing protocol to the central managed IP telephony system.
- Admission Probability
- R-Factor
RTP TCRTP RTP
MUX/DEMUX MUX/DEMUX
IP network
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
14
CAC systems
- Measurement-based: Use the state of the network to take admission decisions
- Parameter-based: Some measurements are carried out during system’s set up, and a maximum number of calls is set.
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
15
- «Rule of the thumb»: Bandwidth-delay product.
- «Stanford model»: Division by sqrt(N) (N:number of TCP flows).
- Other proposal: time-limited buffer. Interesting for this work. Limits OWD. But penalizes big packets.
Buffer size and buffer policies
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
16
- IPHC: Only compresses TCP, UDP and IP headers
- CRTP: Also RTP
- ECRTP: Enhanced CRTP
- ROHCv2: Uses more recent compressing algorithms
- TCRTP uses ECRTP
Header compressing techniques
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
17
TCRTP
PPP
PPP Mux
ECRTP
samples
IP
UDP
RTP...
ECRTP
samples
L2TP
IP
IP headerL2TP
Header
PPP
headerSamples
Reduced
header
PPP
Mux
header
PPP
Mux
header
Reduced
headerSamples
CH MH RH S MH RH S
...
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
18
- As bandwidth is saved, parameter-based CAC can support a bigger number of simultaneous conferences.
TCRTP Bandwidth saving
0.7
0.8
0.9
1
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 2 3 4 5 6 7 8 910
1112
1314
1516
1718
1920
prob. of reduced header
X
k
Bandwidth saving X
0.8-0.9
0.7-0.8
0.6-0.7
0.5-0.6
0.4-0.5
0.3-0.4
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
20
- Offices in different countries
- Dial plan only at the PBX
- Internet used for VoIP traffic
- The system does not use any reservation protocol
- VoIP traffic is the only real-time one we are going to take care of in a special way
- A parameter-based CAC is used
IP Telephony system
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
21
- Each office has a gateway and an Internet access
IP Telephony system
IP network
PSTN
Office 1 Office 2
Country 1
Area 1
Office 3
Country 2
Office 4 Office 5
Country 3
Area 2
Office 6 Office 7
Country 4
Area 3
CAC limit
Gateway’s
lines limit
GWGWGWGWGWGWGW
Data Center
PBX
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
22
- Each office has a gateway and an Internet access
IP Telephony system
IP network
PSTN
Office 1 Office 2
Country 1
Area 1
Office 3
Country 2
Office 4 Office 5
Country 3
Area 2
Office 6 Office 7
Country 4
Area 3
CAC limit
Gateway’s
lines limit
GWGWGWGWGWGWGW
Data Center
PBX
Signaling (SIP) goes to the PBX
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
23
- Each office has a gateway and an Internet access
IP Telephony system
IP network
PSTN
Office 1 Office 2
Country 1
Area 1
Office 3
Country 2
Office 4 Office 5
Country 3
Area 2
Office 6 Office 7
Country 4
Area 3
CAC limit
Gateway’s
lines limit
GWGWGWGWGWGWGW
Data Center
PBXRTP uses a star topology: tunnels between offices
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
24
- All signaling messages pass through it
- Counts the number of calls
- In charge of admission decissions
Local Agent (SIP proxy)
INVITE
100 Trying
INVITE
100 Trying
183 Session
Progress
183 Session
Progress
INVITE
480 Temporarily
Unavailable
480 Temporarily
Unavailable
480 Temporarily
Unavailable
IP phone IP phoneLocal agent Local agent
Office 1 Office i
database
PBX
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
25
- All signaling messages pass through it
- Counts the number of calls
- In charge of admission decissions
Local Agent (SIP proxy)
INVITE
100 Trying
INVITE
100 Trying
183 Session
Progress
183 Session
Progress
INVITE
480 Temporarily
Unavailable
480 Temporarily
Unavailable
480 Temporarily
Unavailable
IP phone IP phoneLocal agent Local agent
Office 1 Office i
database
PBX
There is no place for this call
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
27
Scheme of tests
Traffic
Generation
RouterTraffic
Capture
Real Traffic in a testbed
Network
delays
+
Dejitter
buffer
Offline post-processing
Traffic
Trace
QoS
parameters
VoIP
Background
Buffer
policies
Scenario
parameters
Conferences/
office
Simulated
scenarioFinal trace
Simulation in Matlab
Final results
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
28
Scheme of tests
Traffic
Generation
RouterTraffic
Capture
Real Traffic in a testbed
Network
delays
+
Dejitter
buffer
Offline post-processing
Traffic
Trace
QoS
parameters
VoIP
Background
Buffer
policies
Scenario
parameters
Conferences/
office
Simulated
scenarioFinal trace
Simulation in Matlab
Final results
Emulation in a testbed
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
29
- Xen Virtualization-based testbed
- Each computer is translated into a VM
- Bandwidth of office’s routers emulated with Linux tc (Traffic Control)
- Codec used: G.729a with 2 samples per packet
Testbed
Virtual network
Physical
machine
xenbr0
Public IP address
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
30
Scheme of tests
Traffic
Generation
RouterTraffic
Capture
Real Traffic in a testbed
Network
delays
+
Dejitter
buffer
Offline post-processing
Traffic
Trace
QoS
parameters
VoIP
Background
Buffer
policies
Scenario
parameters
Conferences/
office
Simulated
scenarioFinal trace
Simulation in Matlab
Final results
Addition of delays
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
31
System delays
IP network
MUX DEMUX
Tprocess Tqueue Tnetwork Tprocess TdejitterTretentionTpacketization
.
.
.
.
.
.
Added offline
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
32
Scheme of tests
Traffic
Generation
RouterTraffic
Capture
Real Traffic in a testbed
Network
delays
+
Dejitter
buffer
Offline post-processing
Traffic
Trace
QoS
parameters
VoIP
Background
Buffer
policies
Scenario
parameters
Conferences/
office
Simulated
scenarioFinal trace
Simulation in Matlab
Final results
Simulation of the whole scenario
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
34
- Each office has 25 users
- Gateways have 6 lines
- CAC limit=6 (variable in some tests)
- Different values of l and number of offices
Admission probability
... ...
IP network
M1 M2AI12AP1
AO1
AI21 AP2
AO2
N1 N2
PSTN PSTN
...
...
...
...
Office 1 Office 2
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
35
Admission probability
80
85
90
95
100
3 3,5 4 4,5 5
Pe
rce
nta
ge o
f ad
mit
ted
co
nfe
ren
ces
(%)
λ (conferences per hour per user)
Admission probability 3 offices
5 offices
7 offices
10 offices
15 offices
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
36
Admission probability
80
85
90
95
100
3 3,5 4 4,5 5
Pe
rce
nta
ge o
f ad
mit
ted
co
nfe
ren
ces
(%)
λ (conferences per hour per user)
Admission probability 3 offices
5 offices
7 offices
10 offices
15 offices
Increasing the number of offices is beneficial
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
37
- Influence of CAC limit
Admission probability
80
85
90
95
100
1 2 3 4 5 6 7 8 9 10 11 12 13
Ad
mis
sio
n p
rob
abili
ty (
%)
CAC limit
Admission probability2 offices and isolated mode
2 offices and sharing mode
4 offices and isolated mode
4 offices and sharing mode
6 offices and isolated mode
6 offices and sharing mode
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
38
- Influence of CAC limit
Admission probability
80
85
90
95
100
1 2 3 4 5 6 7 8 9 10 11 12 13
Ad
mis
sio
n p
rob
abili
ty (
%)
CAC limit
Admission probability2 offices and isolated mode
2 offices and sharing mode
4 offices and isolated mode
4 offices and sharing mode
6 offices and isolated mode
6 offices and sharing mode
Sharing mode is better than isolated mode
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
39
- Influence of CAC limit
Admission probability
80
85
90
95
100
1 2 3 4 5 6 7 8 9 10 11 12 13
Ad
mis
sio
n p
rob
abili
ty (
%)
CAC limit
Admission probability2 offices and isolated mode
2 offices and sharing mode
4 offices and isolated mode
4 offices and sharing mode
6 offices and isolated mode
6 offices and sharing mode
Increasing the number of offices is beneficial
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
40
- Influence of CAC limit
Admission probability
80
85
90
95
100
1 2 3 4 5 6 7 8 9 10 11 12 13
Ad
mis
sio
n p
rob
abili
ty (
%)
CAC limit
Admission probability2 offices and isolated mode
2 offices and sharing mode
4 offices and isolated mode
4 offices and sharing mode
6 offices and isolated mode
6 offices and sharing mode
In Sharing mode, the increase of CAC limit improves the Admission probability
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
41
- Each office has 25 users
- Background traffic: 80% of the capacity
R-factor
0 200 400 600 800 1000 120060
62
64
66
68
70
72
74
76
78
80
Conferences
R-f
acto
r
R-factor average
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
42
R-factor
0 200 400 600 800 1000 120060
62
64
66
68
70
72
74
76
78
80
Conferences
R-f
acto
r
R-factor average
Better values for sharing mode
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
43
R-factor
0 200 400 600 800 1000 120060
62
64
66
68
70
72
74
76
78
80
Conferences
R-f
acto
r
R-factor average
Less variance for sharing mode
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
44
- Original vs Multiplexing as a function of CAC limit
R-factor
66
68
70
72
74
76
78
80
82
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
R-f
ac
tor
CAC limit
R-factor
Simple RTP, λ = 2
Simple RTP, λ = 4
Simple RTP, λ = 6
Simple RTP, λ = 8
Simple RTP, λ = 10
TCRTP, λ = 2
TCRTP, λ = 4
TCRTP, λ = 6
TCRTP, λ = 8
TCRTP, λ = 10
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
45
- Original vs Multiplexing as a function of CAC limit
R-factor
66
68
70
72
74
76
78
80
82
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
R-f
ac
tor
CAC limit
R-factor
Simple RTP, λ = 2
Simple RTP, λ = 4
Simple RTP, λ = 6
Simple RTP, λ = 8
Simple RTP, λ = 10
TCRTP, λ = 2
TCRTP, λ = 4
TCRTP, λ = 6
TCRTP, λ = 8
TCRTP, λ = 10
Increasing CAC limit makes average
quality fall
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
46
- Original vs Multiplexing as a function of CAC limit
R-factor
66
68
70
72
74
76
78
80
82
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
R-f
ac
tor
CAC limit
R-factor
Simple RTP, λ = 2
Simple RTP, λ = 4
Simple RTP, λ = 6
Simple RTP, λ = 8
Simple RTP, λ = 10
TCRTP, λ = 2
TCRTP, λ = 4
TCRTP, λ = 6
TCRTP, λ = 8
TCRTP, λ = 10
Increase of CAC limit for a desired R-factor
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
47
- Tradeoff Quality vs Admission Probability
R-factor
66
68
70
72
74
76
78
80
82
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
R-f
ac
tor
CAC limit
R-factor
Simple RTP, λ = 2
Simple RTP, λ = 4
Simple RTP, λ = 6
Simple RTP, λ = 8
Simple RTP, λ = 10
TCRTP, λ = 2
TCRTP, λ = 4
TCRTP, λ = 6
TCRTP, λ = 8
TCRTP, λ = 10
Less quality but more admission probability
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM TESTS AND RESULTS CONCLUSIONS
Index
SPECTS, Jun 27-30 2011. The Hague Improving Quality in a Distributed IP Telephony System
49
- An SIP-based IP telephony system using a CAC has been tested. The scenario mathches an enterprise with several offices.
- QoS parameters are obtained in a testbed.
- Sharing the gateways increases admission probability.
- TCRTP saves bandwidth so R-factor can be improved.
- Tradeoff admission probability vs QoS
Conclusions
INTRODUCTION RELATED WORKS SYSTEM ARCHITECTURE TEST PLATFORM RESULTS CONCLUSIONS
Presentación
Jenifer Murillo
Jose Saldana
Julián Fernández Navajas
José Ruiz Mas
José I. Aznar
Eduardo Viruete Navarro
O M U N I C A C I O N E S
TRUPO DE
CECNOLOGÍAS
GDE LAS
CPS - University of Zaragoza, Spain
Presentación
<>
SPECTS 2011
June 27-30, 2011, The Hague, Netherlands