improving quality in a distributed ip telephony system by the use of multiplexing techniques

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

http://www.ntms-conf.org/

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


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



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



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



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



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.



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.



11

Introduction - Advantage of grouping traffic:

- Overhead reduction

- Disadvantage:

- Added delays

RTP TCRTP RTP

MUX/DEMUX MUX/DEMUX

IP network



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



Index


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.



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



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



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

...



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



Index


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



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



22


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



23


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



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



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



Index


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



28

Scheme of tests

Traffic

Generation

RouterTraffic

Capture


Network

delays

+

Dejitter

buffer


Traffic

Trace

QoS

parameters

VoIP

Background

Buffer

policies

Scenario

parameters

Conferences/

office

Simulated

scenarioFinal trace


Final results

Emulation in a testbed



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



30

Scheme of tests

Traffic

Generation

RouterTraffic

Capture


Network

delays

+

Dejitter

buffer


Traffic

Trace

QoS

parameters

VoIP

Background

Buffer

policies

Scenario

parameters

Conferences/

office

Simulated

scenarioFinal trace


Final results

Addition of delays



31

System delays

IP network

MUX DEMUX

Tprocess Tqueue Tnetwork Tprocess TdejitterTretentionTpacketization

.

.

.

.

.

.

Added offline



32

Scheme of tests

Traffic

Generation

RouterTraffic

Capture


Network

delays

+

Dejitter

buffer


Traffic

Trace

QoS

parameters

VoIP

Background

Buffer

policies

Scenario

parameters

Conferences/

office

Simulated

scenarioFinal trace


Final results

Simulation of the whole scenario



Index


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



35


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



36


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



37

- Influence of CAC limit


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






38



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







Sharing mode is better than isolated mode



39



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







Increasing the number of offices is beneficial



40



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







In Sharing mode, the increase of CAC limit improves the Admission probability



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



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



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



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



45


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



46


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



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



Index


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


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

http://www.ntms-conf.org/

improving quality in a distributed ip telephony system by the use of multiplexing techniques

Education

hagueimproving quality

ip network zone

bad quality

ip headers crtp

ip networkip callspects

traditional telephony

accepted quality estimator

pstn country