Cisco Systems - VoIP Networking Designed_Slides

VoIP
Networking
Design
1171_04F8_c1

1


Tim Danford

+1.978.244.8911

1171_04F8_c1

2


Agenda
•Intended VoIP Applications
•VoIP Introduction
•Packet Networking Challenges
•Cisco QoS Toolkit
•Voice Network Design Issues
•Network Design Examples
1171_04F8_c1

3


VoIP Gateway Applications
•PSTN gateway service

•Route replacement/toll bypass
Most common application

•PBX OPX “extension”
•H.323 interoperability
Supports voice-enabled Web applications

1171_04F8_c1

4


Internet Telephony Service Provider
ISP “A”

Settlement Provider

Local
PSTN

(Trusted 3rd Party)
Authentication, Call
Routing, Billing and
Settlement Server

V

QoS
Interconnect
(or Internet)

ISP “B”

POP (i)

ISP “A”
Backbone

V
POP (ii)

1171_04F8_c1

Local
PSTN

ISP “B”
Backbone

Local
PSTN

V

5


Route Replacement
PBX

PSTN
T1,E1

PBX

Telco
Switch

V
V

QoS
WAN
(Intranet/Internet)

Branch Office

1171_04F8_c1

Main Office

6


PBX OPX Transport
PSTN

PBX

Telco

Switch
4 to 12 Analog

V

3600’s with
Voice Module
V
Fax

QoS
WAN
Branch Office

1171_04F8_c1

Main Office

7


H.323 Interoperability
• H.323 VoIP Local Loop Bypass
• Integrated Messaging: Email, VMail, FaxMail

Business

• Interoperability with NetMeeting type programs
PSTN
PBX

PBX

I-Phone
H.323 S/W

V

I-Phone
H.323 S/W

Router
+ VoIP

QoS
WAN

Local
PSTN

POP

Residential

Internet
xDSL

I-Phone
H.323 S/W

Residential
1171_04F8_c1

V

DSLAM

xDSL
Modem

2nd Line
Phone

Main Office
8


Agenda
•Intended VoIP Applications
• VoIP Introduction
•Packet Networking Challenges
•Cisco QoS Toolkit
•Voice Network Design Issues
•Network Design Examples
1171_04F8_c1

9


Network Convergence

Applications

IP

IP

PPP
802.N

WAN

Campus

L3

L2

Service
Adaptation

Frame
Relay

ATM
Sonet

L1

1171_04F8_c1

F-T1

DS1

DS3

OC3 - OCn

10


L3/L2 Transport Characteristics
• L3— VoIP

• L2— VoFR, VoATM

Flexible— IP is ubiquitous

“Hard” Qos

“Soft” form of QoS

Infrastructure can be rigid

IP/UDP/RTP overhead
(RTP compression)

Standards-based

Quickly emerging

technology

Better suited for high
volume bulk voice

Standards-based H.323

1171_04F8_c1

11


Voice over IP Protocols
Presentation
Session

G.729(A)/G.723(.1)/G.711
H.323/H.323Gateway

Transport

RTP/UDP/RSVP

Network

IP/WFQ/IP-prec

Link
Physical

1171_04F8_c1

MLPPP/FR/ATM AAL1
–––

12


VoIP— Uses Voice Component of H.323
System
Control and
User Interface

Video
I/O
Equipment

Audio
I/O
Equipment

Video Codec
H.261, H263

Audio Codec
G.711, G.722,
G.723, G.723.1,
G.728, G.729

User Data

Applications
T.120

System Control
H.245
Control
Call Control
H.225.0
RAS Control
H.225.0

Session Layer
and Above

Receive Path
Delay

H.225.0 Layer
LAN Stack
1171_04F8_c1

13


H.323 Infrastructure
H.323 Terminal

Gatekeeper

Corp LAN

Router

Gateway
Proxy
H.320
(Over ISDN)

Intranet

Real-Time
Network

Telephone
Network

Typical H.323 Applications
Internet Phone/I-Fax (VOIP)
H.323

H.324
(Over POTs)

Speech Only
(PSTN)

Data Conferencing (T.120)
Video Conferencing

1171_04F8_c1

14


H.323 Signaling
Admission Request

V

H.323
Gateway

Admission Confirm

Setup
Connect

RAS
Gatekeeper

H.225
(Q.931)

H.323
Gateway

Capabilities Exchange
Open Logical Channel

V

H.245

Open Logical Channel Acknowledge

Path
Resv
RTP Stream
RTP Stream
RTCP Stream

1171_04F8_c1

RSVP
Media

15


PBX to Router VoIP Signaling
2

5278305

H.225 (Q.931)

Corporate
Intranet

5278305

Switch
V

1

3

Analog Signaling

Digital Trunk Signaling

FXO/FXS

1171_04F8_c1

H.323 Gateway

CAS:
E&M
CCS:
Q.931/PRI

16


RTP/RTCP— RFCs 1889/1890
• End-to-end network transport function
Payload type identification
Sequence numbering
Timestamping

Delivery monitoring

• RTCP (Real-Time Control Protocol) provides
feedback on the quality of the distribution
• RTP does not address: Resource reservation
or guaranteed quality of service

1171_04F8_c1

17


Bandwidth Requirements
Voice Band Traffic
Encoding/
Compression
G.711 PCM
A-Law/u
A-Law/u-Law

64 kbps (DS0)

G.726 ADPCM

16, 24, 32, 40 kbps

G.727 E-ADPCM

16, 24, 32, 40 kbps

G.729 CS-ACELP

8 kbps

G.728 LD-CELP

16 kbps

G.723.1 CELP

1171_04F8_c1

Result
Bit Rate

6.3/5.3 kbps
Variable
18


G.729 CS-ACELP
•80 sample frames (10ms) of 16-bit
linear PCM data into 10 8-bit
codewords
•15ms (10ms frame + 5ms look ahead)
•8kb/s data rate

1171_04F8_c1

19

Agenda
•Intended VoIP Applications
•VoIP Introduction
• Packet Networking Challenges
•Cisco QoS Toolkit
•Voice Network Design Issues
•Network Design Examples
1171_04F8_c1

20


Mean Opinion Score
Source

Channel
Simulation

Impairment
Codec
‘X’

1

2

3

4

5

1

2

3

4

5

“Nowadays, a chicken leg is a rare dish.”
Rating Speech Quality Level of Distortion
5

Excellent

Imperceptible

4

Good

Just perceptible, not annoying

3

Fair

Perceptible, slightly annoying

2

Poor

Annoying but not objectionable

1

Unsatisfactory

Very annoying, objectionable

MOS of 4.0 = Toll Quality

1171_04F8_c1

21


Voice Transport Requirements
• Subjective quality (MOS)

• Background noise

MOS

• Silence suppression

• Delay and delay variation
• Echo cancellation

Comfort noise

• Language sensitivity

VoIP Challenges in the WAN
Loss
Bandwidth
Delay
Delay Variation (Jitter)
(Amplified with Coexistence of Voice and Data)

1171_04F8_c1

22


VoIP (G.729) Is Tolerant of
“Occasional” Packet Loss
missing packet
G.729 vocoder algorithm

• The friendly “retransmission” is of no use in the
Voice world… late is as good as never
• Complex “concealment strategy” in algorithm
interpolates lost packets based on context

1171_04F8_c1

23


Consecutive Packet Losses Degrade
Voice Quality (Mean Opinion Scores)
Consecutive
Frames Lost:

M.O.S. :

1

2

3

4

5

4.2

3.2

2.4

2.1

1.7

“G.729 Error Recovery for Internet Telephony”,
Jonathan Rosenberg, Lucent Technology and Columbia University
V.O.N. Conference 9/97
1171_04F8_c1

24


Echo Is Always Present
•Echo as a problem is a function of
the echo delay, and the magnitude
of the echo
(dB)

Echo Is Unnoticeable

Echo Path Loss

Echo Is a Problem

Echo Path Delay (ms)
1171_04F8_c1

25