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VoIP and QoS

This presentation runs through QoS and its influence with VoIP
by

Eugene Blanchard

on 7 December 2013

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Transcript of VoIP and QoS

VoIP and QoS

V
oice
o
ver
IP

and

Q
uality
o
f
S
ervice

by Eugene Blanchard
www.TelecomWorld101.com

The Problem...
Voice communication is
real-time
traffic
Voice traffic
cannot
be delayed
Round Trip Time (RTT) max:
300 mSec
Lost packets are
dropped
Delayed
packets are
dropped
Lost
packets are
not
re-requested
Intelligence Lost..
When voice packets are
dropped
intelligence is
lost

in the conversation
Solution
: only transmit
20 mSec
at a time
Fighting for Bandwidth
Voice
and
Data
fight
for
same
network bandwidth
During
large
data transfers
Voice packets
are lost, delayed and packets
dropped
!
Voice quality
suffers
!
Solution:
Separate

physical networks
One for
Voice
One for
Data
Not
practical
Waste
of resources
Convergence
Share the
same
network
infrastructure
Divide the network
virtually
using VLANs
one VLAN for
Voice
another VLAN for
Data
Problem Areas
Where Voice and
Data

share
the

same

physical
connection
WAN
link
Trunks
MultiVLANs
Quality of Service
to the rescue
Gives
priority
to
Voice
traffic
over
Data
traffic
Two
network layer (IP) QoS
schemes
ToS

and
DiffServ
Type of Service
IP Header
has
ToS field
3 bits
assign a priority:
0-7
0
-
default
and
lowest
priority
7 -
highest
priority
Voice
set to
5
Set ToS
In VoIP device's
configuration file
Global file
or at device
DiffServ

Improved
ToS scheme
Shares IP header ToS/
DSCP
field
6 bits
- priority from
0 - 63
0
- default:
lowest
priority
63
- highest priority
Voice
set to
46
Diff
erentiated
Serv
ices Code Point
VLAN Priority
Switches are
layer 2
devices
Can give
VLANs
priority
when using
Dot1Q
trunks
C
lassification
o
f
S
ervices (
CoS
) field
3 bits - priority of 0-7
Little more
complicated
and leads to
MPLS
IEEE802.1Q
Ethernet frame
QoS
Voice
will
not
breakup during large
data
transfers
Can
control
everything
within
our
LAN
But
NOT
the
WAN traffic
WAN Problem!
Can control
outgoing
WAN traffic
Need a QoS
agreement
with
service provider
for
incoming

Voice traffic
Routers
Some routers
allow
priorities
to be set
to the
physical
LAN ports
ex. DD-WRT or Tomato firmware
for traffic going
to
WAN
A
pplication
L
ayer
G
ateways
Examine the
contents
of traffic
Can assign
priority
to
Voice
PROTOCOLS:
SIP
,
RTP
,
RCTP
,
IAX
,
H323
,
SCCP
...
IEEE802.1p
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