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Voice Over Internet Protocol (VoIP)
Presentation 10 – Quality
of Service (QoS)
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved
Objectives
At the end of this presentation,
you will be able to:
2
 List
four different definitions of the term
Quality of Service (QoS)
 List
three IETF initiatives related to QoS.
 Explain
the basic idea behind Integrated
Services (IntServ).
 Explain
the basic idea behind
Differentiated Services (DiffServ).
 Explain
the basic idea behind MultiProtocol Label Switching (MPLS).
3
General QoS Definitions

Networking – Refers to the probability of the network
meeting specified conditions.

Networking – Refers to how well a logical or physical
connection is performing.

Telephony – Indicates how well a telephone
connection is performing.

Telephony – Refers to the lack of noise, extraneous
tones, echoes, etc. on a given circuit. Includes factors
like sufficient loudness, appropriate clarity, etc.
4
QoS as Related to VoIP
 The
capability for preferential handling
of different types of packets.
 Measurable,
objective characteristics
of network performance.
 Did
the experience meet your
expectations?
5
Ways to Insure QoS
– Provide enough
bandwidth, processing power, etc. to
insure that your packets get through
even at the busiest of times.
 Over-engineer
 Make
reservations ahead of time
 Receive
preferential treatment
6
IETF Initiatives
 Differentiated
 Integrated
Services (DiffServ)
Services (IntServ)
 Multiprotocol
Label Switching
(MPLS)
7
Differentiated Services
(DiffServ)
 Takes
the preferential treatment
approach to QoS.
 It
provides a mechanism whereby
different types of network traffic can
be divided into classes of service
(CoS).
8
Class of Service (CoS)
 Indicates
the degree of preferential
treatment or priority given to a packet.
 Classes:
 Expedited
 Assured
Forwarding (EF)– Highest Priority
Forwarding (AF)
 Class
1
 Class 2
 Class 3
 Class 4
9
EF
AF-1
AF-2
AF-3
AF-4
10
EF
AF-1
AF-2
AF-3
AF-4
11
EF
AF-1
AF-2
AF-3
AF-4
12
Nature of the Priority
absolute – EF packets are not
automatically sent to the head of the
line.
 Not
– EF packets are given a
higher probability of being sent to the
head of the line.
 Probabilistic
13
EF
AF-1
AF-2
AF-3
AF-4
14
Differentiated Services Code
Point (DSCP)
 Included
in the Header of IP packets.
 A 6-bit
code that can be used to assign
a class of service (CoS) to a packet.
 Replaces
the old and rarely used ToS
field.
15
The IP Header
IP Header
Ver IHF
ToS
Length
TTL
Protocol
Check Sum
Source Address
Destination Address
DSCP
16
Per Hop Behavior (PHB)

A set of behaviors from which an application can
select.

The node’s behavior can be customized on the fly
to make it more appropriate for a particular class
of service.

The node’s behavior can be tailored to increase its
probability of providing no worse than a specified
delay, a specified level of jitter, a specified
bandwidth, etc.
17
DiffServ Review

“Rob Peter to pay Paul” approach.

Different types of packets are given
different priorities.

The higher priority packets are given
preferential treatment, often at the expense
of lower priority packets.

While it can be used for any application, it
is particularly valuable with VoIP because
of the time-sensitive nature of real-time
packets.
18
Integrated Services (IntServ)
 A series
of protocols developed by
IETF to integrate real-time and voice,
video into the classical data streams.
 QoS
Strategy: Find and reserve the
required resources needed for a
particular level of QoS.
19
Resource Reservation Protocol
(RSVP)

Allows an application (say, VoIP) to request
minimum specified resources throughout
the path that the session will use.

“Hey, I am about to call ______. Can you
give me a bandwidth of X-kbps, with a
delay no greater than Y-milliseconds, and
jitter no worse than Z- milliseconds?”
20
Sender
RSVP
PATH
Router
Router
Router
Recipient
RESV
21
The RSVP Compliant Router
 Requires
an RSVP Daemon.
Control – Does the node
have the resources available?
 Admission
Control – Does the user have
permission to make the reservation?
 Policy
22
Multi-Protocol Label Switching
(MPLS)
 QoS
Strategy: Increase packet
forwarding performance and path
selection flexibility.
 Adds
a “label” between the data linklayer and the network layer headers.
23
Ethernet/IP Packet
14-Byte
Ethernet
Header
20-Byte
IP Header
IP Data
MPLS
Label
24
MPLS Network
Label
Edge
Router
(LER)
Label
Switch
Routers
(LSR)
25
IETF Initiatives
 Differentiated
 Integrated
Services (DiffServ)
Services (IntServ)
 Multiprotocol
Label Switching
(MPLS)
26
Differentiated Services
(DiffServ)
A service architecture that can select
network node behavior, appropriate to
the class of service, based on the
Differentiated Services field in the
header of the IP datagram.
27
Integrated Services
(IntServ)
A service architecture that can find and
reserve resources at each network node
in its path appropriate to the class of
service being transported for as long as
needed to complete a session.
28
Multi-Protocol Label Switching
(MPLS)
A service architecture that makes
forwarding decisions based solely on a
label that is added between the datalink and network headers.
29
Voice Over Internet Protocol (VoIP)
End
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved