Voice Over Internet Protocol (VoIP)

Copyright © 2006 Heathkit Company, Inc. All Rights Reserved

Presentation 10 – Quality of Service (QoS)

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Objectives

At the end of this presentation, you will be able to:

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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 Multi-Protocol Label Switching (MPLS).

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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.

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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?

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Ways to Insure QoS

Over-engineer – Provide enough bandwidth, processing power, etc. to insure that your packets get through even at the busiest of times.

Make reservations ahead of time

Receive preferential treatment

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IETF Initiatives

Differentiated Services (DiffServ)

Integrated Services (IntServ)

Multiprotocol Label Switching (MPLS)

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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).

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Class of Service (CoS)Indicates the degree of preferential

treatment or priority given to a packet.

Classes: Expedited Forwarding (EF)– Highest Priority Assured Forwarding (AF)

Class 1Class 2Class 3Class 4

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EF AF-1 AF-2 AF-3 AF-4

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EF AF-1 AF-2 AF-3 AF-4

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EF AF-1 AF-2 AF-3 AF-4

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Nature of the Priority

Not absolute – EF packets are not automatically sent to the head of the line.

Probabilistic – EF packets are given a higher probability of being sent to the head of the line.

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EF AF-1 AF-2 AF-3 AF-4

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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.

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The IP Header

Source Address

Destination Address

IP Header

Length

Check SumTTL Protocol

ToSVer IHF

DSCP

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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.

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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.

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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.

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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?”

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Router Router Router

Sender

Recipient

RSVPPATH

RESV

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The RSVP Compliant Router

Requires an RSVP Daemon.

Admission Control – Does the node have the resources available?

Policy Control – Does the user have permission to make the reservation?

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Multi-Protocol Label Switching (MPLS)

QoS Strategy: Increase packet forwarding performance and path selection flexibility.

Adds a “label” between the data link-layer and the network layer headers.

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14-ByteEthernet Header

20-ByteIP Header

IP Data

Ethernet/IP Packet

MPLSLabel

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MPLS Network

Label Edge Router(LER)

Label Switch Routers

(LSR)

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IETF Initiatives

Differentiated Services (DiffServ)

Integrated Services (IntServ)

Multiprotocol Label Switching (MPLS)

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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.

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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.

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Multi-Protocol Label Switching (MPLS)

A service architecture that makes forwarding decisions based solely on a label that is added between the data-link and network headers.

Voice Over Internet Protocol (VoIP)

Copyright © 2006 Heathkit Company, Inc. All Rights Reserved

End