Quality of Service(QoS)

Outline

• Why QoS is important? • What is QoS?• QoS approach.• Conclusion.

Outline

• Why QoS is important? • What is QoS?• QoS approach.• Conclusion.

Why QoS is important?

• Today, network traffic is highly diverse, with the explosive growth of the Internet, most network traffic is IP-based.

• Having a single end-to-end transport protocol is beneficial, because networking equipment became less complex to maintain.

• Traditional transport service of the Internet is best-effort service.

Why QoS is important?

• The IP protocol was originally designed to reliably get a packet to it’s destination with less consideration to the amount of time.

• But now, IP networks must support many different type of applications, and these applications require low latency.– E.g. videoconferencing, VoIP…

• The best-effort IP network introduces a variable and unpredictable amount of delay.

Why QoS is important?

• Today, all data networks are converging on IP transport because the applications have migrated towards being IP-based.

• The converged network mixes different types of traffic, and each with very different requirement.

• So, QoS technologies play a crucial role in a multiservice IP network.

Outline

• Why QoS is important?• What is QoS?• QoS approach.• Conclusion.

What is QoS?

• A broad term used to describe the overall experience a user or application will receive over a network.

• Involves a broad range of technologies, architecture and protocols.

• A special type of connection-oriented routing in witch different connections are assigned different priority.

What is QoS?

• The goal of QoS is to provide preferential delivery service for the applications that need it by ensuring sufficient bandwidth, controlling latency and jitter, and reducing data loss.

What is QoS?

• QoS performance dimensions :– Bandwidth.– Delay.– Jitter.– Loss.

What is QoS?

• Application requirement : Application Bandwidth Sensitivity to :

Delay Jitter Loss

VoIP Low High High Med

Video Conferencing

High High High Med

Streaming Video

High Med Med Med

Streaming Audio

Low Med Med Med

E-mail Low Low Low High

File transfer Med Low Low High

What is QoS?

• Qos is a control mechanism.

Outline

• Why QoS is important?• What is QoS?• QoS approach.• Conclusion.

QoS approach

• Internet Engineering Task Force(IETF) : – Develops and promotes Internet standards.– The goal of the IETF is to make the Internet work

better.

QoS approach

• Integrated Service(IntServ)– Per flow state and processing.

• Differentiated Service(DiffServ)– Per class state and processing.

Integrated Service(IntServ)

• Best-effort service.• Resource Reservation Protocol(RSVP).• Virtual circuit.

Integrated Service(IntServ)

• Advantage– Controlled load service.– Guaranteed service.• With bandwidth, bounded delay, and no-loss

guarantees

• Disadvantage – Many states must be stored in each router.– Works on a small-scale well, but on Internet is not

suitable.

Differentiated Service(DiffServ)

• Since modern data networks carry many different types of traffic.

• Traffic is classified based on priority.• Traffic management mechanisms– Traffic Conditioning Block(TCB).

Traffic Conditioning Block(TCB)

• Classifier : – Differentiated Services Code Points(DSCP).– By many different parameters(source address,

destination address, traffic type..).

• Meter :– Measuring traffic rate.

• Marker :– Mark DSCP.

Traffic Conditioning Block(TCB)

• Per-Hop Behavior(PHB) :– define the packet forwarding properties

associated with a class of traffic.– EF : low delay, lost and jitter, high priority.– AF : median priority.– BF : low priority.

DS Network Architecture

• DS domain :– A group of routers that implement common,

administratively defined DiffServ policies.

• Service Level Agreement(SLA) :– a part of a service contract where the level of

service is formally defined.

• Bandwidth Broker(BB) :– Control the resource in a DS domain.

DS Network Architecture

Differentiated Service(DiffServ)

• Advantage :– Router only use to transport. – Easy to implement.

• Disadvantage :– Does not keep per flow state information, so it

more difficult to support End-to-End QoS.– Because there are no reservations, there is a

possibility that the network can get congested.

Outline

• Why QoS is important?• What is QoS?• QoS approach.• Conclusion.

Conclusion

• Qos is a control mechanism.• Ensuring high-quality performance for critical

application. • Controlling latency and jitter effectively.• Reduce data loss.• QoS can not produce additional bandwidth.