school of information technologies ip quality of service nets3303/3603 weeks 10-11

School of Information Technologies

IP Quality of Service

NETS3303/3603

Weeks 10-11

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Outcomes

• Understanding components of IP QoS– What they do– Why they are used or proposed

• Have knowledge of some case study technologies

• Understanding the relevance to real-time multimedia delivery

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What is QoS ?

• Many definitions in literature

• Comer’s definition:– Bounds on loss, delay, jitter and minimum

throughput that a network guarantees to deliver

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IP QoS

• IP provides only Best Effort service:– No guarantees full stop– No guaranteed packet delivery– No guaranteed time– No guaranteed order

• IP is ignorant of packet content• No “Flows” in IP• Compare telephony network

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QoS

Internet Internet

Network parameters•Packet loss•Delay•Jitter

Getting lost is

easy here honey.

Lost speech:“ing”, “is easy here honey”

Get lost

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QoS

Internet Internet

Network parameters•Packet loss•Delay•Jitter

Getting lost is

easy here honey.

Delay 1000 ms

Where did he go?

Silence

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QoS

Internet Internet

Network parameters•Packet loss•Delay•Jitter – variability in delay

Getting lost is

easy here honey.

Delay 1000 ms

What the

G ettinglos tis easyhere h on ey

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Types of Traffic

• Different applications generate different types of traffic e.g.– Web pages (delay sensitive)– FTP (BW sensitive)– Streamed Media (BW sensitive)– Conversational Multimedia (delay and BW)

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Building blocks

Network Region

Network Region

Network Region

Network Region

End host End host

Edge Router Edge Router

Routers Routers

•End – to – end signalling•Routers: Queuing and Scheduling•Edge Routers: Add admission control•A defined set of rules or classes to request

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Integrated Services (IntServ)

• First QoS proposal for IP• Offers a set of service classes per flow

– Guaranteed Service• Hard guarantees (Conversational MM)

– Controlled Load Service• Same behaviour as lightly loaded BE network (adaptive MM

etc.)

– Best Effort Service• All other types of traffic

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IntServ Functions• Admission control

– Check bw availability and make reservation– For specific QoS, reservation required for new

flow• Resource reSerVation Protocol (RSVP) used

• Forwarding– Base decision on QoS parameters

• Queuing and scheduling discipline– Take account of different flow requirements

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Is there a problem with the per-flow specification?

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Resource Reservation Protocol (RSVP)

• Create notion of flow in IP:– E2E Signalling

• IETF proposal– Resource Reservation Protocol, RSVP

• Allows applications to make reservations

• But only keeps soft-state

• If routing path change, need to re-reserve on new routers!!

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RSVP

• Sender announces meta-info of flow• Receiver app fills in Traffic specification (T-Spec)• Each router: admission control• If requirements met: make reservations

End Host End Host

Router RouterRouter

Can I get?Can I get? Can I get?Can I get?

OKFlow

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Queuing

• Traditional queuing: one queue and FIFO service

• For QoS, need to separate traffic into classes– So can provide different priority to different

classes

• Need to manage the different queues

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Priority Queuing

• K queues– 1 ≤ k ≤ K– Queue k+1 higher prio. than queue k– Higher prio. served first

• Simple implementation• Low processing overhead • No fairness

– low prio. queues can be starved!!

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QoS Router

• Standard QoS Router Components– Routing Policy (rules for classification)– Routing table (Where to send packets)– Input Lines (where packets come in, no queue)– Output queues (where packets wait to be sent)– Classifier (puts packets into queues acc. to

policy)– Scheduler (decides which queue to empty)

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Scheduling

• Generally, the scheduler assigns resources to tasks

• In a computer: divide CPU time to processes

• In a router: divide available BW (output queues) to packets– Operates based on router policy

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Weighted Fair Queuing (WFQ)

• Involves multiples queues• Generalized Round Robin• Each class gets weighted amount of service in

each cycle => enables prioritisation• E.g. 2 queues with weight ratio 1:2 (both queues

full)– 1 2 2 1 2 2 1 2 2 …

• Variant implemented by manufacturers

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Question:Can we do QoS management

without Queuing / Scheduling?

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Differentiated Services (DiffServ)

• A newer QoS framework for IP• IntServ per-flow has scalability problem• Solution: aggregate flows

– Treat classes not individual flows

– Thus, tables kept small

• IP TOS field becomes DSCP– 6 bit identifier of class

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DiffServ domainIngressRouter

EgressRouter

CoreRouter

CoreRouter

Dimensioned to meetIngress router admissioncontrol

PHB PHBPHB

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DiffServ Architecture

Edge/Boundary router:-per-flow traffic management-admission control

Core/Interior router:

- per class traffic management

- queuing and scheduling

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Forwarding (PHB)

• Per Hop Behaviour results in a different observable (measurable) forwarding performance behaviour

• PHB does not specify what mechanisms to use to ensure required behavior

• PHB examples: – Class A gets x% of outgoing link bandwidth over time

intervals– Class A packets leave first before packets from class B

©J.F Kurose and K.W. Ross

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Forwarding (PHB) II

Two PHBs introduced:• Expedited Forwarding: pkt departure rate of a

class equals or exceeds specified rate – c.f. logical link with a minimum guaranteed rate

• Assured Forwarding: 4 classes of traffic– each guaranteed minimum amount of bandwidth

– each class with three drop preference partitions

©J.F Kurose and K.W. Ross

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DiffServ

• Scales well• Provides statistical guarantee only• There are also hybrids of IntServ + DiffServ• Other popular mechanisms outside IP

– Multi-Protocol Label Switching (MPLS)– Better type of tx media such as optical fibre

with wavelength division multiplexed (WDM) systems

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Summary

• IP, no flows, no traffic separation

• Different types of traffic, different needs

• QoS management:– Admission control

– Classification

– Queuing/scheduling

• IntServ and DiffServ

• Supports higher level protocols such as RTP – next!