Bjorn Landfeldt, The University of Sydney 1 NETS3303 Networked Systems.

Bjorn Landfeldt, The University of Sydney

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NETS3303Networked Systems


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Section 2 IP QoS


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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 MM delivery


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IP QoS

• Today’s Outline– What is QoS?– Types of traffic– IntServ– Signalling– Queuing and Scheduling– DiffServ


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QoS ?

• Many definitions in literature

• My definition is:– “A perceived level of quality of a service or

function in relation to the wanted or expected level of quality”

• In this course, application behaviour depending on network performance


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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


Getting lost is

easy here honey.

Delay 1000 ms

Where did he go?

Silence


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QoS

Internet Internet


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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IntServ

• Provides a set of service classes per flow– Guaranteed Service

• Hard guarantees (Conversational MM)

– Controlled Load• Same behaviour as lightly loaded BE network

(adaptive MM etc.)

– Best Effort• All other types of traffic


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Is there a problem with the per-flow specification?


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RSVP

• Create notion of flow:– E2E Signalling

• IETF proposal– Resource Reservation Protocol, RSVP

• Allows Applications to make reservations


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RSVP

• 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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Why is signalling receiver-based?


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Admission Control

• Token Bucket (rate r, size b)– Start with full bucket– If enough tokens in bucket accept packets and

remove tokens– Tokens keep filling with rate r


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Queuing

• Traditional queuing: FIFO, one input one output

• Need to separate traffic into classes

• Need to give different priority to different classes

• Need to manage the different queues


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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 com 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

• The scheduler assigns resources to tasks

• In a computer: divide CPU runtime to processes

• In a router: divide available BW (output queues) to packets

• Operates based on router policy


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FCFS

• Work Conserving (if packet waiting, serve)• Klienrock Conservation Law

Cqn

N

nn

=∑=1ρ

If delay for one flow is lowered, the delay for one or more other flows must increase

ρ = link utilisationq = mean scheduler delayC = a constant


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Non Work Conserving

• Scheduler can be idle even if packets waiting

• Switches packets to– The right destination– At the right time

• Reduces jitter

• Makes traffic predictable


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Scheduling Requirements

• Easy to implement– Simple makes fast– Few states allows HW

implementation• High speed routing

• Fairness– Local means global– Protect from other

misbehaving flows

• Performance bounds– Per flow bounds

• Deterministic guaranteed)

• Statistical

– Data rate, jitter, delay, loss

• Admission Control– Easy to implement

– efficient


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Scheduling choices

• Priority levels– How many– Serve higher priority

queues first? (can cause starvation)

• Work conserving?– Delay/jitter control

required?– Extra cost acceptable?

• Flow Aggregation– Granularity?

• Per flow• Per application• Per terminal

• Per queue policy– FCFS?– Look inside each

packet and decide?– Performance/overhead


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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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WFQ

• Round robin scheme – Estimate time to send packet (finish number)– Tag packet with finish number– Serve packet with smallest finish number

• Regardless of queue

• Weights can be assigned to enable prioritisation

• Implemented by manufacturers


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CBQ

• Assigns fractions of BW to class nodes

• Values minimum• Nodes can borrow

unused BW• Priority to flows

within a class

100 %

40 %

20 %

60 %

40 %

Root

X Y

RT NRT


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Question:Can we do QoS

management without Queuing / Scheduling?


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DiffServ

• IntServ per-flow 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 domain

IngressRouter

EgressRouter

CoreRouter

CoreRouter

Dimensioned to meetIngress router admissioncontrol

PHB PHBPHB


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DiffServ PHB

• Expedited Forwarding, EF– Highest priority– WFQ suitable

• Assured Forwarding, AF– Three drop probability classes– Graceful behaviour


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What if two DiffServ domains have

different definitions of what a DSCP translates to?


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The QoS stair

A DCB

QoSLevel

Domain


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DiffServ:Scales wellStatistical guarantee only


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Summary

• IP, no flows, no traffic separation• Different types of traffic, different needs• QoS management:

– Classification– Signalling– Admission control– Queuing/scheduling

• IntServ, DiffServ, RSVP


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Reading

• Deeper understanding:– RFCs 2205-2216, 2474-2475


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Other areas• MPLS

• VLANS

• Working Intserv and Diffserv together

• QoS in 3G, bearer services, signalling etc.

• Service Level Agreements

• Billing and business models

• Fibre, channel allocations DWDM etc.

Bjorn Landfeldt, The University of Sydney 1 NETS3303 Networked Systems.

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