Bjorn Landfeldt, The University of Sydney 1 NETS3303 Networked Systems

Bjorn Landfeldt, The University of Sydney 2 Section 2 IP QoS

Bjorn Landfeldt, The University of Sydney 3 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

Bjorn Landfeldt, The University of Sydney 4 IP QoS Today’s Outline –What is QoS? –Types of traffic –IntServ –Signalling – Queuing and Scheduling –DiffServ

Bjorn Landfeldt, The University of Sydney 5 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

Bjorn Landfeldt, The University of Sydney 6 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

Bjorn Landfeldt, The University of Sydney 7 QoS Internet Network parameters Packet loss Delay Jitter Getting lost is easy here honey. Lost speech: “ing”, “is easy here honey” Get lost

Bjorn Landfeldt, The University of Sydney 8 QoS Internet Network parameters Packet loss Delay Jitter Getting lost is easy here honey. Delay 1000 ms Where did he go? Silence

Bjorn Landfeldt, The University of Sydney 9 QoS Internet Network parameters Packet loss Delay Jitter Getting lost is easy here honey. Delay 1000 ms What the G ettinglos tis easyhere h on ey

Bjorn Landfeldt, The University of Sydney 10 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)

Bjorn Landfeldt, The University of Sydney 11 Building blocks Networ k Region End host Edge Router Routers End – to – end signalling Routers: Queuing and Scheduling Edge Routers: Add admission control A defined set of rules or classes to request

Bjorn Landfeldt, The University of Sydney 12 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

Bjorn Landfeldt, The University of Sydney 13 Is there a problem with the per-flow specification?

Bjorn Landfeldt, The University of Sydney 14 RSVP Create notion of flow: –E2E Signalling IETF proposal –Resource Reservation Protocol, RSVP Allows Applications to make reservations

Bjorn Landfeldt, The University of Sydney 15 RSVP App fills in Traffic specification (T-Spec) Each router: admission control If requirements met: make reservations End Host Router Can I get? OK Flow

Bjorn Landfeldt, The University of Sydney 16 Why is signalling receiver-based?

Bjorn Landfeldt, The University of Sydney 17 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

Bjorn Landfeldt, The University of Sydney 18 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

Bjorn Landfeldt, The University of Sydney 19 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)

Bjorn Landfeldt, The University of Sydney 20 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

Bjorn Landfeldt, The University of Sydney 21 FCFS Work Conserving (if packet waiting, serve) Klienrock Conservation Law If delay for one flow is lowered, the delay for one or more other flows must increase ρ = link utilisation q = mean scheduler delay C = a constant

Bjorn Landfeldt, The University of Sydney 22 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

Bjorn Landfeldt, The University of Sydney 23 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

Bjorn Landfeldt, The University of Sydney 24 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

Bjorn Landfeldt, The University of Sydney 25 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

Bjorn Landfeldt, The University of Sydney 26 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

Bjorn Landfeldt, The University of Sydney 27 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 RTNRT

Bjorn Landfeldt, The University of Sydney 28 Question: Can we do QoS management without Queuing / Scheduling?

Bjorn Landfeldt, The University of Sydney 29 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

Bjorn Landfeldt, The University of Sydney 30 DiffServ domain Ingress Router Egress Router Core Router Core Router Dimensioned to meet Ingress router admission control PHB

Bjorn Landfeldt, The University of Sydney 31 DiffServ PHB Expedited Forwarding, EF –Highest priority –WFQ suitable Assured Forwarding, AF –Three drop probability classes –Graceful behaviour

Bjorn Landfeldt, The University of Sydney 32 What if two DiffServ domains have different definitions of what a DSCP translates to?

Bjorn Landfeldt, The University of Sydney 33 The QoS stair ADCB QoS Level Domain

Bjorn Landfeldt, The University of Sydney 34 DiffServ: Scales well Statistical guarantee only

Bjorn Landfeldt, The University of Sydney 35 Summary IP, no flows, no traffic separation Different types of traffic, different needs QoS management: –Classification –Signalling –Admission control –Queuing/scheduling IntServ, DiffServ, RSVP

Bjorn Landfeldt, The University of Sydney 36 Reading Deeper understanding: –RFCs ,

Bjorn Landfeldt, The University of Sydney 37 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.