Chapter 7Packet-Switching NetworksTraffic Management Packet LevelFlow LevelFlow-Aggregate Level

Quan ly lu lngQuan ly lu lng giao thngen giao thng & tin hiu iu khin lung lu lng giao thngMuc ich: ti a hoa lung giao thng vi thi gian tr cho phepPhn quyn u tinXe canh sat, cu thng, KSQS,Lung ring cho xe busXe tai khng vao thanh ph ban ngay

Quan ly lu lng packetC cu ghep va truy nhp iu khin dong lu lng packetMuc ich: s dung mt cach co hiu qua tai nguyn mang va am bao QoSPhn quyn u tinCac goi khi phuc li (fault-recovery packets)Lu lng thi gian thc (real-time traffic)Lu lng doanh nghip (Enterprise (high-revenue) traffic)Lu lng bng thng cao (High bandwidth traffic)

Phn loai quan ly lu lngDa trn cu truc cua lu lng va thi gian co th chia quan ly lu lng thanh 3 mcPacket LevelLin quan n thu tuc xp hang (queueing) & inh trinh (scheduling) cac goi tai cac im ghepXac inh phm cht cho cac packets trong mt khoang thi gian ngn (microseconds) Flow LevelQuan ly cac dong lu lng va phn b tai nguyn am bao vic phn phi QoS (t msec n sec)Phi hp cac lung lu lng theo tai nguyn sn co; iu khin lung Flow-Aggregate Levelinh tuyn cac lung lu lng tng hp qua mang tn dung hiu qua tai nguyn va ap ng cac cp dich vuTraffic Engineering, (minutes to days)

Chapter 7Packet-Switching NetworksTraffic Management Packet LevelFlow LevelFlow-Aggregate Level

c im packet switchPacket switch nh mt node Packet ti demultiplexed, switched, va remultiplexed thanh lung raPacket swicth co buffer tranh mt goi khi co cac goi ti ng thing i cua packets qua mang c m hinh nh mt chui cua cac h thng xp hang

End-to-End QoSPacket i qua mang gp phai tr va tht thoat tai cac im ghepPhm cht E2E la tich luy cua phm cht tai tng chngTng tr gia E2E la tng cua tr tai mi h thngTr trung binh E2E la tng cua tr trung binh thanh phn Giam tr tai mi h thng cho phep am bao tr E2E di mt bin trn nht inh

QoS parametersTrJitter: bin ng v tr goi chnh lch gia min delay va max delayPacket loss: xay ra khi packet ti nhng khng co bufferMang h tr a dich vu vi cac yu cu khac nhau v QoSam bao bng cach thc hin cac chin lc:Queueing sheduling: iu khin tc bit truyn dn cung cp cho cac dong thng tin khac nhauQueueing management: quan ly xp hang cua cac packet tai h thng ch

Cac chin lc xp hangFIFO va Priority QueuesFair Queueing: Xp hang cng bngWeighted fair queueing: xp hang cng bng co trong sRandom Early Detection: Phat hin sm ngu nhin

FIFO QueueingGiai phap inh trinh xp hang n gian nhtTruyn theo trinh t ti: First-In, First-OutTt ca cac lung packet chia se chung bufferQui tc buffering: loai bo cac packet ti nu buffer y (Alternative: loai bo ngu nhin; loai bo packet cu)Delay va loss phu thuc vao interarrival time & packet lengthInterarrival time hoc packet length bin ng nhanh se lam cho cac goi xp hang dai tai cac packet phm cht bi suy giam

FIFO Queueing (2)i x vi cac goi nh nhauKhng th cung cp QoS khac nhau cho cac lung packet khac nhauSa i FIFO queueing management cung cp cac c tinh mt goi khac nhau cho cac loai lu lng khac nhauFIFO Queueing with Discard PriorityHead of line (HOL) priority queueingDue date scheduling

FIFO Queueing with Discard PriorityPackets of low priority experience higher packet loss

HOL Priority QueueingMi priority class co mt buffer ringKhi ng truyn ri, packet u hang (HOL) cua hang co u tin cao nht (khng rng) c chon Kich thc buffer cua cac class co th la chon theo yu cu khac nhau v xac sut liLung co u tin cao phai ch ngn hn

HOL Priority QueueingNhc im:Khng cho phep am bao mt mc truy nhp ng truyn nht inh cho cac class u tin thpKhng phn bit c cac lung cung cp u tint bin tng hang u tin cao co th lam cho hang u tin thp bi bao hoa

inh trinh theo hanXp xp packet vao buffer theo theo priority tagPriority tagPriority class + arrival timeDue date (han)Packets yu cu tr nho co due date smPackets khng co yu cu v tr co due date lu hoc bng v cung

Fair QueueingCung cp truy nhp cng bng ti bng thng truyn dnMi lung co mt buffer ring: t c xac sut mt goi khac nhauBng thng C bits/sec c phn b u cho cac hang i khng trngtransmission rate = C / n(t), where n(t)=# non-empty queues

Fair QueueingLung packet trong buffer co th coi nh lung cht long chay lin tuc m hinh nh h thng dong chay cht long Thc t khng th thc hin c chia u dung lngGiai phap phuc vu mi hang tun t 1bit/ln (round-robin)Tuy nhin, co kho khn v x ly ong khung lai u ra Giai phap ATM: phuc vu 1 packet/ln

Fluid flow vs Packet flowS dung m hinh dong cht long khng d dang trong trng hp cac goi co dai khac nhauGia thit cac buffer c phuc vu 1 packet/lnKich thc packet lung 1 gp i lung 2Sau thi gian dai lung 2 se chim hai ln bng thng so vi lung 1Giai phap: truyn cac packet sao cho thi gian kt thuc ging trng hp dong cht long

Packet-by-Packet Fair QueueKhi packet ti buffer, tinh toan thi gian kt thuc theo h thng dong cht longGan thi gian kt thuc cho packet (finish tag)Khi kt thuc truyn mt packet, chon packet co finish tag nho nht trong cac buffer truynTinh toan finish tag nh th nao?

Bit-by-Bit Fair QueueingGia thit n lung, n hang1 round = 1 cycle phuc vu tt ca n queuesMi hang ch c ly 1 bit/cycle 1 round = # active queuesRound number = s cycle phuc vu a kt thucNu packet n hang ch ri:Finishing time = round number + packet size [bits]Nu packet n hang ch bn: Finishing time = finishing time of last packet in queue + packet size

Differential Service: Nu mt lung lu lng nhn bng thng gp i bng thng cua lung thng thng, thi thi gian kt thuc bng 1/2

Computing the Finishing TimeF(i,k,t) = thi gian kt thuc cua packet th k n lung i vao thi im tP(i,k,t) = kich thc cua packet th k n lung i vao thi im tR(t) = s th t round tai tFair Queueing: F(i,k,t) = max{F(i,k-1,t), R(t)} + P(i,k,t)Weighted Fair Queueing: F(i,k,t) = max{F(i,k-1,t), R(t)} + P(i,k,t)/wiGeneralize so R(t) continuous, not discreteR(t) tng theo tc ti l nghich vi n(t)

Weighted Fair QueueingTrng hp cac ngi dung co yu cu khac nhauMi ngi dung co mt buffer vi mt trong s (weight) xac inh mc chia se bng thngNu buffer 1 co weight 1, buffer 2 co weight 3Khi ca hai buffer khng trngBuffer 1 nhn 1/(1+3) =1/4 bng thngBuffer 2 nhn 3/(1+3)= 3/4 bng thng

Buffer 1at t=0Buffer 2at t=01t12Fluid-flow system:packet from buffer 1served at rate 1/4;

Packet from buffer 1 served at rate 1Packet from buffer 2served at rate 3/401t12Packet from buffer 1 served at rate 1Packet frombuffer 2 served at rate 1Packet frombuffer 1 waiting0Packet-by-packet weighted fair queueing:buffer 2 served first at rate 1;then buffer 1 served at rate 1

Packetized GPS/WFQCompute packet completion time in ideal systemadd tag to packetsort packet in queue according to tagserve according to HOL

WFQ and Packet QoSWFQ tao c s cung cp QoS trong packet networksThc hin vi tc cao, ti 10 Gbps va co th cao hnWFQ phai kt hp vi cac c cu khac cung cp end-to-end QoS

Buffer ManagementPacket drop strategy: Which packet to drop when buffers fullFairness: protect behaving sources from misbehaving sourcesAggregation: Per-flow buffers protect flows from misbehaving flowsFull aggregation provides no protectionAggregation into classes provided intermediate protectionDrop priorities: Drop packets from buffer according to prioritiesMaximizes network utilization & application QoSExamples: layered video, policing at network edgeControlling sources at the edge

Early or Overloaded Drop

Random early detection:Loai bo packet nu trung binh ngn han cua hang vt qua ngngXac sut loai bo packet tng tuyn tinh vi dai hang chanh du cac packet vi pham Tng hiu nng hp tac cua cac ngun TCPTng xac sut mt goi cua cac ngun hoat ng khng theo qui tc (misbehaving)

Random Early Detection (RED)Giam tc phat packets cua TCP theo tc nghen cua mangEarly drop: loai bo packets trc khi buffer yRandom drop: lam cho mt s ngun giam tc trc mt s ngun khac, lam ch tc tng hp giam dn

Algorithm:Duy tri trung binh cua dai hang QavgNu Qavg < minthreshold, thut toan khng kich hoatNu Qavg > maxthreshold, loai bo packetNu maxthreshold > Qavg > minthreshold, loai bo packet theo xac sutCac lung truyn nhiu packets d chiu anh hng cua mt packet hn

Packet Drop Profile in RED

Chapter 7Packet-Switching NetworksTraffic Management at the Flow Level

Tc nghen xay ra khi co t lu lng lam qua tai tai nguyn mangCac giai phap iu khin Tc nghen: Giai phap ngn nga: inh trinh & t ch Giai phap Phan ng: Phat hin & iu tit/Loai bo

Hiu qua ly tng cua iu khin lung: Tai nguyn c s dung hiu qua ti mc dung lng cho phep

Open-Loop ControlPhm cht mang c am bao cho tt ca cac lung lu lng a c chp nhn vao mangNgn tc nghen xay ra bng cach am bao la lung lu lng do ngun tao ra khng gy suy giam phm cht mang di QoS cho trcKhng s dung thng tin phan hi i pho vi tc nghenCac c cu ChinhAdmission ControlPolicingTraffic ShapingTraffic Scheduling

Admission ControlBan u c phat trin cho VC packet network, nhng cung a c xut cho datagram networkAdmission control la mt chc nng mang thc hin tinh toan yu cu v tai nguyn (bng thng, buffer) cua mt lung miXac inh xem tai nguyn trn ng co cho phep hay khngNgun khi tao lung mi cn xin giy phep t AC entityACE quyt inh xem lung c chp nhn hay t chiChp nhn nu QoS (max delay, loss probability..) c am bao, nu khng t chi xac inh cn bit yu tham s lu lng (peak rate, average rate, max burst size) va yu cu QoS cua lung xac inh contract gia ngun va mang

Admission ControlAC entity tinh toan bandwidth cho lungEffective bandwidth: b/w aver. and max rateTc b bit yu cu bi mt ngun thng tin VBR

PolicingMang giam sat va cng ch cac lung lu lng lin tuc sau khi c chp nhn vao mang theo hp ng lu lngKhi co mt packet vi pham hp ng, mang co th loai bo hoc anh du packet o thanh packet co u tin thpNu xay ra tc nghen, cac goi c anh du se bi loai bo trcLeaky Bucket Algorithm la thut toan ph bin nht s dung policing mechanismBucket co tc poll xac inh theo tc trung binh a thoa thunBucket co su nht inh ap ng cac bin ng v tc tiGoi n c goi la phu hp nu no khng lam trao x

Leaky Bucket algorithm co th s dung khng ch tc ti cua dong packett: X = la dung lng bucket tai thi im packet phu hp ti cui cungt: ta thi gian ti cua packet phu hp cui cung = mc do bucket

Leaky Bucket (Contd)

Leaky Bucket (Contd)Bucket

Leaky Bucket (Contd)BucketEmpty

Leaky Bucket (Contd)BucketHole

Leaky Bucket (Contd)BucketWaterHole

Leaky Bucket (Contd)

Leaky Bucket (Contd)Drip

Leaky Bucket (Contd)

Leaky Bucket (Contd)

Leaky Bucket (Contd)

Leaky Bucket (Contd)Constantrate stream ofdrips, all nicelyspaced, periodic

Leaky Bucket (Contd)Constantrate stream ofdrips, all nicelyspaced, periodicStorage areafor dripswaiting to go

Leaky Bucket AlgorithmTc do: 1 packet per unit time

L+I = Bucket Depth

I = chi s tng mi ln ti, (interarrival time danh inh)Interarrival timeCurrent bucketcontentarriving packetwould cause overflowemptyNon-emptyconforming packet

Leaky Bucket ExampleI = 4 L = 6Non-conforming packets not allowed into bucket & hence not included in calculations

Policing ParametersT = 1 / peak rateMBS = maximum burst sizeI = nominal interarrival time = 1 / sustainable rate

Dual Leaky BucketDual leaky bucket to police PCR, SCR, and MBS:

Traffic ShapingNetworks police the incoming traffic flowTraffic shaping c s dung am bao lung lu lng tun theo cac tham s cua leaky bucketNetworks can shape their traffic prior to passing it to another network

Leaky Bucket Traffic ShaperBuffer incoming packetsPlay out periodically to conform to parametersSurges in arrivals are buffered & smoothed outPossible packet loss due to buffer overflowToo restrictive, since conforming traffic does not need to be completely smooth

Token Bucket Traffic ShaperToken rate regulates transfer of packetsIf sufficient tokens available, packets enter network without delayK determines how much burstiness allowed into the networkAn incoming packet must have sufficient tokens before admission into the network

Token Bucket Shaping EffectThe token bucket constrains the traffic from a source to be limited to b + r t bits in an interval of length tb + r t

Packet transfer with Delay GuaranteesToken ShaperBit rate > R > re.g., using WFQAssume fluid flow for informationToken bucket allows burst of b bytes 1 & then r bytes/secondSince R>r, buffer content @ 1 never greater than b byteThus delay @ mux < b/RRate into second mux is r

Delay Bounds with WFQ / PGPSAssume traffic shaped to parameters b & rschedulers give flow at least rate R>r H hop pathm is maximum packet size for the given flowM maximum packet size in the networkRj transmission rate in jth hopMaximum end-to-end delay that can be experienced by a packet from flow i is:

Scheduling for Guaranteed ServiceSuppose guaranteed bounds on end-to-end delay across the network are to be providedA call admission control procedure is required to allocate resources & set schedulersTraffic flows from sources must be shaped/regulated so that they do not exceed their allocated resourcesStrict delay bounds can be met

Current View of Router Function

Closed-Loop Flow ControlCongestion controlfeedback information to regulate flow from sources into networkBased on buffer content, link utilization, etc.Examples: TCP at transport layer; congestion control at ATM levelEnd-to-end vs. Hop-by-hopDelay in effecting controlImplicit vs. Explicit FeedbackSource deduces congestion from observed behaviorRouters/switches generate messages alerting to congestion

End-to-End vs. Hop-by-Hop Congestion Control

Traffic EngineeringManagement exerted at flow aggregate levelDistribution of flows in network to achieve efficient utilization of resources (bandwidth)Shortest path algorithm to route a given flow not enoughDoes not take into account requirements of a flow, e.g. bandwidth requirementDoes not take account interplay between different flowsMust take into account aggregate demand from all flows

Shortest path routing congests link 4 to 8Better flow allocation distributes flows more uniformly