Chapter 7 Lecture Presentation

Bai giangMang Vin thng Trn Xun NamKhoa V tuyn in tHoc vin Ky thut Qun s 13/20/2013 9:16:33 AMBi 6Packet-Switching NetworksRouting in Packet NetworksShortest Path Routing

23/20/2013 9:16:33 AM2Bai 6Packet-Switching NetworksRouting in Packet Networks

3123456Node (switch or router)inh tuyn trong Packet NetworksCo 3 tuyn (routes) t 1 ti 6:1-3-6, 1-4-5-6, 1-2-5-6Tuyn nao tt nht?Tr nho nht? S chng it nht? Bng thng ln nht? Chi phi thp nht? Tin cy nht?44Yu cu v thut toan inh tuynap ng nhanh khi co thay iCu hinh hay bng thng, nghen Xac inh nhanh cac router tao nn tp hp cac tuynTi uMc s dung tai nguyn, dai ng Manh (robustness)Lam vic c trong iu kin tai cao, nghen mach, hong hoc thit bi, trin khai nhm.n gianThc hin phn mm hiu qua, tai x ly nho55inh tuyn Tp trung hay Phn taninh tuyn Tp trungNut trung tm xac inh tt ca cac tuynTt ca thng tin trang thai c truyn v nut trung tmGp phai vn thich nghi vi thay i cu hinh thng xuynKha nng m rng khoinh tuyn Phn tanCac router xac inh tuyn s dung thut toan phn tanThng tin trang thai trao i bi cac routersThich nghi vi cu hinh va cac thay i khacM rng tt hn

6inh tuyn Tinh va inh tuyn nginh tuyn TinhThit lp nhn cng, khng thay i; yu cu quan triHoat ng khi lu lng xac inh trc & mang n gianS dung bo qua mt s tuyn do thut toan ng tinh tuyn ngThich nghi vi thay i v trang thai mangT ngTinh toan tuyn da trn thng tin trang thai mang nhn c

7123456ABCD15237185423652Switch or routerHostVCIinh tuyn trong Virtual-Circuit Packet NetworksTuyn xac inh trong qua trinh thit lp kt niBang inh tuyn trong switches thc hin chuyn tip theo tuyn a chon88Incoming OutgoingNode VCI Node VCI A 1 3 2 A 5 3 3 3 2 A 1 3 3 A 5Incoming OutgoingNode VCI Node VCI 1 2 6 7 1 3 4 4 4 2 6 1 6 7 1 2 6 1 4 2 4 4 1 3Incoming OutgoingNode VCI Node VCI 3 7 B 8 3 1 B 5 B 5 3 1 B 8 3 7Incoming OutgoingNode VCI Node VCI C 6 4 3 4 3 C 6Incoming OutgoingNode VCI Node VCI 2 3 3 2 3 4 5 5 3 2 2 3 5 5 3 4Incoming OutgoingNode VCI Node VCI 4 5 D 2 D 2 4 5Node 1Node 2Node 3Node 4Node 6Node 5Bang inh tuyn trong VC Packet NetworksExample: VCI from A to DFrom A & VCI 5 3 & VCI 3 4 & VCI 4 5 & VCI 5 D & VCI 299 2 2 3 3 4 4 5 2 6 3Node 1Node 2Node 3Node 4Node 6Node 5 1 1 2 4 4 4 5 6 6 6 1 3 2 5 3 3 4 3 5 5Destination Next node 1 1 3 1 4 4 5 5 6 5 1 4 2 2 3 4 4 4 6 6 1 1 2 2 3 3 5 5 6 3Destination Next nodeDestination Next nodeDestination Next nodeDestination Next nodeDestination Next nodeBang inh tuyn trong Datagram Packet Networks10100000 0111 1010 11010001 0100 1011 11100011 0101 1000 11110011 0110 1001 1100R1125430000 1 0111 1 1010 1 0001 4 0100 4 1011 4 R2ia chi khng phn cp va inh tuynKhng co quan h gia cac ia chi gn nhauBang inh tuyn cn 16 s11110000 0001 0010 00110100 0101 0110 01111100 1101 1110 11111000 1001 1010 1011R1R21254300 1 01 3 10 2 11 300 3 01 4 10 3 11 5ia chi co Phn cp va inh tuynCac tip u chi thi mang tram ni tiBang inh tuyn chi cn 4 s1212inh tuyn c bitanh tran (Flooding)Hu ich khi thit lp mangHu ich khi lan truyn thng tin ti cac nut

anh lch (Deflection Routing)C inh, thu tuc inh tuyn t trcKhng tng hp tuyn13FloodingGi mt packet ti tt ca cac nut trong mangKhng co bang inh tuynS dung khi cn quang ba packet ti tt ca cac nut (VD: lan truyn thng tin trang thai link)Giai phapGi packet ti tt ca cac ports tr port tiS lng packet truyn tng theo ham mu14123456anh tran t Nut 1: truyn trn Chng 1 3 packets 1515123456anh tran t Nut 1: truyn trn Chng 2 7 packets1616123456anh tran t Nut 1: truyn trn Chng 3 15 packets1717Flooding Gii hanS packets truyn sau mi chng tng theo ham mu, co th gy tc nghen mangGiai phap gii han s packetsTrng Time-to-Live mi packet gii han s chng ti mt ng kinh nht inhMi switch b sung ID cua no trc khi flooding; loai bo truyn lpTram ngun t s th t mi packet; switch ghi lai ia chi ngun va s th t va loai bo truyn lp18Deflection RoutingNut mang chuyn packets ti cng la chon (prefferd port)Nu cng la chon (preferred port) bn, anh lch packet ti port khacLam vic tt vi cac cu hinh thng thng (regular topology)Mang Manhattan streetMang vung cua cac nutNut c ky hiu (i,j) Hang chay mt chiuCt chay 1 chiuHoat ng khng cn buffer (bufferless) xut cho mang optical packet

19/960,00,10,20,31,01,11,21,32,02,12,22,33,03,13,23,3Tunnel from last column to first column or vice versa20200,00,10,20,31,01,11,21,32,02,12,22,33,03,13,23,3busyExample: Node (0,2)(1,0)2121Chapter 7Packet-Switching NetworksShortest Path Routing

223/20/2013 9:16:17 AMShortest Paths & RoutingCo nhiu ng ni ngun bt ky ti ich bt kyinh tuyn lin quan n vic chon ra ng s dung thc hin mt chuyn tip packetCo th gn mt gia tri chi phi hay c ly cho mt tuyn ni hai nut manginh tuyn tr thanh bai toan tim ng ngn nht (shortest path problem) 23Routing MetricsLa phng tin o mong mun cua mt ng (path) dai ng (Path Length) = tng chi phi hay c lyCac ai lng o (metrics) co th S chng (Hop count): la ai lng th (rough) v tai nguyn s dung tin cy (Reliability): kha dung cua tuyn; BERTr (Delay): tng tr theo ng (path); phc tap & co tinh ngBng thng (Bandwidth): dung lng kha dung trong mt ngTai (Load): Mc s dung tuyn & router trn mt ng Chi phi: $$$

24Cac giai phap Shortest PathCac giao thc Vector C ly (Distance Vector Protocols)Cac nut k (neighbors) trao i danh sach cac c ly ti ichXac inh chng tip theo tt nht cho tng ichThut toan (phn tan) ng ngn nht Ford-FulkersonCac giao thc Trang thai Tuyn (Link State Protocols)Thng tin trang thai tuyn c anh tran (flood) ti tt ca cac routersCac routers co y u thng tin v topology cua mangTinh toan ng ngn nht (Shortest path) va chng tip theoThut toan (tp trung) ng ngn nht Dijkstra

25Ha Long QL5Ha Long QLHa Long QL18Ha Long QL

Vector C lyDo you know the way to Ha Long?26Vector C lyCac bin chi ng tai chHng C ly

Bang inh tuynDanh sach thng tin cho tng ich:Nut tip theoC lyPhng phap tng hp BangCac nut k (neighbors) trao i cac d liu (entries)Xac inh chng tip theo tt nht hin xac inh cThng bao cho cac nut k bitTheo chu kySau khi co thay idestnextdist

27ng ngn nht ti HLijHa LongCijDjDiNu Di la c ly ngn nht t nut i ti HL,va nu j la nut k trn ng ngn nht tim c, thi Di = Cij + DjCac nut tim ng ngn nht ti mt nut ich, vd., ti Ha Long28i khng bit ng ngn nht ti HL machi co thng tin tai ch t cac nut kDj"CijiHa LongjCijDjDij"Cij'j'Dj'Chon ng ngn nht hin taing ngn nht ti HL29Why Distance Vector WorksHa Long1 HopFrom HL2 HopsFrom HL3 HopsFrom HLAccurate info about HL ripples across network,Shortest Path ConvergesHL sendsaccurate infoHop-1 nodescalculate current (next hop, dist), &send to neighbors30Bellman-Ford AlgorithmXet tinh toan cho mt ich dKhi taoBang cua mi nut co 1 hang cho ich dC ly cua nut d ti chinh no bng 0: Dd=0C ly cua mt nut khac j ti d bng v cung: Dj=, for j dNut cua chng tip theo nj = -1 chi thi cha c xac inh cho j dBc TruynTruyn vector c ly mi ti cac nut k trung gian qua tuyn tai ch (local link)Bc NhnTai nut i, tim chng tip theo co c ly ti d nho nht, minj { Cij + Dj }Thay (nj, Dj(d)) cu bng (nj*, Dj*(d)) mi nu tim thy nut tip theo mi hoc co c ly miChuyn ti Bc Truyn

31Bellman-Ford AlgorithmXet trng hp tinh toan song song cho tt ca cac ich dKhi taoMi nut co 1 hang cho mi ich dC ly cua nut d ti ban thn bng 0: Dd(d)=0C ly cua mt nut khac nut j ti d bng v cung: Dj(d)= , for j dNut tip theo nj = -1 do cha xac inhBc TruynTruyn vector c ly mi ti cac nut k trung gian qua tuyn tai chBc NhnVi mi ich d, tim chng tip theo co c ly nho nht ti d, minj {Cij+ Dj(d)}Thay (nj, Di(d)) cu bng (nj*, Dj*(d)) mi nu tim thy nut tip theo mi hay c ly miChuyn n Bc Truyn32IterationNode 1Node 2Node 3Node 4Node 5Initial(-1, )(-1, )(-1, )(-1, )(-1, )123315462234211235Ha LongD liu Bang @ nut 1ti ich HLD liu Bang @ nut 3ti ich HL33IterationNode 1Node 2Node 3Node 4Node 5Initial(-1, )(-1, )(-1, )(-1, )(-1, )1(-1, )(-1, )(6,1)(-1, )(6,2)23Ha LongD6=0D3=D6+1n3=6315462234211235D6=0D5=D6+2n5=6021Iteration 1: Nut 6 truyn thng tin cho 3 va 5 34IterationNode 1Node 2Node 3Node 4Node 5Initial(-1, )(-1, )(-1, )(-1, )(-1, )1(-1, )(-1, )(6, 1)(-1, )(6,2)2(3,3)(5,6)(6, 1)(3,3)(6,2)3Ha Long315462234211235012336Iteration 2: Nut 3 va nut 5 truyn thng tin cho 1, 4 va 2 35IterationNode 1Node 2Node 3Node 4Node 5Initial(-1, )(-1, )(-1, )(-1, )(-1, )1(-1, )(-1, )(6, 1)(-1, )(6,2)2(3,3)(5,6)(6, 1)(3,3)(6,2)3(3,3)(4,4)(6, 1)(3,3)(6,2)Ha Long3154622342112350124334Iteration 3: Cp nht36IterationNode 1Node 2Node 3Node 4Node 5Initial(3,3)(4,4)(6, 1)(3,3)(6,2)1(3,3)(4,4)(4, 5)(3,3)(6,2)23Ha Long315462234211235

012334Mang bi t; Vong lp tao ra gia nut 3 va 45Trng hp: bao lam t tuyn 3-637IterationNode 1Node 2Node 3Node 4Node 5Initial(3,3)(4,4)(6, 1)(3,3)(6,2)1(3,3)(4,4)(4, 5)(3,3)(6,2)2(3,7)(4,4)(4, 5)(5,5)(6,2)3Ha Long315462234211235

02533475Nut 4 co th chon 2 la nut tip theo do co c ly nh nhau 38IterationNode 1Node 2Node 3Node 4Node 5Initial(3,3)(4,4)(6, 1)(3,3)(6,2)1(3,3)(4,4)(4, 5)(3,3)(6,2)2(3,7)(4,4)(4, 5)(5,5)(6,2)3(3,7)(4,6)(4, 7)(5,5)(6,2)Ha Long315462234211235

02557476Nut 2 co th chon nut 5 la nut k do co c ly bng nhau39354622342112351IterationNode 1Node 2Node 3Node 4Node 5Initial(3,3)(4,4)(6, 1)(3,3)(6,2)1(3,3)(4,4)(4, 5)(3,3)(6,2)2(3,7)(4,4)(4, 5)(5,5)(6,2)3(3,7)(4,6)(4, 7)(5,5)(6,2)4(2,9)(4,6)(4, 7)(5,5)(6,2)Ha Long

0775692Nut 1 co th chon nut 3 la nut k do co c ly bng nhau403124111312411X(a)(b)UpdateNode 1Node 2Node 3Before break(2,3)(3,2)(4, 1)After break(2,3)(3,2)(2,3)1(2,3)(3,4)(2,3)2(2,5)(3,4)(2,5)3(2,5)(3,6)(2,5)4(2,7)(3,6)(2,7)5(2,7)(3,8)(2,7)Counting to Infinity ProblemNodes believe best path is through each other(Destination is node 4)41Problem: Bad News Travels SlowlyGiai phap khc phucSplit HorizonKhng thng bao thng tin v tuyn n ich cho nut k a nhn thng tinPoisoned ReverseThng bao thng tin v tuyn n ich cho nut k a nhn thng tin, nhng vi c ly bng v cungCho phep pha v cac vong trc tip bi liKhng co tac dung mt s vong khng trc tip

423124111312411X(a)(b)Split Horizon with Poison ReverseNodes believe best path is through each otherUpdateNode 1Node 2Node 3Before break(2, 3)(3, 2)(4, 1)After break(2, 3)(3, 2)(-1, )Node 2 advertizes its route to 4 to node 3 as having distance infinity; node 3 finds there is no route to 4

1(2, 3)(-1, )(-1, )Node 1 advertizes its route to 4 to node 2 as having distance infinity; node 2 finds there is no route to 4

2(-1, )(-1, )(-1, )Node 1 finds there is no route to 4

43Link-State AlgorithmY tng chinh: cn giao thc hai bcMi nut ngun ly mt ban cua tt ca cac nut va link metrics (link state) cua toan b mang Tim ng ngn nht trn ban t nut ngun n nut ichQuang ba thng tin trang thai tuyn (link-state info.)Tt ca cac nut i trong mang phat quang ba ti tt ca cac nut khac trong mang:Cac ID cua cac nut k: Ni=tp hp cac nut k cua nut iC ly ti cac nut k vi no: {Cij | j Ni}S dung anh tran quang ba packets

44Tim cac ng ngn nht bng thut toan Dijkstrasww"w'Nut k gn nht cach s 1 chngw"xx'Nut k gn th hai tip theo cach s hay w 1 chng xzz'Nut gn k th 3 cach s mt chng t s, w, hay xw'Tim cac ng ngn nht t ngun s ti tt ca cac ich45Thut toan DijkstrasN: tp hp cac nut nm trn ng shortest path da chonKhi tao: (Bt u t nut ngun s)N = {s}, Ds = 0, s cach ban thn c ly bng khngDj=Csj vi tt ca j s, c ly s ti cac nut k ni trc tiepBc A: (Tim nut co c ly nho nht i) Find i N sao choDi = min Dj for j N B xung vao NNu N cha tt ca cac nut thi dng laiStep B: (cp nht cac chi phi ti thiuVi mi nut j NDj = min (Dj, Di+Cij)Quay v bc AC ly ti thiu t s ti j qua nut i trong N46Execution of Dijkstras algorithmIterationND2D3D4D5D6Initial{1}3251{1,3}32432{1,2,3}324733{1,2,3,6}324534{1,2,3,4,6}324535{1,2,3,4,5,6}324531245611232352431245611232352433124561123235243124561123235243312456112323524331245611232352433124561123235243347Shortest Paths in Dijkstras Algorithm1245611232352433124561123235243124561123235243312456112323524331245611232352433124561123235243348Phn ng vi Hng hcNu c tuyn b li,B nh tuyn t c ly tuyn bng v cng & nh trn mng bng mt packet cp nhtTt c cc b nh tuyn cp nht ngay c s d liu ca chng & tnh ton li cc ng ngn nhtCho php khi phc rt nhanhTuy nhin, cn thn trng vi cc bn tin cp nht cCn b sung time stamp hay s th t vo mi bn tin cp nhtKim tra xem mi bn tin cp nht nhn c c phi mi hay khngNu mi, b sung bn tin vo database v qung bNu c, gi bn tin cp nht trn tuyn ti

49Ti sao thut ton trng thi tuyn tt hn?Nhanh, hi t khng cn lpH tr cc metrics chnh xc, v a metrics nu cn thit (throughput, delay, cost, reliability)H tr a ng ti mt chThut ton c th thay i tm ra cc ng ngn nht50Source RoutingSource host la chn ng cho mt packetStrict: chui cc nodes trong ng c chn vo headerLoose: chui cc nodes trn path c xc nhCc switch trung gian c a ch chng tip theo v loi b a chSource host cn thng tin trng thi hoc truy nhp ti route serverSource routing cho php host iu khin cc ng thng tin i qua trong mngL phng tin tim nng cho khch hng la chn cc dch v ca nh cung cp51123456ABSource hostDestination host1,3,6,B3,6,B6,BBExample5252