Lecture6-Routing in Packet Switching Networks.pdf

Bai giang Mang Vin thng

Trn Xun Nam

Khoa V tuyn in t

Hoc vin Ky thut Qun s

1 Trn Xun Nam, Hoc vin KTQS

Bai 6 Packet-Switching

Networks

Routing in Packet Networks

Shortest Path Routing


Bai 6 Packet-Switching

Networks

Routing in Packet Networks


Trn Xun Nam, Hoc vin KTQS

1

2

3

4

5

6

Node

(switch or router)

inh tuyn trong Packet Networks

Co 3 tuyn (routes) t 1 ti 6:

1-3-6, 1-4-5-6, 1-2-5-6

Tuyn nao tt nht?

Tr nho nht? S chng it nht? Bng thng ln nht? Chi phi thp nht? Tin cy nht?

4


Yu cu v thut toan inh tuyn

ap ng nhanh khi co thay i

Cu hinh hay bng thng, nghen

Xac inh nhanh cac router tao nn tp hp cac tuyn

Ti u

Mc 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 gian

Thc hin phn mm hiu qua, tai x ly nho

5


1

2

3

4

5

6 A

B

C

D

1

5

2

3

7

1

8

5 4

2

3

6

5

2

Switch or router

Host VCI

inh tuyn trong Virtual-Circuit Packet Networks

Tuyn xac inh trong qua trinh thit lp kt ni

Bang inh tuyn trong switches thc hin chuyn tip theo tuyn a chon

8


Incoming Outgoing

Node VCI Node VCI A 1 3 2

A 5 3 3

3 2 A 1

3 3 A 5

Incoming Outgoing

Node 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 3

Incoming Outgoing

Node VCI Node VCI 3 7 B 8 3 1 B 5

B 5 3 1

B 8 3 7

Incoming Outgoing

Node VCI Node VCI C 6 4 3

4 3 C 6

Incoming Outgoing

Node VCI Node VCI 2 3 3 2

3 4 5 5

3 2 2 3

5 5 3 4

Incoming Outgoing

Node VCI Node VCI 4 5 D 2

D 2 4 5

Node 1

Node 2

Node 3

Node 4

Node 6

Node 5

Bang inh tuyn trong VC Packet Networks

Example: VCI from A to D From A & VCI 5 3 & VCI 3 4 & VCI 4

5 & VCI 5 D & VCI 2 9


2 2

3 3

4 4

5 2

6 3

Node 1

Node 2

Node 3

Node 4

Node 6

Node 5

1 1

2 4

4 4

5 6

6 6

1 3

2 5

3 3

4 3

5 5

Destination 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 3






Bang inh tuyn trong Datagram Packet Networks

10


0000

0111

1010

1101

0001

0100

1011

1110

0011

0101

1000

1111

0011

0110

1001

1100

R1

1

2 5

4

3

0000 1

0111 1

1010 1

0001 4

0100 4

1011 4

R2

ia chi khng phn cp va inh tuyn

Khng co quan h gia cac ia chi gn nhau

Bang inh tuyn cn 16 s

11


0000

0001

0010

0011

0100

0101

0110

0111

1100

1101

1110

1111

1000

1001

1010

1011

R1 R2

1

2 5

4

3

00 1

01 3

10 2

11 3

00 3

01 4

10 3

11 5

ia chi co Phn cp va inh tuyn

Cac tip u chi thi mang tram ni ti

Bang inh tuyn chi cn 4 s

12


inh tuyn c bit

anh tran (Flooding)

Hu ich khi thit lp mang

Hu ich khi lan truyn thng tin ti cac nut

anh lch (Deflection Routing)

C inh, thu tuc inh tuyn t trc

Khng tng hp tuyn

13


Flooding

Gi mt packet ti tt ca cac nut trong mang

Khng co bang inh tuyn

S dung khi cn quang ba packet ti tt ca cac nut (VD: lan truyn thng tin trang thai link)

Giai phap

Gi packet ti tt ca cac ports tr port ti

S lng packet truyn tng theo ham mu

14


1

2

3

4

5

6

anh tran t Nut 1: truyn trn Chng 1 3 packets

15


1

2

3

4

5

6

anh tran t Nut 1: truyn trn Chng 2 7 packets 16


1

2

3

4

5

6

anh tran t Nut 1: truyn trn Chng 3 15 packets 17


Flooding Gii han

S packets truyn sau mi chng tng theo ham mu, co th gy tc nghen mang

Giai phap gii han s packets

Trng Time-to-Live mi packet gii han s chng ti mt ng kinh nht inh

Mi switch b sung ID cua no trc khi flooding; loai bo truyn lp

Tram ngun t s th t mi packet; switch ghi lai ia chi ngun va s th t va loai bo truyn lp

18


Deflection Routing

Nut mang chuyn packets ti cng la chon (prefferd port)

Nu cng la chon (preferred port) bn, anh lch packet ti port khac

Lam vic tt vi cac cu hinh thng thng (regular topology) Mang Manhattan street

Mang vung cua cac nut

Nut c ky hiu (i,j)

Hang chay mt chiu

Ct chay 1 chiu

Hoat ng khng cn buffer (bufferless) xut cho mang optical packet

19/96


0,0 0,1 0,2 0,3

1,0 1,1 1,2 1,3

2,0 2,1 2,2 2,3

3,0 3,1 3,2 3,3

Tunnel from

last column to

first column or

vice versa

20


0,0 0,1 0,2 0,3

1,0 1,1 1,2 1,3

2,0 2,1 2,2 2,3

3,0 3,1 3,2 3,3

busy

Example: Node (0,2)(1,0)

21

Chapter 7

Packet-Switching

Networks

Shortest Path Routing



Shortest Paths & Routing

Co nhiu ng ni ngun bt ky ti ich bt ky

inh tuyn lin quan n vic chon ra ng s dung thc hin mt chuyn tip packet

Co th gn mt gia tri chi phi hay c ly cho mt tuyn ni hai nut mang

inh tuyn tr thanh bai toan tim ng ngn nht (shortest path problem)

23


Routing Metrics

La phng tin o mong mun cua mt ng (path)

dai ng (Path Length) = tng chi phi hay c ly

Cac 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; BER

Tr (Delay): tng tr theo ng (path); phc tap & co tinh ng

Bng thng (Bandwidth): dung lng kha dung trong mt ng

Tai (Load): Mc s dung tuyn & router trn mt ng

Chi phi: $$$

24


Cac giai phap Shortest Path

Cac giao thc Vector C ly (Distance Vector Protocols)

Cac nut k (neighbors) trao i danh sach cac c ly ti ich

Xac inh chng tip theo tt nht cho tng ich

Thut toan (phn tan) ng ngn nht Ford-Fulkerson

Cac giao thc Trang thai Tuyn (Link State Protocols)

Thng tin trang thai tuyn c anh tran (flood) ti tt ca cac routers

Cac routers co y u thng tin v topology cua mang

Tinh toan ng ngn nht (Shortest path) va chng tip theo

Thut toan (tp trung) ng ngn nht Dijkstra

25


Ha Long QL5

Ha Long QL

Vector C ly Do you know the way to Ha Long?

26


Vector C ly

Cac bin chi ng tai ch

Hng

C ly

Bang inh tuyn

Danh sach thng tin cho tng ich:

Nut tip theo

C ly

Phng phap tng hp Bang

Cac nut k (neighbors) trao i cac d liu (entries)

Xac inh chng tip theo tt nht hin xac inh c

Thng bao cho cac nut k bit Theo chu ky

Sau khi co thay i

dest next dist

27


ng ngn nht ti HL

i j

Ha Long

Cij

Dj

Di Nu 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 + Dj

Cac nut tim ng ngn nht ti mt nut ich, vd., ti Ha Long

28


i khng bit ng ngn nht ti HL ma chi co thng tin tai ch t cac nut k

Dj"

Cij

i

Ha Long

j Cij Dj

Di j"

Cij'

j'

Dj'

Chon ng ngn nht hin tai

ng ngn nht ti HL

29


Why Distance Vector Works

Ha

Long 1 Hop

From HL 2 Hops

From HL 3 Hops

From HL

Accurate info about HL

ripples across network,

Shortest Path Converges

HL sends

accurate info

Hop-1 nodes

calculate current

(next hop, dist), &

send to neighbors

30


Bellman-Ford Algorithm

Xet tinh toan cho mt ich d

Khi tao

Bang cua mi nut co 1 hang cho ich d

C ly cua nut d ti chinh no bng 0: Dd=0

C ly cua mt nut khac j ti d bng v cung: Dj=, for j d

Nut cua chng tip theo nj = -1 chi thi cha c xac inh cho j d

Bc Truyn

Truyn vector c ly mi ti cac nut k trung gian qua tuyn tai ch (local link)

Bc Nhn

Tai 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 mi Chuyn ti Bc Truyn

31


Bellman-Ford Algorithm

Xet trng hp tinh toan song song cho tt ca cac ich d

Khi tao

Mi nut co 1 hang cho mi ich d

C ly cua nut d ti ban thn bng 0: Dd(d)=0 C ly cua mt nut khac nut j ti d bng v cung: Dj(d)= , for j d Nut tip theo nj = -1 do cha xac inh

Bc Truyn

Truyn vector c ly mi ti cac nut k trung gian qua tuyn tai ch

Bc Nhn

Vi 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 mi

Chuyn n Bc Truyn

32


Iteration Node 1 Node 2 Node 3 Node 4 Node 5

Initial (-1, ) (-1, ) (-1, ) (-1, ) (-1, )

1

2

3

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 Ha Long

D liu Bang

@ nut 1

ti ich HL

D liu Bang

@ nut 3

ti ich HL

33



Initial (-1, ) (-1, ) (-1, ) (-1, ) (-1, )

1 (-1, ) (-1, ) (6,1) (-1, ) (6,2)

2

3

Ha

Long

D6=0

D3=D6+1

n3=6

3 1

5

4

6

2

2

3

4

2

1

1

2

3

5

D6=0 D5=D6+2

n5=6

0

2

1

Iteration 1: Nut 6 truyn thng tin cho 3 va 5

34



Initial (-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

Ha

Long

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 0

1

2

3

3

6

Iteration 2: Nut 3 va nut 5 truyn thng tin cho 1, 4 va 2

35



Initial (-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

Long

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 0

1

2 4

3

3

4

Iteration 3: Cp nht

36



Initial (3,3) (4,4) (6, 1) (3,3) (6,2)

1 (3,3) (4,4) (4, 5) (3,3) (6,2)

2

3

Ha

Long

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 0

1

2

3

3

4

Mang bi t; Vong lp tao ra gia nut 3 va 4

5

Trng hp: bao lam t tuyn 3-6

37



Initial (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

Ha

Long

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 0

2

5

3

3

4

7

5

Nut 4 co th chon 2 la nut tip theo do co c ly nh nhau 38



Initial (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

Long

3 1

5

4 6

2

2

3

4

2

1

1

2

3

5 0

2

5

5 7

4

7

6

Nut 2 co th chon nut 5 la nut k do co c ly bng nhau 39


3

5

4 6

2

2

3

4

2

1

1

2

3

5

1


Initial (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

0

7 7

5

6

9

2

Nut 1 co th chon nut 3 la nut k do co c ly bng nhau 40


3 1 2 4 1 1 1

3 1 2 4 1 1

X

(a)

(b)

Update Node 1 Node 2 Node 3

Before 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 Problem

Nodes believe best

path is through each

other

(Destination is node 4)

41


Problem: Bad News Travels Slowly

Giai phap khc phuc

Split Horizon

Khng thng bao thng tin v tuyn n ich cho nut k a nhn thng tin

Poisoned Reverse

Thng bao thng tin v tuyn n ich cho nut k a nhn thng tin, nhng vi c ly bng v cung

Cho phep pha v cac vong trc tip bi li

Khng co tac dung mt s vong khng trc tip

42


3 1 2 4 1 1 1

3 1 2 4 1 1

X

(a)

(b)

Split Horizon with Poison Reverse

Nodes believe best

path is through

each other

Update Node 1 Node 2 Node 3

Before 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

43


Link-State Algorithm

Y tng chinh: cn giao thc hai bc

Mi 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 ich

Quang 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 i

C ly ti cac nut k vi no: {Cij | j Ni}

S dung anh tran quang ba packets

44


Tim cac ng ngn nht bng thut toan Dijkstra

s

w

w"

w'

Nut k gn nht cach s 1 chng

w"

x

x'

Nut k gn th hai tip theo cach s hay w 1 chng

x

z

z'

Nut gn k th 3 cach s

mt chng t s, w, hay x w'

Tim cac ng ngn nht t ngun s ti tt ca cac ich

45


Thut toan Dijkstras

N: tp hp cac nut nm trn ng shortest path da chon

Khi tao: (Bt u t nut ngun s)

N = {s}, Ds = 0, s cach ban thn c ly bng khng

Dj=Csj vi tt ca j s, c ly s ti cac nut k ni trc tiep

Bc A: (Tim nut co c ly nho nht i)

Find i N sao cho

Di = min Dj for j N

B xung vao N

Nu N cha tt ca cac nut thi dng lai

Step B: (cp nht cac chi phi ti thiu

Vi mi nut j N

Dj = min (Dj, Di+Cij)

Quay v bc A C ly ti thiu t s ti j qua nut i trong N

46


Execution of Dijkstras algorithm

Iteration N D2 D3 D4 D5 D6

Initial {1} 3 2 5

1 {1,3} 3 2 4 3

2 {1,2,3} 3 2 4 7 3

3 {1,2,3,6} 3 2 4 5 3

4 {1,2,3,4,6} 3 2 4 5 3

5 {1,2,3,4,5,6} 3 2 4 5 3

1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3

47


Shortest Paths in Dijkstras Algorithm

1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3

1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3

1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3 1

2

4

5

6

1

1

2

3 2

3

5

2

4

3 3

48


Phan ng vi Hng hoc

Nu co tuyn bi li,

B inh tuyn t c ly tuyn bng v cung & anh tran mang bng mt packet cp nht

Tt ca cac b inh tuyn cp nht ngay c s d liu cua chung & tinh toan lai cac ng ngn nht

Cho phep khi phuc rt nhanh

Tuy nhin, cn thn trong vi cac ban tin cp nht cu

Cn b sung time stamp hay s th t vao mi ban tin cp nht

Kim tra xem mi ban tin cp nht nhn c co phai mi hay khng

Nu mi, b sung ban tin vao database va quang ba

Nu cu, gi ban tin cp nht trn tuyn ti

49


Tai sao thut toan trang thai tuyn tt hn?

Nhanh, hi tu khng cn lp

H tr cac metrics chinh xac, va a metrics nu cn thit (throughput, delay, cost, reliability)

H tr a ng ti mt ich

Thut toan co th thay i tim ra cac ng ngn nht

50


Source Routing

Source host la chon ng cho mt packet Strict: chui cac nodes trong ng c chn vao header Loose: chui cac nodes trn path c xac inh

Cac switch trung gian oc ia chi chng tip theo va loai bo ia chi

Source host cn thng tin trang thai hoc truy nhp ti route server

Source routing cho phep host iu khin cac ng thng tin i qua trong mang

La phng tin tim nng cho khach hang la chon cac dich vu cua nha cung cp

51


1

2

3

4

5

6

A

B

Source host

Destination host

1,3,6,B

3,6,B 6,B

B

Example

52

Documents

Lecture6-Routing in Packet Switching Networks.pdf