Nghiên cứu vấn đề điều khiển lưu lượng trong MPLS

DAI HOC QUOC GIA HA NOI

Ten de tai
^v

r

NGHIEN CU'U VAN DE
DIEU KHIEN LU'U LLPQNG TRONG
MPLS
•

Ma so: QC 07-18

Chu nhiem de tai: Ths. Pham Thj Hong

DAI HOC Ql.OC GIA HA NCI
TRUNb lAfvi IHOIMG TIN I H U VIEN

OOO6000004^

Hanoi 2010


1. MUC LUC

1. Muc luc

1

2. Bang giai thich cac chu viet tat

2

3. Danh sach nhihig nguoi tham gia thuc hien de tai

7

4. Danh muc cac bang so lieu

g

5. Danh muc cac hinh

8
.X

, ,

6. Tom tat cac ket qua nghien cuu chinh cua de tai
7. BAG CAO TONG KET

q
10

7.L Dat van de
10
7.2. Tong quan cac van de nghien cuu
7.3. Muc tieu va Noi dung Nghien cuu cua De tai
7.4. Dja diem, thoi gian va phuang phap nghien ciru
7.5. Ket qua nghien cuu

7.6 Thao luan
7.7 Ket luan va kien nghi
7.8 Tai Heu tham khao


2. Bang giai thich cac chu' vi§t tat:
Tieng

Ky hieu

Tieng Viet

Anh

AS

Autonomous System

He tu tri

ATM

Asynchronous Transfer Mode

Che dp truyen khong ddng bp

BGP

Border Gateway Protocol

Giao thuc Cong bien gidi

BTT

Bidirectional Traffic Trunk

Luu lupng 2 chieu trung ke

CR-

Constraint Routing Label Distribution

Giao thuc phan phoi nhan gidi han

LDP

Protocol

tuyen

CSPF

Constraint Shortest Path First

Gidi ban

DS

Differentiated Services

Cac dich vu phan biet

DSCP

DS Code Point

Diem ma hda DS

DiffServ

Differentiated Services

Cac dich vu dupc phan biet

EGP

Exterior Gateway Protocol

Giao thi'rc cong Ext

L-LSP

EXP-Inferred-PSC LSP

l u ) e n chu)en mach nhan EXP

FEC

Forwarding Equi\'alence Class

Ldp chuyen tiep tuong duong

FF

Fixed Filter

Lpc dupe CO dinh

FR

Frame Relay

Khung Relay

IETF

Internet Engineering Task Force

Lyc lirang kiem soat cdng nghe Intem

IGP

Interior Gatew a> Protocol

Giao thuc edng Int.

ILM

Incoming Label Map

Anh xa nhan loi \ ao

IP

Internet Protocol

Giao thi'rc Internet

IPOA

IP over ATM

lntSer\

Integrated Ser\ ices

Cac dich \ u tieh hpp

IS-IS

Intermediate S>stem-Intermediate

I le thong tuc ihdi


IS-IS

Intermediate System

He thdng tiic thdi

ISP

Internet Service Provider

Nha cung cap dich vu Internet

LDP

Label Distribution Protocol

Giao thtic phan phdi nhan

L-LSP

Label-only-inferred-PSC LSP

Nhan LSP

LSP

Label Switching Path

Tuyen chuyen mach nhan

LSR

Label Switching Router

Router chuyen mach nhan

NHLFE

Next Hop Label Forwarding
Entry

Ldi vao chuyen tiep nhan Hop
tiep theo

MF

Multi-Field

Da trudng

MPLS

Multi Protocol Label Switching

Chuyen mach nhan da giao thuc

OSPF

Open Shortest Path First

Tuyen ngan nhat

PHB

Per-hop Behavior

PSC

PHB Scheduling Class

Ldp lap lich PHB

QoS

Quality of Service

Chat lupng dich vu

RIP

Routing Information Protocol

Giao thuc thdng tin tuyen

RSVP

Resource Reservation Protocol

Giao thuc dy trir tai nguyen

SE

Shared Explicit

Chia xe

TCP

Transmission Control Protocol

Giao thuc dieu khien truyen tin

TE

Traffic Engineering

Luu lupng

ToS

Type of Service

Loai dich vu

UDP

User Datagram Protocol

Giao thuc bao dir lieu ngudi dung

VC

Virtual Circuit

Kenh ao

VCI

Virtual Circuit Identifier

Nhan dang kenh ao

VPI

Virtual Path Identifier


3. Danh sach nhirng nguai tham gia thyc hien de tai (hoc ham, hoc vi, co quan cong tai

•

Chu tri de tai :
Ho vd ten :

Pham Thi Hdng

Ndm sinh:

1/1981

Nam

Z

, nit-

~

Chuyen mdn ddo tgo : Dien tu - Vien thdng
Hoc hdm, hgc vi:
Chirc vu:

Thgc sT

Cdn bd gidng day tgi bd mdn He thdng Vien thdng

Ca quan cdng tdc : Khoa Dien tie Vien thdng. Tnrdng Dgi hoc Cdng nghe

•

TT

Cac can bo tham gia

Ho va ten

Hoe vi

Chuven nehanh

Nguyen Kim Giao

Gs. Ts.

Dien tu Vien

thona

Nguyen Qudc Tuan

Ths.

Dien tu Vien
th6n£i

Bui Truna Ninh

Cu nhan,

Dien tu Vien
thons

Mau \ an Phuans

Cu nhan

Dien tu Vien
I hon a

Co quan cong tac
Dai hpc Cong nghe DHQl
Ha noi
Dai hpc Cong nghe DHQ(
Ha noi
Dai hpc Cong nghe DHQI
Ha noi

Dai hpc Cong nghe DHQI
Ha noi


4. Danh muc cac bang so lieu

5. Danh muc cac hinh
Hinh 7.1 Mgng lot (core) MPLS
Hinh 7.2 Mot vi du ve dinh tuyen rdng budc
Hinh 7.3 Tdc nghen gdy ra bdi ky thuat chon dudng ngdn nhdt
Hinh 7.4 Gidi phdp cho vdn de sir dung ky thudt liru lugng ...
Hinh 7.5 : Thii tuc khdi phuc mgng 2'tuyen
Hinh 7.6 .• Md hinh todn hoc cua mgng 2 tuyen
Hinh 7.7 .• Mo hinh 3D MDP khoi phuc mgng
Hinh 7.8 .• Trgng thdi dich chuyen Markov (0, 0, 0)
Hinh 7.9 ." Trgng thdi dich chuyen Markov (0, x2, 0)
Hinh
Hinh
Hinh
Hinh
Hinh
Hinh
Hinh
Hinh

7.10 : Trgng thdi dich chuyen Markov (0,M, 0)
7.11 : Trgng thdi dich chuyen Markov (xl, 0,0)
7.12 : Trgng thdi dich chuyen Markov (M, 0, 0)
7.13 : Trgng thdi dich chuyen Markov (xl, x2, 0), khi xl+ x2 < M
7.14: Thiet lap tuyen ngugc

7.15: Phdt hien loi tuyen
7.16: Thiet lap tuyen du phdng
7,17 : Dinh tuyen lgi

8
9
11
11
13
15
16
17
18
18
19
19
20
23
23
25
25


6. Tom tSt cac ket qua nghien cuu chinh cua de tai
6.1 Ket qua khoa hoc
•

02 bao cao khoa hpc tai cic hpi nghi Quoc te to chuc trong nudc

6.2 Ket qua Crng dung

•

San pham cdng nghe:
Chua cd

•

Kha ning ung dung thuc te ciia cac ket qua:

-

Cho cac mang NGN.

-

Cho cac mang khdng day the he 3,5G khac (HSDPA)

6.3 Ket qua dao tao
•

San pham dao tao
•

•

Dai hpc: 02 khda luan tot nghiep sinh vien Dai hpc chat lupng cao

Bo xung tai lieu eho giao trinh
- Bd xung mpt phan kien thuc cho giao trinh giang day Dai hpc lien quan den
mang NGN

6.4 Ket qua ve tang cw&ng item IIFC cho dan vj
•

Ket qua bdi dirdng cdn bd: Giup cac can bp tang cudng kha nang nghien cuu. tii
can cac phuong phap nghien cuu cac giao thuc mang mdi dya tren mo phong

•

D6ng gop cho \"iec tang cudng trang thiet bj:
Khong nhieu


7. BAO CAO TONG KET

7.1. Dat van de
May nam gan day, cung vdi sy phit trien cua cic cdng nghe mang, ngudi
ta mdi nhan thay rd rang la mang vien thdng, mang may tinh ... deu mong mudn
su dung cac dich vu dya tren IP. Cac dich vy dya tren IP (chu yeu la cac dich vu
Internet, dich vu gia tri gia tang ..) la cac dich vu phd bien ca sd deu cd the thyc
hien noi thdng cic mang khic nhau;
Giao thuc IP thyc te da trd thanh giao thuc mang cho Internet nhung giao
thiic nay tdn tai nhiing nhupc diem cd hiiu cua nd nhu i) khdng ddm bdo chdt
lugng dich vu vi ban than nd la giao thiic truyen khdng lien ket va ii) tdc do
chuyen tiep tin thdp do phai xii If tieu de Idp mang nham djnh tuyen - tim tuyen
ndi tdi tram dich.
Sy phat trien cua mang vien thong can phai dinh tuyen va chuyen mach toe
dp cao cho cac dich vu dya tren IP nham dam bao bang thdng trong mang loi de
truyen du lieu, thoai va video vdi QoS chap nhan dupc.. .Chinh nhirng dieu dd da
lam cac nha quan tn mang da va dang tim mpt phuong thiic chuyen mach cd the

phoi hop uu diem cua IP va ATM de dap ling nhu cau phat trien cua mang ludi
trong giai doan tiep theo, trong do cd viec nghien ciiu cong nghe chuyen mach
nhan MPLS.
Cdng nghe MPLS la ket qua phit trien cua cdng nghe chuyen mach IP sudung CO che hoan doi nhan nhu cua ATM de tang tdc dp truyen gdi tin ma khdng
can thay doi cac giao thiic dinh tuyen cua IP. MPLS tach chiic nang cua IP thanh
hai phan rieng biet: chiic nang chuyen gdi tin va chiic nang dilu khiln. Ben canh
do, MPLS cung hd trp viec quan ly de dang ban.
Trong nhiing nam gan day, MPLS da dupc lya chpn dl don gian boa va
tich hop mang trong mang Idi. Nd cho phep cac nha khai thac giam chi phi, don
gian hoa viec quan ly luu lupng va hd trp cic djch vu Internet. Quan trpng hon ca,
nd la mpt budc tien mdi trong viec dat muc tieu cho NGN vdi cic dich vu thoai,
dii lieu vahinh anh...


7.2. T d n g q u a n cac v i n d§ nghien CLFU

MPLS la cong nghe thudng dung trong mang loi (core), bdi vi trong mang core la
ma mpi du lieu se dupc dinh tuy^n va chuyen mach va truyen dan tdi mang khac vdi tO(
cao nhit, dim bao QoS theo yeu cau dich vu, vi vay mang core chiu mpt tai trpng rat ldn
chi su dung cac cdng nghe binh thudng, chi cd mang MPLS cd the dap ling dupc cac yeu
khac khe tren.
Bo dmh luyen chuyen rnaih nhan loi
iCon; LSRl

Wnh 7.1 .Miin^ loi (core) MPLS

MPLS ho trp tat ca cac giao thiic dinh tuyen (tinh. IGP. EGP). Nhung de tri^n khai
thuat luu lupng can biet dupe cac thong so tai nguyen mang. dieu nay chi dupc thuc hi
tren cac giao thiic Link State (OSPF. IS-IS).
Mpt cai tiln quan trpng cua MPLS trong ky thuat luu lupng la hd trp "dinh tuyen ra

buoc". Vdi dinh tuvin rang buoc, vin dh su dung tai nguyen va phan phdi luu lupng tro!
mang dupe tdi uu. Thue chit "dinh tu>Cm rang buoc" dupe nang cao tir cac giao thuc dn
ixxyin thong thudng. Qua trinh thyc hien dinh tu> C^n rang buoc gdm 2 budc:
• Budc 1: boat dpng cua cac giao thuc dinh lu_\in
• Budc 2: qua trinh tinh loan thiet lap tu\en diinu CSPF
7.2.1 Dinh tuyen rang buoc


7.2.1 Djnh tuyen rang buoc
Dinh tuyen rang budc la mpt phuang tien de thyc hien xii Iy ty dpng hoa
ky thuat luu luang, khac phuc duac cac han che cua dinh tuyen theo dich. Nd xac
dinh cic route khdng chi dua tren topo mang ma cdn sii dung cac metric die thu
khac nhu bang thdng, tre, cost va bien dpng tre. Giai thuat chpn dudng cd khi
nang toi uu hda theo mpt hoac nhieu metric nay, thdng thudng ngudi ta dung
metric dya tren sd bop va bang thdng, Chpn dudng ngan nhat trong so tat ca cac
dudng cd bang thdng kha dung thoa man yeu cau.

Egress Kot-ter

600 Kbps
->- 300 Kbps
•>• 200 Kbps

Kenh 1 Mbpi

Hinh 7.2 Mot vi du ve dinh tuyen rang buoc

Dinh tuyen rang budc cd 2 kieu online va offline. Kieu online cho phep cac
router tinh dudng cho cac LSP bat ki luc nao. Trong kieu offline, mpt server tinh
dudng cho cac LSP theo dinh ki ( chu ki cd the dyoc chpn bdi nha quan tri,

thudng la vai gid hoac vai ngay ). Cic LSP dupc bao hieu thiet lap theo cic
dudng da chpn.
7.2.2 Djnh tuyen tucmg minh
Dinh tuyen tudng minh la tap con ciia dinh tuyen rang budc, trong dd sy
rang budc la ddi tugng tudng minh. Tuyen tudng minh ER la mpt danh sach cic
mit triru tupng m i mpt dudng chuyen mach nhan rang budc CR-LSP phai di qua.
Niit triru tugng cd the la mpt niit hoac mpt nhdm niit. N I U ER chi quy dinh mpt
nhdm trong sd cic mit ma CR-LSP di qua thi nd dugc gpi la tuyen tudng minh
tha long (loose ER). Ngugc lai, nlu ER quy dinh toan bp cac mit tren CR-LSP thi
9


7.2.3 Dieu khi^n luu lirong dua tren MPLS
MPLS-TE dk cap din kha nang dilu khien cua nhiing luong luu lupng trong ma
vdi muc dich giam thieu tic nghen va tao ra miic su dung hieu qua nhat cbo cac phuang t
sin cd. Luu lupng IP truyin thdng dinh tuyen theo "Hop by Hop" co ban va theo IGP k
sii dung ky thuat dudng dan ngan nhat de truyen luu lupng. Luu lugng dudng dan IP coi
khong dat tdi uu vi nd phu thupc vao thdng tin Link Metric tinb khdng ciing vdi bat ky n
hieu biet nao ciia tai nguyen mang sin cd hoac cac yeu cau cua luu lugng can thiet de ma
tren dudng dan dd. Su dung ky thuat dudng dan ngin nhat cd the gay ra cac van de sau :
^

Dudng dan ngan nhat tii cac tai nguyen khac nhau chong lan len mpt so link, g

ra tie nghen tren cac link dd.
^

Luu lupng tu mpt nguon di tdi mpt dich cd the vugt qua dung lugng ciia ky thi

dudng dan ngin nhat, trong khi mot dudng dan dai hon giua hai Router dd dupc dugc;

dung khong diing miic.
Ky thuat luu lupng trong pham vi MPLS phat sinh tu nhu cau khai thac mang de cur
cap mpt CO sd ha tang mang dang tin cay va dua ra su thyc hien nhat quan cho mang. F
thuat luu lugng cho phep ngudi khai thac mang kha nang dinh tuyen lai luong luu lugng
dudng dan cost thap nhat "least cost" dugc tinh toan boi cac giao thiic djnh tuyIn va nhui
dudng dan vat ly it bi tac nghen trong mang do. Va ket qua la eo sy gia tang rit manh n
trong nhu cau ve tai nguyen mang va su canh tranh giiia cac nha cung cip. Ky thuat li
lugng da tro thanh ling dung hang dau eho MPLS. Muc dich eua ky thuat luu lupng laph
su dung hieu qua \ ao tai nguy en mang gidi ban.
Trong hinh 7.3. ed hai dudng dan tir Router C tdi Router E dugc bieu thj boi cac duor
dan 1 \a 2. neu mpt Router chpn mpt trong cac dudng din theo ky thuat dudng dan ngi
nhat tir C tdi E ( C-D-E). thi sau do no se mang tit ca luu lugng cua dich eho E thong qi
dudng din. Dung lupng luu lupng eu6i eung tren duang din dd co the gay ra tic nghe
trong khi mpt dudng din khac (C-F-G-H-E) khong duge su dung. De toin'the mang^ho
dpng hieu qua nhdt no cd the thilt kl nham tha> doi mpt xai phan s6 (fraction) eua luu \m
tir link nay toi link khae. Trong khi ta co eost duong din C-D-L ngang bang vdi cost duc^
din C-F-(;-H-E nhu la N iee tiln lai gdn hon va\ su cdn hang tai se gay can tro. nlu khonel


Trong hinh 7.3, cd hai dudng dan tir Router C tdi Router E dugc bieu thi
bdi cac dudng dan 1 va 2, neu mpt Router chpn mpt trong cac dudng dan theo ky
thuat dudng dan ngan nhat tir C tdi E ( C-D-E), thi sau dd nd se mang tat ca luu
lugng cua dich cho E thong qua dudng dan. Dung lugng luu lugng cudi ciing
tren dudng dan dd cd the gay ra tac nghen, trong khi mot dudng dan khac (C-FG-H-E) khdng dugc sir dung, De toan the mang boat dpng hieu qua nhat nd cd
the thiet ke nham thay ddi mpt vai phan sd (fraction) cua luu lugng tir link nay
tdi link khic. Trong khi ta cd cost dudng dan C-D-E ngang bang vdi cost dudng
dan C-F-G-H-E nhu la viec tien lai gan hon vdi sy can bang tai se gay can trd,
neu khdng the cd dugc mpt Topo mang chat che. Cac dudng dan ciia dinh tuyen
tudng minh, dugc thyc hien sir dung MPLS, cd the dugc sir dung de hieu ban va
mem deo han ciia viec dinh dia chi van de nay.

De giai quyet van de dieu khien luu lugng dua vao mpt thyc te la cac nhan
va cac dudng dan Label-switched cd the dugc thiet lap mpt each da dang ciia
each kieu dieu khien khic nhau. Vi du, kieu dieu khien luu lugng cd the thiet
lapmpt dudng dan Label-switched tir B tdi C tdi F tdi G tdi H tdi E (dudng dan
1) va mpt dudng dan khac tir A tdi C tdi D tdi E (dudng dan 2) nhu dugc chi ra d
hinh 7.4.
Router D
Router A
Router E

Router B
Router F
Router G

Hinh 7.3 Tdc nghen gdy ra bai ky thudt chon dudng ngdn nhdt

11


link-state IGP. Theo yeu cau de dilu khien dudng dan LSP dat hieu qua. moi LSP co
dugc gan mpt hoac nhieu hon cic thupc tinh. Nhiing thupc tinh nay se xem xet trong du
dan may tinh de cho LSP. Cic thupc tinh nay va y nghia ciia chiing dugc long ket nhu sau
^

Bandwidth: Dp rpng bang thdng du trir tdi thieu cua dudng dan cho LSP d

thiet lap dpc theo dudng dan dd.
^

Path Attribute: Mpt thupc tinh dupc quyet dinh la dudng dan ciia LSP co tb

Manually specified hoac Dynamically hay khdng thi dupc tinh bdi Constraint-Based roulii
^

Setup Priority: Thupc tinh nay se quyet dinh la LSP nao se tao ra tai ngu]

khi nhieu LSP hoan thanh cho nd.
^

Holding Priority: Thupc tinh nay se quyet dinh la mpt tai nguyen dugc giir

mpt thiet lap LSP thi se dupc uu tien trudc bdi mpt LSP mdi hay khong.
^

Affinity (Color): Viec quan ly die trung die tinh ciia mdt LSP.

^

Adaptability: Cd hay khong viec chuyen mach LSP tdi mpt dudng dan toi

hon khi no tro nen cd san.
^

Resilience: Thupc tinh se dupc quyet dinh hay khong de djnh tuyen lai LSPl

dirdng dan cd anh hudng do loi.
Kha nang cua MPLS la cung cap viec dinh tuyen ro rang, boat dpng qua bat ky ir
phuong tien nao va cd the tap hgp so lieu thong ke nhirng LSP. dl dl nghi nd la thich h
cho cung edp kha nang ky thudt luu lugng.
IETF dua ra gia thiet ve 2 giao thu'c khac nhau cho vice danh rieng tai nguyen tro

pham vi cu the la MPLS, dinh tuyIn dua tren sy rang budc Constraint-Based Routing, da
su dung giao thirc phdn phoi nhan LDP (CR-LDP). vd giao thiic danh rieng tdi nguyen RS^
de cung cdp cho ky thudt luu lugng trong pham vi miln MPLS.
7.2.4 Phan tich thuat toan
•

Mieu td md hinh

Trong cdc mang MPLS, khi ed mpt lien kit hay mpt tram bj ldi thi ede ludng luu lug
qua tuyen chira lien kit bi 16i thi cae cupc gpi hoac la bi ngin quang (dropped) hoac lapl
djnh tuyen lai nlu eon eo tuyIn du phong. Khi tuy In bj ldi duge nhd lai. ngirdi ta cd thexc
xet hoac la tra lai tuy In dd luu lugng nguyen thuy ban ddu. Mot tiln tiinh Markov qu)
djnh (A Markox Decision Process - MDP) dupc lua chpn de xem xet mot cdch tdi uu M
lieu tra lai luu lugng cuoc gpi tir tuyIn du phong tro lai tuyIn ban ddu la nhu thi nao (b
nhieu ??) .P. Aukia \1\ da dua ra dl xudt nhu sau .


Kha nang ciia MPLS la cung cap viec dinh tuyen rd rang, hoat dpng qua bat
ky mpt phuang tien nao va cd the tap hgp sd lieu thong ke nhimg LSP, de de
nghi nd la thich hgp cho cung cap kha nang ky thuat luu lugng.
IETF dua ra gia thiet ve 2 giao thiic khac nhau cho viec danh rieng tai
nguyen trong pham vi cu the la MPLS, dinh tuyen dya tren sy rang budc
Constraint-Based Routing, dang sir dung giao thiic phan phdi nhan LDP (CRLDP), va giao thiic danh rieng tai nguyen RSVP de cung cap cho ky thuat luu
lugng trong pham vi mien MPLS.
7.2.4 Phan tich thuat toan
•

Mieu td mo hinh

Trong cac mang MPLS, khi cd mpt lien ket hay mpt tram bi ldi thi cic ludng

luu lugng qua tuyen chira lien ket bi loi thi cic cupc gpi hoac la bi ngan quang
(dropped) hoac la phai dinh tuyen lai neu cdn cd tuyen dy phdng. Khi tuyen bi loi
dugc nhd lai, ngudi ta cd the xem xet hoac la tra Iai tuyen dd luu lupng nguyen
thuy ban dau. Mpt tien trinh Markov quyet djnh (A Markov Decision Process MDP) dugc lya chgn de xem xet mpt each tdi uu viec lieu tra lai luu lugng cupc
gpi tu tuyen dy phdng trd lai tuyen ban dau la nhu the nao (bao nhieu ??) .P.
Aukia [7] da dua ra de xuat nhu sau .
•

Md hinh tuyen A'2

Tir [1, 3, 4, 5], ngudi ta da cau hinh trudc tao ra tuyen dy phdng trong mang
de khoi phuc tuyen mpt each nhanh nhat, Vi the mpt md hinh 2 tuyen (ma chimg
dugc coi nbu 2 tuyen song song vdi nhau) ndi giira tram nguon S vdi tram dich D.
Tuyen nguyen thuy (tuyen so cap) dugc gpi la P va tuyen thii cap (tuyIn dy
phdng) dupc gpi la B. Mdi cupc gpi dugc gii thiet la chiing cd ciing mpt dan vi
bang thong (trudng hgp tong quit thi moi cupc gpi se cd bang thdng khong nhu
nhau, nhung se dugc de cap sau nay). Tuyen so cap P cd the bi Ioi hay bi gian
doan do mpt tram hay mpt lien ket bi diit. Sau khi Idi xay ra, tat ca cac cupc gpi
qua tuyen dd se dugc di chuyen tir tuyen so cap P tdi tuyen dy phdng B. TuyIn
so cap dugc nhd lai sau khi toan bp hay mpt phan luu lupng cac cupc gpi qua
dudng dy phdng B se dugc di chuyen trd Iai dudng so cap P. (xem hinh 7.5,
trong dd - LHS: trudc khi hdng ; MID: sau khi hdng ; RHS:sau khi nhd Iai).

n


dugc chuyen lai ve tuyen so cap P vdi mpt chi phi nhat dinh (mui ten xanh luc o hinh 7
luu lugng dugc chuyen la cd ban, thudng bj gidi ban bdi cdng suit cua tuyen so cap P hi
cua tuyen thir cap B. neu luu lugng d tuyen P ldn hon d tuyen B, mot sd nhirng cupc gpi
bi loai bd trong luc ddi hudng ldi. nhu vdy. luu lupng cdn lai sau khi tuyen so cap hoi pl

se van la hiiu han. va nhu the, chiing ta se chi xem xet trudng hpp gidi ban tren la cong s;
ciia tuyen so cap bdi trudng hpp gidi ban tren la cong suat tuyen thir cap cung tuong tu.
•

Cdc dgi lugng vd cdc luu y

• M: Dung lupng ciia tuyen nguyen thiiy (so cap) xac djnh so cupc gpi toi da cot
chiem giir.
• / / : Toe dp loi eua tuyen so cap.
• /// -• Toe dp nhd lai tuyen so cdp. Thdi gian nhd lai trung binh la (p-1),.
• / ; Toe dp cupc gpi den .
• jU- T. Thdi gian phuc vu cupc gpi trung binh cua cac cupc gpi.
.A.-

Q;^T-'^~~^
,^'X^

""^--.^

I

/")

7^,

ITinh ~ 6 • Mo hinh loan hoc cua mang 2 iiivSn

• Cl.- Giu trpng so toe dp cupc gpi qua tuyIn so cap P.
• Cy- Giu trpng so toe dp cupc gpi qua tuyIn du phong B .
• C/A-/+ C2X:: Giir trpng so cdc cupc gpi tir S tdi D. Trpng s6 dupe gia djnh la mot ha

tuyen tinh cua cdc cupc gpi hien hdnh dang chiim giCr.
• em: Di chu>en trpng s6 tie dp cupc gpi. Di chuyen trpng sd dupe gia djnh la mgl h^
tu>en tinh eua tong s6 cac cupc gpi dang dupc di chuyen cm.
• (A-/, A-:, p,): Trang thai hien hdnh. trong do Xj. xj Id cdc cupc gpi chiim giir tren tuyeni
edp P N a tuyen du phong B. va p, la trang thai hien hanh cua^uyen so cdp . Khi p, ='
luyen so cap lam Nice vd khi p^ - 1 thi tuyIn so edp bj 16i (dirt).
Co hai mat phang trong hinh 7.7. Mat phang thir nhdt khi p, = 0. dilu nav cd nghia
tu>en so cdp lam Mee u3t. Lue ddu tien . ngudi ta gia djnh eo v cuoc goi qua tuyIn so cap


Xf: Tdc dp ldi cua tuyen so cap.
Pf: Tdc dp nhd lai tuyen so cap. Thdi gian nhd lai trung binh la
X : Toe dp cupc gpi den .
p-l: Thdi gian phuc vu cupc gpi trung binh cua cac cupc gpi.

ZD o

«jp=@

(p-l)/.

/;

j'-,n.'l

^

X

= n + -(-.: V ;

D
Hinh 7.6 : Mo hinh todn hoc ciia mang 2 tuyen

• c/.- Giir trpng sd tdc dp cupc gpi qua tuyen so cap P.
• C2: Giir trpng sd toe dp cupc gpi qua tuyen dy phong B .
• C/Xy+ C2X2: Giu trpng so cac cupc gpi tir S tdi D. Trpng sd dugc gia dinh la
mpt ham tuyen tinh cua cac cupc gpi hien hanh dang chiem giir.
• cm: Di chuyen trpng so toe dp cupc gpi. Di chuyen trpng sd dupc gia dinh
la mpt ham tuyen tinh cua tdng so cac cupc gpi dang dupc di chuyen zm.
• (xi, X2, Pf): Trang thai hien hanh, trong dd x/, X2 la cac cupc gpi chiem giir
tren tuyen so cap P va tuyen du phdng B, va pf la trang thai hien hanh ciia
tuyen so cap . Khi pf = 0, tuyen so cap Iam viec va khi pf = I thi tuyen so cap
bi loi (diit).
Cd hai mat phang trong hinh 7.7. Mat phang thii nhat khi pf ^ 0, dieu nay
cd nghia la tuyen so cap lam viec tot, Luc dau tien , ngudi ta gia dinh cd y cupc
gpi qua tuyen so cap B va khong cd cupc gpi nao qua tuyen dy phdng B. Khi P bj
Ioi (bi diit), cac ludng dupc di chuyen tir P tdi B. Vi the trang thai cua he thong
thay ddi tir (y, 0, 0) thanh (0, y, 1) vdi tdc dp dich chuyen la X/. Khi P dupc nhd
lai vdi tdc dp pf, ngudi ta phai ra quyet dinh xem cd bao nhieu cupc gpi se dugc
di chuyen trd lai P. Trang thai cua he thdng Iai thay doi tir (xi, X2, 0) trong dd Xi
+ X2 < y (tiiy thupc vao cd dich vu nao da dupc hoan thien tren B trong khi nhd
lai cac tien trinh ciia P). Khi tuyen so cap lam viec tot trd Iai, ngudi ta cd thi gia
dinh lai cd them mpt sd cupc gpi mdi den hoac di tren ca P Ian B ...

15


Do dd p.d.f f^iT) = re-''.T>0
El T] = r rre-'dr

vdi tat ca gia tri cua x . z . Ky v(

= - . Trang thai va dilu khien tai thdi diem t bdt ky dupc dinh ng

S)

y

bdi x(i) va r(/) tuong irng va khong doi giiia cac chuyen giao.
Chung ta su dung cac dinh nghia sau:
-

t/, la thdi gian chiem ciia chuyen giao thir k (t,, = 0).
r^. I t^ -r^._,: khoang thdi gian chuyen giao thir k
x^ ~ x(/r): chimg ta cd x{(} = .\^ vdi /^
-

Zk Z z(k):

chiing tacd r(/) = ^ vdi t^
Chiing ta xem xet mpt ham chi phi cd dang:
Y\m^{[

cCx{t).'z{t))dt\

Trong do. c la mpt ham cho trudc (ham djch chuyen va/hoac ham giir) dupc mo
trong phdn trudc. Tuong ty vdi bai loan thdi gian rdi rac. mpt chinh sat

Z = |z„,Z|.....| trong dd Zk la mpt trang thai anh xa ham den cdc dieu khien v
Zk(x)GZ{x)

vdi tat ca gia tri x . Vdi z. dieu khien dupc dp dung trong khoar

[r^,?^.,,) la

Zk{xk).

Do trang thai khong doi giira cae chuyen giao (nghla la trong thdi gian /"'). hai
chi phi dupc cho bdi:
K(xo) = ^ £ { [ ' e~'c(xk.Zk(xk
'.' Xk,Zk{xk)

))dt \ xn}

Id cae hang so trong khoang

\lk^h-\)

X ^ l | ' c ( x . , z ^ ( x O ) ^ r j - ^ ( £ ( r ) £ ! c ( x . . z O i ) = X - ' ^ i ^ ( - ^ ^ ' ^ 01
^•='-'

•

k--i)

i=(,

Y

Chiing ta sir dung cac dinh nghia sau:
-

tk la thdi gian chiem cua chuyen giao thii k {to = 0).

-

'^k=t,,- ^i_,: khoang thdi gian chuyen giao thir k
Xk = x(k): chiing ta cd x(/) = x^ vdi /^ < / < /^^i
Zk = z{k)

:

chiing

ta

cd

z{t) = z^

vdi

h-^*^

h+\ •

z = {a,d,r^^,r^^}e{O^Y

Chung ta xem xet mpt ham chi phi cd dang:

lim^lt ^(ko,kt))dt}
Trong dd, c la mpt ham cho trudc (ham dich chuyen va/hoac ham giir)
dupc mo ta trong phan trudc. Tuang ty vdi bai toan thdi gian rdi rac, mpt
chinh sach Z = |zo,Zi,....} trong dd zk la mpt trang thii anh xa ham den cic
dieu khien vdi zk(x) e Z(x) vdi tat ca gia tri x. Vdi z , dieu khien dupc ip
dung trong khoang [^^,^^^+1) la Zk(xk).
Do trang thai khdng doi giira cac chuyen giao (nghia la trong thdi gian
/ " ' ) , ham chi phi dugc cho bdi:
^(^0) = ^E{1*'e~'c(xk,Zk{xk))dt\
k=0

Xo}

''

'.' Xk, Zk {xk) la cic hang so trong khoang [ij^, ^^+1)

.^X£{|"'c(i.,z.(xO)^0 = Z(£(O^{c(x,,iO}) = X-^{c(x.,zO}
k=0

"

k=0

k=0 Y

Trong dd, mot tien trinh Markov thdi gian lien tuc vdi chi phi
\™^^^E\r

c{x(t\z{t))dt\vk

toe dp chuyen giao y se tuong duong vdi

mpt tien trinh Markov thdi gian rdi rac vdi chi phi long-run tren mpt giai
,
,, c(x,z)
doan la -^^

DAI HOC QUOC GIA HA Npi
TRUNG T A M THONG TIN THU VIEN

mioQO(}0^9

17


Trong hinh 7.9 , tir trang thai hien thdi (0. X2. 0), cac su kien co the den ducn^
dan so cdp P la sy kien den ciia 1 luong. mpt that bai va sy kien di tir duong dy phorij
B . C h o Yo X. 0 "^ ^~^ '^'/ '^ ^iM ^ chiing ta cd:

K(0.x,,0) = — ^ { c , x , + / l F _ , ( l x . , 0 ) + /l,F_,(O.A%.l) + x.;/F.,(0.x,-1.0)1

+ 1.0]

1. /.•.!*
0. r.. i

Hinh " 9 : Trang ihdi dich chuven Markov (0. x2. 0)

lii)

.V/= 0,.v_7= M, /7y = 0
Nhu thdy trong hinh 7.10. khi xj - M. tdt ea eae su kien den cua luong deu bj kh(
d dd\. chiing ta khong xet den trudng hgp khi ma cac luong bi nghen ludng dugc dii
tuyen den dudng du phdng. Chi eo the xay ra cac su kien di \ a that bai. Cl
/(, A,„ = X^ + Mj.1. chiing ta cd
r(O.A/.0)

!c.A/ + ;.,i;_,(L.\/.i) + A///r;_,(O.A/-i.O)

I

V^

M. 1
1 r.

'II ;>/

Iiinh " in

iv)

l.n,

Trang lhai Jich Jmycn Markov i(),M, ())

0

c,x,-^AV„_,{lx,,0)^Ay_,(0,x,A)^x,pV^_,(0,x,-lO)}

Kio,x„o) =
^0,^2,

(0. .1-2 +1.0)

l-.rz.O

(Cro-l)

fCro-LOi
Hinh 7.9 : Trgng thdi dich chuyen Markov (0, x2, 0)

iii)

A:; =

0, XJ = M , /?/ = 0
Nhu thay trong hinh 7.10, khi X2 = M, tat ca cac sy kien den ciia luong
deu bi khoi. d day, chiing ta khdng xet den trudng hgp khi ma cac luong
bi nghen ludng dugc dinh tuyen den dudng dy phdng. Chi cd the xay ra
cac sy kien di va that bai. Cbo YQM o- ^r "•"^/^' chiing ta cd:
(c,A/+ A/„_, (I, M, I) + A//iK _, (0, M -1,0)}

p;(o,A/,o)
^O.jr, 0

(0. A/, 1

O . A / - l.rr

Hinh 7.10 : Trang thdi dich chuyen Markov (OM, 0)
iv)

0 < Xl < A/,

A:^ =

0, pf= 0

Hinh 7.11 cho thay khdng cd Iuong nao tren dudng dy phdng B va
dudng so cap P khdng bi lap day bdi cic ludng, cd cac sy kien thit bai, sy
kien den va di. Vdi tdc dp dau ra long la Y.^^.o^ - ^ + ^f+x^jj, ^ chimg ta
CO

19


luu tru hoac that bai. Khong co su can bang luu
<.V/

lugng a day. Cho

. = 2 + /l^+(x, + x . ) / / , chung tacd:
^„(^P^2^0) = ^ ^ { c , x , + c , x ,

+2F_,(x,+Lx,.0) + ;.JK_,(0.x,+x,.l) + c,,x,] + x,/^K,,_,(x,-l.x,.0)

+x,/^K„^,(x,.x,-lO)}
+ Lro

U l + 1../-

I.l

Ml..ri +..-.J.1
[j-i.j-2

-

1-'-"

Hinh "". 13 : Markov Iransitions of the slale (xl. x2, 0). khi xl + x2 < M

• Ap dung giai thudt dieu khien lint lugng trong mgng MPLS
Tir eae mo hinh todn hpc tren. trong cac giai thudt thyc te cdn dam bao rang tdt ea cac Im
lugng mang phai dugc djnh tuyen mpt each hieu qua. ddng tin cdy vd cd chat lugng djch vi
(QoS) cao. Hon niia. luu lugng eua mang dupe phdn phoi mpt cdch hieu qua trong cac la
nguyen mang. Trong mang MPLS, ky thudt luu lupng mang su dung ky thuat tim duani
cudng birc ngan nhdt (CSPF) thay vi OSPF trong cac mang IP trudc dd de thuc hien diei
khien luu lupng. CSPF tim dudng di cho dir lieu can cir \'ao ede dieu kien dinh tuyen duara
Tu\en nay c6 the khong phai la tuyen ngan nhdt nhung it nghen hon tuyen ngan nhat. Djn,
luyen tudng minh la mpt tap hpp con eua eae tuy en cudng birc thdng thudng dudi dieu kie
cudng birc nhu la mpt tuyen tirdng minh. Mot tuyen tirdng minh la mpt LSP ma nd gui d
lieu tren mpt tuyen nhdt djnh thong qua mien MPLS.
Trong mang MPLS, dang thong tin trao doi giua cac tuyen phu thupe vao giao thuc ba
hieu se duge su dung. Cd bon phuong thirc duge xae djnh nhu sau 1111: Giao thirc phdn phi

1
^.(^p^2.0)


{c,Xj+C2X2
'•-I"! ' "2^2

(x,.x, + 1.0)

xi + Lx9,0}

(xi - l , x

(0, Xl +.r2,1)
[xi.xo-

1,0}

///rt/i 7. / J .• Trgng thdi dich chuyen Markov (xl, x2, 0), khi xl + x2 < M

•

Ap dung gidi thuat dieu khien luu lugng trong mgng MPLS

Tir cac md hinh toan hpc tren, trong cic giai thuat thyc te can dam bao rang
tat ca cic luu lugng mang phai dugc dinh tuyen mpt each hieu qui, ding tin cay
va cd chat lugng dich vu (QoS) cao. Han nira, luu lugng cua mang dugc phan
phdi mpt cich hieu qua trong cac tai nguyen mang. Trong mang MPLS, ky thuat

luu lugng mang sir dung ky thuat tim dudng cudng biic ngan nhat (CSPF) thay vi
OSPF trong cac mang IP trudc dd de thuc hien dieu khien luu lugng. CSPF tim
dudng di cho du lieu can cii vao cac dieu kien dinh tuyen dua ra. Tuyen nay cd
the khdng phai la tuyen ngan nhat nhung It nghen ban tuyen ngan nhat. Dinh
tuyIn tudng minh la mpt tap hgp con ciia cac tuyen cudng biic thong thudng
dudi dilu kien cudng birc nhu la mpt tuyen tudng minh. Mpt tuyen tudng minh
la mpt LSP ma nd giri du* lieu tren mpt tuyen nhat dinh thong qua mien MPLS.
Trong mang MPLS, dang thdng tin trao ddi giu:a cac tuyIn phu thupc vao
giao thirc bao hieu se dugc sii dyng. Cd bon pbuang thirc dugc xac dinh nhu sau
[11]: Giao thirc phan phoi nhan (LDP), giao thirc dinh tuyIn cudng birc vdi LDP
21


Thdi gian gian doan djch vu = Thdi gian do loi + thdi gian thong bao den toan
mang + Thdi gian tinh toan dU phdng + Thdi gian chuyen tiep ludng lUu lu'dng.

•

Cdc ca che khdi phuc tuyen trong mgng MPLS

Khoi phuc tuyen trong MPLS la co che trong dd luu lugng dang dugc truyen tai dugi
chuyen tiep cho mpt tuyen mdi dupc gpi Id tuyen dy phdng khi ma tuyen hien tai xay ra loi
Qua trinh ndy nham ddm bao thong tin truyen dan khong bj mdt. Tuyen dy phdng dugc tinl
loan vd thiet lap dua vdo co che khoi phuc. 1 rong RSVP-'FE. loi cd the dugc phat hien hdi
cdc ban tin Hello hoac trang thai mem RSVP-TL. Mot khi ldi dugc phat hien vd thdng bac
den node loi vdo. nd sc co gang de thiet lap lai mpt LSP tuong ty. Neu LSP nay dugc dinli
tuyen mpt each long leo thi LSR loi vao cd the thu tim mpt tuyen va node ma khae tuyen vdi
node dau vdo va co gang thiet lap mpt LSP tren tuyen mdi de thay the. Hay ndi mot each
khac. no se co gang thiet lap mpt LSP va de node bien bj loi tinh todn mpl tuyIn mdi tu
node/link den LSR bien. Sau khi tuyen mdi dupe thiet lap. tdt ca cac luu lugng dugc chuyen

tiep \ao tuyen nay.
Co hai loai co che sua tuyen. ehiing dupe gpi la eo che sua tuyen loan cue va sua tuy^J
cue bp.
I
•

Sua chua toan cue dupe khoi tao giua ede nodes dau eudi. I uyin dupc lya chon la
tuyen dupc tinh loan trudc dd hoac la tuy en dupc tinh todn mot cdch nang dpng lu cac
node bien (bao gom node dau vao vd node dau ra). TuyIn dupe lya chpn Id tuyIn bao
ve cua tuy en dang cd du lieu truyen qua.

•

Sua chira cue bp dupc su dung de sua ldi tai cac dilm xay ra ldi hoac gan diem xay ra
loi. Do \ ay. nd giam thieu so lugng mat goi dir lieu. Flon thi nira. qud trinh sua loi
dugc thuc hien mot cdch cue bp din node or link xay ra ldi do vdy qua trinh khoi phuc
se dien ra nhanh hon.

•

Mot so md hinh khdi phuc tiivin

Cd rat nhieu mo hinh khoi phuc LSP trong mang MPLS, nhung mo hinh Makam va Haskiij
dupe coi Id mo hinh phii hgp nhdt. Mo hinh cua Makam va Haskin dai dien eho hai phuanij
thue khdi phuc tuyen: todn cue xh cue bp. Han nira. hai mo hinh ndy t6t hem cae md hinli
khoi phuc khde tren phirong dien s6 lupng gdi bj mdt. s6 lugng mdt trat ty ^(^^ tin.

'

i

Khi mpt link hoac mdt node tren tuyen giiia node truyen va node nhan bi
ldi, dich vu se bj ngat cho den khi bon budc tren dugc hoan thanh. Thdi gian giin
doan dich vu la khoang thdi gian giiia bit truyen di cuoi cimg trudc khi ldi xay ra
dugc nhan va thdi diem bit dau tien cua dii lieu ma sir dung tuyen dy phdng den
dugc bp nhan. Tdng thdi gian gian doan dugc tinh toan theo cdng thiic sau:
Thdi gian gian doan djch vu = Thdi gian do loi + thdi gian thong bao den toan mang
+ Thdi gian tinh toan du* phong + Thdi gian chuyen tiep luong lUu (Udng.

•

Cdc ca che khoi phuc tuyen trong mgng MPLS

Khdi phuc tuyen trong MPLS la ca che trong do luu lugng dang dugc truyen
tai dugc chuyen tiep cho mpt tuyen mdi dugc gpi la tuyen dy phdng khi ma
tuyen hien tai xay ra ldi. Qua trinh nay nham dam bao thdng tin truyen dan
khdng bi mat. Tuyen dy phdng dupc tinh toin va thiet lap dya vao co che khdi
phuc. Trong RSVP-TE, ldi cd the dugc phat hien bdi cic ban tin Hello hoac trang
thii mim RSVP-TE. Mpt khi ldi dupc phit hien va thong bao den node loi vao,
nd se cd ging de thiet lap lai mpt LSP tuong ty. Neu LSP nay dugc dinh tuyen
mpt each ldng leo thi LSR loi vio cd the thir tim mpt tuyen va node ma khac
tuyIn vdi node dau vao va co gang thiet lap mpt LSP tren tuyen mdi de thay the.
Hay ndi mpt each khac, nd se co gang thiet lap mpt LSP va de node bien bi ldi
tinh toan mpt tuyen mdi tir node/link den LSR bien. Sau khi tuyen mdi dupc thiet
lap, tit ca cac luu lugng dugc chuyen tiep vao tuyen nay.
Cd hai loai co che sira tuyen, chimg dugc gpi la ca che sira tuyen toan cue va
sira tuyen cue bp.
•

Sira chiia toan cue dugc khdi tao giira cac nodes dau cudi. Tuyen dugc lya
chpn la tuyIn dugc tinh loan trudc dd hoac la tuyen dugc tinh toan mpt
cich nang dpng tir cac node bien (bao gom node dau vao va node dau ra).
TuyIn dugc lya chpn la tuyen bio ve ciia tuyen dang cd dir lieu truyin qua.

•

Sira chira cue bp dugc sir dung de sira ldi tai cac diem xay ra 16i hoac gdn
dilm xay ra Ioi. Do vay, nd giim thieu so lugng mat gdi dir lieu. Hon thi
nira, qua trinh sira Idi dugc thyc hien mdt each cue bd din node or link
xay ra ldi do vay qua trinh khoi phuc se dien ra nhanh hon.
23


Mpt khi node S do thay ldi tren tuyen dang van hanh. tdt ca luu lugng se dugi
chuyen tilp tryc tilp tren tuyIn dy phdng thay vi tuyen so cdp. Mpt dieu dang luu)
niia la khi node S nhdn dugc gdi tin ddu tien tir tuyen ngupc. cac gdi tin tiep tuc duo(
giri thong qua tuyIn so cap bi loi. Nhirng gdi tin nay se bj tre tren 2 tuyen trong kh:
truyin tren dudng vdng ngugc tir node ddu vdo den LSR cudi cimg tai diem xay ra loi,
Mpt dilm bdt lgi nira la cic gdi tin den tir hudng ngugc se bi trpn vdi cac gdi tin dang
dupc truyin din. Do dd. cac gdi tin se bj mat trat ty khi qua tuyen dy phdng trong qua
trinh khoi phuc tuyln. Diem bdt Ipi cuoi ciing la tai thdi diem xay ra loi. cac goi tin
quay vong tren cdc link loi cd the bj mat.
ii)

Md hinh cita Makam
Trong mo hinh nay [3, 4]. tie gid Makam da de xudt mpt phuong phap su dung
cac dudng dy phdng dugc thiet lap tir trudc.
Budc ddu tien. nha quan trj mang se tinh loan tuyen tdi uu va thiet lap no la
tuyen so cap. va chpn tuyen toi uu thir hai ldm tuyen du phdng. Sau dd, thong tin se

dugc truyen tren tuyen so cdp
LSR 3
Pre-established
alternaln/e pat

LSR 2

Hinh ~.I6: Thiei lap luven du phong

Khi CO loi xdy ra tren bdt cir lien ket nao tren tuyln so cdp. node LSR se gui'
ban tin FIS de danh dau cd loi va chuyen ban tin nay ngugc lai node ddu vao. Mpt khi
node ddu vao nhdn dugc ban tin FIS. no se chuyen ngugc todn bp luu lupng ddu vao
den tuyen dy phdng. Va ciing tai thdi diem dd. lien kit ldi tren tuyln so cap se dugc
sua ehira. (Hinh ve)
,