baigiang mpls version 3

Li Noi auNgay nay, Internet a tr thanh t ng rat quen thuoc tren toan the gii. Internet a va ang chiem v tr quan trong, phuc vu cho con ngi trong moi lnh vc: quan ly, san xuat kinh doanh, hoc tap, nghien cu, thong tin lien lac va nhng sinh hoat thng nhat. e Internet co c anh hng sau rong nh hom nay khong the khong ke en s phat trien nhanh chong cua ky thuat. Va ky thuat chuyen mach nhan a giao thc MPLS a tr thanh mot ky thuat nen tang quan trong trong Internet. Nhieu nha cung cap dch vu Internet ISP a trien khai ky thuat MPLS e giai quyet nhng van e nh: ky thuat lu lng (traffic engineering) ong thi cung cap hieu qua nhng dch vu IP tren mang ng truc . Quyen nay gom co chn chng: Chng 1: Trnh bay nhng nguyen nhan dan en s ra i ky thuat chuyen mach nhan noi chung va MPLS noi rieng, ong thi neu ra nhng van e ln ma ky thuat chuyen mach nhan can phai giai quyet. Chng 2 va chng 3: Trnh bay nhng khai niem c ban ve ky thuat chuyen mach nhan cung vi hai ky thuat quan trong at nen tang cho s ra i cua MPLS. Ben canh o, la phan trnh bay ve kien truc va nhng giao thc chnh cua MPLS. Chng 4: Trnh bay ve vai tro cua MPLS trong viec cung cap chat lng dch vu va phng thc ma hai mo hnh cac dch vu tch hp (Integrated Services) va cac dch vu phan biet (Differentiated Services) c ho tr trong mang MPLS. Chng 5: Trnh bay chc nang nh tuyen rang buoc MPLS, cac giao thc chnh va nhng ng dung cua no. Chng 6: Trnh bay ve mo hnh mang rieng ao BGP/MPLS VPN. Chng 7: Trnh bay cach thc xay dng mot mang ng truc MPLS. Chng 8: Trnh bay s bo ve mang quang va m rong ra ve y tng hng tng lai cua mang quang la ky thuat ve GMPLS va MPS. Chng 9: Trnh bay ve mot vai mo phong minh hoa cho hoat ong nh tuyen mang MPLS ky thuat DIFFSERV da tren phan mem ma nguon m NS va MNS. V ky thuat chuyen mach nhan noi chung va MPLS noi rieng la mot van e rong nen s trnh bay chac chan khong tranh khoi nhng thieu sot. Xin quy v oc gia ong gop y kien ve a ch E-mail: [email protected]

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Li Ni u CHNG 1: GII THIEU

MC LCTrang 1 Trang 2 Trang 13 Trang 13 Trang 14 Trang 15 Trang 18 Trang 19

1.1. Cac yeu to dan en viec nghien cu chuyen mach nhan1.1.1. S phat trien cua Internet 1.1.2. Gia ca va hieu qua 1.1.3. S tch hp IP tren ATM 1.1.4. M rong cac chc nang nh tuyen 1.2. Tom tat lch s

1.2.1. Bo nh tuyen chuyen mach te bao CSR (Cell Switching Router) cuaToshiba 1.2.2.Chuyen mach IP (IP Switching) 1.2.3.Chuyen mach the (Tag Switching) 1.2.4.ARIS cua IBM Trang 20 Trang 20 Trang 21 Trang 21

1.2.5.Chuyen mach nhan a giao thc (Multiprotocol Label Switching) Trang 21

1.3. Ket luan

CHNG 2: LY THUYET C BAN CUA CHUYEN MACH NHAN Trang 22 2.1.Tong quan 2.2.Khai niem va hoat ong c ban trong MPLS 2.2.1.Mat phang d lieu va mat phang ieu khien 2.2.2.Mat phang d lieu va mat phang ieu khien trong IP 2.2.3.Mat phang d lieu va mat phang ieu khien trong MPLS Trang 22 Trang 25 Trang 25 Trang 25 Trang 26

2.2.4.Nhng lp chuyen tiep tng ng (Forwarding Equivalence Classes FECs) 2.2.5.nh tuyen nhat quan Trang 28 Trang 28 Trang 28

2.3.Chuyen mach nhan: Thanh Phan nh tuyen2.3.1.Nhan la g ?

Bien soan: TS.Tran Cong Hung

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Version 3

2.3.2.Bang chuyen mach nhan 2.3.3.S mang nhan trong goi 2.3.4.Thuat toan nh tuyen chuyen mach nhan 2.3.5.Thuat toan nh tuyen n 2.3.6.Multiprotocol : ben tren va ben di

Trang 28 Trang 31 Trang 31 Trang 32 Trang 33 Trang 34 Trang 35 Trang 36 Trang 36 Trang 37 Trang 37 Trang 40 Trang 42 Trang 42 Trang 42 Trang 43

2.4.Thanh phan ieu khien2.4.1.Ket hp trong va ket hp ngoai 2.4.2.Ket hp ngc dong va ket hp xuoi dong 2.4.3.Nhan t do 2.4.4.Ket hp nhan tuyen ieu khien va tuyen d lieu 2.4.4.1.Hieu qua 2..4.4.2.Van e phat trien 2.4.4.3.S Linh Hoat 2.4.5.S phan bo thong tin ket hp nhan 2.4.5.1.at tren nh cua cac Protocol nh tuyen 2.4.5.2.Nhng giao thc phan bo nhan

2.4.5.3.S thc thi cua cac mat phang ieu khien trong vung chuyen mach nhan 2.4.5.4.Chuyen oi nhan (label swapping) 2.4.6.ieu khien nh tuyen tc thi Trang 45 Trang 47 Trang 48

2.5.Thiet b ra (Edge devices)

2.6.S quan he gia chuyen mach nhan va viec nh tuyen, anh a ch lp mang Trang 49 2.7.Chuyen mach IP (IP Switching)2.7.1.Tong quan ve IP Switching 2.7.2.Cac thanh phan c ban cua chuyen mach IP (IP Switching) 2.7.2.1.Luong 2.7.2.2.Cac kieu luong 2.7.2.3.Phan nhan dang luong Trang 49 Trang 49 Trang 54 Trang 54 Trang 54 Trang 55


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Version 3

2.7.2.4.Phan phan loai luong 2.7.2.5.chuyen mach IP (IP Switch) 2.7.2.6.IFMP 2.7.2.7.GSMP 2.7.2.8.Chuyen mach IP (IP Switch) au va cuoi

Trang 55 Trang 55 Trang 55 Trang 55 Trang 56

2.7.3.Giao thc quan ly luong Ipsilon IFMP (Ipsilon Flow Management Protocol) 2.7.3.1.Giao thc gan ke cua IFMP 2.7.3.2.Giao thc nh tuyen lai cua IFMP 2.7.3.3.S ong goi cho luong Trang 56 Trang 57 Trang 58

2.7.4.Giao thc quan ly chuyen mach chung GSMP (General Switch Management Protocol ) Trang 60 2.7.4.1.Cac kieu ban tin GSMP 2.7.4.2.GSMP V.2 2.7.5. Thc te Trang 61 Trang 62 Trang 63 Trang 63

2.8.Tom tat

CHNG 3: Chuyen mach nhan a giao thc MPLS (Multiprotocol Label Switching) 3.1.Tong Quan chuyen mach the (Tag Switching). 3.1.1. Ho tr cho nh tuyen da vao a ch ch 3.1.2. nh tuyen phan cap (Hierarchy of Routing Knowlegde) 3.1.3. Multicast 3.1.4. Chuyen mach the tren ATM 3.1.4.1.Thong tin nhan 3.1.4.2.Chuyen tiep da tren ch (Destination_based forwarding) 3.1.4.3.S ong goi d lieu tren nhng lien ket non_ATM 3.1.5. Kiem soat lap vong trongnh tuyen tc thi Trang 64 Trang 64 Trang 69 Trang 73 Trang 75 Trang 76 Trang 76 Trang 77 Trang 78

3.2.Chuyen mach nhan a giao thc MPLS (Multiprotocol Label Switching)3.2.1.Nhng iem quan trong cua ky thuat chuyen mach nhan a giao thc MPLS 3.2.2.Cac thanh phan cua mang MPL Trang 81

3.2.2.1.Bo nh tuyen chuyen mach nhan LSR (Label Switching Router) Trang 81


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Version 3

3.2.2.2.LSR ra (LER Label Edge Router)

Trang 81

3.2.2.3.Giao thc phan bo nhan LDP (Label Distribution Protocol) Trang 81 3.2.2.4.ng chuyen mach nhan LSP (Label Switching Path) Trang 81 3.2.2.5.Cac lp chuyen tiep tng ng FEC(ForwardingEquivalent Classes) 3.2.2.6.Nhan (Label) 3.2.2.7.Chong nhan (Label stack ) Trang 82 Trang 82

3.2.3.iu khin LSP th t (Order LSP control) va iu khin LSP c lp (Independent LSP control): Trang 83 3.2.3.1.ieu khien LSP oc lap (Independent LSP control) 3.2.3.2.ieu khien LSP th t (Order LSP control) 3.2.4.S ong goi d lieu 3.2.5.Giao thc phan phoi nhan LDP (Label Distribution Protocol) 3.2.5.1.S kham pha lang gieng LSR (LSR Neighbor Discovery) 3.2.5.2.Cac ban tin LDP 3.2.6.Cac kieu phan phoi nhan (Label Distribution Modes) 3.2.7.ATM Trang 83 Trang 84 Trang 85 Trang 86 Trang 86 Trang 87 Trang 89 Trang 90 Trang 92

3.3.Tom tat

CHNG 4: CHAT LNG DCH VU 4.1.Cac mo hnh chat lng dch vu 4.1.1.Cac khai niem va thuat toan 4.1.1.1.Toc o nh 4.1.1.2.Toc o cam ket 4.1.1.3.Kch thc chum vt troi 4.1.1.4.Token Bucket toc o nh 4.1.1.5.Token Bucket toc o cam ket 4.1.1.6.Bo o toc o trung bnh 4.1.1.7.Bo o trung bnh van chuyen co trong so theo ham mu 4.1.1.8.Bo o Token Bucket 4.1.1.9.V du WFQ va luong MPLS 4.1.2.Tch hp dch vu (Integrated Service)

Trang 93 Trang 94 Trang 94 Trang 94 Trang 94 Trang 95 Trang 95 Trang 95 Trang 95 Trang 95 Trang 96 Trang 96 Trang 98

4.1.2.1.Giao thc danh trc tai nguyen mang RSVP (Resource Reservation Protocol) 4.1.2.2.Cac thanh phan cua RSVP 4.1.2.3.Lien he gia RSVP va MPLS Bien soan: TS.Tran Cong Hung Trang 100 Trang 102

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Version 3

4.1.2.4.MPLS ho tr IntServ

Trang 103 Trang 104 Trang 106 Trang 107 Trang 108 Trang 110 Trang 114 Trang 115 Trang 115 Trang 115 Trang 116

4.1.3. Dch vu phan biet (Differentiated Servives)4.1.3.1.Mien DiffServ 4.1.3.2.Phan loai va ieu khien lu lng 4.1.3.3.iem ma DS 4.1.3.4.MPLS va DIFFSERV 4.1.3.5.Lien mang gia CR-LDP va kien truc mang DS

4.2.VIRTUAL LEASED LINE4.2.1.Dch vu am bao bang thong 4.2.2.Cac ac tnh cua mat phang ieu khien 4.2.3.Cac ac tnh cua mat phang chuyen tiep

4.2.4.Cac bc thc hien e am bao chat lng dch vu trong mang loi Trang 117 4.2.5.Cac dch vu bang thong am bao vi MPLS 4.2.5.1.IP Virtual Leased-Line 4.2.5.2.Virtual Leased-Line lp 2 Trang 118 Trang 118 Trang 119 Trang 120

4.3.Tom tat

CHNG 5: NH TUYEN5.1. TONG QUAN GIAO THC NH TUYEN 5.2. CAC GIAO THC NH TUYEN

Trang 121 Trang 121 Trang 122

5.2.1. Giao thc thong tin nh tuyen RIP (Routing Information Protocol) Trang 122 5.2.2. Giao thc nh tuyen noi IGRP (Interior Gateway Routing Protocol) Trang 122 5.2.3. Giao thc nh tuyen noi cao cap EIGRP (Enhanced Interior Gateway Routing Protocol) Trang 122 5.2.4. M ra ng i ngan nhat au tien OSPF (Open Shortest Path First) Trang 123 5.2.5. Giao thc cong bien BGP (Border Gateway Protocol ) 5.2.5.1.Cac tnh chat cua BGP 5.2.5.2.Thc thi chnh sach 5.2.5.3.Thuoc tnh cua BGP 5.2.5.4.Hoat ong cua BGP Trang 131 Trang 132 Trang 132 Trang 133 Trang 134


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Version 3

5.2.6.CAU HNH RIP, OSPF VA BGP 5.3.KIEN TRUC NH TUYEN INTERNET5.3.1.nh tuyen chnh sach (Policy routing) 5.3.2.Tnh on nh 5.4.NH TUYEN RANG BUOC (CONSTRAINED BASED ROUTING) 5.4.1.nh tuyen rang buoc la g? 5.4.2.Nhng yeu cau ky thuat cua chc nang nh tuyen rang buoc

Trang 138 Trang 141 Trang 145 Trang 147 Trang 150

Trang 150 Trang 151 Trang 152 Trang 154 Trang 155 Trang 155 Trang 155 Trang 156 Trang 157 Trang 157 Trang 158 Trang 159 Trang 159 Trang 160 Trang 161 Trang 166 Trang 166 Trang 166

5.4.3.CSPF (Constrained Shortest Path First) 5.5.MPLS (Multiprotocol label switching)5.5.1.Giao thc RSVP m rong 5.5.1.1.Ban tin PATH 5.5.1.1.1.Label _Request object 5.5.1.1.2.Explicit Route object(ERO) 5.5.1.1.3.Record_route object(RRO) 5.5.1.2.Ban tin RESV 5.5.1.3.Qua trnh xay dng LSP 5.5.1.3.1.Qua trnh gi ban tin Path 5.5.1.3.2.Qua trnh gi ban tin RESV 5.5.1.3.3.ng i cua goi d lieu t igress LSR en egress LSR

5.5.2.CR_LDP (Constrained Label Distribution Protocol) 5.5.3.So sanh gia CR_LDP va RSVP5.5.3.1.Giong nhau 5.5.3.2.Khac nhau

5.5.4.Giao thc ginh trc tai nguyen ho tr phan phoi nhan_RSVP-TE Trang 167

5.5.5.ng dung chc nang nh tuyen rang buoc vao van e quan ly lu lng5.5.5.1.Tai sao quan ly lu lng quan trong oi vi cac nha cung cap dch vu? 5.5.5.2.Ky thuat lu lng trong mang ATM va Frame Relay 5.5.5.3.Mot mang IP co giai quyet c van e nay khong ? 5.5.5.4.Giai quyet van e Bien soan: TS.Tran Cong Hung -7Trang 175 Trang 177 Trang 178 Version 3

5.5.5.5.nh tuyen rang buoc MPLS vi chc nang ky thuat lu lng

Trang 178

5.5.5.6.Chc nang nh tuyen rang buoc trong nh tuyen lai nhanh (Fast Rerouting)5.5.5.7.Chc nang nh tuyen rang buoc vi van e tai nh tuyen nhanh (fast rerouting) 5.5.5.8.PHAT HIEN VA NGAN CHAN VONG LAP TRONG MPLS Trang 182

5.5.6.Chat lng dch vu QoS5.5.6.1.Moi lien he gia chat lng dch vu va nh tuyen 5.5.6.2.LSP Bang thong am bao (Guaranteed Bandwith LSPs)

Trang 184Trang 184 Trang 184

5.6.Tom tat

Trang 185

CHNG 6: MANG RIENG AO (VIRTUAL PRIVATE NETWORKS)

Trang 186

6.1.Nh the nao la mang rieng ao (Virtual Private Networks) Trang 186 6.2.Mo hnh chong lap (Overlay model)6.3.Mo hnh ngang cap (Peer_to_peer model) Trang 186 Trang 190

6.4.Phan bo rang buoc thong tin nh tuyen (Constrained Distribution of routing information) Trang 192 6.5.Bang a chuyen tiep (Multiple Forwarding Table)6.6.a ch VPN_IP (VPN_IP addresses) Trang 194 Trang 195 Trang 196 Trang 198 Trang 198

6.7.MPLS (Multiprotocol Label Switching) 6.7.1.Bao mat (Security)6.7.2.Ho tr chat lng dch vu


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Version 3

6.7.2.1.Mo hnh Pipe (Pipe model) 6.7.2.2.Mo hnh Hose (Hose model)

Trang 199 Trang 200 Trang 202 Trang 202

6.7.3.Kha nang m rong (Scalability) 6.8.Tom tat

CHNG7: XAY DNG MANG NG TRUC MPLS

Trang 203 Trang 203 Trang 204 Trang 205 Trang 205 Trang 208 Trang 208 Trang 208 Trang 209 Trang 209 Trang 209 Trang 210 Trang 1 Trang 211 Trang 211 Trang 212

7.1.Mang MPLS tren goi 7.2.Mang MPLS tren ATM 7.3.Mang MPLS tren hon hp gia ATM va goi 7.4.Tch hp MPLS vao mang ATM7.4.1.Nhng van e can quan tam khi chon thiet b LSR ATM ra 7.4.2.Nhng yeu cau trong la chon LSR ATM

7.5.Xay dng mang MPLS7.5.1.Thiet ke iem truy cap (point of presence PoP) 7.5.2.Thiet ke PoP cua mot LSR ATM n ra 7.5.3.Thiet ke PoP cho cac LSR ra va LSR ATM 7.5.4.Thiet ke bo tap trung, LSR ra va mot LSR ATM 7.5.5.Thiet ke PoP cua mot LSR 7.6.nh hnh lien ket backbone MPLS 7.6.1.Thiet ke iem truy cap 7.6.2.c tnh lu lng t moi PoP 7.6.3.c tnh ma tran lu lng n hng 7.6.4.c tnh ma tran lu lng song hng 7.6.5.Thiet ke cau hnh backbone trung ke 7.6.6.c tnh bang thong ket noi

Trang 213Trang 214 Trang 214 Trang 215


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Version 3

7.6.7.Gan dung lng ket noi 7.6.8.ieu chnh d phong 7.6.9.La chon thiet b thch hp 7.7.Thiet ke nh tuyen lp 3 7.8.nh hnh LVC MPLS 7.8.1.Tien to a ch ch 7.8.2.LVC va s don VC 7.8.3.Thiet ke tnh toan cho LSR ra 7.8.4.Thiet ke tnh toan cho LSR ATM vi s don VC 7.8.5.Thiet ke tnh toan cho LSR ATM ma khong co s don VC CHNG 8: MANG QUANG, GMPLS VA MPS

Trang 216 Trang 216 Trang 217 Trang 217 Trang 219 Trang 219 Trang 219 Trang 220 Trang 222 Trang 223 Trang 224 Trang 224 Trang 225

8.1.WDM va Mang Quang 8.2.Chuyen mach Lambda a giao thc

8.2.1.Anh xa gia chuyen mach nhan a giao thc va bc song quang Trang 225 8.2.2.Loi cua cac ket noi quang 8.2.3.Tng thch ieu khien Trang 227 Trang 227 Trang 227 Trang 228 Trang 229

8.3.GMPLS va dung GMPLS cho Mang quang8.3.1.Xem xet lien mang gia tang 1 lambda va tang 2 nhan 8.3.2.Cac hoat ong cua GMPLS

CHNG 9: MO PHONG HOAT ONG MANG MPLS VA DIFFSERV

9.1.Cau truc NS9.2. DIFFSERV 9.3.Chng trnh mo phong hoat ong mang MPLS: MNS 9.3.1.Gii thieu 9.3.2.MNS ho tr cac chc nang sau cho MPLS PHU LUC A A.1.Cac ng dung cua MPLS

Trang 237 Trang 240 Trang 244 Trang 244 Trang 244 Trang 253 Trang 253


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Version 3

A.2.MPLS VA ATM A.3.MPLS VA FRAME RELAYPHU LUC B

Trang 255 Trang 266 Trang 269

CAU HNH OSPF VA BGPLab 1 Lab 2 Lab 3 Lab 4 Lab 5 PHU LUC C LEASED LINE AO LP 3 VA LP 2 Cau hnh cho mang loi IP Virtual Leased-Line Virtual Leased-Line lp 2 PHU LUC D HIEN THC MPLS TREN LINUX PHU LUC E Ket Luan Thuat Ng Viet Tat TAI LIEU THAM KHAO Trang 286 Trang 281

Trang 293 Trang 303 Trang 304 Trang 307

DERIVEIT CHNG TRNH GIA LAP CHO MANG GMPLS/MPLS


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Version 3

CHNG 1: GII THIEU Internet la mot moi trng kha ly tng cho nhng phat minh ve ky thuat mi. Khi nhng ky thuat ve mang mi ra i th co mot vai y tng hap dan oi vi cac nha nghien cu va au t. Ky thuat chuyen mach nhan a giao thc MPLS (MultiProtocol Label Switching) la mot trong nhng ky thuat o. Chung ta se khao sat s lc ve ky thuat MPLS va tra li mot so cau hoi ve ky thuat nay. Nh la, MPLS la g? No hoat ong nh the nao? Va no se mang lai nhng li ch g? . MPLS c phat trien t nhng ky thuat tng t a c nghien cu gia thap nien 90. Trong o, ky thuat c biet en nhieu nhat la chuyen mach IP (IP Switching) do cac ky s cua cong ty Ipsilon nghien cu, nhng trc o Toshiba a mo ta mot cach thc tng t t nghien cu bo nh tuyen chuyen mach te bao CSR (Cell Switching Router) cua ho va nhieu nghien cu khac a c cong bo, ang chu y la chuyen mach the (Tag Switching) cua Cisco va chuyen mach IP da tren nh tuyen tong hp ARIS (Aggregate Route-based IP Switching) cua IBM. Tat ca cac nghien cu tren co vai ac iem chung la ho eu s dung ky thuat trao oi nhan e nh hng d lieu, dung nhng mau ieu khien cua bo giao thc Internet. Ngha la, ho s dung a ch IP va cac giao thc chuan nh hng d lieu dung trong Internet nh OSPF va BGP. Tuy nhien, nhng nghien cu o khac nhau chu yeu muc ch cua no cung nh chi tiet xay dng tao thanh. Vi cac hoat ong nh vay, IETF (Internet Engineering Task Force) a thanh lap mot nhom nghien cu e chuan hoa nhng ket qua chung da tren nhng y tng tren. V khong muon trung ten vi cac san pham cua cac cong ty, IETF a at ten cho nhom la MPLS (MultiProtocol Label Switching). Ky thuat MPLS dan ang tr thanh 1 chuan cong nghiep. Chung ta se nghien cu tong quan va phan tch ve ky thuat MPLS cung nh nhng van e lien quan. e de dang hn trong qua trnh tm hieu, chung ta se lam ro vai thuat ng c s dung thng xuyen: Chuyen tiep (forwarding) : la hoat ong chuyen (switch) va nh tuyen (route) mot goi (packet) : nhan goi mot ngo vao, xac nh no can i en au bang cach xem xet trng thong tin trong no va gi no ra ung ngo ra thch hp. Nhan (label) : n gian la mot khung nhan dang ngan, co chieu dai co nh c dung e nh tuyen cac goi. Gia tr cua nhan thng c gan vi 1 lien ket n ( single link) . Nhan khong co cau truc, ngha la no khong bao gom nhng thanh phan phan biet. Mot thiet b chuyen mach nhan se thay nhan trong mot goi bang mot gia tr mi trc khi chuyen tiep no ti iem tiep theo, do o chung ta goi thuat toan nh tuyen la thuat toan trao oi nhan. Ngoai ra chung ta con nh ngha mot thiet b chuyen mach nhan la Bo nh tuyen chuyen mach nhan LSR (Label Switching Router), dung nhng giao thc ieu khien IP chuan (v du giao thc nh tuyen RSVP) e xac nh phai chuyen tiep goi i au. Chung ta cung se khao sat nhng ky thuat co trc MPLS, cac ky thuat nay eu la ky thuat chuyen mach nhan, nhng moi cai co cach thc hien rieng. NhngBien soan: TS.Tran Cong Hung - 12 Version 3

ten khac c cac nha nghien cu at cho LSR la Bo nh tuyen chuyen mach te bao CSR (Cell Switching Router), chuyen mach IP (IP Switching), Bo nh tuyen chuyen mach the TSR (Tag Switching Router) hay chuyen mach the (Tag Switch) va Bo nh tuyen chuyen mach tch hp ISR (Integrated Switch Router). Ngoai ra con co nhieu nghien cu khac ma chung ta khong e cap ay v no khong khac bon nghien cu tren lam. Chung ta cung khong xet en cac bo nh tuyen da tren chuyen mach (Switch-based Routers), co hoat ong giong mot router bnh thng nhng c lam ben trong mot Switch hon hp. Nhng thiet b o la nhng thiet b hu dung nhng dung e giai quyet cac van e khac ch khong phai la LSR. Trc khi xem xet chi tiet cac nghien cu tren, chung ta can nen biet qua 1 so yeu to sau: 1.1. Cac yeu to dan en viec nghien cu chuyen mach nhan Co nhieu yeu to dan en s phat trien cua chuyen mach nhan. Trc kia ngi ta ch quan tam en mot yeu to, o la yeu cau co nhng bo nh tuyen IP gia re, nhng toc o nhanh. No co the ung cho mot hoac hai nghien cu trc MPLS, chung ta se e cap phan sau, noi chung chuyen mach nhan c thuc ay phat trien bi nhieu yeu to khac hn la yeu cau ve toc o. Trong phan sau, ta se e cap en tam quan trong cua tng yeu to trong s phat trien cua chuyen mach nhan. Tuy nhien, s ket hp cua tat ca cac yeu to o lai se cho ta thay tai sao MPLS dng nh chac chan la mot phan cua cong nghe ve mang trong hien tai va tng lai.1.1.1. S phat trien cua Internet

Internet ro rang ang phat trien khong ngng, va chnh s phat trien nay a cho thay cac iem yeu cua cac ky thuat cu. S gia tang ca ve so lng ngi dung a lam tang yeu cau ve bang thong c cung cap t cac nha cung cap dch vu Internet (ISP). e thoa man yeu cau ve bang thong, cac ISP can co nhng san pham chuyen mach va nh tuyen co hieu qua cao. Chung ta se thao luan ve anh hng va hieu qua trong phan ke tiep. Khi phat trien nhanh, cac mang phai oi mat vi s gia tang so lng nut mang, so lng router trong cac bang nh tuyen, so lng cac luong i qua mot nut mang,. Nhn chung, cac nha cung cap mang can quan tam en van e kha nang phat trien, ngha la, kha nang phat trien moi hng. Chuyen mach nhan c thuc ay 1phan cung do nhu cau cua van e phat trien. Nhng co le yeu to quan trong nhat la nhu cau a dang chc nang nh tuyen cua Internet va cua mang IP (IP Network) noi chung. S phat trien cua Internet lien tuc at ra nhng yeu cau mi cho cac giao thc nh tuyen. Trc kia, cac chc nang nh tuyen kho co the a dang, mot phan ly do la s giong nhau gia van e nh tuyen va chuyen tiep trong mang IP. V du, xem xet qua trnh x ly trong viec s dung nh tuyen lien mien khong phan lp CIDR (Classless Interdomain Routing). S anh hng cua CIDR la e noi ve tien to mang IP, trc kia la 8, 16 hay 24 bit, gi co the lay tuy y. S m rong nay cho phep m rong a ch va thong tin nh tuyen. Tuy nhien, thc hien thay oi nay cung yeu cau thay oi giai thuatBien soan: TS.Tran Cong Hung - 13 Version 3

nh tuyen cua tat ca cac bo nh tuyen IP, bi v tien to co the lay bat c gia tr nao. Nhng giai thuat nay a c thc hien ca phan cng lan phan mem, do o viec thay oi no khong phai la chuyen n gian. Mot trong nhng iem thu v cua chuyen mach nhan la giai thuat nh tuyen th co nh va nhng cach ieu khien mi co the s dung ma khong can phai thay oi no, va chung ta se thay trong cac phan tiep la cac cach ieu khien khac nhau co the c s dung e ieu khien qua trnh chuyen mach nhan va chung hau nh s dung chung giai thuat nh tuyen. Do o, co the a toan bo viec thc hien giai thuat nh tuyen bang phan cng hay bang mot phan mem co toc o cao ma khong quan tam en viec phai toi u lai no moi khi trien khai mot chc nang nh tuyen mi. No ha hen hap dan trong viec phat trien va trien khai nhng chc nang mi trong mang IP. Va ay co the chnh la li ch ln nhat cua chuyen mach nhan va ket qua la chuyen mach nhan dng nh thc hien nen mong cho the he tiep theo cua kien truc nh tuyen.1.1.2. Gia ca va hieu qua

Trong bat k mang nao ma da tren bo giao thc cua Internet, th mot trong cac thanh phan quan trong la bo nh tuyen (router). Nhiem vu c ban nhat cua mot router la nh tuyen cac goi IP (hoac datagram) qua mang. Ngoai ra, router con thc hien cac chc nang khac nh la loc ra mot luong cua cac goi t nhng phan khac nhau cua mang. That s, tnh chat quan trong nhat cua mot router cho nhieu ng dung khong phai la toc o ma la s a dang ve chc nang ma no cung cap. Mot bo phan quan trong khac trong mang o la chuyen mach (switch). Trong khi router la thiet b lp 3 (no nh tuyen cac goi IP) th switch la thiet b lp 2 (no nh tuyen cac goi cua giao thc lp 2). So sanh vi router th switch n gian hn, no ch cung cap mot so lng rat gii han cac giao thc va cac kieu giao tiep, con router thng cung cap mot lng ln cac giao thc, nhieu kieu giao tiep va toc o. Giai thuat nh tuyen cua switch th n gian va t thay oi, nhieu kieu chuyen mach (switch) nh chuyen mach ATM (ATM switch) hay chuyen mach Frame Relay (Frame Relay switch) s dung giai thuat nh tuyen da tren viec trao oi nhan. Vi s khac nhau nh vay gia switch va router, th ng nhien co s khac nhau ve gia ca/ hieu qua gia chung. Nhng trc het chung ta phai xem hieu qua la g trong trng hp nay, viec nay kha phc tap v b anh hng bi nhieu yeu to, tuy nhien thong thng no c tnh la so lng goi ma thiet b co the nh tuyen trong 1 giay gia ngo vao va ngo ra tren tong dung lng bang thong cua no. Khi chung ta xem xet gia ca/ hieu qua cua switch va router, ta thay switch thng troi hn. Ngha la, vi mot mc hieu qua nh trc, gia cua mot router thng cao hn gia cua mot switch tng ng, ngc lai, vi mot chi ph cho trc, mot switch thng cho hieu qua cao hn mot router v ta thay router phai nh tuyen goi va thc hien cac dch vu khac trong khi o switch ch nh tuyen goi. Van e ma chung ta ban en ay nham muc ch ch ra la switch thng co hieu qua cao hn router.Bien soan: TS.Tran Cong Hung - 14 Version 3

Switch dan ra mot s yeu to thuc ay a ra chuyen mach nhan. Chung ta co the xay dng mot thiet b ma co the thc hien hau het cac cong viec cua mot router ma s dung phan cng giong mot switch. Khi quy mo Internet c m rong va IP la giao thc duy nhat c s dung th viec nh tuyen IP mc gia ca / hieu qua cua mot switch qua la hap dan.1.1.3. S tch hp IP tren ATM

Chung ta biet rang kien truc cua ATM rat khac vi kien truc cua IP, trong khi IP phan phoi cac datagram va s dung kieu khong ket noi th ATM da tren kieu hng ket noi hay ket noi ao. ATM va IP cung hoan toan khac nhau trong cach anh a ch cac host. Nhng s khac nhau nay a a ra nhieu thach thc ln, chuyen mach nhan ra i cung nham ap ng cac thach thc nay. Vi nhng u iem cua ATM va s phat trien ngay cang ln cua Internet a a ra van e lam sao a kien truc IP vao mang ATM. S khac nhau ve hieu qua gia cac chuyen mach ATM va cac router hien tai a lam cho van e them phc tap. Phan ln mang hom nay c xay dng theo kieu la cac router toc o cham bao xung quanh cac chuyen mach ATM (ATM switch) nh hnh 1.1.

Hnh 1.1.Mo hnh IP tch hp tren ATM [1]. Kieu cua mang nay thng goi la kieu xep chong, y tng la mang IP nam ben tren mang ATM. Mang ATM cung cap ket noi toc o cao va mang IP gom cac router c ket noi vi nhau bi cac ket noi ao cua ATM. Van e anh xa IP vao ATM c nghien cu bi nhieu nhom ngoai hai to chc chnh la ATM Forum va IETF nh la : Nhom IPATM (The IP over ATM) nghien cu s goi cac IP datagram vao lp PDU cua ATM va mot giao thc phan giai a ch ATMARP e anh xa a ch IP vao a ch ATM.Bien soan: TS.Tran Cong Hung - 15 Version 3

Nhom IPLPDN (IP over Large Public Data Networks) va sau o la nhom ROLC (Routing over Large Clouds) a ra NHRP (Next Hop Revolution Protocol) cho phep cac host va router co the tao mot ket noi ao trc tiep thong qua mang ATM. Nhom LANE (The LAN Emulation) a ra nhng thu tuc e lam cho mang ATM hoat ong giong mang LAN a truy cap. Nhom MPOA (Multiprotocol over ATM) a ket hp va phat trien cac ket qua cac nhom khac e a ra s ho tr nhieu giao thc (protocol) lp mang (trong o co IP). Hau het cac nhom tren eu a ra vai kieu server (ATMAPR, MARS, NHRP, BUS,) e thc hien viec anh xa nay cung nh nhng giao thc can thiet e giao tiep vi cac server nay. Van e tiep theo la phai co them cac server khac cung vi cac giao thc ong bo e gi chung hoat ong ong bo vi nhau. Tai sao van e lai phc tap nh vay, la do cac giao thc Internet va cac giao thc ATM c phat trien oc lap vi nhau va hoat ong tren cac iem khac nhau. Va co nhieu ngi t hoi neu mot chuyen mach ATM (ATM switch) co the s dung cac giao thc khac ngoai nhng giao thc do ATM Forum va ITU nh la cac giao thc phu hp vi kien truc IP hn th se giam nhieu s phc tap cua viec anh xa. Nhieu ky thuat chuyen mach nhan thc s tao ra nhng giao thc nh vay, no co the ieu khien mot chuyen mach ATM (ATM switch) hoat ong nh la nh tuyen cac goi IP mot cach t nhien ma khong can nh en cac server anh xa gia IP va ATM. Thay v co hai kien truc giao thc khac nhau vi s khac nhau ve cach anh a ch, cac giao thc nh tuyen, cac ke hoach nh tai nguyen, th chuyen mach nhan cho phep nhng giao thc ieu khien IP chay trc tiep tren phan cng cua ATM. Nhng chuyen mach ATM (ATM switch) th van nh tuyen cac goi nh ky thuat trao oi nhan, nhng cach thc ma no tao bang nh tuyen va tnh toan tai nguyen eu c ieu khien bi cac giao thc ieu khien cua IP. Vi cach thc ieu khien nh vay, chuyen mach ATM (ATM switch) tr thanh cac router cua IP do o loai bo yeu cau phai anh xa gia IP va ATM. * Van e phat trien ay la van e t c biet en nhng lai tr nen quan trong khi mot mang IP c xay dng xep chong tren mot lp 2 khac kieu, nh la Frame Relay hay ATM.


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Hnh 1.2.: Cac kenh ao (Virtual circuits) gia cac router trong mang IP/ATM [1].

Xem xet mang trong hnh 1.2, mang ATM trung tam cung cap ket noi toc o cao cho tat ca cac router bang cac kenh ao noi gia chung, nh ta thay luon co mot router nam gia cac cap router va ieu nay co the gay ra s nghen tai router nay. Tuy nhien, mot ket noi hoan toan cac kenh ao cho phep cac router co the noi trc tiep en cac router con lai. Trong hnh 1.2 ch ve nhng kenh ao cho 1 router e tranh lam roi hnh ch that s la co n(n-1) kenh ao, la 55 trong hnh. e co the hieu ro van e ay, chung ta can biet qua cach hoat ong cua cac giao thc nh tuyen. Moi router thng c cau hnh co mot ch so gan cho moi router khac ket noi trc tiep vi no, ch so nay cho phep router luon biet nhng router ma ket noi en no va biet ca ket noi nao khong the hoat ong, no con c dung e trao oi thong tin nh tuyen gia cac router. Nhieu nghien cu a thc hien e lam giam nhe van e phat trien. Trong o co cach la khong lam ket noi hoan toan gia cac router, ngha la co vai ket noi gia hai router phai qua mot router trung gian khi ma hieu qua cua router trung gian nay chap nhan c. Cach khac, Next Hop Resolution Protocol (NHRP) cho phep router thiet lap nhng kenh ao en nhng tram ma no can gi d lieu ma khong can phai thiet lap cac ch so nh tuyen qua kenh ao. Tuy nhien, no co nhng van e rieng nh la no can phai co cac NHRP server va phai co kha nang khong cho xay ra viec nh tuyen lap vong. NHRP ch phu hp cho cac lu lng unicast, no khong ho tr cho multicast. Nhng nghien cu khac giai quyet van e nay bang chuyen mach nhan. au tien, nhac lai la mot LSR s dung cac giao thc ieu khien cua IP, bao gom ca cacBien soan: TS.Tran Cong Hung - 17 Version 3

giao thc nh tuyen chay tren phan cng cua ATM. Do o, vi cau truc mang nh hnh 1.2, chung ta co the giam ang ke so lng ch so cua cac router s dung giao thc cua IP tren nen ATM, co the thay ieu nay tren hnh 1.3.

Hnh 1.3.Thay chuyen mach ATM bang LSR [1]. V chuyen mach ATM co the chay cac giao thc nh tuyen cua IP, nen cac tram trung gian thay v la cac router th nay la cac LSR, do o so lng cac ch so ma cac router phai co giam ang ke va se khong tang theo kch thc cua mang. Chu y rang hnh 1.2 cac router co 10 ch so th nay ch co 1 (noi vi LSR), va LSR co khong qua 5 ch so, 3 noi vi 3 router, 2 noi vi LSR khac. Ta thay no luon gi ch so o khi mang c m rong, va van e phat trien a co the c chap nhan.1.1.4. M rong cac chc nang nh tuyen

ieu quan trong chung ta phai chu y ay la chuyen mach nhan khong ch nham bien mot phan cng ATM hoat ong giong mot router ma no con cung cap nhng chc nang mi ma cac ky thuat nh tuyen IP hien tai khong cho phep. ay cung la mot yeu to thuc ay s ra i cua chuyen mach nhan. phan nay chung ta se tm hieu them ve s phat trien cua viec nh tuyen a noi trong phan trc. Hien nay, viec nh tuyen trong mang IP la da vao a ch ch, ngha la quyet nh phai gi goi i au la da vao a ch ch. Ve nguyen tac, cac trng khac trong tieu e IP (IP header) (a ch nguon, kieu cua dch vu) eu co the c s dung trong viec quyet nh cho goi tin nhng hau het cac nghien cu thiet ke cho router eu ch s dung a ch ch. Trong khi o cac ky thuat mang ma co s dung ky thuat trao oi nhan nh la Frame Relay hay ATM co the cung cap nhng chc nang khac nhau. e co the hieu chuyen mach nhan ho tr nhng ky thuat mi nh the nao, ta xet mang co cau truc trong hnh 1.4.Bien soan: TS.Tran Cong Hung - 18 Version 3

ay la mot v du ien hnh ve cac chc nang ma kieu nh tuyen truyen thong kho the cung cap. Xem xet trng hp khi router B la mot router kieu truyen thong, nh tuyen cac goi bang cach s dung a ch IP ch. Khi mot goi en B t mot trong cac router lan can, quyet nh nh tuyen ch da vao a ch ch ma khong b anh hng bi bat c yeu to khac. Nhng gi gia s ta muon nhng goi i t router A e en router F th i qua router D con nhng goi khac en router F th i qua router E, ro rang c che nh tuyen ch da vao a ch ch khong the thc hien c ieu nay. Nhng se de dang thc hien ieu nay tai router B neu B nh tuyen goi bang ky thuat chuyen mach nhan. Nguyen nhan chnh la A va C s dung cac nhan khac nhau, gia s A s dung nhan co gia tr la 5 cho cac goi co ch la F con C s dung nhan 12. Do o, tai B khi cac goi en no se nh tuyen goi co nhan 5 en D va goi co nhan 12 en E. Mac du v du nho nay khong i sau vao chi tiet nhng no cho ta thay chuyen mach nhan ho tr nhieu chc nang nh tuyen mi ma kieu nh tuyen truyen thong khong the ho tr. 1.2. Tom tat lch s Bay gi chung ta a biet nhng ly do tai sao cac nha nghien cu lai quan tam en ky thuat chuyen mach nhan, va chung ta cung nen co mot cai nhn tong quan ve cac s kien a dan en tnh hnh hien nay.1.2.1. Bo nh tuyen chuyen mach te bao CSR (Cell Switching Router) cuaToshiba

Bo nh tuyen chuyen mach te bao (Cell Switching Router) cua Toshiba la nghien cu au tien ve chuyen mach nhan c cong bo. Kien truc cua CSR a gii thieu y tng la mot phan cng ATM hon hp co the c ieu khien bi IP (nh la cac giao thc nh tuyen IP hay RSVP) hn la cac giao thc bao hieu cua ATM (nh Q.2931). Theo nghien cu nay th co the bo cac bao hieu ATM va ca chc nang anh xa gia IP va ATM. Y tng CSR au tien c trnh bay trc IETF vao cuoi nam 1994 va au 1995, vao thi iem nay cung co nhieu nhom nghien cu khac ang tap trung vao phat trien y tng tng t.


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1.2.2.Chuyen mach IP (IP Switching) [4]

Vi nhieu nguyen do, bao gom toi u ve thi gian, san pham co chat lng, cach thc tiep th hieu qua, chuyen mach IP (IP Switching) c nh ngha ban au bi cong ty Ipsilon a anh hng ln len th trng va gii ky thuat hn la nghien cu CSR. Ipsilon cong bo nghien cu cua ho vao au nam 1996. Ve mat ky thuat th hai nghien cu co nhieu iem tng ong, tuy nhien nhng u iem cua chuyen mach IP hn cac nghien cu trc o co the de dang thay c nh sau: Chuyen mach IP cho phep 1 thiet b vi hieu qua cua mot chuyen mach ATM ma co the thc hien cong viec cua mot router. Nhng router toc o cao (khong phai la chuyen mach ATM ) co the thc hien bi v IP va cac giao thc cua Internet ang la nhng giao thc chu yeu hien nay ma cac router hien tai th qua cham. Bao hieu ATM va viec anh xa IP vao ATM a tr nen qua phc tap, cho muc ch nh tuyen IP chung ta cung khong can cac giao thc ieu khien ATM. Nhng tai lieu cua Ipsilon c cong bo trong mot so cac tai lieu Internet la RFC. Mac du khong phai tat ca RFC eu la tieu chuan, cac tai lieu cua Ipsilon c coi la nghien cu m v vai giao thc c cong bo a c thc hien. Mot ong gop co gia tr na la viec lam ro mot giao thc ieu khien chuyen mach n gian GSMP cho phep bien bat c mot chuyen mach ATM nao thanh mot chuyen mach IP vi nhng chc nang mi c bo sung. e ro rang, chung ta se s dung thuat ng chuyen mach IP la noi ve nghien cu cua Ipsilon, mac du no thng c s dung cho khac e e cap en viec m rong van e cua cac nghien cu khac. Thuat ng tong quat c s dung khi can thiet th chung ta s dung thuat ng chuyen mach nhan.1.2.3.Chuyen mach the (Tag Switching)

Vai thang sau khi Ipsilon cong bo nghien cu cua ho, Cisco Systems cong bo mot nghien cu khac ve chuyen mach nhan ma ho at ten la chuyen mach the. Nh chung ta se thay phan sau, chuyen mach the la mot ky thuat xuat sac xuat phat t cac nghien cu chuyen mach IP va CSR. V du la no khong da tren dong lu lng d lieu e thiet lap bang nh tuyen trong chuyen mach va no con c lam e phu hp vi nhieu ky thuat lp lien ket (link layer) khac na ngoai ATM. Giong Ipsilon, Cisco dung 1 RFC e mo ta nghien cu cua ho, nhng khong giong Ipsilon, Cisco cong bo phat minh cua ho e thuyet phuc s tieu chuan hoa cua chuyen mach the qua IETF. Va sau o, mot lng ln cac bai viet ve Internet c cong bo, mo ta nhng k vong cua chuyen mach the, bao gom hoat ong tren ATM, PPP, lien ket 802.3, ho tr cho nh tuyen multicast, cho s d tr tai nguyen s dung RSVP. S tieu chuan hoa nhng co gang lam viec cua Cisco a ra a tr thanh chuyen mach nhan a giao thc MPLS (Multiprotocol Label Switching) va MPLS hien nay c s dung rong rai nh la mot thuat ng cua chuyen mach nhan.


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1.2.4.ARIS cua IBM

Ch sau s cong bo cua Cisco va viec co gang tieu chuan hoa cua IETF mot thi gian ngan, mot lng bai viet Intenet a c phat hanh bi cac tac gia t IBM, mo ta mot nghien cu khac ve chuyen mach nhan goi la chuyen mach IP da tren bo nh tuyen tong hp (Aggregate Router-based IP Switching) hay ARIS. ARIS th giong vi chuyen mach the hn la cac nghien cu khac nh la viec dung lu lng ieu khien e thiet lap bang nh tuyen ch khong phai dung lu lng d lieu, nhng ARIS khac vi chuyen mach the vai iem ang ke. Nhieu y tng cua ARIS a co trong viec tieu chuan hoa MPLS.1.2.5.Chuyen mach nhan a giao thc (Multiprotocol Label Switching)

Khi Cisco cong bo ve chuyen mach the, ho cung mong muon c tieu chuan hoa ky thuat nay. Sau mot loat bao cao au tien cua chuyen mach the tren bao cao Intenet, mot hoi ngh BOF ( Birds of a Feather), la hoi ngh can thiet trc khi to chc mot nhom nghien cu, va xac nh van e nao can tieu chuan hoa) c to chc vao thang 12 nam 1996, vi s trnh bay cua Cisco, IBM, va Toshiba (luc nay cong bo nhng bao cao mi ve CSR). Hoi ngh BOF nay la mot trong cac buoi tham d tot nhat trong lch s IETF. Vi mc o quan tam trong BOF va vi thc te la co qua nhieu cong ty a ra nhieu giai phap tng t ch cho 1 van e, th viec tieu chuan hoa phai ra i la chuyen phai lam. Do o viec thanh lap nhom nghien cu cho viec tieu chuan hoa c IETF chap nhan vao au nam 1997. Va cuoc gap au tien cua nhom dien ra vao thang 4 nam 1997. Nh a noi tren, ten chuyen mach nhan a giao thc (Multiprotocol Label Switching) c chap nhan chu yeu bi ten chuyen mach IP va chuyen mach the a c at cho san pham cua cac cong ty. Mac du dung ten la a giao thc (Multiprotocol) nhng chu yeu ch tap trung vao cac giao thc cua IP hn la cac giao thc cua lp mang khac. 1.3. Ket luan Chung ta a khao sat mot cach s lc s ra i cua ky thuat chuyen mach nhan. Va e hieu ro hn ve ky thuat nay chung ta se xem xet cac nghien cu tieu bieu cho ky thuat nay, o la chuyen mach IP, chuyen mach the , sau cung la MPLS.


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Version 3

CHNG 2: LY THUYET C BAN CUA CHUYEN MACH NHAN 2.1.Tong quan

Khi mang internet ngay cang m rong cung vi s phat trien cua cac dch vu gia tang cung nh cac yeu cau ve chat lng dch vu va tnh bao mat, MPLS la mot giai phap toi u. No ket hp cac u iem cua IP va ATM ma chi ph trien khai cung khong qua at, co the phoi hp va nang cap t cac mang ATM hoac Frame Relay a co san. Ngoai ra, MPLS con la mot giai phap toi u cho dch vu VPN va cac ng dung oi hoi ve chat lng dch vu va ky thuat lu lng. Hau het cac mang dien rong Viet Nam eu c to chc vi ket noi s dung dch vu thue kenh rieng, X25 hoac Frame Relay thong qua cac nha cung cap dch vu vien thong. Hau het chung eu hoat ong da tren nh tuyen IP truyen thong vi khong t nhc iem, ap ng cham khi co yeu cau x l luong lu lng ln tren mang, lam cho viec x ly tai cac router b qua tai. Hau qua la mat lu lng, mat ket noi va lam giam ac tnh mang. Ngoai ra, moi nut trong mang eu phai thc hien hai chc nang la nh tuyen va chuyen tiep. Qua trnh chuyen tiep ch da tren a ch ch cua goi ma khong da tren cac tham so chat lng dch vu. MPLS c xem la giai phap cho cac van e nay. iem noi bat cua cong nghe MPLS la kha nang chuyen tiep lu lng nhanh, n gian, ieu khien phan luong, nh tuyen linh hoat va tan dung tai nguyen mang. No ket hp nhng ac iem tot nhat cua chuyen mach kenh trong ATM va chuyen mach goi trong IP, co kha nang chuyen tiep goi rat nhanh trong mang loi va nh tuyen nh bnh thng mang bien. Khi cac goi i vao mien MPLS, thng la mang truc cua nha cung cap dch vu, chung c chuyen mach n gian bang chuyen mach nhan. Cac nhan con giup xac nh chat lng dch vu ma cac goi nhan c. Khi chung ra khoi mang th cac nhan se c cat bo cac router bien mang va c nh tuyen nh thong thng. MPLS co mot so u iem hn nh tuyen IP nh chuyen cac goi qua mang nhanh hn router IP. Trong IP, viec nh tuyen ch da vao tieu e cua goi con MPLS co the phan biet cac giao dien khac nhau, cac thong tin khac nhau e xac nh chnh sach x l thch hp, oi khi goi co the c nh tuyen theo mot ng biet trc khi goi i vao mang. Ta xet qua hoat ong cua cac router ho tr MPLS, goi la bo nh tuyen chuyen mach nhan LSR (Label Switching Router): chang au tien trong mang MPLS, router chuyen tiep goi da vao a ch ch (hoac bat c thong tin nao phan tieu e theo chnh sach cuc bo); sau o no xac nh mot nhan thch hp gia tr nay c xac nh cho mot lp chuyen tiep tng ng FEC gan nhan cho goi va chuyen no ti nut tiep theo. chang tiep theo, router dung gia tr cua nhan nh mot ch muc cua mot bang e xac nh nhan mi. LSR gan nhan mi roi chuyen goi en nut tiep theo. Tuyen ng ma mot goi gan nhan i qua c goi la ng- 22 -

chuyen mach nhan LSP (Label Switched Path). Do MPLS s dung nhan e quyet nh chang tiep theo nen router t phai lam viec hn va hoat ong gan giong vi switch. V cac nhan the hien cac tuyen ng i trong mang nen cac nha quan tr mang co the ieu khien chnh xac hn cac qua trnh x l lu lng trong mang bang cach dung cac chnh sach nhan. Co hai cach chnh e gan va phan phoi nhan la mo hnh lai d lieu va mo hnh lai s kien. Mo hnh lai d lieu nh chuyen mach IP (Ipsilon) hay bo nh tuyen chuyen mach te bao (Toshiba). Mo hnh lai ieu khien nh chuyen mach the (Cisco), IP Navigator (Ascend/Lucent) va ARIS MPLS (IBM), MPLS. Khac vi qua trnh nh tuyen va chuyen mach thong thng cua mang IP la da tren tieu e cua goi tin IP, trong mang MPLS, qua trnh chuyen mach da tren mot nhan gan them vao goi tin. Con qua trnh nh tuyen th khong khac biet nhieu lam, tc van da vao a ch IP va cac giao thc nh tuyen e nh tuyen. Tuy nhien router con phai nam gi s thay oi ve nhan cua cac goi tin khi i cac goi nay c chuyen tiep qua router. Nh vay, khac vi router thong thng, cac router trong mang MPLS phai hieu c cac giao thc phan phoi nhan. (Tuy nhien, vi nh tuyen rang buoc, ta co the ch nh mot con ng oc lap vi cac giao thc nh tuyen). e minh hoa hoat ong cua MPLS, ta hay xet ng i cua mot goi tin theo tng bc trong mang sau.

Thiet b PE1 P1 P2 PE2

Serial 0/0 192.168.1.10 192.168.1.9 192.168.1.13 192.168.1.17

Serial 0/1

Loopback 0 192.168.1.1

192.168.1.14 192.168.1.18

192.168.1.2 192.168.1.3 192.168.1.4

a ch IP cac thiet b


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Version 3

Trc het, cac giao thc nh tuyen nh OSPF, IS-IS hoat ong e xay dng nhng router ke can trong bang nh tuyen cua mot router. (Router ke can la router ke tiep ma goi tin can c truyen en e en c mot ch nao o). Ta co the dung lenh:PE1#show ip route

Ke en, giao thc phan phoi nhan se hoat ong e gan nhan va ta se co mot s tng ng gia mot nhan va mot router ke can cung vi cong ngo ra tng ng. Trong mang MPLS, bo nh tuyen ngoai ra co 2 ngo la ingress (ngo vao) va egress (ngo ra). Bo nh tuyen ngo vao se nhan vao mot goi IP va thc hien so sanh trong bang nh tuyen, sau o gan nhng dch vu tng ng len goi tin o, va cuoi cung gan nhan thch hp da tren nhng dch vu o. Nhng nhan khac nhau se bieu th nhng mc dch vu khac nhau trong mang Va khi goi tin a co nhan, no c chuyen en thiet b ke tiep va router ke tiep se xem trong bang chuyen tiep e xac nh cong ra va nhan can dung cho goi tin. Ta co the dung lenh:PE1#show mpls forwarding-table

Sau khi i qua mot bo chuyen mach nhan gia th nhan cua moi goi tin se thay oi. Moi bo chuyen mach nhan gia ch hoat ong n gian la chuyen oi (swapping) nhan. Va hoat ong tng t nh the xay ra thiet b ke tiep cho en khi goi tin en thiet b cuoi cung la bo nh tuyen chuyen mach nhan ngo ra. Bo nh tuyen nay biet no la thiet b cuoi cung trong mang MPLS. No se tach nhan ra va gi goi tin IP en chang ke tiep tc vao mang IP cua khach hang. Qua trnh di chuyen tiep theo cua goi th hoan toan tng t nh trong trng hp mang IP thong thng. Nh vay ay, ta thc hien chuyen cac goi tin trong mang ch da vao nhan goi tin thay v a ch. Va qua ay ta cung thay c mot so u iem tuyet vi cua chuyen mach nhan. au tien la toc o rat nhanh va o tre cung nh o tre rung pha (jitter) la rat thap. Do nhan dung e tham chieu (index) trc tiep en bang chuyen tiep cua router nen ch yeu cau truy cap bang nay mot lan, trong khi nh tuyen truyen thong phai yeu cau truy cap bang nh tuyen hang ngan lan e tm ra a ch IP phu hp nhat. Do o chuyen mach nhan giam c o tre va thi gian ch ap ng tai moi nut keo theo lam giam o bien ong tre rung pha cong don khi goi tin i qua nhieu nut, ieu nay rat co y ngha oi vi cac ng dung thi gian thc. Tuy nhien, l do e s dung chuyen mach nhan khong ch dng ay ma con do tnh n gian va de m rong cua no. Chuyen mach nhan cho phep ghep nhieu a ch IP vi mot hoac mot so nhan ma thoi nen lam giam kch thc cua bang a ch, cho phep router ho tr nhieu ngi dung hn. Va oi vi cac c s ha tang mang von co san chc nang chuyen mach, chuyen tiep trong phan cng nh cac router hay cac chuyen machBien soan: TS.Tran Cong Hung - 24 Version 3

ATM, Frame Relay, ta ch can phu len them phan mem tng ng e ieu khien viec chuyen mach nhan ma thoi.2.2.Khai niem va hoat ong c ban trong MPLS

2.2.1.Mat phang d lieu va mat phang ieu khien Mot mat phang ieu khien (control plane) la mot tap hp phan mem va/hoac phan cng trong mot thiet b, chang han mot router, va c dung e ieu khien nhieu hoat ong thiet yeu trong mang, nh phan phoi nhan, tm tuyen mi, va khac phuc loi. Nhiem vu cua mat phang ieu khien la cung cap cac dch vu cho mat phang d lieu. Mat phang d lieu chu trach nhiem chuyen tiep lu lng ngi dung qua router. Cac thuat ng mat phang ngi dung (user plane) hoac mat phang truyen dan (transport plane) cung c dung e mo ta mat phang d lieu. 2.2.2.Mat phang d lieu va mat phang ieu khien trong IP Hnh 2.2 mo ta moi quan he gia mat phang ieu khien IP va mat phang d lieu IP. oi vi cac giao thc Internet, cac v du cua mat phang ieu khien la cac giao thc nh tuyen nh OSPF, IS-IS, BGP. No cho phep IP chuyen tiep lu lng mot cach chnh xac. Cac ban tin ieu khien c trao oi gia cac router e thc hien nhieu hoat ong khac nhau, bao gom: Trao oi cac ban tin gia cac nut e thiet lap mot tuyen lien ket. Trao oi cac ban tin theo chu k (goi la ban tin hello) e chac rang cac nut gan ke hoat ong tot. Trao oi cac ban tin quang cao (advertisement) ve a ch va tuyen e xay dng cac bang nh tuyen c s dung bi IP e chuyen tiep lu lng.Router

OSPF, IS-IS, BGP

Mat phang ieu khien Lp nh tuyenBang nh tuyen

OSPF, IS-IS, BGP

Goi d lieu IP

Mat phang d lieu Lp chuyen tiep

Goi d lieu IP

Hnh 2.2 : Mat phang ieu khien va d lieu IP.


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Version 3

2.2.3.Mat phang d lieu va mat phang ieu khien trong MPLS MPLS cung hoat ong vi cac mat phang ieu khien va d lieu, nh mo ta hnh 2.3. Nhiem vu chnh cua mat phang ieu khien la quang cao cac nhan, a ch va lien ket chung. Bo nh tuyen chuyen mach nhan la mot router c cau hnh e ho tr MPLS. No dung c s thong tin chuyen tiep nhan (Label Forwarding Information Base_LFIB) e xac nh cach x l cac goi MPLS en, chang han xet xem nut ke tiep nhan goi la nut nao.LSRLDP, RSVP-TE, OSPF-E, BGP-E Mat phang ieu khien (Lp lien ker) LDP, RSVP-TE, OSPF-E, BGP-E

LFIB

Goi tin MPLS

Mat phang d lieu (Lp chuyen tiep)

Goi tin MPLS

Hnh 2.3 : Mat phang ieu khien va d lieu

Cac ban tin ieu khien c trao oi gia cac LSR e thc hien nhieu hoat ong khac nhau, bao gom thiet lap lien ket. Sau khi hoat ong nay hoan thanh, cac nut c goi la cac LSR ngang hang (peer), trao oi cac ban tin chu k (ban tin hello) e chac rang cac nut gan ke hoat ong tot, trao oi cac ban tin a ch va nhan e lien ket cac a ch vi nhan va xay dng bang chuyen tiep cho mat phang d lieu MPLS. Mat phang d lieu MPLS se chuyen tiep lu lng bang cach kiem tra nhan trong tieu e goi MPLS, a ch IP khong can kiem tra. Tieu e nhan sau o b bo i, va a ch IP lai c dung e phan phoi lu lng en ngi dung cuoi.2.2.4.Nhng lp chuyen tiep tng ng (Forwarding Equivalence Classes FECs)

* Lp chuyen tiep tng ng FEC Thuat ng lp chuyen tiep tng ng c s dung trong hoat ong chuyen mach nhan. FEC mo ta s lien he gia cac goi vi a ch ch ngi nhan cuoi, FEC cung co the lien ket vi mot a ch ch va loai lu lng lien quan en mot cong ch nao o.


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Version 3

Tai sao lai s dung FEC? Trc tien, no cho phep nhom cac goi vao cac lp khac nhau, co the s dung e ho tr chat lng dch vu hieu qua. V du, FEC co the lien ket vi o u tien cao, lu lng thc FEC c xac nh duy nhat bang viec s dung mot nhan. oi vi cac lp dch vu khac nhau, ngi ta s dung cac FEC va cac nhan lien ket khac nhau. Vi Internet, cac gia tr sau c s dung e thanh lap mot FEC: a ch IP nguon va/hoac ch, so cong nguon va/hoac ch, nhan dien giao thc (PID), iem ma (codepoint) cua cac dch vu khac biet Ipv4, dong nhan Ipv6. Chung ta co the ngh ve cac thu tuc c s dung bi thanh phan nh tuyen nh la cach chia thanh tap tat ca cac goi ma router co the nh tuyen vao mot so hu han cac subnet ri nhau. T quan iem nh tuyen, nhng goi trong moi subnet c router oi x nh nhau (ngha la chung eu c gi en cung mot tram ke tiep) ngay ca neu nhng goi trong subnet khac nhau ve nhng thong tin con lai trong tieu e (header) lp mang. Chung ta xem cac subnet nh la cac lp chuyen tiep tng ng ( FEC). Nguyen nhan ma router nh tuyen tat ca cac goi trong 1 FEC giong nhau la v s anh xa gia thong tin c mang trong tieu e lp mang va nhng muc trong bang nh tuyen la nhieu mot (ma mot - mot la trng hp ac biet). Ngha la nhng goi khac nhau ve noi dung trong tieu e lp mang co the c anh xa vao cung mot muc trong bang nh tuyen khi muc o c gan vi mot FEC xac nh. Mot v du cua FEC la mot tap cac goi unicast ma a ch ch lp mang co cung tien to a ch IP xac nh. Mot v du khac cua FEC la mot tap cac goi multicast co cung a ch nguon va ch lp mang. Mot phan quan trong cua mot muc nh tuyen c duy tr bi router o la a ch router ke tiep. Mot goi khi ri vao mot FEC ma lien ket vi mot muc nh tuyen xac nh th c nh tuyen en router ke tiep c ch ro bi muc o. Do o viec xay dng bang nh tuyen bi thanh phan ieu khien co the xem nh la viec xay dng mot tap FEC va tram ke tiep cho moi FEC o. Mot tnh chat quan trong cua mot FEC la tnh nh tuyen phan cap cua no. V du nh mot FEC co the bao gom nhng goi ma co a ch ch lp mang gan vi cung mot tien to a ch xac nh. Kieu nay cua FEC cung cap nh tuyen tho. Mac khac, mot FEC co the bao gom ch nhng goi thuoc vao mot ng dung xac nh chay gia hai may tnh, ngha la no ch bao gom nhng goi co cung a ch nguon va ch lp mang (a ch hai may tnh) cung nh cung so port lp van chuyen (nhng port nay xac nh ng dung trong may tnh). Kieu nay cua FEC cung cap nh tuyen tinh. Co the thay ro rang la nh tuyen tho can thiet cho viec m rong toan mang. Nhng mac khac neu ch ho tr nh tuyen tho se lam mang hoat ong khong c uyen chuyen, nh vay no khong cho phep co nhieu kieu lu lng khac nhau. Nhng nhan nh tren cho thay muon xay dng mot he thong ln va co nhieu chc nang th yeu cau he thong phai ho tr nhieu kieu nh tuyen cung nh kha nang tron lan va ket hp nhieu kieu nh tuyen khac nhau.Bien soan: TS.Tran Cong Hung - 27 Version 3

2.2.5.nh tuyen nhat quan

Mot he thong nh tuyen chnh xac yeu cau co s nhat quan qua nhieu router. S nhat quan nay c thiet lap bi s ket hp cua nhieu c che . Thanh phan ieu khien chu trach nhiem phan bo nhat quan cac thong tin nh tuyen c s dung bi router cho viec xay dng bang nh tuyen cua no. Thanh phan ieu khien con chu trach nhiem trong viec nhat quan cac thu tuc ma router dung e xay dng bang nh tuyen. Ket hp hai yeu to nay cho phep co s nhat quan gia cac bang nh tuyen. Thanh phan nh tuyen chu trach nhiem nhat quan cac thu tuc trong viec lay thong tin t cac goi cung nh viec s dung thong tin nay e tm mot muc thch hp trong bang nh tuyen, ket qua la co s nhat quan trong anh xa nhng goi vao cac FEC qua nhieu router. Va s nhat quan nay cho phep he thong co chc nang nh tuyen chnh xac. 2.3.Chuyen mach nhan: Thanh Phan nh tuyen S phan tch viec nh tuyen lp mang ra lam hai phan : ieu khien va nh tuyen khong ch c ap dung vao kieu nh tuyen truyen thong ma con co the ap dung cho ky thuat chuyen mach nhan. Trong phan nay chung ta mo ta vai ly thuyet nen tang lien quan en thanh phan nh tuyen cua chuyen mach nhan. Thuat toan ma thanh phan nh tuyen cua chuyen mach nhan s dung e a ra quyet nh nh tuyen cho mot goi tin se s dung hai nguon thong tin : thong tin th nhat la bang nh tuyen c duy tr bi mot router chuyen mach nhan (Label Switching Router : LSR) va th hai la mot nhan cha trong goi.2.3.1.Nhan la g ?

Nhan la mot khung nhan dang ngan, co chieu dai co nh va khong co cau truc. Mot nhan khong thc hien trc tiep bat c thong tin nao t tieu e lp mang. Dang cua nhan se c xet phan sau.2.3.2.Bang chuyen mach nhan

LIB vaLFIB Hnh 2.4 la c s d lieu thong tin nhan_LIB cua nut D cho cac lien ket nhan ma no tao va nhan c t cac hang xom MPLS cho tien to a ch 192.168.20.0/24. Cac thc the LIB cua cac LSR khong phai ke can th khong can lu trong LIB v khong can thiet cho viec chuyen tiep goi. Theo hoat ong cua cac giao thc nh tuyen, nut D co the en 192.168.20.0/24 thong qua nut I, E hoac J. Mot cau hoi rat hp l c at ra la tai sao no phai cha tat ca lien ket nhan cua tat ca cac hang xom trong khi mot so trong chung khong phai la xuoi dong theo a ch ch va tham ch mot so khong trong LSP. Cau tra li se c giai thch phan sau.


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Version 3

192.168.20.1

192.168.20.9

192.168.20.7

A48 30 192.168.20.3 192.168.20.4 40

I53 192.168.20.5 38 89 192.168.20.6 47 67

G

C35

D87

E

F

192.168.20.0/24 77

End nodes

LIB

B192.168.20.2

J192.168.20.10

H192.168.20.8

Vi a ch 192.168.20.0/24 a ch Nhan 192.168.20.3 40 192.168.20.9 48 192.168.20.10 87 192.168.20.5 38

Hnh 2.4: LIB cho nut D

Hnh 2.5 la bang LFIB tai nut D cho tien to a ch 192.168.20.4/24. Lu y rang bang nay ch cha thong tin can thiet e chuyen tiep goi en chang ke trong LSP, no chnh la tap con cua LIB. Nhan 40 c dung cho LSP gia nut C va D, nhan 38 gia D va E, nhan 47 gia E va F. Nhan 40 la nhan noi (local label) cua nut D v no c tao bi D va phan phoi en tat ca cac ngang cap cua D. Con nhan 38 c cap bi nut E. Do o hai nhan nay la nhan c gan bi nut xuoi dong en nut ngc dong tng ng vi tien to 192.168.20.0/24. Trong bang LFIB tai D ta thay (a) nhan noi cho tien to a ch 192.168.20.0/24 la 40, (b) nhan ra la 38 von c gan trc o bi nut E, (c) giao tiep vat ly e en chang ke tc hop E la giao tiep n. Hai ieu quan trong can nh la neu LSR khong nhan thong iep lien ket nhan t LSR ke, goi tin se c chuyen i bnh thng ma khong gan nhan. Con neu LSR nhan c thong iep lien ket nhan t LSR ke th nhan nay va nhan noi se c them vao LFIB. Khi mot lien ket hay mot nut b phat hien la h bang giao thc phan phoi nhan hay bang giao thc nh tuyen lp 3, cac s kien sau se lan lt xay ra: v du nut D phat hien lien ket en E b h. LFIB c cap nhan e phan anh s h hong nay bang cach xoa lien ket t D en E. Giao tiep cua lien ket b h cung c xoa khoi bang nh tuyen. Viec xoa nay kch hoat OSPF chon ra mot lien ket thay the khac va a vao bang nh tuyen, v du lien ket gia D va J. Viec them mot FEC mi vao bang nh tuyen lp 3 se kch hoat nut D cap nhat LFIB ma khong can trieu goi giao thc phan phoi nhan bi v trc o nut D a thiet lap moi quan he MPLS ngang hang vi tat ca nut lan can va a cai at lien ket nhan cho nhng nut nay trong bang LIB roi. Do o nut D se gan nhan 87 cho cac goi en 192.168.20.0/24 va gi chung en nut J. J luc nay la thanh vien mi cua con ng chuyen mach nhan en 192.168.20.0/24.


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Version 3

192.168.20.1

192.168.20.9

192.168.20.7

A48 30 192.168.20.3 192.168.20.4 40 n

I53 192.168.20.5 38 89 192.168.20.6 47 67

G

C35

D

E

F

192.168.20.0/24 77

End nodes

87

LFIB

B192.168.20.2

J192.168.20.10

H192.168.20.8

Vi a ch 192.168.20.0/24 Nhan noi Nhan ra Giao dien 40 38 n

Hnh 2.5: LFIB cho nut D

Mot bang nh tuyen bao gom chuoi cac muc, moi muc bao gom mot nhan vao va mot hay nhieu muc con, moi muc con bao gom mot nhan ra, mot giao dien ngo ra va mot a ch tram ke ( hnh 2.6). Nhng muc con khac nhau trong tng muc rieng co the co cung hoac khac nhan ra. ay co nhieu muc con la e kiem soat nh tuyen multicast, khi ma mot goi en t mot ngo vao can c gi en nhieu giao dien ngo ra.

Bang nh tuyen c anh ch so muc bi gia tr cha trong nhan vao. Ngha la gia tr cha trong nhan vao cua muc th N trong bang la N. Ngoai thong tin dung e ieu khien nh tuyen mot goi, mot muc trong bang nh tuyen co the cha thong tin lien quan en nhng tai nguyen ma goi tin co the s dung, nh la mot hang i ngo ra ma goi tin c at vao. Mot LSR co the duy tr mot bang nh tuyen n hay la nhieu bang nh tuyen, moi bang cho moi giao dien cua no. Vi trng hp sau, viec x ly mot goi tin c xem xet khong bi ch nhan cha trong goi ma ca giao dien nao ma goi tin i ti, con trong trng hp au th ch can thong tin cha trong nhan. LSR co the s dung trng hp mot hoac hai nh la mot tuy chon, hay co the ket hp ca hai.


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2.3.3.S mang nhan trong goi

Mot chc nang quan trong cua thanh phan nh tuyen chuyen mach nhan la kha nang mang nhan trong goi, co nhieu cach e thc hien ieu nay. Vi cac ky thuat lp lien ket, nh ATM va Frame Relay, co the mang nhan nh mot phan cua tieu e (header) lp lien ket cua no. Cu the, vi ATM, nhan co the c mang trong trng VCI hay VPI cua tieu e ATM. Con vi Frame Relay, nhan co the c mang trong trng DLCI cua tieu e Frame Relay. S dung tuy chon viec mang nhan nh la mot phan cua tieu e lp lien ket cho phep ho tr chuyen mach nhan vi mot so ky thuat lp lien ket ch khong phai la tat ca. Bat buoc chuyen mach nhan ch cho nhng ky thuat lp lien ket ma co the mang nhan trong tieu e lp lien ket se gii han nhieu en s hu dung cua chuyen mach nhan (han che s s dung chuyen mach nhan tren nhng moi trng khac nh Ethernet hay lien ket point-to-point). Mot cach cho phep chuyen mach nhan hoat ong tren nhieu ky thuat lp lien ket khi ma nhng ky thuat o khong the mang nhan trong tieu e cua no la bang cach mang nhan trong mot tieu e nhan rieng. Tieu e nhan nay c xen vao gia tieu e lp mang va tieu e lp lien ket (xem hnh 2.7), nen do o co the c s dung bi bat c ky thuat lp lien ket nao nh Ethernet, FDDI, Token Ring, point-to-point.

2.3.4.Thuat toan nh tuyen chuyen mach nhan

Thuat toan nh tuyen ma c s dung bi thanh phan nh tuyen cua chuyen mach nhan da vao s hoan oi nhan. Thuat toan hoat ong nh sau. Khi LSR nhan mot goi tin, no se lay nhan trong goi lam ch muc e xac nh trong bang nh tuyen. Mot khi muc trong bang nh tuyen c tm thay (muc nay co nhan vao bang vi nhan cha trong goi tin), trong moi muc con se thay the nhan trong goi tin bang vi nhan ra cua no va gi goi tin ra giao dien ngo ra e en tram ke tiep c xac nh bi muc con o. Trong phan trc, chung ta gia s la mot LSR duy tr mot bang nh tuyen n, tuy nhien, mot LSR co the duy tr 1 bang nh tuyen rieng biet cho moi giao dien cua no. Trong trng hp nay, sau khi LSR nhan goi tin, LSR s dung giao dien ma goi tin i ti e la chon bang nh tuyen e nh tuyen goi tin o. Nhng ai quen thuoc vi ATM chu y rang khi LSR duy tr bang nh tuyen tren moi giao dien cua no, thuat toan nh tuyen tren tuy thuoc vao thuat toan nh tuyen cua chuyen mach ATM. ay la yeu to quan trong cua mot so nghien cu chuyen mach nhan va chung ta se thao luan phan sau.Bien soan: TS.Tran Cong Hung - 31 Version 3

Mot nhan luon luon mang thong tin nh tuyen va con co the mang ca thong tin tai nguyen danh rieng. Nhan mang thong tin nh tuyen la v noi dung cua no xac nh mot muc trong bang nh tuyen va muc nay cha thong tin xac nh phai nh tuyen goi tin i au. Con nhan co the mang thong tin ve viec e danh tai nguyen la v muc ma c xac nh bi nhan co the, tuy chon, bao gom thong tin lien quan ti tai nguyen nao ma goi tin co the s dung, v du nh la mot hang i xac nh ma goi tin c at vao. Khi nhan c mang trong tieu e ATM (header ATM) hay Frame Relay, nhan phai mang ca hai thong tin nh tuyen va tai nguyen danh rieng. Con khi nhan c mang trong mot tieu e rieng, th thong tin ve tai nguyen ma goi tin co the s dung co the b ma hoa nh la mot phan cua tieu e o, nen nhan ch mang thong tin ve nh tuyen. Nhng viec ma hoa phan thong tin cua nhan la tuy chon do o mot nhan trong tieu e rieng co the mang ca hai thong tin tren. n gian hoa thuat toan nh tuyen ma c s dung bi thanh phan nh tuyen chuyen mach nhan se lam n gian viec tao thuat toan bang phan cng va se cho phep nh tuyen nhanh hn ma khong can en cac phan cng at tien. Mot tnh chat quan trong cua thuat toan nh tuyen c s dung bi chuyen mach nhan la mot LSR co the lay tat ca thong tin can thiet cho viec nh tuyen mot goi tin cung nh phai quyet nh tai nguyen nao ma goi tin co the s dung ch trong mot lan truy cap bo nh. Bi v mot muc trong bang nh tuyen co cha tat ca cac thong tin can thiet va nh co nhan ma ta se xac nh ung muc can tm. Chnh ac iem nay lam cho chuyen mach nhan thch hp nh la mot ky thuat cho hieu qua nh tuyen cao. Viec trao oi nhan ket hp vi kha nang mang nhan trong cac ky thuat lp lien ket se cho phep nhieu thiet b khac nhau co the c s dung e lam LSR. V du, mang nhan trong trng VCI cua te bao ATM cho phep bien phan cng cua chuyen mach ATM thanh LSR vi viec cung cap them phan mem ieu khien thch hp. Tng t, viec mang nhan trong tieu e rieng trong goi tin lam cho cac router truyen thong co the x ly no bang phan mem, do o, vi mot phan mem thch hp, mot router truyen thong co the tr thanh mot LSR.2.3.5.Thuat toan nh tuyen n

Trong kien truc nh tuyen truyen thong, nhng chc nang khac nhau c cung cap bi thanh phan ieu khien (nh la nh tuyen unicast, nh tuyen multicast, nh tuyen unicast vi kieu cua dch vu) yeu cau nhng thuat toan khac nhau trong thanh phan nh tuyen ( xem hnh 2.8) .


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Chc nng nh tuyn Thut ton nh hng

nh tuyn unicast Kt hp di nht vi a ch ch

nh tuyn unicast vi Type of Service Kt hp di nht vi a ch ch + kt hp chnh xc vi Type of Service

nh tuyn multicast Kt hp di nht vi a ch ngun + kt hp chnh xc vi a ch ch v giao din ng vo

Hnh 2.8 Kin trc nh tuyn truyn thng

Mot tnh chat quan trong cua chuyen mach nhan la se khong co nhieu thuat toan nh tuyen khac nhau trong thanh phan nh tuyen cua no, thanh phan nh tuyen ch gom mot thuat toan da tren viec trao oi nhan (xem hnh 2.9). ay la iem phan biet quan trong gia hai kieu kien truc nh tuyen,

Chc nng nh tuyn Thut ton nh hng

nh tuyn unicast

nh tuyn unicast vi Type of Service

nh tuyn multicast

Thut ton nh hng chung (trao i nhn) Hnh 2.9 Kin trc chuyn mch nhn

Chung ta co the ngh rang neu thanh phan nh tuyen ch co mot thuat toan nh tuyen co the han che en cac chc nang c ho tr bi chuyen mach nhan. Nhng that s th khong phai vay, kha nang ho tr nhieu chc nang nh tuyen vi ch mot thuat toan nh tuyen la mot trong nhng iem quan trong cua chuyen mach nhan. Thc s, nh chung ta se xem sau, th chc nang ma chuyen mach nhan ho tr nhieu hn so vi cac kien truc nh tuyen truyen thong.2.3.6.Multiprotocol : ben tren va ben di

T nhng mo ta trc ve thanh phan nh tuyen chuyen mach nhan, chung ta co the thay ro hai ieu quan trong. ieu au tien la thanh phan nh tuyen khong lam ro la vi mot lp mang nao ca, v du, cung mot thanh phan nh tuyen co the c s dung e chuyen mach nhan vi IP cung nh chuyen mach nhan vi IPX. ieu nay lam cho chuyen mach nhan nh la mot giai phap a giao thc (multiprotocol) tng thch vi cac giao thc lp mang. ( xem hnh 2.10) Ngoai ra, kha nang a giao thc cua chuyen mach nhan vt xa kha nang ho tr nhieu giao thc lp mang khac nhau, chuyen mach nhan con co kha nang hoat ong tren bat ky giao thc lp lien ket nao. ieu nay lam cho chuyen mach nhan nh la mot giai phap a giao thc tng thch vi cac giao thc lp lien ket.


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IPv6

IPv4

IPX

Apple Talk

Protocol lp mng

Label Switching

Protocol lp lin kt

Hnh 2.10 Multiprotocol trn v di

Nhng tnh chat tren cua chuyen mach nhan a giai thch tai sao nhom lam viec IETF at ten cho viec tieu chuan hoa ky thuat mi nay la: Multiprotocol Label Switching (MPLS)_Chuyen mach nhan a giao thc. 2.4.Thanh phan ieu khien Nh ta a e cap tren, viec tach phan nh tuyen lp mang thanh hai phan nh tuyen va ieu khien khong ch ap dung cho kieu kien truc nh tuyen truyen thong ma con co the ap dung cho chuyen mach nhan. Thanh phan ieu khien cua chuyen mach nhan chu trach nhiem ve viec phan bo cac thong tin nh tuyen gia cac LSR va nhng thu tuc ma nhng LSR o s dung e oi cac thong tin nay thanh bang nh tuyen e s dung bi thanh phan nh tuyen trong he thong. Giong nh cac thanh phan ieu khien cua cac he thong nh tuyen khac, thanh phan ieu khien cua chuyen mach nhan phai ap ng s phan bo nhat quan ve thong tin nh tuyen gia cac LSR cung nh cac thu tuc nhat quan e xay dng bang nh tuyen. Co s giong nhau rat ln ve thanh phan ieu khien gia kieu kien truc truyen thong va chuyen mach nhan. Thc te, thanh phan ieu khien cua chuyen mach nhan bao gom tat ca cac giao thc nh tuyen (nh la OSPF, BGP, PIM,) a c s dung bi thanh phan ieu khien cua kieu nh tuyen trc. Va co the hieu la thanh phan nh tuyen kieu truyen thong la mot phan cua thanh phan nh tuyen chuyen mach nhan. Tuy nhien, thanh phan ieu khien cua kieu nh tuyen truyen thong khong u e ho tr chuyen mach nhan. Bi v thong tin nh tuyen c cung cap bi thanh phan nay khong u e xay dng bang nh tuyen cho thanh phan nh tuyen cua chuyen mach nhan, v bang nay phai cha s anh xa gia nhan va tram ke tiep. e co the ho tr c th chung ta can co nhng thu tuc e LSR co the Tao s ket hp gia nhan va FEC. Thong tin cho cac LSR khac ve s ket hp nay. S dung hai thu tuc tren e xay dng va duy tr bang nh tuyen e chuyen mach nhan s dung.Bien soan: TS.Tran Cong Hung - 34 Version 3

Toan bo cau truc cua thanh phan ieu khien chuyen mach nhan c trnh bay nh trong hnh 2.11

Nhng giao thc nh tuyen lp mang cung cap cho LSR s anh xa gia cac FEC va a ch tram ke tiep. Nhng thu tuc e tao ra s ket hp gia nhan va FEC, va phan bo thong tin ket hp nay gia cac thiet b chuyen mach nhan cung cap cho LSR s anh xa gia cac FEC va nhan. S ket hp hai anh xa tren cung cap nhng thong can thiet e xay dng bang nh tuyen c s dung bi thanh phan nh tuyen chuyen mach nhan (xem hnh 2.12).

n hx

g i aF EC

v t

r m

k

EC aF i g hx n

n nh v

2.4.1.Ket hp trong va ket hp ngoai

Nhac lai la moi muc trong bang nh tuyen c duy tr bi LSR cha mot nhan vao va mot hay nhieu nhan ra. Tng ng vi hai kieu nhan trong bang nh tuyen, thanh phan ieu khien cung cap hai kieu ket hp nhan. Kieu ket hp au tien xay ra khi router tao s ket hp vi nhan c chon va gan mot cach noi bo. Kieu ket hp nhan th hai xay ra khi router nhan cac thong tin ket hp nhan cua nhng LSR khac. iem khac nhau quan trong gia ket hp trong va ket hp ngoai la vi ket hp trong nhan uc chon mot cach noi bo, bi chnh LSR o, trong khi o th vi ket hp ngoai th nhan c chon bi cac LSR khac.Bien soan: TS.Tran Cong Hung - 35 Version 3

2.4.2.Ket hp ngc dong va ket hp xuoi dong

Thanh phan ieu khien chuyen mach nhan s dung ca hai kieu ket hp trong va ngoai e xay dng bang nh tuyen vi nhan vao va nhan ra. Co hai cach e thc hien ieu nay. Cach au tien la khi nhan t ket hp trong c dung la nhan vao va nhan t ket hp ngoai c dung la nhan ra. Cach th hai th hoan toan ngc lai, nhan t ket hp trong c dung lam nhan ra va nhan c dung t ket hp ngoai c dung lam nhan vao. Cach au tien c goi la ket hp nhan xuoi dong (downstream label binding) v s ket hp gia mot nhan c mang trong goi tin va mot FEC c tao bi mot LSR xuoi dong (downstream LSR) so vi LSR gan nhan vao goi tin (xem hnh 2.13). Ro rang rang vi ket hp nhan xuoi dong, goi tin mang nhan chay ngc hng so vi chieu chay cua luong thong tin ket hp nhan.

Cach th hai goi la ket hp ngc dong (upstream label binding) bi v s ket hp gia mot nhan c mang trong goi tin va mot FEC c tao bi cung mot LSR ma at nhan vao goi tin, ngha la s ket hp nhan ngc dong so vi luong chay cua goi tin (xem hnh 2.13). Ro rang rang vi ket hp nhan ngc dong, goi tin mang nhan chay cung hng so vi chieu chay cua luong thong tin ket hp nhan.2.4.3.Nhan t do

Mot LSR luon co mot tap cac nhan t do (nhan ma cha co ket hp). Khi LSR c khi tao, tap nay cha tat ca cac nhan ma LSR co the dung e ket hp trong. Kch thc cua tap se xac nh bao nhieu s ket hp nhan ong thi ma LSR co the ho tr. Khi router tao ra mot ket hp trong mi, router lay mot nhan trong tap, khi router huy bo mot ket hp, no se tra lai nhan nay cho tap nhan. Nhac lai la mot LSR co the duy tr mot bang nh tuyen n hay la nhieu bang nh tuyen, moi bang cho mot giao dien. Khi router duy tr mot bang nh tuyen, noBien soan: TS.Tran Cong Hung - 36 Version 3

se duy tr mot tap nhan t do, con khi router duy tr nhieu bang th no se duy tr nhieu tap nhan, moi tap cho mot bang.2.4.4.Ket hp nhan tuyen ieu khien va tuyen d lieu

LSR tao ra hay huy bo mot ket hp nhan gia mot nhan va mot FEC khi co mot s kien xay ra. S kien o co the c kch hoat bi nhng goi d lieu ma c nh tuyen bi LSR o hay bi nhng thong tin ieu khien nh tuyen (nh la cac ban tin OSPF routing updates, PIM JOIN/PRUNE, RSVP PATH / RESV) ma c x ly bi LSR o. Khi viec tao ra hay huy bo ket hp c kch hoat bi cac goi d lieu th chung ta goi o la ket hp nhan tuyen d lieu (data_driven label binding), con khi c kch hoat bi thong tin ieu khien, chung ta goi la ket hp nhan tuyen ieu khien (control_driven label binding). Co nhieu tuy chon oi vi ca hai loai tren. V du, phan tuyen d lieu se tao ra s ket hp cho mot luong goi cua mot ng dung ngay khi no thay goi tin au tien cua luong, hay no se i cho en khi co nhieu goi tin hn e luong u dai e c phep tao ket hp. S la chon gia cac phng phap thiet lap ket hp ro rang anh hng en hieu qua va van e phat trien (c e cap phan trc), ngha la phng phap thiet lap o hoat ong nh the nao khi mang phat trien. Va chung ta cung xet vai anh hng en s linh hoat, c hieu la cac phng phap hoat ong nh the nao trong cac ieu kien khac nhau. 2.4.4.1.Hieu qua ieu au tien phai chu y ve hieu qua la, di ieu kien ly tng, mot LSR co the nh tuyen d lieu tai bat c toc o nao ma thanh phan nh tuyen chuyen mach nhan hoat ong, bat ke en LSR s dung ket hp nhan tuyen d lieu hay la tuyen ieu khien. Trong nhieu trng hp, ieu nay c quyet nh bi toc o phan cng nam di. Do o, v du, neu mot chuyen mach nhan chay tren mot chuyen mach ATM, th hieu qua nh tuyen cao nhat la hieu qua cao nhat cua chuyen mach ATM o. Hau het chuyen mach ATM co the nh tuyen lu lng vi van toc ng day tai tat ca giao tiep cua no. Do o, v du, mot chuyen mach 16 cong OC-3 se co kha nang nh tuyen gan ti 16*155 Mb/sec = 2.5 Gb/sec. Trong ieu kien ly tng, bat c chuyen mach nhan nao s dung chuyen mach nay eu co the at c cung thong lng tren. ieu quan trong ay la trong ieu kien ly tng. Cau hoi c at ra la moi trng hoat ong thc te gan vi ieu kien ly tng nh the nao. Cau hoi nay that s kho ma tra li, at biet oi vi ket hp hng d lieu. V du, ieu kien ly tng cho ket hp hng d lieu ma nhan c lien ket vi luong d lieu ng dung la khi luong o co chieu dai vo tan. Trong trng hp nay, cai gia thiet lap ng dan chuyen mach nhan cho mot luong c tra dan qua chieu dai vo han cua luong o tr nen khong the chap nhan c. Cac nghien cu a c thc hien e xac nh cac mang thc te cach xa bao nhieu so vi ieu kien ly tng. Phan kho khan cua cac nghien cu tren la tm cacBien soan: TS.Tran Cong Hung - 37 Version 3

so lieu thong ke lu lng thc te, v hau het cac nha van hanh mang rat khong thch thu trc viec a ra chi tiet cac dau tch lu lng cua ho trc cong chung. Ngoai ra, ngay ca neu co lay c cac d lieu can thiet th cung khong am bao rang no se phan anh chnh xac mot mang tieu bieu ngay tai thi iem no c thu thap. Ket hp nhan tuyen d lieu gia s rang mot LSR ho tr ca hai thanh phan nh tuyen cua chuyen mach nhan va cua kieu nh tuyen truyen thong. Hieu qua chnh cua tuyen d lieu khi ma ieu kien hoat ong chech khoi ieu kien ly tng la cac goi tin nao khong c chuyen mach nhan th phai c x ly bi thanh phan nh tuyen truyen thong, va ng nhien, kha nang nh tuyen cua no phai be hn so vi thanh phan nh tuyen cua chuyen mach nhan. ieu quan tam ay la bao nhieu tai co the c chuyen cho thanh phan nh tuyen truyen thong. Neu chung ta thch tao ket hp nhan bang ket hp tuyen d lieu, v du, bang cach tao ket hp nhan tai goi tin au tien cua mot luong mi, th co the chung ta khong can dung ti thanh phan nh tuyen truyen thong v thanh phan nay ch nh tuyen mot goi cho moi luong. Nhng ieu nay se co anh hng ngc lai len van e phat trien, va trong luc ban au e tao ket hp nhan chung ta phai i qua trnh phan bo va thiet lap ket hp nhan tai cac LSR khac, se hieu qua hn neu trong khi o, cac goi tin bat au cua mot luong c nh tuyen bang thanh phan nh tuyen truyen thong. Nhng chung ta can phai biet ay la bao nhieu goi tin bat au cua mot luong c nh tuyen bi thanh phan nh tuyen truyen thong th u (trong qua trnh ket hp nhan), cac goi sau o se c nh tuyen bang chuyen mach nhan (khi qua trnh ket hp nhan xong). Phan goi tin c nh tuyen bi thanh phan nh tuyen truyen thong phu thuoc vao toc o cua luong mi en va so lng goi tin moi luong ma khong c chuyen mach nhan. Toc o cua luong en bang vi tai a ra trong cac goi tin trong mot giay chia cho so lng goi tin trung bnh trong moi luong. PPS(Packet per second) yeu cau = ( cac goi c nh tuyen moi luong) * (PPS a ra)/ (so goi moi luong). Phan kho cho nay la so cac goi c nh tuyen moi luong. Ngay ca neu phan nhan dang dong co mot quy luat n gian nh tao ket hp nhan cho bat c luong nao ma dai hn 10 goi, se co nhieu luong ch co mot goi, se at nhieu tai len phan nh tuyen truyen thong. S thong nhat cua nghien cu la hieu qua cua ket hp tuyen d lieu trong ieu kien tai thc te kha cao 70-80% va do o co the at c hieu suat cua phan cng nam di. Phan quan tam chnh cua tuyen d lieu la van e phat trien va s linh hoat trong ieu kien co s thay oi lu lng. Mot he qua na phat sinh bi viec tuyen d lieu ( va t anh hng bi tuyen ieu khien la phan tai nguyen c yeu cau cua thanh phan ieu khien chuyen mach nhan. Moi lan mot LSR quyet nh mot luong co the c chuyen mach nhan, no can phai trao oi thong tin ket hp nhan vi cac LSR xung quanh, ma no co the can thay oi vai trang thai ket hp trong cua no. Tat ca cac viec tren se tieuBien soan: TS.Tran Cong Hung - 38 Version 3

ton tai nguyen cua thanh phan ieu khien chuyen mach nhan. That la kho ma tnh c hoat ong cua viec thiet lap va phan bo ket hp nhan se tieu ton bao nhieu tai nguyen, nhng ma ta de dang thay c hieu qua cua tuyen d lieu de b anh hng bi viec nay nhat. Neu LSR khong thiet lap va phan bo trang thai ket hp nhan tai toc o yeu cau bi thuat toan phat hien dong(flow detection algorithm), th ch co phan nho cua luong c chuyen mach nhan, va do o hieu qua cung giam. The th con ket hp tuyen ieu khien th sao? Giong nh tuyen d lieu, no co the hoat ong tai toc o phan cng nam di trong ieu kien ly tng, nhng nh ngha cho ly tng th rat khac. V du, khi cung cap chc nang nh tuyen da vao a ch ch, th ieu kien ly tng cho hng ieu khien kha n gian : chng nao ma cau truc mang con on nh, th tat ca lu lng ma en tai mot LSR ( khong phai ra) co the c chuyen mach nhan ma khong co 1 goi nao phai c chuyen cho phan x ly ieu khien. Khong giong vi tuyen d lieu, chung ta co the tng tng mang trong ieu kien ly tng co the ton tai trong mot khoang thi gian dai. Khi cau truc mang thay oi, th van co kha nang cho tuyen ieu khien at c hieu qua ly tng, nhac lai la mot ket hp tuyen ieu khien co the biet thong tin ket hp cho router t nhng lang gieng(neighbor) ma khong phai la tram ke tiep cua router o, trong trng hp cau hnh mang thay oi lam nhng lang gieng o tr thanh nhng tram ke tiep th chuyen mach nhan cung khong b gian oan (co the co tren vai nen phan cng, co mot vai goi tin b mat trong khi bang nh tuyen b thay oi). Chu y la khi cau hnh mang thay oi th cung anh hng en hieu qua cua tuyen d lieu. Neu ng dan cua mot luong thay oi, th oi vi cac LSR mi tren ng dan o xem nh la mot luong mi c tao ra. Va nhng luong o au tien phai c nh tuyen bang thanh phan nh tuyen truyen thong. Do o, khi mang thay oi se at ganh nang len LSR nao b tr thanh mot tram ke mi cho vai LSR khac. au tien, no ot nhien nhan c mot lng ln cac luong ma thng i bang ng dan khac. Sau o cac luong mi nay can c phan tch bi cac thuat toan phat hien luong, va no se at them tai len ca hai thanh phan nh tuyen truyen thong va chuyen mach nhan lam giam hieu qua cua chuyen mach nhan. Mot van e ang chu y ve hieu qua phat sinh khi co s tap trung nh tuyen xay ra . Va chung ta lai se thay co s xung ot gia van e phat trien va hieu qua.Hnh 2.14 trnh bay tnh huong co s tap trung nh tuyen xay ra, LSR X co the giao tiep vi mang co tien to 10.0.1/24 (/24 ngha la tien to nay co 24 bit) qua LSR Y va co the giao tiep vi mang co tien to 10.0.0/24 qua LSRZ. Nhng tien to nay co cung 23 bit cao va do o chung co the c tong hp lai thanh 10.0.0/23. Do o, LSR X co the quang ba tien to tong hp nay cho LSR M, ngha la, neu LSR X va M tao ket hp nhan cho tien to tong hp nay trong bang nh tuyen cua no, th X ch co the quang ba mot nhan n en M cho tien to tong hp nay. Khi LSR X nhan nhng goi t M ma cha nhan nay, no khong the xac nh chnh xac la phai nh tuyen goi tin i au va no phai dung nh tuyen truyen thong s dung tieu eBien soan: TS.Tran Cong Hung - 39 Version 3

lp 3 e nh tuyen. Chu y rang X van co the chuyen mach nhan cho cac goi khac, cac goi t Y sang Z va ngc lai.Routing area A Routing area B

Y 10.0.1/24 10.0.0/24 Z X M

Hnh 2.14 nh hng ca s tp trung route

Tnh huong nay la tnh huong te nhat oi vi tuyen ieu khien LSR. Van e phat trien ch ra rang s ket hp a ch la tot, nhng no lai tao ra tnh huong ma nh tuyen kieu truyen thong thc hien nhieu hn chuyen mach nhan. S anh hng en hieu qua ng nhien tuy thuoc vao bao nhieu phan cua lu lng khong the thc hien bang chuyen mach nhan va vao s tng quan cua hai thanh phan nh tuyen . Chung ta cung nen chu y rang viec ket hp a ch khong phai xay ra ngau nhien, no c chon ky lng bi cac nha thiet ke mang e nang cao kha nang phat trien mang. Do o, co the d oan trc cho nao no se gay ra anh hng, va viec thiet ke mang nh vay, co s ket hp a ch, khong c at nhng ni ma chuyen mach nhan c s dung chu yeu, nh la phan chnh cua mang backbone toc o cao. Va cac nha thiet ke mang phai can than am bao rang neu mot LSR c at tai mot iem ket hp th no phai co u kha nang nh tuyen kieu truyen thong e x ly mot phan lu lng khong the c chuyen mach nhan. 2..4.4.2.Van e phat trien Nh chung ta a va thao luan, hieu qua va van e phat trien kha lien quan en nhau va thng xung ot vi nhau. Mot cach e c nh tnh chat phat trien cua mot chuyen mach nhan la xem bao nhieu nhan c ch nh trong cac tnh huong khac nhau. Tong quat, nhng bc e nang cao hieu qua nh tang s nhay cam cua thuat toan phat hien dong, co nhng anh hng ngc lai oi vi van e phat trien v tang so lng nhan. e co cai nhn sau hn ve moi quan he gia hieu qua va van e phat trien cua ket hp tuyen d lieu, chung ta se xem xet mot vai d lieu lu lng c thu thap t nam 1995 tai mot iem trao oi Internet vnh San Francisco. D lieu nay c phan tch bi cac nha nghien cu cua Ipsilon a da ra cac hnh ve 2.15 va 2.16. Chung ta chu y la tong cac lu lng chay qua iem thuBien soan: TS.Tran Cong Hung

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thap tng oi nho (so vi nc My), ch vao khoang 30-40 Mbps, nen thong tin chu yeu ay chu yeu la ve y tng hn la cac so lieu chnh xac.

600 S kt ni thit lp/giy 500 400 300 200 100 0 0 10 20 30 40 50 60 70 80

45000 40000 35000 30000 25000 20000 15000 10000 5000 0 90 100

Tng cc kt ni

S kt ni/s Tng kt ni

Cc gi c nhn trc khi chuyn mch lung

Hnh 2.15 nh hng ca nhy ca s phn loi dng

Hnh 2.15 [1] ch ra ca hai so lng nhan (c ket hp) tc thi va so lng trao oi thong tin ket hp nhan (e thiet lap ket noi) tren moi giay c yeu cau nh la mot chc nang cua so lng goi tin trong mot luong xem xet trc khi thiet lap ng chuyen mach nhan. De dang trong thay, neu giam s nhay cua thuat toan phat hien dong se nhanh chong lam giam so lng nhan can thiet.110 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Cc gi nhn c trc khi chuyn mch lung

Phn trm

Phn trm byte c chuyn mch Phn trm gi c chuyn mch

Hnh 2.16 [1] cho thay phan tram cua so byte va so goi tin ket thuc c chuyen mach nhan, mot lan na la mot chc nang cua so lng cac goi tin c xem xet tai bat au moi luong trc khi no c chuyen mach nhan. ieu tot ay la tong lng d lieu ma co the c chuyen mach nhan c o bang byte hoac bang goi se giam cham so lng nhan yeu cau cho thuat toan phat hien dong giam (chu y rang mot nhan la tng ng vi mot ket noi). No co ngha la chung ta se xem xet nhieu goi tin hn trc khi quyet nh chuyen mach nhan cho mot luong.


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Vi ket hp tuyen ieu khien, tnh chat phat trien khong phu thuoc vao tnh t nhien cua lu lng d lieu nhng vao tnh chat cua lu lng ieu khien, ma no lai phu thuoc vao cau truc mang. V du, trong ket hp nhan tuyen ieu khien cho moi tien to trong bang nh tuyen, so lng cua nhan de dang co the tnh c, vao nam 2000, nhng bang nh tuyen ln nhat trong backbone Internet cha khoang 60.000 tien to mang. ng nhien, khong ket hp mot nhan cho moi muc trong bang nh tuyen. Nh chung ta se thay sau, v du mot LSR tai loi cua Internet co the ket hp mot nhan cho moi router ra(edge router) cua mot mien ma no trong, tren th t vai tram nhan. 2.4.4.3.S Linh Hoat Trong khi so sanh s linh hoat cua cac nghien cu khac nhau, chung ta co gang tra li cau hoi Cai nao de b anh hng hn ve hieu qua va van e phat trien khi moi trng mang thay oi ?. Nh vai thao luan trc a ch ra, ket hp tuyen d lieu dng nh khong theo kp vi tuyen ieu khien. Bi v ieu nay kha trc giac: s thay oi cua luong d lieu luon kho d oan hn luong thong tin ieu khien. e tao thay oi trong luong d lieu la mot ng dung mi hay la mot thay oi trong viec s dung cua mot ng dung ang dung. V du, gia s mot Web site cung cap vai dch vu giao dch nh nh gia co phieu tren Internet, ot nhien luong lu lng en Web site o se bao gom nhieu luong nho ma khong the c chuyen mach nhan, lam gia tang tai lu lng len thanh phan nh tuyen truyen thong. Khong kho e a ra nhieu tnh huong khac nhau ve s thay oi cach s dung cua ngi s dung hay cua ng dung se co the gay anh hng nghiem trong trong ket hp tuyen d lieu. Nhng nhng thay oi o kho co the anh hng en tuyen ieu khien. Thng thng, khong co s thay oi cua thong tin nh tuyen trong mot khoang thi gian ngan, ch co nhng thay oi can ban thc s trong cach xay dng mang mi co the anh hng en ket hp tuyen ieu khien.2.4.5.S phan bo thong tin ket hp nhan

Mot khi tao ra hay huy bo mot ket hp gia mot nhan c chon noi bo va mot FEC, LSR can thong bao cho cac LSR khac ve viec nay e cac LSR khac tao ra hay huy bo ket hp nhan ngoai. Phan bo thong tin ket hp nhan co the thc hien bi nhieu cach. 2.4.5.1.at tren nh cua cac Protocol nh tuyen Mot cach e phan bo thong tin ket hp la at thong tin nay vao cac giao thc nh tuyen. ieu nay ch thc hien c oi vi ket hp tuyen ieu khien, bi v no cot(ties) s phan bo thong tin nhan vao s phan bo thong tin ieu khien (nh tuyen), va no co vai tnh chat kha hap dan. au tien, no lam s phan bo thong tin ket hp nhan phu hp vi s phan bo cua thong tin nh tuyen. No con tranh c hien tng tranh chap, khi thong tin ket hp nhan (ket hp gia nhan va FEC) co mat, nhng thong tin nh tuyen lien quan en (la thong tin ket hp gia FEC va


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tram ke tiep) khong co. Sau o no lam n gian hoat ong cua he thong bi no lam giam s can nhieu giao thc e phan bo thong tin nh tuyen. Tuy nhien, no cung co nhng nhc iem nhat nh. Trc het, thong tin nh tuyen ma c phan bo bi mot giao thc xac nh co the khong phu hp cho s phan bo thong tin ket hp nhan, ch co nhng giao thc ma phan bo thong tin nh tuyen ro rang co cha anh xa gia FEC va a ch tram ke th co the phu hp cho viec at vao giao thc. V nguyen nhan nay ma nhng giao thc nh tuyen trang thai lien ket (Routing Link-State) (nh OSPF) khong phu hp cho yeu cau phan bo thong tin ket hp nhan. Nhng oi vi cac giao thc khac nh BGP va PIM dng nh hoan toan phu hp cho yeu cau nay. Nhng ngay ca neu s phan bo thong tin nh tuyen bi mot giao thc nao o phu hp cho viec phan bo thong tin ket hp nhan, th s m rong giao thc e mang thong tin nay co the khong luon luon kha thi. Bi v s m rong giao thc co the lien quan en s thay oi khuon dang cua ban tin c s dung bi giao thc o, va ieu nay co the gay ra s khong tng thch gia cac he thong. Chung ta co the quan tam en trng hp giao thc mang thong tin nhan en mot thiet b khong hieu nhan se gay ra nhng hieu nham khong mong muon. 2.4.5.2.Nhng giao thc phan bo nhan Tien than cua MPLS trc ay la chuyen mach the cua Cisco, s dung giao thc phan phoi the la TDP. Giao thc nay ve hoat ong th giong LDP nhng khong tng thch hoan toan vi LDP do no lang nghe tren cong 711 trong khi TDP lang nghe tren cong 646. He ieu hanh Cisco IOS t phien ban 11.1 a ho tr chuyen mach the, t 12.3 tr len mi ho tr MPLS. Cu phap lenh tuy thuoc vao IOS. Giao thc LDP giong OSPF cho cac lang gieng thay nhau mot cach t ong nh giao thc hello, giong BGP cho cac lang gieng dung ket noi TCP e thiet lap mot kenh truyen thong tin cay. iem khac biet cua LDP la thu tuc trao oi thong tin nhan cua no nh nhan cac lang gieng, thiet lap phien, trao oi nhan, duy tr nhan, chong vong lap ma ta se e cap. Ket hp noi bo va t xa Thuat ng ket hp lien quan en mot hoat ong tai LSR ma trong o mot nhan c ket hp vi mot FEC. Ket hp nhan noi bo la mot hoat ong trong o router noi bo thiet lap moi ket hp nhan vi mot FEC. Router co the lam viec nay khi no nhan c thong tin ieu khien t router lan can. Thong thng th router an nh mot nhan cho moi tien to IP ma no biet va sau o quang cao s ket hp nay. Con ket hp xa thng c thc hien bi cac ban tin ieu khien.


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2.4.5.3.S thc thi cua cac mat phang ieu khien trong vung chuyen mach nhan Mang chuyen mach nhan c to chc thanh cac vung chuyen mach nhan. Cac vung thuoc ve mot ISP hoac mot cong ty rieng va giao tiep vi nhau bang cac thoa thuan. Ta xet hnh 2.17, 2.18, 2.19 co cac nut ngi dung la 172.16.1.1 (ngc dong) va 172.16.2.1 (xuoi dong). Theo dong d lieu t nut 172.16.1.1 en nut 172.16.2.1, LSR A la nut ngo vao, LSR C la nut ngo ra. LSR B c goi la LSR chuyen tiep, LSR noi hay LSR loi. Cac hnh nay ch ra cach ma cac nut biet c a ch 172.16.2.1 bang cach s dung giao thc nh tuyen nh OSPF, BGP e quang cao nhan (hnh 2.17) hay dung giao thc phan phoi nhan LDP theo yeu cau (hnh 2.18) hoac khong theo yeu cau (hnh 2.19). Ket qua la cac nut eu biet ve a ch 172.16.2.1 va cach e i en nut o. Thong tin nay se c gi trong c s thong tin nhan. Chung ta xet hai kch ban trong viec an nh nhan cua giao thc LDP. Hnh 2.18 minh hoa hoat ong phan phoi nhan theo yeu cau (solicited hoac downstreamon-demand). Ban tin yeu cau nhan c gi i trc khi ban tin lien ket that s c gi.Ngc dong Vung chuyen mach nhan 172.16.1.1 a b A d a B c d C a 172.16.2.1 c Xuoi dong

1. Advertise 2. Advertise 3. Advertise 4. Advertise Cac goi quang cao la lu lng OSPF, IS-IS,

Hnh 2.17 : S tm ra a ch va v tr cua chung.


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172.16.1.1 a 1. Yeu cau 2. Gan nhan21 b

B d a

C c d

D a

172.16.2.1 c

3. Yeu cau 4. Gan nhan30 5. Yeu cau 6 Gan nhan21 7. Yeu cau 8. Gan nhan55

Hnh 2.18 : Lien ket nhan theo yeu cau172.16.1.1 a b B d a C c d Gan nhan 21 Gan nhan 30 Gan nhan 21 D a 172.16.2.1 c Gan nhan 55

Hnh 2.19: Lien ket nhan khong theo yeu cau

Hnh 2.19 la mot v du ve lien ket nhan khong theo yeu cau (unsolicited). ay nut xuoi dong ben phai hnh gi ban tin lien ket en cac nut ngc dong, va chung tiep tuc gi en cac nut ngc dong ke tiep trong vung chuyen mach nhan. Cac nut ngc dong khong yeu cau lien ket nhng lai nhan cac lien ket mot cach t do.

2.4.5.4.Chuyen oi nhan (label swapping)Gia tr nhan b thay oi khi goi d lieu truyen qua vung chuyen mach nhan. Thong thng moi LSR nhan c mot goi tin vao va thay oi gia tr cua nhan trc khi gi goi en nut ke tiep trong lo trnh.


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172.16.1.1a

21 b

Ad

30 a

Bc

21 d

Ca

55

172.16.2.1c

IP 172.16.2.1

OUT a.21

IN b.21

OUT d.30

IN a.30

OUT c.21

IN d.21

OUT a.55

IN c.55

OUT 172.16.2.1

Hnh 2.20 : Bang au vao LS cho mot LSR gia 2 ngi dung

Chung ta can quan tam cac iem sau. Th nhat, phai co mot phng tien e lien ket cac nhan vi FEC, va s ket hp nay phai c thc hien tai moi thiet b tham gia vao LSP t au cuoi en au cuoi. Th hai, trong v du nay, nhan ch co y ngha cuc bo trong giao dien ngo ra cua ngi gi vi giao dien ngo vao cua ngi nhan. Nh vay, nhan co the c s dung lai tai moi giao dien trong bo chuyen mach hay thiet b ngi dung. S la chon cac nhan la mot van e gia cac chuyen mach gan ke. V du, nhan 21 c s dung hai lan, gia 172.16.1.1 va chuyen mach A, va gia chuyen mach B va chuyen mach C. Th ba, viec lien ket nhan ch xay ra theo mot hng. S dung chuyen mach nhan theo hai hng th mot ket noi hai hng phai c lap cho moi hng cua ket noi. Lu y chuyen mach nhan ch dung cac giao thc phan bo thong tin nh tuyen e phan bo thong tin ket hp nhan la khong the. Mot cach khac la phan bo thong tin ket hp nhan bang cac giao thc rieng. Nhng no co mat han che, o la kho tranh hoan toan hien tng tranh chap, ban co the ket thuc trong tnh huong khi ma mot LSR co thong tin ket hp nhan (gia nhan va FEC) nhng khong co thong tin nh tuyen ( FEC va tram ke tiep) can e s dung thong tin ket hp nhan va ngc lai, v hai giao thc nay khong lien quan en nhau. Mot nhc iem khac cua nghien cu nay la no phai a ra mot giao thc mi cho he thong, se lam tang o phc tap cua he thong. Neu thanh phan ieu khien chuyen mach nhan ch s dung mot giao thc phan bo nhan, th no se kho ma lam s phan bo thong tin ket hp nhan nhat quan vi s phan bo cua thong tin nh tuyen. e thay ieu nay th chung ta xem xet cac giao thc nh tuyen, trong khi mot vai giao thc trao oi thong tin nh tuyen da tren s cap nhat dan dan va bat buoc phuc ap (nh la BGP), con cac giao thc khac s dung s lam ti(refresh) mot cach tuan hoan cua thong tin nh tuyen (nh PIM). Mot cach e tranh s mat thong nhat nay la co nhieu hn mot giao thc phan bo thong tin nhan. Vi phng phap nay ban co the tao mot giao thc phan bo nhan e s dung lien ket vi OSPF va se da tren s cap nhat dan dan va bat buoc phuc ap, trong khi o tao mot giao thc khac e dung lien ket vi PIM vase da tren s lam ti mot cach tuan hoan cua thong tin ket hp. Mat du ieu nay giai quyet van e nhat quan phan bo cua thong tin ket hp nhan, no se a ra nhieu giao thc cho he thong va se lam tang s phc tap cua he thong.Bien soan: TS.Tran Cong Hung - 46 Version 3

Da vao nhng thao luan tren, ta thay s chon at thong tin ket hp

baigiang mpls version 3

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