feb. 20, 2002 - mmlab.snu.ac.krmmlab.snu.ac.kr/links/hsn/workshop/hsn2002/documents/iii_2.pdf · 9...

Ethernet Survivability

정 우 영

R&D Center, Corecess Inc.Mail : [email protected] : www.corecess.com

Feb. 20, 2002

Table of Contents

1. Ethernet Survivability 배경

2. STP & RSTP (802.1D, 802.1w)

3. Link Aggregation (802.3ad)

4. Automatic Protection Switching

5. Optical Layer Restoration

5. Resilient Packet Ring (802.17)

6. 결론

Simple and Flexible

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Contents

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Simple and Flexible

3

Ethernet Survivability 배경

Network Survivability의 개념Link 혹은 Node의 장애에 대한 Connectivity의 유지

Protection100%의 여유 자원에 의한 투명한 즉시 복구 (수십 ms)

Restoration적절한 예비용량을 활용한 망의 전부 혹은 제한된 복구

Protection을 포함한 포괄적인 개념으로도 사용됨

수단Link 혹은 Node의 RedundancyRestoration Mechanism/Algorithm

4

Simple and Flexible

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Network Architecture

IP

ATM

SONET

WDM

Fiber

IP

SONET

WDM

Fiber

WDM

Fiber

IP/MPLS

Ethernet

Fiber

IP

5

Simple and Flexible

5


Network Architecture

IP 평면

SONETADM

SONETADM

SONETADM

SONETADM

SONET 평면

WDM 망(OADM/OXC)

Optical 평면

6

Simple and Flexible

6


Ethernet Architecture (LAN)

Ethernet Switched LAN

10Base-T

100Mbps/1GbpsBackbone

NMS Server

10/100MbpsPublic

Network

100Mbps

100Mbps

File/VODServer

100Mbps

100Mbps/1Gbps


High Speed Workgroup

10/100Base-T

10/100Base-T

7

Simple and Flexible

7


Ethernet Architecture (MAN)

File/VODServer

IDCIP 망 (L3)

Ethernet SW

Ethernet SW

File/VODServer

IDCMPLS/Ethernet (L2)

Ethernet SW

Ethernet SW(LER)

Ethernet SW

Ethernet SW(LSR)

Ethernet SW

8

Simple and Flexible

8

STP & RSTP (802.1D, 802.1w)

STP (Spanning Tree Protocol) 개요IEEE 802.1D 규격1990년 최초 규격 이후 수 차례 개선L2 routing protocolLoop free topologyRoot로 가장 비용이 작은 경로 선정Convergence time: 30 ~ 50초(너무 긴 시간이 필요함)최근 수렴시간을 개선한 RSTP 제정(RSTP = Rapid STP: IEEE 802.1w)RSTP 수렴시간: 수ms ~ 수초Algorithm 개념 발전tree 형성 후 frame forwarding (timeout기반)

tree 형성과 동시에 forwarding실제망은 초기 구성부터 가급적 tree 배제

RootBridge

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STP & RSTP (802.1D, 802.1w)

주요개념

Root bridge: 브리지 번호가 가장 작은 브리지로 Configuration message를 정기적으로 initiation한다.Designated bridge: 해당 subnetwork (LAN)에서 root bridge방향으로 frame을 forwarding하는 브리지Root port: Designated bridge에서 root bridge방향으로 frame을forwarding하는 portDesignated port: Designated bridge에서 leaf방향으로 frame을forwarding하는 port

브리지 번호 (Bridge Identifier)

포트 번호 (Port identifier)

Priority (2B) Bridge MAC address (6B)

Priority (1B) Port No. (1B)

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STP & RSTP (802.1D, 802.1w)

Bridge 0

Bridge 2 Bridge 3

Bridge 4

Bridge 1

Bridge 5

LAN 1

LAN 2

LAN 3

Designated Bridgeof LAN 2

Root bridgeDesignated port

Root port

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Simple and Flexible

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STP & RSTP (802.1D, 802.1w)

IEEE Recommended Link Cost

Data RateRecommendedLink cost range

RecommendedLink cost value

4Mb/s 100 ~ 1000 250

10Mb/s 50 ~ 600 100

16Mb/s 40 ~ 400 62

100Mb/s 10 ~ 60 19

1Gb/s 3 ~ 10 4

10Gb/s 1 ~ 5 2

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STP & RSTP (802.1D, 802.1w)

STP Port State Transition Diagram

Disabled

Listening

Forwarding

LearningBlocking

Failure or NMS

BPDUs or timeout BPDUs

ForwardingTimer expire

(normally 15초)

ForwardingTimer expire

(normally 15초)

BPDUs

BPDUs

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STP & RSTP (802.1D, 802.1w)

DisabledData frame과 BPDU를 전송하지 못하는 상태

BlockingData frame은 송수신 못함. BPDU는 수신만 함.

ListeningData frame은 송수신 못함.BPDU는 송수신할 수 있음.STP 계산 상태

LearningData forwarding 준비 상태MAC address를 익혀 forwarding table을 준비하는 상태

Forwarding정상적으로 Data frame을 forwarding하는 상태

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Simple and Flexible

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STP & RSTP (802.1D, 802.1w)

Another Issues in STP & RSTPCommon spanning tree or each one per Virtual LAN (VLAN)

Bridge 1

Bridge 3Bridge 2

VLAN 1의 spanning tree

VLAN 2의 spanning treePort 1Port 0

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Simple and Flexible

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Link Aggregation (802.3ad)

Link Aggregation 개요IEEE 802.3 규격 (1999년)LAN link를 point-to-point로 여러개 연결하여 운영성능증가

1 ~ 8개까지의 link를 병렬로 연결가능Load sharing

Availability 증가: 일부 link의 장애가 발생할 경우 생존성 보장자동구성가능

LACP (Link Aggregation Control Protocol)

각 Conversation (Flow)은동일 link를사용해야함.

•••

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10Base-T

100M/1GBackbone

NMS Server

IPNetwork

100Mbps

File/VODServer

100Mbps


10/100Base-T

•••

•••

•••

•••

Link Aggregation ExampleSwitch–to-switchSwitch-to-station (server or router)Station-to-station

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Simple and Flexible

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MAC MAC MAC MAC

Port1 Port2 Port N-1 Port N

FilteringDatabase

Dispatcher

Link AggregationControl

Link AggregationControl Protocol

LACPDU

Marker Generator/Receiver(optional)

MarkerResponder

Marker Parser

Marker Frame

Marker Request / Response

Aggregator 1 Aggregator M

Aggregator 1Aggregation Control

Station의기능도

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Simple and Flexible

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Issues in Link AggregationUnique MAC address in Aggregated linksNo mechanism for subdividing frameMaintaining link invariantConversation (≈ flow)별로 동일 link로 frame 전송( frame reordering 문제 배제)Conversation 분류 기준

Source/Destination MAC addressIP addressHigher layer parameter (TCP port number, …)

Distribution changeLink addition/deletionTraffic imbalanceTimeout-based or explicit protocol (Marker/Response)

서로 다른 속도의 link간에는 aggregation 불가Autosensing (10M/100M/G): (?)

Automatic link aggregationLACP: Link Aggregation Control ProtocolGroup “Key” concept

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Simple and Flexible

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Distributor(+ Marker)

Interface1

Interface2

Collector(+ Response)

Interface1

Interface2

Link 1 Link 2

D3 C3 D2 D1 C2 C1

A1B1B2A2 Marker

Response


Frame Distribution

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Simple and Flexible

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Automatic Protection Switching

Specified in ITU-T G.783Applied for line switching procedure using SDH K1/K2 bytes.Restoration time is within 50 msec.

APS의 주된 기능네트웍 장비에서의 failure 검출Traffic을 복구하기 위해 예비 장비(standby facility)로의 전환SDH에서 Multiplex Section(MS)만이 보호됨

Multiplex Section Overhead에 있는 K1 및 K2 byte 사용Optical section 상에서 transmission 보호

Path Protection은 상위 계층에서 처리

Protection Switching 초기화by Signal Failure, Signal degrade, or NMS

Modes of APS1+1 Protection Switching1:1 Protection Switching1:N Protection Switching

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Simple and Flexible

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STM –1 Frame 구조및 K1/K2 bits

RSOH

AU pointer

MSOH

Payload

9B 261B

1

4

9

AU pointer

A1A1A1A2A2A2

K1 K2기타 field 생략

22

Simple and Flexible

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STM-1 신호의 Multiplex Section Overhead에있는 K1/K2 byte가 Near End와 Far End 사이에서 Multiplex Section Protection (MSP) protocol을전송

Protection Switching 조절

1 2 3 4 5 6 7 8

K1

switch priority switch actionchannel request

1 2 3 4 5 6 7 8

K2

provisionedbi-directional switchuni-directional switch

channel numberbridged

Provisioned1:n / 1+1

Multiplex SectionAlarm Indication Signal

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Simple and Flexible

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RX

RX

bridge switch

Near End

Working fiber

TX

TX

Far EndProtection

fiber

1+1 SONET Protection

Working fiber와 Protection fiber가하나씩존재Near End 에서신호는 working fiber 및 protection fiber 양쪽모두로동시에보낸다.Working fiber 및 protection fiber로보내지는신호는동일함

Far End 에서두신호에대해개별적으로오류(failure) 검사를실시두신호중에서양호한쪽을선택 switchsignal fail 이나 signal degrade이선택기준

Signal fail : Loss of Frame (LoF) 같은 hard failure 등Signal degrade : 기준치를초과하는 error rate에의한 soft failure 등

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Simple and Flexible

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일반적으로 1+1 Protection Switching은Unidirectional and non-rivertive

Switching은 Revertive or Non-RevertiveRevertive : failure correction 후즉시 working fiber로전환Non-revertive : failure 이후 protection fiber가 working fiber처럼사용됨

Near End과 Far End 사이의 SignalingK1 및 K2 bytes를사용하여 APS channel로전송됨

25

Simple and Flexible

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1:1 SONET Protection

RX

RX

switch switch

Near End

Working fiber

TX

TX Far EndProtection

fiber

Working fiber와 Protection fiber가하나씩존재정상동작시는 working fiber를통해트래픽전송Failure 발생시 protection fiber쪽으로전환정상동작시에 protection fiber를통해 low-priority traffic이전달될수있음

working fiber에 failure가발생하면 working fiber를통해전달되던 traffic에의해선점됨(preemption)

Revertive Protection SwitchingFailure correction 후즉시 working fiber 쪽으로전환

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Simple and Flexible

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Working fiber와 Protection fiber가하나씩존재정상동작시는 working fiber를통해트래픽전송Failure 발생시 protection fiber쪽으로전환정상동작시에 protection fiber를통해 low-priority traffic이전달될수있음

working fiber에 failure가발생하면 working fiber를통해전달되던 traffic에의해선점됨(preemption)


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Simple and Flexible

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W1

P

W2

WN

•••

RXTX

RXTX

RXTX

RXTX

switch switch

Near End 1 Far End 1

W i : i-th working fiber P : protection fiber

X

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Simple and Flexible

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여러개의 working fiber에대해하나의 protection fiber 사용Working fiber의개수는 1 ~ 14 사이Working fiber를통해서만신호전송Protection fiber는 failure가발생하기전까지 free


Near End과 Far End 사이의 SignalingK1 및 K2 bytes를사용하여 APS channel로전송Far End에서 Failure를감지했을때의동작

K1 byte의 5~8 위치에 switching action message를담아 Near End로전송Near End는이메시지를받자마자 protection fiber 쪽으로전환여러 failure가발생했을때는 Near End가우선순위가높은 channel을선택, protection fiber쪽으로연결K2 byte의 1~4 위치에 protection fiber로전환된 channel 정보를담아 Far End로전송K1 byte를사용해 Far End도 protection fiber쪽으로전환할것을요구K1 메시지를받은 Far End도 protection fiber로 channel 전환

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Simple and Flexible

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SONET Self-healing RingsUPSR (Unidirectional Path-Switched Ring)

1+1 protection수신부에서전적으로 fault recovery (No signalling)두링은서로반대방향으로전송

주로 access 망에서사용됨.

BLSR (Bidirectional Line-Switched Ring)Also referred to as shared protection ring (SPRING)두링은서로반대방향으로전송

2 fiber 방식과 4 fiber 방식이있음.대개 core 망에서사용됨.

Working

Protection

W&P

W&P

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Simple and Flexible

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RX

bridge switchNear End Working

fiber

TX

Far End

Protectionfiber

Optical Layer Restoration

1+1 Protection in Optical Layer

Not the same as 1+1 SONET protectionTX/Bridge, RX/Switch 위치가바뀜광소자들은전기신호의 Quality (Bit error rate, …)등에대한지능이없음.

31

Simple and Flexible

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RX

switch switchNear End W1

TX

Far End

APS Signalling Channel

Optical Layer Restoration

1:1 or 1:N Protection in Optical Layer

RXTX

W2

Wn

P

••••••

Additional Siganlling Channel Required

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Simple and Flexible

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Resilient Packet Ring (802.17)

RPR 개요Metro fiber ring network을 위해 고안된 새로운 MAC protocolIEEE 802.17 WG에서 표준화 진행중Ethernet의 MAN 적용에 영향받음.

RPR 특징Packet ADM ArchitecturePhysical layer Versatility

Ethernet, SONET, WDM

Bandwidth FairnessResiliency

Intelligent Protection Switching (IPS)< 50ms 이내복구

Broadcast and Multicast traffic SupportSimplified Service ProvisioningScalability

Up to 128 nodes

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Simple and Flexible

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RPR node의 동작Insertion : 링에 새로운 패킷을 삽입Forwarding : 패킷을 진행방향으로 전달Stripping : 링에서 패킷을 제거Wrapping: Failed link의 양단 node가 In/Out ring간에 loopbackSteering: Ring내의 모든 node가 failure를 통보 받아 최적 루트 설정

Node n-1 Node nNode n+1

Priority-based transit buffer

Priority-based transit buffer

O-RX (TX): Outer Ring RX (TX)

I-RX (TX): Inner Ring RX (TX)

O-RX O-TX

I-RXI-TX

X

L3 Engine

RPR MAC RPR MAC

CAM

CAM

34

Simple and Flexible

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SONET/SDN-based TDM TransportAccepted Transport ArchitecturePerformance Monitoring and Self-HealingExpensive and Inefficient for Packets

Multiple equipment layersBandwidth inefficiency

SONETADM

SONETADM

SONETADM

SONETADM

working

protection

provisionedconnections

35

Simple and Flexible

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표준화동향

Gandalf proposal vs Alladin proposal Darwin Proposal

GandalfTraffic management를 위해 fairness scheme 사용Cisco의 Spatial Reuse Protocol 기술에 기반새로운 패킷 포맷 사용

Wizard appeared in The Load of the Rings by J.R.R. TolkienCisco Systems, Riverstone Networks, Mindspeed

AlladinTraffic management를 위해 Virtual Output Queueing 사용Traffic management를 위해 Gandalf보다 복잡한 MAC scheme 사용Ethernet과 같은 패킷 포맷 사용

Additional RPR tag 사용

Alcatel, Luminous Networks, Lantern Communications, Nortel Networks

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Simple and Flexible

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Timeline

2000. 4Q

2001. 1Q

2001. 2Q

2001. 3Q

2001. 4Q

2002. 1Q

2002. 2Q

2002. 3Q

2002. 4Q

2003. 1Q

2003. 2Q

Jan. 2002: First draft expected

Dec. 2000: IEEE 802.17 WG 발족March. 2001: Objectives defined

July. 2001: Consolidated technology proposal

March. 2003: Standard ratification expected

IEEE 802.17 WG

April ~ June 2002: Standard ratification forsome technical specifications expected

October 2001: Technical specifications for architecture,Etherne services and protection in MANs defined

Aug. 2001: Technical Committee launched

June. 2001: Metro Ethernet Forum 발족Metro Ethernet

Forum

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Global Fairness 란?링상의각노드가링대역폭의 fair share를갖도록하는것어떻게 : forward 되는 packet rate과노드에서생성되는 packet rate을

(SRP-fa의룰에따라) 적절하게조절해서목적 : misbehaving node가링대역폭을독식함으로써다른노드들을굶주리게하거나(starve) 과도한딜레이를발생시키는것을방지

A

B

C

D

E

F

C2 C3

50 Mbps

50 Mbps

각각 100 Mbps씩요구

링대역폭 : 100 Mbps

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A

B

C

D

E

F


WrappingFailure link 양끝의두노드만이 failure detect해당노드 wrappingFailure 사실이링내의네트웍에알려짐Optimal direction을통해패킷전송 (not part of the protection switching)

before wrapping

after wrapping(non-optimal path)

after wrapping and topology

discovery(optimal path)

39

Simple and Flexible

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SteeringFailure detect 링위의모든노드에 failure 통보50 msec 이내에링위의모든트래픽제거 Packet loss모든노드에의해 ring protection 개시

Ring topology에대한지식사용

Topology Discovery 시작Routing table update

최적경로로경로재설정

A

B

C

D

E

F

before wrapping


discovery

40

Simple and Flexible

40


Steering after Wrapping or Wrapping then Steering각노드의 forward table이 update될때까지 wrappingFailure를발견한두노드가전체노드에게 failure 통보및 TD 시작패킷손실최소화

빠른반응시간및라우팅최적화의조화

노드의복잡성증가 비용증가 단점

장점

A

B

C

D

E

F

before wrapping


discovery

41

Simple and Flexible

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Comparison of Data LossAssumption

Fiber cut type : Double fiber cutFiber cut detection time : 0.4 msWrap time : 0.1 ms for 20 Km ring spanNumber of Nodes : 32Line rate : 10 GbpsMean transit queue size : 16 KB

In Wrapping Case{fiber cut detection time + Wrap time} × {Line rate}

= (0.4 ms + 0.1 ms) × 10 Gbps = 5 MbIn Steering Case

{fiber cut detection time +N node delays + node steering response time} × {Line rate} + {up to (N/2) transit buffer}

= (0.4 ms + 32 nodes × 0.1 ms/node + 1 ms) × 10 Gbps + 16 nodes × 16 KB/node = 48 Mb

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Simple and Flexible

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결론

Ethernet에내재된고유한 survivability 기능은 STP/RSTP 및Link Aggregation 기능정도로제한적임.Survivability 측면에서는 Ethernet을 MAN/WAN등의광역망에적용하는데는 Network Architecture에대한많은고려가필요할것임.이는결국경제성과운용성측면에서 Service Provider들의사업목표와연계된선택의문제가될것으로판단됨.

기타L3 계층의 OSPF/BGP등의 routing protocol과의상관성MPLS 도입시 CR-LDP/RSVP-TE등의 signalling protocol이갖고있는survivability 기능과의상관성

feb. 20, 2002 - mmlab.snu.ac.krmmlab.snu.ac.kr/links/hsn/workshop/hsn2002/documents/iii_2.pdf · 9...

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